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PubMed2003

Noninvasive molecular detection of cancer -- the bench and the bedside.

The more profound understanding of the genetics and molecular pathways driving human tumorigenesis is paralleled by an ongoing interest to translate this knowledge into development of cancer biomarkers, termed molecular tumor markers. The molecular changes observed in tumors frequently constitute early events which are detectable as signatures of malignancy in body fluids and their occurrence may precede clinical cancer diagnosis. Thus, beyond applicability on tissue samples, molecular markers for tumor signatures should allow noninvasive or minimally invasive diagnosis in blood and/or other body fluid samples. However, to qualify as a clinically useful molecular tumor marker for initial diagnosis and detection of recurrent disease, a molecular tumor marker must have better test characteristics (sensitivity, specifity) than currently applied tumor markers. A molecular tumor marker should also be suitable for screening purposes by defining the subset of individuals for which definite cancer diagnosis by more invasive and/or expensive additional investigations is indicated. In addition, there is a demand for molecular tumor markers to be used as reliable surrogate endpoints in cancer prevention trials. Recommendation for the use of individual molecular tumor markers within evidence-based medicine criteria should ideally be derived from their overall efficacy to reduce tumor-specific mortality. This review focuses on DNA based, RNA based and proteomics based molecular methods of noninvasive cancer detection in bodily fluids and assess the value of these methods for the current and future clinical management of cancer patients.

Biomarkers, Tumor↗
PubMed2004

[Clinical and pathological significance of the genetic analysis in colorectal carcinomas].

The molecular genetics of colorectal carcinomas are among the best understood of common human cancers. Three inter-related molecular pathways are involved. The chromosomal instability pathway begins with inactivation of the APC/beta-catenin genes followed by activation of oncogenes and inactivation of additional suppressor genes, commonly with high frequency of allelic losses, cytogenetic abnormalities. The microsatellite instability pathway begins with inactivating one of a group of genes responsible for DNA nucleotide mismatch repair leading to extensive mutations in both repetitive and non-repetitive DNA sequences with low frequencies of allelic losses and rare alteration of tumor DNA content. Finally, the CpG island methylation pathway involves inactivation of genes by methylation of cytosines in promoter regions to silence gene expression without DNA sequence alterations. Molecular genetics have the potential for clinical applications. Combination of genetic classification of high levels of microsatellite instability (MSI-H), gene expression analysis of mismatch repair genes and subsequent mutation analysis of inactivated genes can be used as an effective method for the identification of hereditary nonpolyposis colorectal carcinoma patients. Molecular genetic alterations have been proposed to be of prognostic value, including allelic deletion on chromosome 18q, and on chromosome 17p. MSI-H has been reported as a marker for better prognosis. Individualizing chemoradiation by use of predictive markers for response or resistance to therapy is important in patients with advanced disease or candidacy for adjuvant therapy.

Chromosomal Instability↗
PubMed2001

Hamartoma and lentiginosis syndromes: clinical and molecular aspects.

The classic hamartoma syndromes and the related conditions discussed in this chapter show varying degrees of phenotypic and genetic overlap. Knowledge of the susceptibility genes underlying their phenotypes has provided additional information for the classification of these syndromes. Germline PTEN mutations appear to cause both CS and BRR. These two syndromes are therefore likely to be different manifestations of a single disease with variable expression. It has been suggested that PTEN mutation-positive CS and BRR should be grouped as a single entity for clinical purposes and classified as the 'PTEN hamartoma-tumour syndrome' [111]. Germline PTEN mutations are unlikely to cause JPS. However, germline SMAD4 mutation, especially a well-described 4-bp deletion, can be used to confirm a clinical diagnosis of JPS. Like the hamartoma syndromes, the lentiginoses also show substantial clinical overlap; it remains to be seen whether this is reflected in the molecular pathways that are involved in the pathogenesis of these syndromes. Given that the degree and type of cancer susceptibility between the hamartoma and lentiginosis syndromes is different, clarification of these syndromes at the molecular level is predicted to allow directed cancer surveillance. The molecular story is still evolving with regards to aspects of genetic heterogeneity, signalling pathways and the manner in which these hamartoma genes function in the development of their respective syndromes. It is likely that in all of these syndromes, tumours develop against a background created by loss of the growth-suppressive function of their susceptibility gene via mechanisms including disruption of the cell cycle and the activation of anti-apoptotic pathways.

