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J Rak

Publications and source records attributed to J Rak.

At least 37 records · Page 2Linked to original sources
PubMed2001

Possible mechanisms of acquired resistance to anti-angiogenic drugs: implications for the use of combination therapy approaches.

The ultimate target of anti-angiogenic drugs is the genetically stable, activated endothelial cell of a newly forming tumor blood vessel, rather than the genetically unstable tumor cell population per se. This led to the notion that acquired resistance to such drugs may not develop as readily, if at all. While there is some evidence that this lack of resistance development may be the case for some direct-acting angiogenesis inhibitors, it is becoming apparent that resistance can develop over time to many types of angiogenesis inhibitors including, possibly, some direct inhibitors, especially when used as monotherapies. Possible mechanisms for such acquired or induced resistance include: (i) redundancy of pro-angiogenic growth factors when the drug used targets a single such growth factor or its cognate endothelial cell-associated receptor tyrosine kinase; (ii) the anti-apoptotic/pro-survival function of growth factors such as VEGF, which, in high local concentrations, can antagonize the pro-apoptotic effects of various angiogenesis inhibitors; (iii) epigenetic, transient upregulation, or induction, of various anti-apoptotic effector molecules in host-endothelial cells; and (iv) heterogeneous vascular dependence of tumor cell populations. It is suggested that long-term disease control with anti-angiogenic drugs can be best achieved by judicious combination therapy. In this regard, the great molecular diversity of anti-angiogenic drug targets, in contrast to chemotherapy, makes this a particularly attractive therapeutic option, especially when approved, commercially available drugs considered to have anti-angiogenic effects are used in such combination treatment strategies.

Angiogenesis Inhibitors↗
PubMed2001

Multicellular gastric cancer spheroids recapitulate growth pattern and differentiation phenotype of human gastric carcinomas.

BACKGROUND & AIMS: Advanced gastric cancer has a poor prognosis and is largely unresponsive to currently available chemotherapeutic drugs. The development of more effective therapies would be aided by better preclinical models. METHODS: An in vitro multicellular gastric cancer spheroid model was established using the liquid overlay technique and compared with the corresponding xenografts in immunodeficient mice. RESULTS: Twelve of 17 (71%) gastric cancer cell lines reflected growth characteristics of their parental gastric carcinomas in three-dimensional culture. Thus, cell lines derived from peritoneal and pleural carcinomatosis grew as single cells (HSC-39, KATO-II, KATO-III) and cell aggregates (SNU-5, SNU-16). Cell lines representing adenosquamous (MKN-1) and tubular differentiation (MKN-28, MKN-74, N87) formed partly compact multicellular spheroids recapitulating the tumor architecture of the respective original tumor. The differentiated phenotype was lost after subcutaneous implantation of the in vitro spheroids in mice. The degree of morphologic differentiation was reflected by the levels of mucin and constitutive E-cadherin expression. Heterogeneous changes of other adhesion molecules (EpCAM, alpha2beta1, CD44s, Le(x), sLe(x)) were observed. In contrast, cell lines derived from poorly differentiated gastric carcinomas (Hs-746T, RF-1, RF-48) formed fully compact spheroids mimicking the poorly differentiated phenotype, were E-cadherin negative, and showed only CD44s up-regulation. CONCLUSIONS: Recapitulating some complexity of their in vivo counterparts, multicellular gastric cancer spheroids may represent a physiologically valid model for studying the biology of this cancer, and testing new therapeutic strategies.

Animals↗
PubMed2000

Observation of direct photons in central 158A GeV (208)P(208)b+Pb collisions

A measurement of direct photon production in 208Pb+208Pb collisions at 158A GeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central collisions is extracted as a function of transverse momentum in the interval 0.5 1.5 GeV/c. The result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions. It could be significant for diagnosis of quark-gluon-plasma formation.

Journal Article↗
PubMed2000

Oncogenes and tumor angiogenesis: the HPV-16 E6 oncoprotein activates the vascular endothelial growth factor (VEGF) gene promoter in a p53 independent manner.

