High-resolution physical map and transcript identification of a prostate cancer deletion interval on 8p22

The Roles of Tumor-Associated Macrophages in Prostate Cancer

The morbidity of prostate cancer (PCa) is rising year by year, and it has become the primary cause of tumor-related mortality in males. It is widely accepted that macrophages account for 50% of the tumor mass in solid tumors and have emerged as a crucial participator in multiple stages of PCa, with the huge potential for further treatment. Oftentimes, tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) behave like M2-like phenotypes that modulate malignant hallmarks of tumor lesions, ranging from tumorigenesis to metastasis. Several clinical studies indicated that mean TAM density was higher in human PCa cores versus benign prostatic hyperplasia (BPH), and increased biopsy TAM density potentially predicts worse clinicopathological characteristics as well. Therefore, TAM represents a promising target for therapeutic intervention either alone or in combination with other strategies to halt the “vicious cycle,” thus improving oncological outcomes. Herein, we mainly focus on the fundamental aspects of TAMs in prostate adenocarcinoma, while reviewing the mechanisms responsible for macrophage recruitment and polarization, which has clinical translational implications for the exploitation of potentially effective therapies against TAMs.

UHRF1-KAT7-mediated regulation of TUSC3 expression via histone methylation/acetylation is critical for the proliferation of colon cancer cells

The epigenetic factor UHRF1 regulates transcription by modulating DNA methylation and histone modification, and plays critical roles in proliferation, development, and tumorigenesis. Here, we show that Wnt/c-Myc signaling upregulates UHRF1, which in turn downregulates TUSC3, a candidate tumor suppressor gene that is frequently deleted or downregulated in several cancers. We also show that UHRF1-mediated downregulation of TUSC3 is required for the proliferation of colon cancer cells. Furthermore, we demonstrate that UHRF1 suppresses TUSC3 expression by interacting with methylated H3K14 and thereby suppressing the acetylation of H3K14 by the histone acetyltransferase KAT7. Our study provides evidence for the significance of UHRF1-KAT7-mediated regulation of histone methylation/acetylation in the proliferation of tumor cells and in a diverse set of biological processes controlled by Wnt/c-Myc signaling.

TUSC3 as a potential biomarker for prognosis in clear cell renal cell carcinoma

The aim of the present study was to explore the expression levels of tumor suppressor candidate 3 (TUSC3) in human clear cell renal cell carcinoma (ccRCC) and its clinical value. Immunohistochemical staining, western blotting and reverse transcription-quantitative polymerase chain reaction were used to detect TUSC3 expression in paracancerous normal tissues and ccRCC tissues. The tissues were derived from the pathological specimens of 54 patients with ccRCC. Additionally, associations among TUSC3 expression and histological grade and clinicopathological staging of ccRCC were investigated. The results of these comparisons revealed that TUSC3 expression in ccRCC tissues was significantly lower than that in paracancerous tissues (P<0.05). TUSC3 expression in the high differentiation group was higher than that in the median and low differentiation groups (P<0.05). Expression levels of TUSC3 in stage I and II tissues were higher than those in stage III and IV tissues (P<0.05). The expression levels of TUSC3 in the lymph node metastasis group were lower than those in the non-lymph node metastasis group (P<0.05). In conclusion, the expression levels of TUSC3 in human ccRCC tissues were downregulated compared with those found in normal human renal tissue, and TUSC3 may inhibit the progression of ccRCC. Furthermore, the TUSC3 gene may be used as a promising tumor marker for the early diagnosis and prognosis of ccRCC.

TUSC3: functional duality of a cancer gene

Two decades ago, following a systematic screening of LOH regions on chromosome 8p22, TUSC3 has been identified as a candidate tumor suppressor gene in ovarian, prostate and pancreatic cancers. Since then, a growing body of evidence documented its clinical importance in various other types of cancers, and first initial insights into its molecular function and phenotypic effects have been gained, though the precise role of TUSC3 in different cancers remains unclear. As a part of the oligosaccharyltransferase complex, TUSC3 localizes to the endoplasmic reticulum and functions in final steps of N-glycosylation of proteins, while its loss evokes the unfolded protein response. We are still trying to figure out how this mechanistic function is reconcilable with its varied effects on cancer promotion. In this review, we focus on cancer-related effects of TUSC3 and envisage a possible role of TUSC3 beyond endoplasmic reticulum.