Chromosome Mapping↗
PubMed1992

Stimulated and co-operative electron transfer in energy conversion and catalysis.

A new mechanism of electron transfer, stimulated electron transfer, is postulated, in which an electronic feedback is drastically increasing both the rate of electron transfer and the propagation of free energy along electron transferring molecular pathways. In principle, the idea of pushing a system far from equilibrium to achieve a high reaction rate and co-operative phenomena is applied to molecular electron transfer. The effect is calculated from a semiclassical kinetic model of a chain redox reaction with autocatalytic feedback on individual rate constants, where the steps have subsequently been minimized to obtain a continuous electron transfer pathway with electronic feedback. The influence of inhomogeneities and asymmetries in the electron transfer path and of vectorial components (electrical field, gradient of redox potential) are discussed as well as the acceleration of individual and multiple electron transfer as a function of feedback. Examples of autocatalytic feedback are provided including mechanisms involving electron transfer proteins and multi-centre electron transfer catalysts. Such a phenomenon can be described for molecular and interfacial electron transfer in analogy to stimulated and coherent light emission. The results suggest that autocatalytic or stimulated electron transfer may be a key to the understanding of efficient electron transfer and co-operative multi-electron transfer catalysis in biology and a challenge for fuel production mechanisms in artificial photosynthesis and fuel cycles.

Catalysis↗
PubMed2004

Molecular biology of squamous cell carcinoma of the anus: a comparison of HIV-positive and HIV-negative patients.

The molecular mechanisms involved in progression of squamous cell carcinoma of the anus (SCCA) are poorly elucidated, as well as the potential role of HIV infection. Loss of heterozygosity (LOH) is one of the mechanisms responsible for inactivation of tumor suppressor genes. We hypothesized that HIV-induced immunosuppression may contribute to an alternate molecular pathway in SCCA progression, through persistence of human papillomavirus infection within the anal canal. This study was undertaken to compare the molecular biology of SCCA in HIV-positive (HIV+) and HIV-negative (HIV-) patients. We retrieved tumor specimens from 18 HIV- and 10 HIV+ patients diagnosed with SCCA in two institutions. DNA from tumor and normal tissues was extracted and then amplified by polymerase chain reaction. LOH was investigated at 14 loci: three at 18q (DCC), two at 13q (Rb), three at 17p (p53), three at 11q, one at 2p, and two at 5q (APC). LOH was defined by a tumor DNA-to-normal tissue DNA ratio of >2. HIV+ patients were younger (36 +/- 7 years versus 53 +/- 13 years, P=0.001) and showed a trend toward tumors of larger size (3.7 +/- 1.6 cm versus 2.6 +/- 1.5 cm, P=0.09). The median CD4+ count in HIV+ patients at the time of diagnosis was 74 x 10(6)/L (range, 5-900). The overall frequency of LOH was 17.3% (41 LOH of 236 informative loci). Tumors in HIV- patients were more likely to present LOH than were tumors in HIV+ patients (24.1% versus 6.6%, P=0.0004). Differences between the two groups with regard to allelic losses were also observed at specific loci, such as 18q (41% [HIV-] versus 0% [HIV+], P=0.05), 17p (43% versus 10%, P=0.09), and 5q (33% versus 0%, P=0.12). Consistent LOH on chromosomes 17p, 18q, 5q, and 11q were observed in HIV- patients with SCCA. By contrast, allelic losses at 17p, 5q, and 18q seem to be rare in tumors of HIV+ individuals. These data suggest that immunosuppression may promote SCCA progression through an alternate pathway and that persistence of HPV infection within the anal canal may play a central role in this process.

Adult↗
PubMed2005

Docetaxel associated pathways in cisplatin resistant head and neck squamous cell carcinoma: a pilot study.