Like other types of pre-malignant lesions and carcinoma, angiogenesis is associated with high-grade cervical dysplasia and with invasive squamous carcinoma of the cervix. Vascular endothelial cell growth factor (VEGF) is known to be one of the most important inducers of angiogenesis and is upregulated in carcinoma of the cervix. Human Papilloma Virus 16 (HPV-16) has been etiologically linked to human cervical cancer, and the major oncogenic proteins encoded by the viral genome, E6 and E7, are involved in the immortalization of target cells. Because several oncogenes including mutant ras, EGF receptor, ErbB2/Her2, c-myc and v-src upregulate VEGF expression, we asked whether HVP-16 E6 oncoprotein could act in a similar fashion. We found that HPV-16 E6-positive cells generally express high levels of VEGF message. Furthermore, co-expression of the VEGF promoter-Luc (luciferase) reporter gene with E6 in both human keratinocytes and mouse fibroblast showed that E6 oncoprotein upregulates VEGF promoter activity, and does so in a p53 independent manner. An E6 responsive region which comprises four Sp-1 sites, between -194 and -50 bp of the VEGF promoter, is also necessary for constitutive VEGF transcription. Taken together, our results suggest the possibility that the HPV oncoprotein E6 may contribute to tumor angiogenesis by direct stimulation of the VEGF gene.

Autocrine Communication↗
PubMed2000

Activated Ras prevents downregulation of Bcl-X(L) triggered by detachment from the extracellular matrix. A mechanism of Ras-induced resistance to anoikis in intestinal epithelial cells.

Detachment of epithelial cells from the extracellular matrix (ECM) results in a form of apoptosis often referred to as anoikis. Transformation of intestinal epithelial cells by oncogenic ras leads to resistance to anoikis, and this resistance is required for the full manifestation of the malignant phenotype. Previously, we demonstrated that ras-induced inhibition of anoikis in intestinal epithelial cells results, in part, from the ras-induced constitutive downregulation of Bak, a pro-apoptotic member of the Bcl-2 family. Since exogenous Bak could only partially restore susceptibility to anoikis in the ras-transformed cells, the existence of at least another component of the apoptotic machinery mediating the effect of activated ras on anoikis was suggested. Indeed, here we show that, in nonmalignant rat and human intestinal epithelial cells, detachment from the ECM or disruption of the cytoskeleton results in a significant downregulation of the antiapoptotic effector Bcl-X(L), and that activated H- or K-ras oncogenes completely abrogate this downregulation. In addition, we found that enforced downregulation of Bcl-X(L) in the ras-transformed cells promotes anoikis and significantly inhibits tumorigenicity, indicating that disruption of the adhesion-dependent regulation of Bcl-X(L) is an essential part of the molecular changes associated with transformation by ras. While the ras-induced downregulation of Bak could be reversed by pharmacological inhibition of phosphatidylinositol 3 kinase (PI 3-kinase), the effect of ras on Bcl-X(L) was PI 3-kinase- and mitogen-activated protein kinase (MAP kinase)-independent. We conclude that ras-induced resistance to anoikis in intestinal epithelial cells is mediated by at least two distinct mechanisms: one that triggers downregulation of Bak and another that stabilizes Bcl-X(L) expression in the absence of the ECM.

Animals↗
PubMed2000

Oncogenes and tumor angiogenesis: differential modes of vascular endothelial growth factor up-regulation in ras-transformed epithelial cells and fibroblasts.

A possible link between oncogenes and tumor angiogenesis has been implicated by the finding that expression of various oncogenes, particularly mutant ras, can lead to a marked induction of a potent paracrine stimulator of angiogenesis, vascular endothelial growth factor (VEGF). We sought to determine how oncogenic ras induction of VEGF is mediated at the molecular level and whether the mechanisms involved differ fundamentally between transformed epithelial cells and fibroblasts. Our results suggest that in a subline (called RAS-3) of immortalized nontumorigenic rat intestinal epithelial cells (IEC-18) that acquired a tumorigenic phenotype upon transfection of mutant ras, up-regulation of VEGF occurs in the absence of an autocrine growth factor circuit. The expression of VEGF mRNA and protein by RAS-3 cells was strongly suppressed in the presence of LY294002, an inhibitor of phosphatidylinositol 3'-kinase, but remained largely unaffected in the same cells treated with an inhibitor (PD98059) of mitogen-activated protein/extracellular signal-regulated kinase kinase 1 (MKK/MEK-1). This is consistent with the observation that overexpression of a constitutively activated mutant of MEK-1 (AN3/ S222D) in the parental IEC-18 cells did not result in up-regulation of VEGF production. The impact of mutant ras on VEGF expression was also significantly amplified at high cell density, conditions under which RAS-3 cells became less sensitive to LY294002-induced VEGF down-regulation. In marked contrast to cells of epithelial origin, ras-transformed murine fibroblasts (3T3RAS) up-regulated VEGF in a manner that was strongly inhibitable by MEK-1 blockade (ie. treatment with PD98059), whereas these cells were relatively unaffected by treatment with the phosphatidylinositol 3'-kinase inhibitor LY294002. In addition, VEGF was up-regulated by 2-3-fold in NIH3T3 cells overexpressing mutant MEK-1. Collectively, the data suggest that the stimulatory effect of mutant ras on VEGF expression is executed in a nonautocrine and cell type-dependent manner and that it can be significantly exacerbated by physiological/ environmental influences such as high cell density.

