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M Schmitt

Publications and source records attributed to M Schmitt.

At least 91 records · Page 5Linked to original sources
PubMed2001

Proteolysis of oxidized proteins after oxygen-glucose deprivation in rat cortical neurons is mediated by the proteasome.

Oxidative injury contributes to cellular damage during and after cerebral ischemia. However, the downstream catabolic pathways of damaged cellular components in neurons are largely unknown. In the current study, the authors examined the formation of oxidized proteins and their active degradation by the proteasome. In near-pure rat primary cortical neurons, it was found that protein-bound carbonyls as markers for oxidized proteins are increased after oxygen-glucose deprivation (OGD). During and after OGD, degradation of proteins metabolically radiolabeled before OGD increases two-to threefold compared with the normal protein turnover. Proteolysis after reoxygenation was attenuated by the presence of dimethylthiourea, a radical scavenger, and was blocked by lactacystin, a specific proteasome inhibitor. Lactacystin also increased the amount of protein carbonyls formed. In contrast, the activity of the proteasome complex itself after OGD was not different from sham-washed controls. The authors suggest that oxygen-glucose deprivation increases free radicals, which, in turn, oxidize proteins that are recognized and actively degraded by the proteasome complex. This protease itself is relatively resistant against oxidative injury. The authors conclude that the proteasome may be an active part of the cellular defense system against oxidative stress after cerebral ischemia.

Acetylcysteine↗
PubMed2001

beta(3)A-integrin downregulates the urokinase-type plasminogen activator receptor (u-PAR) through a PEA3/ets transcriptional silencing element in the u-PAR promoter.

Migration of cells requires interactions with the extracellular matrix mediated, in part, by integrins, proteases, and their receptors. Previous studies have shown that beta(3)-integrin interacts with the urokinase-type plasminogen activator receptor (u-PAR) at the cell surface. Since integrins mediate signaling into the cell, the current study was undertaken to determine if in addition beta(3)-integrin regulates u-PAR expression. Overexpression of beta(3)-integrin in CHO cells, which are avid expressers of the receptor, downregulated u-PAR protein and mRNA expression. The u-PAR promoter (-1,469 bp) that is normally constitutively active in CHO cells was downregulated by induced beta(3)-integrin expression. A region between -398 and -197 bp of the u-PAR promoter was critical for beta(3)-integrin-induced downregulation of u-PAR promoter activity. Deletion of the PEA3/ets motif at -248 bp substantially impaired the ability of beta(3)-integrin to downregulate the u-PAR promoter, suggesting that the PEA3/ets site acts as a silencing element. An expression vector encoding the transcription factor PEA3 caused inhibition of the wild-type but not the PEA3/ets-deleted u-PAR promoter. The PEA3/ets site bound nuclear factors from CHO cells specifically, but binding was enhanced when beta(3)-integrin was overexpressed. A PEA3 antibody inhibited DNA-protein complex formation, indicating the presence of PEA3. Downregulation of the u-PAR promoter was achieved by the beta(3)A-integrin isoform but not by other beta(3)-integrin isoforms and required the cytoplasmic membrane NITY(759) motif. Moreover, overexpression of the short but not the long isoform of the beta(3)-integrin adapter protein beta(3)-endonexin blocked u-PAR promoter activity through the PEA3/ets binding site. Thus, besides the physical interaction of beta(3)-integrin and u-PAR at the cell surface, beta(3) signaling is implicated in the regulation of u-PAR gene transcription, suggesting a mutual regulation of adhesion and proteolysis receptors.

Amino Acid Sequence↗
PubMed2001

Clinical relevance of the plasminogen activator inhibitor type 1--a multifaceted proteolytic factor.

The plasminogen activator inhibitor type-1 (PAI-1) is a multifaceted proteolytic factor. It not only functions as an inhibitor of the protease uPA (urokinase-type plasminogen activator), but also plays an important role in signal transduction, cell adherence, and cell migration. Thus--an apparent paradox considering its name--although it inhibits uPA during blood coagulation, it actually promotes invasion and metastasis. In the early 1990s, clinical evidence associated elevated PAI-1 levels in tumor tissue with poor clinical outcome in primary breast cancer. These clinical data have since been supported by experimental evidence that the concerted action of uPA, its cell surface receptor uPA-R, and PAI-1 facilitates invasion and metastasis. The strong prognostic impact of PAI-1 in primary breast cancer has been validated by international research groups assessing fresh tumor tissue extracts by ELISA. There is clinical evidence that high-risk patients with elevated PAI-1 in their tumor benefit from adjuvant systemic therapy. uPA also has a strong prognostic impact in primary breast cancer. In node-negative breast cancer, risk-group selection for adjuvant systemic therapy based on tumor levels of both PAI-1 and uPA is close to routine clinical use. Also in other malignancies such as ovarian, esophageal, gastric, colorectal or hepatocellular cancer, elevated PAI-1 is associated with tumor aggressiveness and poor patient outcome. This abundant clinical evidence implicating PAI-1 as a key factor for tumor invasion and metastasis renders it a promising target for tumor therapy. Novel therapeutic approaches targeting the PAI-1/uPA interaction are already in pre-clinical testing.