PURPOSE: This is a pilot study to identify changes in gene and protein expressions after treatment with docetaxel in cisplatin-resistant head and neck squamous cell carcinoma (HNSCC). METHODS: Two cisplatin-resistant HNSCC cell lines, HN30 and HN12, were treated with either docetaxel or cisplatin. After 48 hours, differential gene expression between the two treatment groups (docetaxel-treated cells and cisplatin-treated cells) was analyzed using cDNA microarray. Differential protein expression between these two treatment groups was determined using PowerBlot and Western Blot analysis RESULTS: A total of 150 genes and proteins were found to have differential expression patterns in HNSCC after treatment with docetaxel versus cisplatin. Many of these differentially expressed genes and proteins were involved in the cell cycle (decreased E2F), apoptosis (increased bax), angiogenesis (increased thrombospondin), and signal transduction (decreased epidermoid growth factor receptor) regulatory pathways. CONCLUSIONS: Gene and protein expression are different and distinct between cells treated with docetaxel and cells treated with cisplatin. This finding provides evidence that different molecular pathways leading to cell death are targeted by docetaxel and cisplatin. Future studies focusing on these differentially expressed genes and proteins may improve our understanding, at the molecular level, of the mechanisms responsible for docetaxel-induced apoptosis in cisplatin-resistant HNSCC. Furthermore, these differentially expressed genes and proteins can be exploited as useful surrogate endpoint biomarkers in future clinical trials using docetaxel.

Antineoplastic Agents↗
PubMedDate not supplied

Targeting HSP70-induced thermotolerance for design of thermal sensitizers.

Thermal therapy has been shown to be an extremely powerful anti-cancer agent and a potent radiation sensitizer. However, the full potential of thermal therapy is hindered by a number of considerations including highly conserved heat resistance pathways in tumour cells and inhomogeneous heating of deep-seated tumours due to energy deposition and perfusion issues. This report reviews recent progress in the development of hyperthermia sensitizing drugs designed to specifically amplify the effects of hyperthermia. Such agents might be particularly useful in situations where heating is not adequate for the full biological effect or is not homogeneously delivered to tumours. The particular pathway concentrated on is thermotolerance, a complex, inducible cellular response that leads to heat resistance. This paper will concentrate on the molecular pathways of thermotolerance induction for designing inhibitors of heat resistance/thermal sensitizers, which may allow the full potential of thermal therapy to be utilized.

Animals↗
PubMed1997

PACAP type I receptor activation promotes cerebellar neuron survival through the cAMP/PKA signaling pathway.

The molecular nature, transduction pathways, and neurotrophic functions of pituitary adenylate cyclase activating peptide (PACAP) receptors were studied in primary culture of rat cerebellar granule cells. We show that cerebellar neurons express several PACAP type I receptor (PVR I) isoforms, including the short (PVR Is) and the Hop (PVR I-Hop) splice variants, the latter being restricted to neurons and not found in cerebellar glial cell cultures. In vitro, cerebellar granule cells die rapidly in the absence of a high concentration of K+ (25 mM), as demonstrated by TUNEL histochemistry, which shows that K+ deprivation induces massive neuronal apoptosis within 12 hr. This effect was reversed by PACAP 27 and 38. Both forms of PACAP prevent DNA fragmentation and allow long-term neuronal survival in the absence of high K+ (as shown by MAP2 immunostaining) and stimulate a reporter gene driven by the full-length c-fos promoter. These effects of PACAP are fully abolished upon transient transfection of cells with a dominant inhibitory mutant of the cAMP-dependent protein kinase (PKA). Taken together, these results show that in cerebellar granule neurons, PACAP type I receptors regulate gene expression and promote neuronal survival through the cAMP/PKA pathway.

Animals↗
PubMed2003

Recent advances in intracellular signalling in hypertension.