3T3 Cells↗
PubMed2000

'Accidental' anti-angiogenic drugs. anti-oncogene directed signal transduction inhibitors and conventional chemotherapeutic agents as examples.

A number of drugs currently being tested in clinical trials as possible angiogenesis inhibitors were not originally developed with the intention of suppressing tumour angiogenesis. Thalidomide and interferon alpha are obvious examples of such drugs. This list of 'accidental' angiogenesis inhibitors may include established agents such as conventional cytotoxic chemotherapeutic drugs as well as the new generation of anticancer drugs known as anti-oncoprotein signal transduction inhibitors. With respect to the former, the potential of such drugs to inhibit angiogenesis could be the result of their ability to cause collateral damaging effects on cycling endothelial cells found in newly formed blood vessels, or inhibiting other vital endothelial cell functions necessary for angiogenesis. The antitumour vascular side-effects of chemotherapy may be optimised by administering such drugs continuously on a more frequent (e.g. weekly or even daily) basis at levels well below the maximum tolerated dose (MTD), especially when this is done in combination with newly developed anti-angiogenic drugs such as vascular endothelial cell growth factor (VEGF) receptor blocking antibodies. This strategy may minimise or delay the problems of host toxicity and acquired drug resistance. The possibility of anti-angiogenic effects mediated by signal transduction inhibitors such as ras farnesyltransferase inhibitors (ras FTI's), or drugs which block receptor tyrosine kinases (e.g. ErbB2/neu) such as Herceptin, may be the consequence of such oncogenes inducing or upregulating various pro-angiogenic molecules such as VEGF (vascular endothelial cell growth factor) in tumour cells. Hence, treatment of tumour cells with such drugs can lead to downregulation of tumour cell-associated VEGF expression and this can contribute to an anti-angiogenic effect of the drug in vivo. In addition, some of these drugs may also affect certain 'activated' endothelial cell functions directly so as to block angiogenesis. An awareness of the potential of such conventional or experimental anticancer drugs to affect tumour growth through blockade or suppression of angiogenesis has implications for how anticancer drugs may be used clinically, either alone, or in combination with other drugs to optimally treat cancer.

Angiogenesis Inhibitors↗
PubMed2000

Oncogenes and angiogenesis: signaling three-dimensional tumor growth.

Three-dimensional tumor growth is dependent on the perpetual recruitment of host blood vessels to the tumor site. This recruitment process (mainly via angiogenesis) is thought to be triggered, at least in part, by the very same set of genetic alterations (activated oncogenes, inactivated/lost tumor suppressor genes) as those responsible for other aspects of malignant transformation (e.g., aberrant mitogenesis, resistance to apoptosis). Potent oncogenes are able to deregulate expression of both angiogenesis stimulators and inhibitors in cancer cells. For example, mutant ras expression is associated with increased production of vascular endothelial growth factor (VEGF) and downregulation of thrombospondin-1 (TSP-1). Upregulation of VEGF and angiogenesis can also be induced by constitutive activation of other oncogenic proteins (e.g., EGFR, Raf, MEK, PI3K) acting at various levels on the Ras signaling pathway. The mode and the magnitude of such proangiogenic influences can be significantly modified by cell type (fibroblastic or epithelial origin), epigenetic factors (hypoxia, changes in cell density), and/or presence of additional genetic lesions (e.g., preceding loss of p16 or p53 tumor suppressor genes). Activated oncogenes (e.g., ras, src, HER-2) induce co-expression of angiogenic properties concomitantly with several highly selectable traits (increased mitogenesis, resistance to apoptosis), a circumstance that may accelerate selection of the angiogenic phenotype at the cell population level. On the other hand oncogene-induced reduction in growth requirements may also endow tumor cells with a diminished (albeit not abrogated) dependence on (close) proximity to blood vessels, i.e., with reduced vascular dependence. Thus, oncogenes can impact several interconnected aspects of cellular growth, survival, and angiogenesis. Experimental evidence suggests that, in principle, many of these properties (including angiogenesis) can be simultaneously suppressed (and tumor stasis or regression induced) by effective use of the specific oncogene antagonists and signal transduction inhibitors.