Biomarkers, Tumor↗
PubMed2001

Interaction between hydroxypropyl methylcellulose and biphasic calcium phosphate after steam sterilisation: capillary gas chromatography studies.

The purpose of this study was to check the chemical stability of an injectable bone substitute (IBS) composed of a 50/50 w/w mixture of 2.92% hydroxypropyl methylcellulose (HPMC) solution in deionized water containing biphasic calcium phosphate (BCP) granules (60% hydroxyapatite/40% beta-tricalcium phosphate w/w). After separation of the organic and mineral phases, capillary gas chromatography (GC) was used to study the possible modification of HPMC due to the contact with BCP granules following steam sterilisation and 32 days storage at room temperature. HPMC was extracted from IBS in aqueous medium, and a dialytic method was then used to extract calcium phosphate salts from the HPMC. The percentage of HPMC extracted from BCP was 98.5%+/-0.5%, as measured by UV. GC showed no chemical modifications after steam sterilisation and storage.

Biocompatible Materials↗
PubMed2001

The uPA/uPA receptor system as a target for tumor therapy.

Invasiveness of a variety of tumors depends on the regulated expression of proteolytic enzymes that degrade the surrounding extracellular matrix and dissociate cell-cell and/or cell-matrix attachments. The tumor cell surface-associated urokinase-type plasminogen activator (uPA) system plays an especially important role in tumor cell invasion and metastasis. It consists of the serine protease uPA, its membrane-bound receptor (uPAR, CD87) and one of the natural inhibitors PAI-1 or PAI-2. There are strong indications based on animal experiments that interference with this system by inhibiting the enzymatic activity of uPA and/or antagonizing its binding to the receptor is of therapeutic relevance. With the recent solution of various X-ray structures of uPA/inhibitor complexes, structural information is available for optimizing existing lead compounds in their affinity and selectivity for uPA. Furthermore, peptide compounds capable of mimicking the structural epitope of uPA responsible for binding to the receptor efficiently antagonize this recognition process. Thus, both approaches prove to be well suited for the design of highly promising drugs in human medicine.

Journal Article↗
PubMed2001

High level synthesis of recombinant soluble urokinase receptor (CD87) by ovarian cancer cells reduces intraperitoneal tumor growth and spread in nude mice.

Focussing of the serine protease urokinase (uPA) to the tumor cell surface via interaction with its receptor (uPAR) is an important step in tumor invasion and metastasis. The human ovarian cancer cell line OV-MZ-6#8 was stably transfected with expression plasmids either encoding cell-associated uPAR (GPI-uPAR) or a soluble form of uPAR (suPAR) lacking its glycan lipid anchor. In vitro, high level synthesis of functionally active recombinant suPAR inhibited cell proliferation and led to reduced cell-associated fibrin matrix degradation, whereas fibrinolytic activity was increased in OV-MZ-6#8 cells overexpressing GPI-uPAR. Both OV-MZ-6#8-derived clones were inoculated into the peritoneum of nude mice and tested for tumor growth and spread. High level synthesis of recombinant suPAR (without altering the physiological expression levels of GPI-uPAR and uPA in these cells) resulted in a significant reduction of tumor burden (up to 86%) in the xenogeneic mouse model. In contrast, overexpression of GPI-uPAR in tumor cells did not affect tumor growth. Our results demonstrate that high levels of suPAR in the ovarian cancer cell vicinity can act as a potent scavenger for uPA, thereby significantly reducing tumor cell growth and cancer progression in vivo.

Animals↗
PubMed2001

Cyclo19,31[D-Cys19]-uPA19-31 is a potent competitive antagonist of the interaction of urokinase-type plasminogen activator with its receptor (CD87).