PURPOSE OF REVIEW: Transmission of external signals from the cell surface to the internal cellular environment occurs via tightly controlled complex transduction pathways. Alterations in these highly regulated signalling cascades in vascular smooth cells may play a fundamental role in the structural, mechanical and functional abnormalities that underlie vascular pathological processes in hypertension. The present review focuses on recent developments relating to two novel signalling pathways: angiotensin II signalling through tyrosine kinases; and oxidative stress and redox-dependent signal transduction. These pathways are emerging as critical mediators of hypertensive vascular disease because they influence multiple cellular responses that are involved in structural remodelling, vascular inflammation and altered tone. RECENT FINDINGS: A recent advance in the field of angiotensin II signalling was the demonstration that, in addition to its vasoconstrictor properties, angiotensin II has potent mitogenic-like and proinflammatory-like characteristics. These actions are mediated through phosphorylation of both nonreceptor tyrosine kinases and receptor tyrosine kinases. It is also becoming increasingly apparent that many signalling events that underlie abnormal vascular function in hypertension are influenced by changes in intracellular redox status. In particular, increased bioavailability of reactive oxygen species (oxidative stress) stimulates growth-signalling pathways, induces expression of proinflammatory genes, alters contraction-excitation coupling and impairs endothelial function. SUMMARY: A better understanding of the molecular pathways that regulate vascular smooth muscle cell function will provide further insights into the pathophysiological mechanisms that contribute to vascular changes and end-organ damage associated with high blood pressure, and could permit identification of potential novel therapeutic targets in the prevention and management of hypertension.

Angiotensin II↗
PubMed2005

Molecular control of physiological and pathological T-cell recruitment after mouse spinal cord injury.

The intraspinal cues that orchestrate T-cell migration and activation after spinal contusion injury were characterized using B10.PL (wild-type) and transgenic (Tg) mice with a T-cell repertoire biased toward recognition of myelin basic protein (MBP). Previously, we showed that these strains exhibit distinct anatomical and behavioral phenotypes. In Tg mice, MBP-reactive T-cells are activated by spinal cord injury (SCI), causing more severe axonal injury, demyelination, and functional impairment than is found in non-Tg wild-type mice (B10.PL). Conversely, despite a robust SCI-induced T-cell response in B10.PL mice, no overt T-cell-mediated pathology was evident. Here, we show that chronic intraspinal T-cell accumulation in B10.PL and Tg mice is associated with a dramatic and sustained increase in CXCL10/IP-10 and CCL5/RANTES mRNA expression. However, in Tg mice, chemokine mRNA were enhanced 2- to 17-fold higher than in B10.PL mice and were associated with accelerated intraspinal T-cell influx and enhanced CNS macrophage activation throughout the spinal cord. These data suggest common molecular pathways for initiating T-cell responses after SCI in mice; however, if T-cell reactions are biased against MBP, molecular and cellular determinants of neuroinflammation are magnified in parallel with exacerbation of neuropathology and functional impairment.

Animals↗
PubMed2005

Activation of the mitochondrial apoptotic pathway in a rat model of central retinal artery occlusion.

PURPOSE: Apoptosis is known to play a role in cell death in transient retinal ischemia. Little is known about the specific molecular pathways involved. The purpose of the current study was to evaluate a rat model of central retinal artery occlusion (CRAO) that simulates the clinical features of CRAO in humans and to elucidate whether the mitochondrial apoptotic pathway is involved. METHODS: CRAO was induced in the central retinal artery by intravenous injection of rose bengal and green laser irradiation of the artery. CRAO was documented at 1, 3, 6, and 24 hours after laser irradiation. Changes in Bax (proapoptotic Bcl-2-associated X protein), cytochrome c, and caspase-9 cleavage in the cytosolic and mitochondrial fractions of neural retinal tissues were measured by Western blot analysis. Apoptosis within the retina was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). RESULTS: Complete CRAO was induced; however, occlusion became incomplete with spontaneous reperfusion of branch arteries, starting at 3 hours after laser irradiation. Only one or two branch arteries remained occluded at the 24-hour time point. Time-dependent, apoptotic changes were observed in inner and outer retinal cell layers. Western blot analysis revealed mitochondrial translocation of Bax from the cytoplasm, starting at 3 hours and peaking at 6 hours after laser irradiation. This translocation was accompanied by cytosolic accumulation of cytochrome c and cleavage of caspase-9. CONCLUSIONS: This model is highly relevant to clinical manifestations of CRAO and is an ideal animal model for research. These findings indicate the activation of the mitochondrial pathway in ischemic retina induced by CRAO. The model provides a better understanding of ischemia-induced retinal apoptosis. Antiapoptosis therapy directly targeting the mitochondrial pathway in CRAO or other retinal ischemic diseases may be beneficial.