Animals↗
PubMed2000

Continuous low-dose therapy with vinblastine and VEGF receptor-2 antibody induces sustained tumor regression without overt toxicity.

Various conventional chemotherapeutic drugs can block angiogenesis or even kill activated, dividing endothelial cells. Such effects may contribute to the antitumor efficacy of chemotherapy in vivo and may delay or prevent the acquisition of drug-resistance by cancer cells. We have implemented a treatment regimen that augments the potential antivascular effects of chemotherapy, that is devoid of obvious toxic side effects, and that obstructs the development of drug resistance by tumor cells. Xenografts of 2 independent neuroblastoma cell lines were subjected to either continuous treatment with low doses of vinblastine, a monoclonal neutralizing antibody (DC101) targeting the flk-1/KDR (type 2) receptor for VEGF, or both agents together. The rationale for this combination was that any antivascular effects of the low-dose chemotherapy would be selectively enhanced in cells of newly formed vessels when survival signals mediated by VEGF are blocked. Both DC101 and low-dose vinblastine treatment individually resulted in significant but transient xenograft regression, diminished tumor vascularity, and direct inhibition of angiogenesis. Remarkably, the combination therapy resulted in full and sustained regressions of large established tumors, without an ensuing increase in host toxicity or any signs of acquired drug resistance during the course of treatment, which lasted for >6 months. This article may have been published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

Animals↗
PubMed2000

[Branchiogenic cysts registered at the Otolaryngology Clinic of Medical University in Wrocław in years 1989-1998].

Lateral branchiogenic cysts are relatively rare among neck tumours. However they belong to the most frequent developmental malformation in this area. Their etiology and pathogenesis is not fully explained yet. Over the period of ten years there were 76 patients hospitalized in our clinic with the diagnosis of the lateral branchiogenic cyst. Its prevalence was similar in both sexes and ranged from 3 months to 62 years of age. More than half of the patients were children. In 2 cases, a rare primary cancer rising from a branchiogenic cyst was diagnosed. Positive family history was observed in two children. Surgery was performed in 59 patients. Unsatisfactory results of the surgery were noted in 6 cases and 4 of them were reoperated because of the recurrence. In the case of brachiogenic cysts a full oncologic diagnostics should be performed, as it is done with neck tumour management. The procedures, which enable us to estimate character and extent of a lesion and determine the proper surgical treatment, should include ultrasonography, fine-needle biopsy or CT.

Adolescent↗
PubMed1999

Marked induction of the IAP family antiapoptotic proteins survivin and XIAP by VEGF in vascular endothelial cells.

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that has been shown to act as an endothelial cell mitogen as well as a vascular permeability factor. Several recent reports have also implicated VEGF as a major survival factor for endothelial cells during angiogenesis and vasculogenesis along with other growth factors such as bFGF and angiopoietin-1. VEGF has been shown to mediate this additional function, at least in part through the induction of bcl-2 and the activation of the PI3 kinase-Akt/PKB signaling pathway. We report here that VEGF can also mediate the induction/upregulation of members of a newly discovered family of antiapoptotic proteins, namely the Inhibitors of Apoptosis (IAP), in vascular endothelial cells. We show that VEGF(165) leads to the induction of XIAP (2.9-fold) and survivin (19.1-fold) protein in human umbilical vein endothelial cells (HUVECs). In contrast, bFGF had little effect on XIAP expression, but produced approximately a 10-fold induction on survivin. VEGF-dependent upregulation of survivin could be prevented by cell cycle arrest in the G1 and S phases. These findings implicate that the survival and mitotic functions of VEGF in an angiogenic context may be more intrinsically related than previously anticipated. Moreover, they also raise the possibility of therapeutically targeting XIAP or survivin in antiangiogenic therapy as a means of suppressing tumor growth, in addition to directly targeting tumor cells which express these survival proteins.

Apoptosis↗
PubMed1999

Functional dissociation of anoikis-like cell death and activity of stress activated protein kinase.