Urokinase-type plasminogen activator (uPA) represents a central molecule in pericellular proteolysis and is implicated in a variety of physiological and pathophysiological processes such as tissue remodelling, wound healing, tumor invasion, and metastasis. uPA binds with high affinity to a specific cell surface receptor, uPAR (CD87), via a well defined sequence within the N-terminal region of uPA (uPA19-31). This interaction directs the proteolytic activity of uPA to the cell surface which represents an important step in tumor cell proliferation, invasion, and metastasis. Due to its fundamental role in these processes, the uPA/uPAR-system has emerged as a novel target for tumor therapy. Previously, we have identified a synthetic, cyclic, uPA-derived peptide, cyclo19,31uPA19-31, as a lead structure for the development of low molecular weight uPA-analogues, capable of blocking uPA/uPAR-interaction [Burgle et al., Biol. Chem. 378 (1997), 231-237]. We now searched for peptide variants of cyclo19,31uPA19-31 with elevated affinities for uPAR binding. Among other tasks, we performed a systematic D-amino acid scan of uPA19-31, in which each of the 13 L-amino acids was individually substituted by the corresponding D-amino acid. This led to the identification of cyclo19,31[D-Cys19]-uPA19-31 as a potent inhibitor of uPA/uPAR-interaction, displaying only a 20 to 40-fold lower binding capacity as compared to the naturally occurring uPAR-ligands uPA and its amino-terminal fragment. Cyclo19,31[D-Cys19]-uPA19-31 not only blocks binding of uPA to uPAR but is also capable of efficiently displacing uPAR-bound uPA from the cell surface and to inhibit uPA-mediated, tumor cell-associated plasminogen activation and fibrin degradation. Thus, cyclo19,31[D-Cys19]-uPA19-31 represents a promising therapeutic agent to significantly affect the tumor-associated uPA/uPAR-system.

Amino Acid Substitution↗
PubMed2001

Interference with the urokinase plasminogen activator system: a promising therapy concept for solid tumours.

There is abundant evidence that the plasminogen activator (PA) system with its key components uPA (urokinase-type plasminogen activator), its cell surface receptor uPA-R (CD87) and its inhibitor PAI-1 plays a key role in tumour invasion and metastasis. Elevated levels of these factors in tumour tissue are associated with tumour aggressiveness and poor patient outcome. Animal models suggest that the PA system is not essential for fertility or survival under physiological conditions. Thus, it seems well suited as a therapeutic target for patients with solid malignant tumours. Novel therapy concepts targeting the uPA system are currently being explored. A variety of different synthetic uPA inhibitor classes have been developed over the last decades. First generation inhibitors displayed a low uPA inhibitory potency combined with broad specificity. More recently, structure based design, x-ray crystallographic screening or NMR based screening have revealed a large number of new, potent and selective uPA-inhibitors. A few modern compounds have shown promising results in preclinical testing and are now ready for Phase I clinical studies. Other therapeutic strategies such as antagonists of uPA/uPA-R interaction or gene therapeutic approaches to suppress the uPA-system are still being evaluated in in vitro and in vivo models. For clinical application, a combination therapy targeting more than one of the interacting proteolytic pathways may be required for effective antiproteolytic therapy. In addition, antiproteolytic agents may provide additive or synergistic treatment benefits if used in combination together with conventional therapeutics, in particular in those solid tumours for which potent conventional regimens already exist.

Animals↗
PubMed2001

Increased expression of matrix metalloproteinases (MMP)-2, MMP-9, and the urokinase-type plasminogen activator is associated with progression from benign to advanced ovarian cancer.

Proteases are linked to the malignant phenotype of different solid tumors. Therefore, the expression of the matrix metalloproteinase (MMP)-2 and MMP-9 and of the serine protease urokinase-type plasminogen activator (uPA) and its inhibitor plasminogen activator inhibitor type 1 (PAI-1) in the progression of ovarian cancer was investigated. Gelatinolytic activity and protein expression of MMP-2 and MMP-9 were analyzed in tissue extracts of 19 cystadenomas and 18 low malignant potential (LMP) tumors, as well as 41 primary tumors of advanced ovarian cancer stage International Federation of Gynecology and Obstetrics IIIc/IV and their corresponding omentum metastases by quantitative gelatin zymography and Western blot. In the same tissue extracts, antigen levels of uPA and its inhibitor PAI-1 were determined by ELISA. Protein expression of pro-MMP-2 (72 kDa) and pro-MMP-9 (92 kDa as well as antigen levels of uPA and PAI-1 were low in benign ovarian tumors but increased significantly from LMP tumors to advanced ovarian cancers. The highest values of all of the proteolytic factors were detected in omentum metastases. Active MMP-2 enzyme (62 kDa) was detected only in ovarian cancer (66%) and corresponding metastases (93%) but never in benign or LMP tumors. The activation rate of MMP-2 to its active isoform was higher in the metastases. Comparing both proteolytic systems, higher PAI-1 concentrations were consistently found in cancers with high pro-MMP-9 expression. These data indicate that members of the plasminogen activator system, as well as the metalloproteinases MMP-2/9, increase with growing malignant potential of ovarian tumors. These findings are of particular relevance to the development of protease inhibitors as new therapeutic approaches in ovarian cancer.