Decreased TUSC3 Promotes Pancreatic Cancer Proliferation, Invasion and Metastasis

Pancreatic cancer is an aggressive disease with dismal prognosis. It is of paramount importance to understand the underlying etiological mechanisms and identify novel, consistent, and easy-to-apply prognostic factors for precision therapy. TUSC3 (tumor suppressor candidate 3) was identified as a potential tumor suppressor gene and previous study showed TUSC3 is decreased in pancreatic cancer at mRNA level, but its putative tumor suppressor function remains to be verified. In this study, TUSC3 expression was found to be suppressed both at mRNA and protein levels in cell line models as well as in clinical samples; decreased TUSC3 expression was associated with higher pathological TNM staging and poorer outcome. In three pairs of cell lines with different NF-κB activity, TUSC3 expression was found to be reversely correlated with NF-κB activity. TUSC3-silenced pancreatic cancer cell line exhibited enhanced potential of proliferation, migration and invasion. In an orthotopic implanted mice model, TUSC3 silenced cells exhibited more aggressive phenotype with more liver metastasis. In conclusion, the current study shows that decreased immunological TUSC3 staining is a factor prognostic of poor survival in pancreatic cancer patients and decreased TUSC3 promotes pancreatic cancer cell proliferation, invasion and metastasis. The reverse correlation between NF-κB activity and TUSC3 expression may suggest a novel regulation pattern for this molecule.

Genetic alterations of chromosome 8 genes in oral cancer

The clinical relevance of DNA copy number alterations in chromosome 8 were investigated in oral cancers. The copy numbers of 30 selected genes in 33 OSCC patients were detected using the multiplex ligation-dependent probe amplification (MLPA) technique. Amplifications of the EIF3E gene were found in 27.3% of the patients, MYC in 18.2%, RECQL4 in 15.2% and MYBL1 in 12.1% of patients. The most frequent gene losses found were the GATA4 gene (24.2%), FGFR1 gene (24.2%), MSRA (21.2) and CSGALNACT1 (12.1%). The co-amplification of EIF3E and RECQL4 was found in 9% of patients and showed significant association with alcohol drinkers. There was a significant association between the amplification of EIF3E gene with non-betel quid chewers and the negative lymph node status. EIF3E amplifications did not show prognostic significance on survival. Our results suggest that EIF3E may have a role in the carcinogenesis of OSCC in non-betel quid chewers.

TUSC3 loss alters the ER stress response and accelerates prostate cancer growth in vivo

Prostate cancer is the most prevalent cancer in males in developed countries. Tumor suppressor candidate 3 (TUSC3) has been identified as a putative tumor suppressor gene in prostate cancer, though its function has not been characterized. TUSC3 shares homologies with the yeast oligosaccharyltransferase (OST) complex subunit Ost3p, suggesting a role in protein glycosylation. We provide evidence that TUSC3 is part of the OST complex and affects N-linked glycosylation in mammalian cells. Loss of TUSC3 expression in DU145 and PC3 prostate cancer cell lines leads to increased proliferation, migration and invasion as well as accelerated xenograft growth in a PTEN negative background. TUSC3 downregulation also affects endoplasmic reticulum (ER) structure and stress response, which results in increased Akt signaling. Together, our findings provide first mechanistic insight in TUSC3 function in prostate carcinogenesis in general and N-glycosylation in particular.