Amacrine Cells↗
PubMed2002

Genomic responses to herbal extracts: lessons from in vitro and in vivo studies with an extract of Ginkgo biloba.

Do herbal extracts offer effective dietary supplements to prevent deregulation of the transcriptome? Can they normalize deregulated transcriptomes of chronic human diseases? Are the effects of herbal extracts targeted to specific molecular pathways in tissue-specific manner? Are the effects of herbal supplements reversible? These questions pose important challenges to the fields of molecular nutrition and medicine, which are committed to understanding the molecular basis of physiology during health and disease. Transcription of the molecular information encoded in the deoxynucleotide sequences of DNA to the nucleotide sequences of RNA play a vital, causative, role in the coordinated adaptation of the organism to its changing environment and its nutritional needs. Pathogenesis is a manifestation of defects in transcription of the genome. Herbal extracts may target these obligatory processes. Increased availability of tools for quantitative and comprehensive analysis of messenger RNAs offer powerful means to understand and identify changes in these fundamental processes. Studies with the extract of Ginkgo biloba leaves show that the extract affects transcription of functionally diverse groups of genes in vitro and in vivo. The observations offer molecular evidence for bioactivity of the extract and offer an analytical strategy to define and predict physiological effects of complex mixtures of phytochemicals.

Animals↗
PubMed2026

P2X7 Receptor in Rare Diseases: Shared Molecular Mechanisms and Therapeutic Implications.

Rare diseases (RDs) are individually uncommon but collectively affect a large global population, and the vast majority still lack effective disease-modifying therapies. With advances in genomics and data-sharing platforms, research has increasingly shifted from a single-disease perspective to the search for convergent molecular pathways that might be shared across clinically distinct entities. In this context, the purinergic P2X7 receptor (P2X7R) has emerged as a putative "shared molecular platform" due to its central role in inflammation amplification, cell death and immune regulation. P2X7R is an ATP-gated ion channel with unique structural and functional features: under high extracellular ATP, it not only forms a non-selective cation channel but can also dilate into a "large pore" permeable to macromolecules, thereby triggering Ca2+overload, NLRP3 inflammasome assembly, reactive oxygen species (ROS) production and apoptotic/necrotic-like cell death. This review briefly outlines the epidemiology of RDs and the structural-functional characteristics of P2X7R, then systematically summarizes current evidence linking P2X7R to multiple rare diseases, including Charcot-Marie-Tooth disease, Guillain-Barré syndrome, amyotrophic lateral sclerosis, Huntington's disease, multiple sclerosis, and selected inflammatory and metabolic RDs (CAPS, familial Mediterranean fever, Systemic sclerosis, Dravet syndrome and Gaucher disease). By comparing P2X7R expression and functional alterations, downstream signaling pathways and pharmacological data from animal models across these conditions, we propose that a P2X7R-dependent network centered on a "Ca2+-NLRP3-inflammation/cell death axis" may constitute a common pathogenic backbone for diverse RDs. At the same time, disease-specific spatiotemporal expression patterns of P2X7R in central vs peripheral nervous systems and in immune vs target organ cells confer marked context dependence and "double-edged sword" properties. Finally, we discuss opportunities and challenges for P2X7R-targeted strategies, including the impact of disease stage and sex differences on therapeutic efficacy, and key bottlenecks in translating preclinical findings into clinical benefit. A deeper understanding of both shared and disease-specific roles of P2X7R may provide a conceptual framework and therapeutic entry point for precision stratification and multi-target interventions in rare diseases.