Adult↗
PubMed2001

Prognostic impact of proteolytic factors (urokinase-type plasminogen activator, plasminogen activator inhibitor 1, and cathepsins B, D, and L) in primary breast cancer reflects effects of adjuvant systemic therapy.

PURPOSE: Prognostic and predictive impact of five proteolytic factors associated with tumor invasion and metastasis in primary breast cancer were evaluated after long-term follow-up. EXPERIMENTAL DESIGN: Antigen levels of urokinase-type plasminogen activator, plasminogen activator inhibitor-1 (PAI-1), Cathepsins B, D, and L were determined using immunochemical assays in primary tumor tissue of 276 patients. RESULTS: During follow-up (median 109 months), 119 (43%) patients relapsed, and 117 (42%) died. In the whole collective, lymph node status (P < 0.001; RR 3.8), Cathepsin L (P < 0.001; RR 2.6), and PAI-1 (P = 0.027; RR 1.7) were the only independent significant factors in multivariate analysis for disease-free survival (DFS). For overall survival (OS), lymph node status (P < 0.001; RR 2.9), Cathepsin L (P = 0.017; RR 1.9), PAI-1 (P = 0.01; RR 1.9), and grading (P = 0.026; RR 1.7) were significant. In the node-negative subgroup, PAI-1 was the only significant factor for DFS (P = 0.004; RR 3.7) and the strongest factor (P = 0.004; RR 3.7) for OS next to grading (P = 0.017; RR 3.1). In node-positive patients, Cathepsin L was the only significant factor for both DFS (P < 0.001; RR 3.2) and OS (P = 0.003; RR 2.5). For all proteolytic factors but Cathepsin L, the univariate prognostic impact on DFS was substantial in patients without adjuvant systemic therapy but was diminished if adjuvant therapy had been administered. Cathepsin L maintained its strong prognostic impact on DFS even in patients with adjuvant endocrine therapy (P = 0.01; RR 2.8). CONCLUSIONS: The observed effect of adjuvant systemic therapy on their prognostic strength suggests that the assessed proteolytic factors supply predictive information on therapy response.

Adult↗
PubMed2001

Quantitative assessment of the expression of melanoma-associated antigens by non-competitive reverse transcription polymerase chain reaction.

The assessment of tumor-associated antigens (TAA) recognized by T lymphocytes is a prerequisite for diagnosis and immunotherapy of melanoma. Different reverse transcription-polymerase chain reaction (RT-PCR) protocols allowing the quantification of the TAA mRNA expression in the solid tumor or the detection of circulating melanoma cells have been described. We have recently shown a positive correlation between the amount of specific product formed by RT-PCR and the staining intensity in immunohistochemical analysis of the corresponding sample. Here we describe a quantification procedure based on the direct digitization of the PCR products after separation on ethidium bromide-stained agarose gels, followed by computer-assisted densitometry. To standardize our method, we examined the linear range of the densitometric quantification procedure as reflected by the correlation of signal intensity to the amount of the corresponding DNA. As an internal measure for the so-termed cDNA in the different samples after RNA isolation and reverse transcription, a beta-actin PCR was introduced. Subsequently, we chose four sets of primers for the melanoma-associated antigens MAGE1, tyrosinase, Melan A/MART-1 and gp100/Pmel17 and performed PCR analysis over a range of cycle numbers. In each case, the amplification rate remained constant up to at least 26 cycles under the respective conditions. Plotting the logarithm of the amount of product against the cycle number yields a slope that equals the logarithm of the amplification rate. The amount of starting material can be determined from the intercept with the ordinate. In summary, the method introduced in the present work allows the quantification of TAA in melanoma which might be important for the monitoring of disease. Technically the method is sound and sensitive, avoids post-PCR manipulations and can be performed with the standard equipment of a molecular biology laboratory. It can be applied also to other solid tumors and leukemias.