Tumor suppressor candidate TUSC3 expression during rat testis maturation

Analysis of microarray data obtained by comparing gene expression between 2-week-old infant and 7-week-old mature SD rat testes revealed novel targets involved in tumor suppression. Reverse-transcription polymerase chain reaction and Northern blotting indicated that Tusc3 gene expression was upregulated in the normal maturing testis and prostate and other organs such as the cerebrum and ovary. Tumor suppressor candidate 3 protein expression was detected in these same organs at a size of about 40 kDa, in accord with the predicted molecular size. In situ hybridization and immunohistochemistry showed that mRNA and protein localization were prevalent in the testis spermatocytes and interstitial cells such as the Leydig cells, as well as prostate epithelial cells. These data suggest that TUSC3 is deeply involved in spermatogenesis in the testis, inducing sperm differentiation and maturation, and plays a role in normal prostate development and tumor suppression.

Loss of the oligosaccharyl transferase subunit TUSC3 promotes proliferation and migration of ovarian cancer cells

Consequences of deregulated protein N-glycosylation on cancer pathogenesis are poorly understood. TUSC3 is a gene with a putative function in N-glycosylation, located on the short arm of chromosome 8. This is a chromosomal region of frequent genetic loss in ovarian cancer. We established recently that the expression of TUSC3 is epigenetically decreased in epithelial ovarian cancer compared to benign controls and provides prognostic information on patient survival. Therefore, we analyzed the consequences of silenced TUSC3 expression on proliferation, invasion and migration of ovarian cell lines. In addition, we performed subcellular fractionation, co-immunofluorescence and co-immunoprecipitation experiments to establish the molecular localization of TUSC3 in ovarian cancer cells. We demonstrated that TUSC3 is localized in the endoplasmic reticulum as a subunit of the oligosaccharyltransferase complex and is capable of modulation of glycosylation patterning of ovarian cancer cells. Most importantly, silencing of TUSC3 enhances proliferation and migration of ovarian cancer cells in vitro. Our observations suggest a role for N-glycosylating events in ovarian cancer pathogenesis in general, and identify TUSC3 as a tumor suppressor gene in ovarian cancer in particular.

Methylation status of TUSC3 is a prognostic factor in ovarian cancer

BACKGROUND

Current prognostic information in ovarian cancer is based on tumor stage, tumor grade, and postoperative tumor size. Reliable molecular prognostic markers are scarce. In this article, the authors describe epigenetic events in a frequently deleted region on chromosome 8p22 that influence the expression of tumor suppressor candidate 3 (TUSC3), a putative tumor suppressor gene in ovarian cancer.

METHODS

Messenger RNA expression and promoter hypermethylation of TUSC3 were studied in ovarian cancer cell lines and in tumor samples from 2 large, independent ovarian cancer cohorts using polymerase chain reaction-based methods.

RESULTS

The results indicated that TUSC3 expression is decreased significantly because of promoter methylation in malignant ovarian tumors compared with benign controls. Almost 33% of ovarian cancer samples had detectable TUSC3 promoter methylation. Furthermore, methylation status of the TUSC3 promoter had a significant and independent influence on progression-free and overall survival.

CONCLUSIONS

TUSC3 hypermethylation predicted progression-free and overall survival in ovarian cancer. The current observations suggested a role for N-glycosylating events in ovarian cancer pathogenesis in general and identified the epigenetic silencing of TUSC3 as a prognostic factor in this disease.

DLC1 interaction with α-catenin stabilizes adherens junctions and enhances DLC1 antioncogenic activity

The DLC1 (for deleted in liver cancer 1) tumor suppressor gene encodes a RhoGAP protein that inactivates Rho GTPases, which are implicated in regulation of the cytoskeleton and adherens junctions (AJs), a cell-cell adhesion protein complex associated with the actin cytoskeleton. Malignant transformation and tumor progression to metastasis are often associated with changes in cytoskeletal organization and cell-cell adhesion. Here we have established in human cells that the AJ-associated protein α-catenin is a new binding partner of DLC1. Their binding was mediated by the N-terminal amino acids 340 to 435 of DLC1 and the N-terminal amino acids 117 to 161 of α-catenin. These proteins colocalized in the cytosol and in the plasma membrane, where together they associated with E-cadherin and β-catenin, constitutive AJ proteins. Binding of DLC1 to α-catenin led to their accumulation at the plasma membrane and required DLC1 GAP activity. Knocking down α-catenin in DLC1-positive cells diminished DLC1 localization at the membrane. The DLC1-α-catenin complex reduced the Rho GTP level at the plasma membrane, increased E-cadherin's mobility, affected actin organization, and stabilized AJs. This process eventually contributed to a robust oncosuppressive effect of DLC1 in metastatic prostate carcinoma cells. Together, these results unravel a new mechanism through which DLC1 exerts its strong oncosuppressive function by positively influencing AJ stability.