P2X7 receptor↗
PubMed2004

Increased regulatory activity of the calcineurin/NFAT pathway in human heart failure.

BACKGROUND: Cardiac hypertrophy may initiate progression to a compromised cardiac function. While the clinical consequences of hypertrophy are well understood, only little is known about the underlying molecular pathways. As reported from animal experiments, the Ca(2+)-calmodulin activated phosphatase calcineurin and its downstream transcriptional effector NFAT have been implicated as transducers of the hypertrophic response. METHODS AND RESULTS: To study whether the calcineurin pathway is activated in human heart failure, we investigated samples of human left ventricular myocardium from patients with dilated (idiopathic) cardiomyopathy (DCM, NYHA IV, n=8) in comparison with non-failing controls (NF, n=8). We not only analyzed the pathway by measuring the calcineurin activity, but also by determination of the protein expression of the calcineurin B subunit and additional key markers of the calcineurin signaling cascade (NFAT-3, GATA-4). Calcineurin enzymatic activity was increased by 80% in human dilated cardiomyopathy compared with non-failing human hearts (135.424+/-11.69 and 83.484+/-1.81 nmol Pi/min per microl). This was in line with increased protein expression of calcineurin B in DCM (71.18+9.11 vs. 46.41+/-11.23 densitometric units (DU)/microg protein). In order to verify the activated calcineurin pathway as described in animal models, we compared the protein expression of NFAT-3 in homogenates within nuclear extracts. In nuclear extracts the protein level of NFAT-3 was increased in dilated cardiomyopathy compared with non-failing myocardium (104.01+/-8.85 vs. 71.47+/-8.79 DU/microg protein). In contrast, in homogenates the expression of NFAT-3 was higher in the non-failing tissue indicating subcellular redistribution (19.56+/-3.36 vs. 25.84+/-3.16 DU/microg protein). The protein expression of GATA-4 was increased in DCM (43.14+/-2.89 vs. 29.87+/-2.17 DU/microg protein). CONCLUSIONS: In human heart failure (DCM) the calcineurin signaling pathway is activated not only by an increased activity of calcineurin and expression of GATA-4, but also by the shift from dephosphorylated NFAT-3 to the nucleus indicating subcellular redistribution and regulatory activation.

Adult↗
PubMed2005

The DRY motif as a molecular switch of the human oxytocin receptor.

The human oxytocin receptor is known to exhibit promiscuous activity by coupling to both Galpha(q) and Galpha(i) G proteins to activate distinct signaling pathways. A single-amino acid substitution within the highly conserved E/DRY motif at the cytosolic extension of helix 3 [i.e., D136(3.49)N] increased the rate of both basal and agonist-stimulated inositol phosphate (IP(3)) accumulation of the receptor. Furthermore, like for a typical constitutively active receptor, the partial agonist arginine vasopressin behaved as a full agonist for the D136(3.49)N mutant. Subsequently, both oxytocin and arginine vasopressin showed an increased potency in stimulating IP3 accumulation as compared to the wild-type receptor. Very interestingly, our experiments provide strong evidence that the D136(3.49)N mutant inhibits receptor signaling via Galpha(i)-mediated pathways while increasing the activity through the Galpha(q)-mediated pathways. Molecular simulations of the free and OT-bound forms of wild-type OTR and of the D136(3.49)N constitutively active mutant suggest that the receptor portions close to the E/DRY and NPxxY motifs are particularly susceptible to undergoing structural modification in response to activating mutations and agonist binding. Furthermore, computational modeling suggests that the OT-bound form of wild-type OTR is able to explore more states than the OT-bound form of the D136(3.49)N constitutively active mutant, consistent with its G protein promiscuity. Taken together, these observations emphasize the important role of the E/DRY motif not only in receptor activation but also in the promiscuity of G protein coupling. Knowledge of the mechanism of selective G protein coupling could aid drug discovery efforts to identify signaling specific therapies.