Antigens, Neoplasm↗
PubMed2001

International Proteolysis Society in association with the International Conference on Protease Inhibitors--second general meeting.

Proteinases, their inhibitors, and receptors are multifactorial proteins, several of which function as growth factors, adherence factors, mobility factors or chemoattractants, in addition to their classical proteolytic function. In recent years, they have become novel and attractive targets for therapy and/or prognosis in patients afflicted with cancer, atherosclerosis, neurodegeneration, inflammation and defects in the blood clotting system. About 450 proteinases are known today, although more than 700 are expected to exist, estimated on the analyses of over 30 complete genomes of pro- and eukaryotic organisms. A small percentage (2%) of their genes can be assigned to protein families that contain proteinases. Among other topics in several sessions, the structure-function relationship of proteinases and their inhibitors was discussed. Synthetic small-weight proteinase inhibitors are undergoing preclinical and clinical cancer testing; promising results were reported on the diagnostic and prognostic potential of serine proteinases and their inhibitors in cancer. Thus, proteinases are promising targets for cancer therapy.

Journal Article↗
PubMed2000

Asymptomatic CTG expansion at the SCA8 locus is associated with cerebellar atrophy on MRI.

Spinocerebellar ataxia type 8 (SCA8) is the first example of dominantly inherited ataxia reported to be caused by a dynamic mutation of the untranslated CTG trinucleotide repeat. We performed genetic and clinical analyses of a family with an isolated case with young onset cerebellar ataxia carrying an expanded 95 CTA/CTG repeats, and revealed that the asymptomatic father was also carrying a much greater expansion of 136 repeats. This paternal transmission developed a large contraction of -41 CTG repeats. The ataxia patient showed almost pure cerebellar symptoms, and a cerebral MRI of the patient demonstrated significant atrophy of the cerebellar vermis and hemispheres with preservation of brainstem and cerebrum. Although the father did not show any neurological abnormalities, his MRI demonstrated mild atrophy of the cerebellar hemispheres. The genetic phenomenon on this family has not been observed in other types of SCAs, and this reduced penetrance may cause reproduction of sporadic SCA8 frequently. Therefore, we must perform careful interviews regarding family history, and suggest the genetic and neuroradiological investigations on family members when we encounter a sporadic patient with the CTG expansion at the SCA8 locus.

Adult↗
PubMed2000

A novel type of bifunctional inhibitor directed against proteolytic activity and receptor/ligand interaction. Cystatin with a urokinase receptor binding site.

Cancer invasion and metastasis is a process requiring a coordinated series of (anti-)adhesive, migratory, and pericellular proteolytic events involving various proteases such as urokinase-type plasminogen activator (uPA)/plasmin, cathepsins B and L, and matrix metalloproteases. Novel types of double-headed inhibitors directed to different tumor-associated proteolytic systems were generated by substitution of a loop in chicken cystatin, which is nonessential for cysteine protease inhibition, with uPA-derived peptides covering the human uPA receptor binding sequence uPA-(19-31). The inhibition constants of these hybrids toward cysteine proteases are similar to those of wild-type cystatin (K(i), papain (pm), 1.9-2.4; K(i), cathepsin B (nm), 1.0-1.7; K(i), cathepsin L (pm), 0.12-0.61). FACS analyses revealed that the hybrids compete for binding of uPA to the cell surface-associated uPA receptor (uPAR) expressed on human U937 cells. The simultaneous interaction of the hybrid molecules with papain and uPAR was analyzed by surface plasmon resonance. The measured K(D) value of a papain-bound cystatin variant harboring the uPAR binding sequence of uPA (chCys-uPA-(19-31)) and soluble uPAR was 17 nm (K(D) value for uPA/uPAR interaction, 5 nm). These results indicate that cystatins with a uPAR binding site are efficient inhibitors of cysteine proteases and uPA/uPAR interaction at the same time. Therefore, these compact and small bifunctional inhibitors may represent promising agents for the therapy of solid tumors.

Amino Acid Sequence↗
PubMed2000

Simple algorithm derived from a geno-/phenotypic database to predict HIV-1 protease inhibitor resistance.