Arylamine N-acetyltransferase 1: a novel drug target in cancer development

The human arylamine N-acetyltransferases first attracted attention because of their role in drug metabolism. However, much of the current literature has focused on their role in the activation and detoxification of environmental carcinogens and how genetic polymorphisms in the genes create predispositions to increased or decreased cancer risk. There are two closely related genes on chromosome 8 that encode the two human arylamine N-acetyltransferases--NAT1 and NAT2. Although NAT2 has restricted tissue expression, NAT1 is found in almost all tissues of the body. There are several single-nucleotide polymorphisms in the protein coding and 3'-untranslated regions of the gene that affect enzyme activity. However, NAT1 is also regulated by post-translational and environmental factors, which may be of greater importance than genotype in determining tissue NAT1 activities. Recent studies have suggested a novel role for this enzyme in cancer cell growth. NAT1 is up-regulated in several cancer types, and overexpression can lead to increased survival and resistance to chemotherapy. Although a link to folate homeostasis has been suggested, many of the effects attributed to NAT1 and cancer cell growth remain to be explained. Nevertheless, the enzyme has emerged as a viable candidate for drug development, which should lead to small molecule inhibitors for preclinical and clinical evaluation.

High-resolution array CGH clarifies events occurring on 8p in carcinogenesis

Background

Rearrangement of the short arm of chromosome 8 (8p) is very common in epithelial cancers such as breast cancer. Usually there is an unbalanced translocation breakpoint in 8p12 (29.7 Mb – 38.5 Mb) with loss of distal 8p, sometimes with proximal amplification of 8p11-12. Rearrangements in 8p11-12 have been investigated using high-resolution array CGH, but the first 30 Mb of 8p are less well characterised, although this region contains several proposed tumour suppressor genes.

Methods

We analysed the whole of 8p by array CGH at tiling-path BAC resolution in 32 breast and six pancreatic cancer cell lines. Regions of recurrent rearrangement distal to 8p12 were further characterised, using regional fosmid arrays. FISH, and quantitative RT-PCR on over 60 breast tumours validated the existence of similar events in primary material.

Results

We confirmed that 8p is usually lost up to at least 30 Mb, but a few lines showed focal loss or copy number steps within this region. Three regions showed rearrangements common to at least two cases: two regions of recurrent loss and one region of amplification. Loss within 8p23.3 (0 Mb – 2.2 Mb) was found in six cell lines. Of the genes always affected, ARHGEF10 showed a point mutation of the remaining normal copies in the DU4475 cell line. Deletions within 12.7 Mb – 19.1 Mb in 8p22, in two cases, affected TUSC3. A novel amplicon was found within 8p21.3 (19.1 Mb – 23.4 Mb) in two lines and one of 98 tumours.

Conclusion

The pattern of rearrangements seen on 8p may be a consequence of the high density of potential targets on this chromosome arm, and ARHGEF10 may be a new candidate tumour suppressor gene.

DLC1: a significant GAP in the cancer genome

Rho GTPases are believed to make important contributions to the development and progression of human cancer, but direct evidence in the form of somatic mutations analogous to those affecting Ras has been lacking. A recent study in Genes & Development by Xue and colleagues (1439-1444) now provides in vivo evidence that DLC1, a negative regulator of Rho, is a tumor suppressor gene deleted almost as frequently as p53 in common cancers such as breast, colon, and lung.