Amino Acid Motifs↗
PubMed2005

A SUMOylation-dependent pathway mediates transrepression of inflammatory response genes by PPAR-gamma.

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) has essential roles in adipogenesis and glucose homeostasis, and is a molecular target of insulin-sensitizing drugs. Although the ability of PPAR-gamma agonists to antagonize inflammatory responses by transrepression of nuclear factor kappa B (NF-kappaB) target genes is linked to antidiabetic and antiatherogenic actions, the mechanisms remain poorly understood. Here we report the identification of a molecular pathway by which PPAR-gamma represses the transcriptional activation of inflammatory response genes in mouse macrophages. The initial step of this pathway involves ligand-dependent SUMOylation of the PPAR-gamma ligand-binding domain, which targets PPAR-gamma to nuclear receptor corepressor (NCoR)-histone deacetylase-3 (HDAC3) complexes on inflammatory gene promoters. This in turn prevents recruitment of the ubiquitylation/19S proteosome machinery that normally mediates the signal-dependent removal of corepressor complexes required for gene activation. As a result, NCoR complexes are not cleared from the promoter and target genes are maintained in a repressed state. This mechanism provides an explanation for how an agonist-bound nuclear receptor can be converted from an activator of transcription to a promoter-specific repressor of NF-kappaB target genes that regulate immunity and homeostasis.

Animals↗
PubMed2005

Endocytic pathways and biological effects induced by UVB-dependent or ligand-dependent activation of the keratinocyte growth factor receptor.

UVB exposure of epidermal cells is known to trigger early and late molecular pathways dependent on receptor tyrosine kinases and reactive oxygen species (ROS). We have recently reported that UVB irradiation induces tyrosine phosphorylation, kinase activation, and internalization of the receptor for the keratinocyte growth factor (KGFR), a paracrine mediator of epithelial growth, differentiation, and survival. Here we analyzed in more detail the UVB-induced endocytic pathway of KGFR and the role of KGFR activation and internalization in regulating UVB-promoted apoptosis and cell cycle arrest. Immunogold electron microscopy and confocal analysis revealed that the UVB-induced endocytosis of KGFR occurs through clathrin-coated pits and that the internalized receptors are sorted to the degradative route and reach the lysosomal compartment with a timing similar to that induced by their ligand KGF. Treatment with the anti-oxidant N-acetylcysteine inhibited KGFR endocytosis, suggesting that the receptor internalization is mediated by the intracellular production of ROS. The ligand-independent KGFR endocytic pathway induced by UVB requires receptor kinase activity and tyrosine phosphorylation and involves transient receptor ubiquitination. Inhibition of KGFR activity reduces both the KGF-mediated proliferative response and the UVB-promoted apoptotic cell death, indicating a different effect of ligand-induced and UVB-induced KGFR triggering. In addition, receptor internalization leads to protection from apoptosis caused by UVB exposure. Finally, we compared directly the behavior of KGFR with that of the epidermal growth factor receptor (EGFR) upon UVB exposure. Surprisingly, biochemical and immunofluorescence analysis showed that EGFR, differently from KGFR, does not undergo UVB-induced tyrosine phosphorylation and internalization. Taken together, our results suggest a differential role of KGFR and EGFR in the response of epidermal cells to UVB possibly because KGFR endocytosis could be crucial for attenuation of survival signals in the suprabasal layers of human skin.

Animals↗
PubMed2005

Protein folding and diseases.

For most of proteins to be active, they need well-defined three-dimensional structures alone or in complex. Folding is a process through which newly synthesized proteins get to the native state. Protein folding inside cells is assisted by various chaperones and folding factors, and misfolded proteins are eliminated by the ubiquitin-proteasome degradation system to ensure high fidelity of protein expression. Under certain circumstances, misfolded proteins escape the degradation process, yielding to deposit of protein aggregates such as loop-sheet polymer and amyloid fibril. Diseases characterized by insoluble deposits of proteins have been recognized for long time and are grouped as conformational diseases. Study of protein folding mechanism is required for better understanding of the molecular pathway of such conformational diseases.

Alzheimer Disease↗