Adhesion to the extracellular matrix is a crucial survival signal for epithelial and endothelial cells. Both cell types activate an endogenous death program termed "anoikis" when detached from the solid substratum. The signaling events culminating in anoikis are still unclear; recent studies have implicated Stress Activated Protein Kinase (SAPK), also known as Jun-N-Terminal kinase, as a potentially crucial signal transducer and mediator of anoikis. However, the generality and the causal role of SAPK in anoikis remain unclear and controversial. For these reasons we decided to examine the relationship between induction of anoikis and SAPK activation in three independent cell systems. We report here that in immortalized rat intestinal epithelial cells (IEC-18) and human umbilical vein endothelial cells (HUVEC), SAPK is activated weakly and transiently upon cell detachment while in canine kidney epithelial cells (MDCK) such induction is strong and protracted. However, cell types fail to commit to anoikis after remaining in three-dimensional culture for the time required for complete activation of SAPK. This suggests that there is no temporal correlation between SAPK activation and the onset of anoikis in any of the cell lines studied. We further examined the potential involvement of SAPK in the IEC-18 system by investigating a ras oncogene-transformed variant of IEC-18 cells (IEC-18 Ras 3) which are highly resistant to anoikis. Ras expression did not abrogate activation of SAPK, although these cells do exhibit altered kinetics of SAPK induction upon cell detachment. These results suggest that SAPK is not involved in anoikis regulation and that SAPK activation is likely a cell-type-specific epi-phenomenon.

Animals↗
PubMed1999

Normoxic and hypoxic regulation of vascular endothelial growth factor (VEGF) by astrocytoma cells is mediated by Ras.

Vascular endothelial growth Factor (VEGF) has been identified as a key angiogenic factor involved in the growth and malignant progression of tumours. Glioblastoma multiforme (GBM) are the most common primary human brain tumours, histo-pathologically characterized by intense tumour angiogenesis. GBMs do not harbour oncogenic Ras mutations, but there is a functional up-regulation of Ras signaling through activation of receptor tyrosine kinases overexpressed by these tumours. We demonstrate that Ras pathway activation regulates VEGF secretion in astrocytoma cell lines. Ras pathway inhibition was carried out using genetic and pharmacologic techniques. Astrocytoma cells that were transfected to express the dominant inhibitory mutant H-Ras(N17) demonstrated a reduction in VEGF secretion under both normoxic and hypoxic conditions. Cells treated with the farnesyl transferase inhibitor L-744,832 demonstrated similar reductions in VEGF secretion. Furthermore, astrocytoma cells expressing a constitutively phosphorylated and truncated EGF-R common in GBMs (EGFRvIII or p140(EGF-R)) demonstrate further elevations in Ras activation, resulting in a further increase in VEGF secretion. We have previously demonstrated that activation of Ras plays a vital role in transducing mitogenic signals in human malignant astrocytoma cells. Our present results further extend the role of Ras activation in modulating tumour angiogenesis in these tumours. We propose that Ras may contribute to the angiogenic switch in astrocytomas.

3T3 Cells↗
PubMed1999

Interleukin-6 dependent induction of the cyclin dependent kinase inhibitor p21WAF1/CIP1 is lost during progression of human malignant melanoma.

Human melanoma cell lines derived from early stage primary tumors are particularly sensitive to growth arrest induced by interleukin-6 (IL-6). This response is lost in cell lines derived from advanced lesions, a phenomenon which may contribute to tumor aggressiveness. We sought to determine whether resistance to growth inhibition by IL-6 can be explained by oncogenic alterations in cell cycle regulators or relevant components of intracellular signaling. Our results show that IL-6 treatment of early stage melanoma cell lines caused G1 arrest, which could not be explained by changes in levels of G1 cyclins (D1, E), cdks (cdk4, cdk2) or by loss of cyclin/cdk complex formation. Instead, IL-6 caused a marked induction of the cdk inhibitor p21WAF1/CIP1 in three different IL-6 sensitive cell lines, two of which also showed a marked accumulation of the cdk inhibitor p27Kip1. In contrast, IL-6 failed to induce p21WAF1/CIP1 transcript and did not increase p21WAF1/CIP1 or p27kip1 proteins in any of the resistant lines. In fact, of five IL-6 resistant cell lines, only two expressed detectable levels of p21WAF1/CIP1 mRNA and protein, while in three other lines, p21WAF1/CIP1 was undetectable. IL-6 dependent upregulation of p21WAF1/CIP1 was associated with binding of both STAT3 and STAT1 to the p21WAF1/CIP1 promoter. Surprisingly, however, IL-6 stimulated STAT binding to this promoter in both sensitive and resistant cell lines (with one exception), suggesting that gross deregulation of this event is not the unifying cause of the defect in p21WAF1/CIP1 induction in IL-6 resistant cells. In somatic cell hybrids of IL-6 sensitive and resistant cell lines, the resistant phenotype was dominant and IL-6 failed to induce p21WAF1/CIP1. Thus, our results suggest that in early stage human melanoma cells, IL-6 induced growth inhibition involves induction of p21WAF1/CIP1 which is lost in the course of tumor progression presumably as a result of a dominant oncogenic event.