Adenovirus-mediated restoration of expression of the tumor suppressor gene DLC1 inhibits the proliferation and tumorigenicity of aggressive, androgen-independent human prostate cancer cell lines: prospects for gene therapy

Our recent study showing highly recurrent loss of function of DLC1 (deleted in liver cancer 1), a tumor suppressor gene in primary prostate carcinoma (PCA), implicates this gene in the pathogenesis of this disease. To evaluate the response of PCA to oncosuppressive activity of DLC1, we examined now the effects of adenoviral vector for human DLC1 transduction into the DLC1-deficient, androgen-independent (AI) and aggressive human PCA cell lines PC-3 and C4-2-B2. Adenovirus-mediated restoration of DLC1 expression inhibited the proliferation, invasiveness and anchorage-independent growth of PC-3 and C4-2-B2 cells in vitro as well as the tumorigenicity of PC-3 cells in nude mice. It also induced cell-cycle arrest, inhibited the activation of RhoA and the formation of actin stress fibers. DLC1 induced apoptosis in C4-2-B2 cells, whereas it did not elicit such an effect in PC-3 cells. The abundance of the antiapoptotic protein Bcl-2 was greater in PC-3 cells than in C4-2-B2 cells, and PC-3 cells were rendered sensitive to DLC1-induced apoptosis by treatment with the Bcl-2 inhibitor HA14-1. These results suggest that adenovirus-mediated DLC1 transfer, alone or together with other agents, such as inhibitors of Bcl-2 or histone deacetylase, might prove effective in the treatment of aggressive, AI-PCA.

Aberrant methylation and deacetylation of deleted in liver cancer-1 gene in prostate cancer: potential clinical applications

PURPOSE

The deleted in liver cancer-1 (DLC-1) gene that encodes a Rho GTPase-activating protein with tumor suppressor function is located on chromosome 8p21-22, a region frequently deleted in prostate carcinomas. This study was designed to determine whether DLC-1 is deregulated in prostate carcinomas and to assess the contribution of DLC-1 alterations to prostate carcinogenesis.

EXPERIMENTAL DESIGN

Primary prostate carcinomas, prostate carcinoma cell lines, benign prostatic hyperplasias, and normal prostatic tissues were examined for detection of functional and structural alterations of the DLC-1 gene by real-time PCR, methylation-specific PCR, and Southern and Western blots.

RESULTS

Down-regulation or loss of DCL-1 mRNA expression was detected in 10 of 27 (37%) prostate carcinomas, 3 of 5 (60%) prostate carcinoma cell lines, and 5 of 21 (24%) benign prostatic hyperplasias. DLC-1 promoter methylation was identified in 13 of 27 (48%) prostate carcinomas and 2 matching normal tissues and in 15 of 21 (71%) benign prostatic hyperplasias but was absent in 10 normal prostatic tissues from noncancerous individuals. Genomic deletions were found in only 3 prostate carcinomas and 1 benign prostatic hyperplasia. DLC-1 protein was not detected in 8 of 27 (30%) prostate carcinomas and 11 of 21 (52%) benign prostatic hyperplasias. Methylation of DLC-1 correlated with age in prostate carcinoma patients (P = 0.006) and with prostate-specific antigen blood levels in benign prostatic hyperplasia patients (P = 0.029). Treatment of the three prostate carcinoma cell lines (PC-3, LNCaP, and 22Rv1) expressing a low level of DLC-1 transcripts with inhibitors of DNA methyltransferase or histone deacetylase increased DLC-1 expression.

CONCLUSIONS

These results show that the transcriptional silencing of DLC-1 by two epigenetic mechanisms is common and may be involved in the pathogenesis of prostate carcinomas and benign prostatic hyperplasias and could have potential clinical application in the early detection and gene therapy of prostate cancer.

Genome-wide screening for genetic changes in a matched pair of benign and prostate cancer cell lines using array CGH

Copy number alterations in a matched pair of benign epithelial and prostate cancer cell lines derived from the same patient were assessed using array-based comparative genomic hybridisation (aCGH). The cancer cell line showed a gain of chromosome 7, deletion of chromosome 8, gains (including high level) and losses on chromosome 11, loss of 18p and gain of 20q. Deletions on chromosome 8 were confirmed with microsatellite markers. The aCGH results were compared to gene expression data obtained using DNA microarrays and suggested the involvement of caspases and ICEBERG on 11q and E2F1 on chromosome 20q.