BACKGROUND: Resistance against protease inhibitors (PI) can either be analysed genotypically or phenotypically. However, the interpretation of genotypic data is difficult, particularly for PI, because of the unknown contributions of several mutations to resistance and cross-resistance. OBJECTIVE: Development of an algorithm to predict PI phenotype from genotypic data. METHODS: Recombinant viruses containing patient-derived protease genes were analysed for sensitivity to indinavir, saquinavir, ritonavir and nelfinavir. Drug resistance-associated mutations were determined by direct sequencing. geno- and phenotypic data were compared for 119 samples from 97 HIV-1 infected patients. RESULTS: Samples with one or two mutations in the gene for the protease were phenotypically sensitive in 74.3%, whereas 83.6% of samples with five or more mutations were resistant against all PI tested. Some mutations (361, 63P, 71V/T, 771) were frequent both in sensitive and resistant samples, whereas others (241, 30N, 461/L, 48V, 54V, 82A/F/T/S, 84V, 90M) were predominantly present in resistant samples. Therefore, the presence or absence of a single drug resistance-associated mutation predicted phenotypic PI resistance with high sensitivity (96.5-100%) but low specificity (13.3-57.4%). A more specific algorithm was obtained by taking into account the total number of drug resistance-associated mutations in the gene for the protease and restricting these to certain key positions for the PI. The algorithm was subsequently validated by analysis of 72 independent samples. CONCLUSION: With an optimized algorithm, phenotypic PI resistance can be predicted by viral genotype with good sensitivity (89.1-93.0%) and specificity (82.6-93.3%). The reliability and relevance of this algorithm should be further evaluated in clinical practice.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Positive influence of the Delta32CCR5 allele on response to highly active antiretroviral therapy (HAART) in HIV-1 infected patients.

The heterozygous 32 base pair deletion of the chemokine receptor 5 (Delta32CCR5) has been associated with a more benign course of HIV-1-infection. To study the influence of Delta32CCR5 on the response to antiviral therapy we analyzed the presence of Delta32CCR5 by PCR in PBMC from 107 randomly selected HIV-1-infected patients treated with HAART for at least three months. 24 of 107 patients were heterozygous for Delta32CCR5 (22.4%). Before initiation of HAART Delta32CCR5 heterozygous patients (d/w) did not differ from homozygous CCR5 wild-type patients (w/w) regarding viral load and CD4 counts. After a median treatment time on HAART of 17.5 months (d/w, range 6-31 months, p = n.s.) or 19 months (w/w, range 3-33 months) all 24 patients (100%) with the Delta32CCR5 mutation, but only 58/83 patients (69.9%) with wild-type CCR5 showed a suppression of HIV-1-viremia below 500 copies/ml (p = 0.0020). Furthermore, 20/24 (83.3%) of the Delta32CCR5 heterozygous patients achieved CD4 counts above 200/microliter, but only 57/83 (68.7%) of the patients homozygous for CCR5 wild-type (p = 0.011). Our data indicate that the presence of heterozygous Delta32CCR5 is associated with a better response to HAART suggesting that therapeutic strategies targeting CCR5 could be of value for a sustained suppression of HIV-1 by HAART.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Rac1 in human breast cancer: overexpression, mutation analysis, and characterization of a new isoform, Rac1b.

Rac1 is a member of the Ras superfamily of small guanosine triphosphatases (GTPases) that act as molecular switches to control cytoskeletal rearrangements and cell growth. Analogous to Ras, constitutively activating point mutations of Rac1 cause tumorigenic transformation of cell lines. However, there is no information about whether Rac1 is also mutated in vivo. After RT - PCR of Rac1, several clones of seven benign and 10 malignant breast cancer tissues as well as eight breast cancer cell lines were sequenced. Only single-nucleotide polymorphisms of Rac1 could be detected, and none of these corresponded to constitutively activating point mutations that have been used in cell lines for transformation. While sequencing Rac1 in breast tissues, a new Rac1 isoform with an insertion of 19 codons within the reading frame of Rac1 close to switch region II was identified and named Rac1b. The Rac1b protein acts like a fast cycling GTPase in GTP binding and hydrolysis assays. In Northern and Western blot experiments both Rac1 RNA and Rac1 protein had a significantly higher expression in breast cancer tissues compared to normal breast tissue samples. Immunohistochemical staining of Rac1 showed weak Rac1 expression in benign breast disease but high expression level in ductal carcinoma-in-situ, primary breast cancer, and lymph node metastases. In addition, breast tumor cells from patients with recurrent disease had Rac1 expression at the plasma membrane, suggesting activation of Rac1, in patients with aggressive breast cancer. Oncogene (2000).

Base Sequence↗