Cell Cycle Proteins↗
PubMed1999

Epidermal growth factor receptor (EGFR), proliferating cell nuclear antigen (PCNA) and Ki-67 antigen in laryngeal epithelial lesions.

The epidermal growth factor receptor (EGFR), proliferating cell nuclear antigen (PCNA) and Ki-67 immunostaining in paraffin sections from 154 cases of laryngeal squamous cell carcinoma, 25 specimens of normal and hyperplastic laryngeal epithelium, and 21 preneoplastic lesions was examined. The difference of EGFR expression and PCNA score between laryngeal cancer and dysplastic lesions vs normal and hyperplastic epithelium was significant. There was significant difference in Ki-67 score between malignant vs premalignant lesions and normal and hyperplastic epithelium. There was significant correlation between PCNA score and histopathological grading of the tumour. The highest PCNA expression was detected in stage G3. Our findings have shown that PCNA and Ki-67 staining can be used as a marker of cell proliferative activity in laryngeal epithelial lesions. EGFR, PCNA and Ki-67 expression correlate with severity of laryngeal lesions. PCNA immunostaining can aid in estimating the histological grade of malignant lesions.

Carcinoma, Squamous Cell↗
PubMed1999

Collateral expression of proangiogenic and tumorigenic properties in intestinal epithelial cell variants selected for resistance to anoikis.

Although in vitro anchorage-independent growth is widely used as a marker of cell transformation, the biological implications of this trait are poorly understood. We previously demonstrated that enforced anchorage-independent growth of a nontumorigenic, immortalized epithelial cell line (IEC-18) in multicellular spheroid culture results in massive apoptotic cell death. This death process, termed anoikis, is prevented by expression of transforming oncogenes, which also confer tumorigenic competence. This study examines whether acquisition of an anoikis-resistant phenotype is causally related to the tumorigenic capacity of transformed epithelial cells. Parental IEC-18 cells were subjected to 10 cycles of selection for survival in speroid culture. Unlike parental cells, the resulting anoikis-resistant variants (AR1.10 and AR2.10) formed relatively large tumors in nude mice. Both anoikis-resistant sublines displayed upregulated expression of vascular endothelial growth factor (VEGF), a potent angiogenesis stimulator. VEGF121 overexpression alone did not induce tumorigenic conversion of parental IEC-18 cells, which remained highly susceptible to anoikis. We postulate that both anoikis-resistance and angiogenic-competence contribute to tumor formation. Development of anoikis-resistance can be then viewed as a precondition for expression of the tumorigenic phenotype. Our results suggest that even when angiogenesis is not a rate limiting factor (e.g. in vitro) the selective pressures of solid tumor-like, 3-dimensional growth conditions favoring anoikis resistance result in collateral induction of a proangiogenic phenotype.

Animals↗
PubMed1998

Downregulation of the pro-apoptotic protein Bak is required for the ras-induced transformation of intestinal epithelial cells.

Anoikis is a form of programmed cell death induced in normal epithelial cells by detachment from the extracellular matrix [1] [2] [3]. In epithelial cells of the intestine and other organs, activated rasinduces resistance to anoikis [3] [4], but the actual molecular effectors directly involved in the apoptotic machinery that execute or block anoikis have not yet been identified. Bak, a pro-apoptotic member of the Bcl-2 family, is downregulated in a high proportion of colorectal tumours [5]. In addition, Bak is an important regulator of apoptosis in normal intestinal epithelial cells [6] [7]. Here, we show that activated rasinduces the downregulation of Bak in rat and human intestinal epithelial cells. This ras-induced downregulation of Bak expression could be suppressed by an inhibitor of phosphatidylinositol (PI) 3-kinase, an enzyme already implicated in ras-induced resistance to anoikis [8]. Ectopic expression of Bak in ras-transformed rat intestinal epithelial IEC-18 cells inhibited ras-induced resistance to anoikis and significantly reduced their tumorigenicity. We conclude, therefore, that the ability of rasto downregulate Bak, and the consequent resistance to anoikis, are essential components of the transforming capacity of this oncogene in intestinal epithelial cells.

Animals↗