Outer breast quadrants demonstrate increased levels of genomic instability

BACKGROUND

Theory holds that the upper outer quadrant of the breast develops more malignancies because of increased tissue volume. This study evaluated genomic patterns of loss of heterozygosity (LOH) and allelic imbalance (AI) in non-neoplastic tissues from quadrants of diseased breasts following mastectomy to characterize relationships between genomic instability and the propensity for tumor development.

METHODS

Tissues from breast quadrants were collected from 21 patients with various stages of breast carcinoma. DNA was isolated from non-neoplastic tissues using standard methods and 26 chromosomal regions commonly deleted in breast cancer were examined to assess genomic instability.

RESULTS

Genomic instability was observed in breast quadrants from patients with ductal carcinomas in situ and advanced carcinomas. Levels of instability by quadrant were not predictive of primary tumor location (P =.363), but outer quadrants demonstrated significantly higher levels of genomic instability than did inner quadrants (P =.017). Marker D8S511 on chromosome 8p22-21.3, one of the most frequently altered chromosomal regions in breast cancer, showed a significantly higher level of instability (P =.039) in outer compared with inner quadrants.

CONCLUSIONS

Non-neoplastic breast tissues often harbor genetic changes that can be important to understanding the local breast environment within which cancer develops. Greater genomic instability in outer quadrants can partially explain the propensity for breast cancers to develop there, rather than simple volume-related concepts. Patterns of field cancerization in the breast appear to be complex and are not a simple function of distance from a developing tumor.

DLC-1 operates as a tumor suppressor gene in human non-small cell lung carcinomas

The deleted in liver cancer (DLC-1) gene at chromosome 8p21-22 is altered mainly by genomic deletion or aberrant promoter methylation in a large number of human cancers such as breast, liver, colon and prostate and is known to have an inhibitory effect on breast and liver tumor cell growth. Given the high frequency of deletion involving region 8p21-22 in human non-small cell lung carcinoma (NSCLC), we examined alterations of DLC-1 in a series of primary tumors and tumor cell lines and tested effects of DLC-1 on tumor cell growth. A significant decrease or absence of the DLC-1 mRNA expression was found in 95% of primary NSCLC (20/21) and 58% of NSCLC cell lines (11/19). Transcriptional silencing of DLC-1 was primarily associated with aberrant DNA methylation, rather than genomic deletion as 5-aza-2'-deoxycytidine induced reactivation of DLC-1 expression in 82% (9/11) NSCLC cell lines showing downregulated DLC-1. It was further evidenced by an aberrant DLC-1 promoter methylation pattern, which was detected by Southern blotting in 73% (8/11) of NSCLC cell lines with downregulation of the gene. The transfer of DLC-1 into three DLC-1 negative cell lines caused a significant inhibition in cell proliferation and/or a decrease in colony formation. Furthermore, stable transfer of DLC-1 abolished tumorigenicity in nude mice of two cell lines, suggesting that DLC-1 plays a role in NSCLC by acting as a bona fide new tumor suppressor gene.

DLC-1 gene inhibits human breast cancer cell growth and in vivo tumorigenicity

The human DLC-1 (deleted in liver cancer 1) gene was cloned from a primary human hepatocellular carcinoma (HCC) and mapped to the chromosome 8p21-22 region frequently deleted in common human cancers and suspected to harbor tumor suppressor genes. DLC-1 was found to be deleted or downregulated in a significant number of HCCs. We expanded our investigations to other cancers with recurrent deletions of 8p22, and in this study examined alterations of DLC-1 in primary human breast tumors, human breast, colon, and prostate tumor cell lines. Genomic deletion of DLC-1 was observed in 40% of primary breast tumors, whereas reduced or undetectable levels of DLC-1 mRNA were seen in 70% of breast, 70% of colon, and 50% of prostate tumor cell lines To see whether DLC-1 expression affects cell growth and tumorigenicity, two breast carcinoma cell lines lacking the expression of endogenous gene were transfected with the DLC-1 cDNA. In both cell lines, DLC-1 transfection caused significant growth inhibition and reduction of colony formation. Furthermore, introduction of the DLC-1 cDNA abolished the in vivo tumorigenicity in nude mice, suggesting that the DLC-1 gene plays a role in breast cancer by acting as a bona fide tumor suppressor gene.

Promoter hypermethylation of DLC-1, a candidate tumor suppressor gene, in several common human cancers

Aberrant methylation of CpG islands within the promoter regions of tumor suppressor or cancer-related genes is a common mechanism leading to the silencing of gene expression. To determine whether aberrant methylation is a contributing factor to transcriptional inactivation of DLC-1 (deleted in liver cancer-1), a candidate tumor suppressor gene, we examined its methylation status in twelve hepatocellular carcinoma. breast, colon, and prostate tumor cell lines with low or undetectable expression of DLC-1. By Southern blot analysis of DNA digested with the methylation sensitive enzyme HpaII, we found a different degree of promoter hypermethylation in all cell lines with aberrant DLC-1 expression. The hypermethylation status was reversed by the addition of 5-aza-2'-deoxycytidine, a demethylating agent, in one human hepatocellular carcinoma line. These observations suggest that hypermethylation is responsible for abrogating the function of the DLC-1 gene in a subset of liver, breast, colon, and prostate cancers.

Gene structure, tissue expression, and linkage mapping of the mouse DLC-1 gene (Arhgap7)

DLC-1 (deleted in liver cancer 1) is a candidate tumor suppressor gene for hepatocellular carcinoma and other cancers. It is the human homologue of rat p122, which has been shown to function as a GTPase activating protein for RhoA, and it may be involved in signal transduction pathways regulating cell proliferation and adhesion. To establish an animal model for studying the regulation and function of DLC-1, we have undertaken the characterization of the mouse DLC-1 gene. Northern blot analysis shows that the mouse DLC-1 mRNA is widely expressed, with the highest levels in heart, liver, and lung. Mouse genomic clones that contain the entire DLC-1 gene of 47 kb were isolated. The mouse gene consists of 14 exons, and the structural organization is highly similar to that of the human gene. The promoter region of the mouse gene was GC-rich and contained potential binding sites for transcription factors SP1, GCF, and AP-2. A polymorphic microsatellite marker in intron 8 was used for mapping the gene (Arhgap7) to 20 cM on mouse chromosome 8 and for allelotyping of mouse liver tumor DNAs.

Identification of a region of homozygous deletion on 8p22-23.1 in medulloblastoma

To identify critical tumor suppressor loci that are associated with the development of medulloblastoma, we performed a comprehensive genome-wide allelotype analysis in a series of 12 medulloblastomas. Non-random allelic imbalances were identified on chromosomes 7q (58.3%), 8p (66.7%), 16q (58.3%), 17p (58.3%) and 17q (66.7%). Comparative genomic hybridization analysis confirmed that allelic imbalances on 8p, 16q and 17p were due to loss of genetic materials. Finer deletion mapping in an expanded series of 23 medulloblastomas localized the common deletion region on 8p to an interval of 18.14 cM on 8p22-23.2. We then searched within the region of loss on 8p for loci that might contain homozygous deletion using comparative duplex PCR. An overlapping homozygous deletion region was identified in a 1.8 cM interval on 8p22-23.1, between markers D8S520 and D8S1130, in two medulloblastomas. This region of homozygous deletion also encompasses the 1.4 cM minimal deletion region detected on 8p in ductal carcinoma in situ of breast. In conclusion, we reported for the first time a detailed deletion mapping on 8p in medulloblastoma and have identified a region of homozygous deletion on 8p22-23.1 that is likely to contain a critical tumor suppressor gene involved in the development of medulloblastoma.