Deletion analysis at the DEL-27, APC and MTS1 loci in bladder cancer: LOH at the DEL-27 locus on 5p13-12 is a prognostic marker of tumor progression

The role of WNT signalling in urothelial cell carcinoma

Urothelial cell carcinoma (UCC) of the bladder is one of the most common malignancies, causing considerable morbidity and mortality worldwide. It is unique among the epithelial carcinomas as two distinct pathways to tumourigenesis appear to exist: low grade, recurring papillary tumours usually contain oncogenic mutations in FGFR3 or HRAS whereas high grade, muscle invasive tumours with metastatic potential generally have defects in the pathways controlled by the tumour suppressors p53 and retinoblastoma. Over the last two decades, a number of transgenic mouse models of UCC, containing deletions or mutations of key tumour suppressor genes or oncogenes, have helped us understand the mechanisms behind tumour development. In this summary, I present my work investigating the role of the WNT signalling cascade in UCC.

Exploring molecular genetics of bladder cancer: lessons learned from mouse models

Urothelial cell carcinoma (UCC) of the bladder is one of the most common malignancies worldwide, causing considerable morbidity and mortality. It is unusual among the epithelial carcinomas because tumorigenesis can occur by two distinct pathways: low-grade, recurring papillary tumours usually contain oncogenic mutations in FGFR3 or HRAS, whereas high-grade, muscle-invasive tumours with metastatic potential generally have defects in the pathways controlled by the tumour suppressors p53 and retinoblastoma (RB). Over the past 20 years, a plethora of genetically engineered mouse (GEM) models of UCC have been developed, containing deletions or mutations of key tumour suppressor genes or oncogenes. In this review, we provide an up-to-date summary of these GEM models, analyse their flaws and weaknesses, discuss how they have advanced our understanding of UCC at the molecular level, and comment on their translational potential. We also highlight recent studies supporting a role for dysregulated Wnt signalling in UCC and the development of mouse models that recapitulate this dysregulation.

Spaceflight alters the gene expression profile of cervical cancer cells

Our previous study revealed that spaceflight induced biological changes in human cervical carcinoma Caski cells. Here, we report that 48A9 cells, which were subcloned from Caski cells, experienced significant growth suppression and exhibited low tumorigenic ability after spaceflight. To further understand the potential mechanism at the transcriptional level, we compared gene expression between 48A9 cells and ground control Caski cells with suppression subtractive hybridization (SSH) and reverse Northern blotting methods, and analyzed the relative gene network and molecular functions with the Ingenuity Pathways Analysis (IPA) program. We found 5 genes, SUB1, SGEF, MALAT-1, MYL6, and MT-CO2, to be up-regulated and identified 3 new cDNAs, termed B4, B5, and C4, in 48A9 cells. In addition, we also identified the two most significant gene networks to indicate the function of these genes using the IPA program. To our knowledge, our results show for the first time that spaceflight can reduce the growth of tumor cells, and we also provide a new model for oncogenesis study.

β-Catenin activation synergizes with PTEN loss to cause bladder cancer formation

Although deregulation of the Wnt signalling pathway has been implicated in urothelial cell carcinoma (UCC), the functional significance is unknown. To test its importance, we have targeted expression of an activated form of β-catenin to the urothelium of transgenic mice using Cre-Lox technology (UroIICRE(+) β-catenin(exon3/+)). Expression of this activated form of β-catenin led to the formation of localized hyperproliferative lesions by 3 months, which did not progress to malignancy. These lesions were characterized by a marked increase of the phosphatase and tensin homologue (PTEN) tumour suppressor protein. This appears to be a direct consequence of activating Wnt signalling in the bladder as conditional deletion of the adenomatous polyposis coli (Apc) gene within the adult bladder led rapidly to coincident β-catenin and PTEN expression. This PTEN expression blocked proliferation. Next, we combined PTEN deficiency with β-catenin activation and found that this caused papillary UCC. These tumours had increased pAKT signalling and were dependent on mammalian target of rapamycin (mTOR). Importantly, in human UCC, there was a significant correlation between high levels of β-catenin and pAKT (and low levels of PTEN). Taken together these data show that deregulated Wnt signalling has a critical role in promoting UCC, and suggests that human UCC that have high levels of Wnt and PI3 kinase signalling may be responsive to mTOR inhibition.

Somatic mutations of adenomatous polyposis coli gene and nuclear b-catenin accumulation have prognostic significance in invasive urothelial carcinomas: evidence for Wnt pathway implication

Wnt pathway signaling is crucial in many cancers and data indicate crosstalk with other key cancer pathways, however in urothelial carcinogenesis it has not been extensively studied. We searched for mutations in adenomatous polyposis coli (APC), a key regulator of the pathway, and studied b-catenin expression and interactions with the expression of other markers of apoptosis, angiogenesis, and proliferation in patients with invasive urothelial cancer. The mutation cluster region of APC was directly sequenced in 70 patients with muscle invasive disease who were treated with surgery and adjuvant chemotherapy. COX-2, p53, Ki67, and b-catenin were studied immunohistochemically and micro vessel density was quantified by CD105 expression. Single somatic amino-acid substitutions (missense) were found in 9 (13%) and frameshift deletions in 2 (3%) tumors, all located in regions adjacent to b-catenin binding sites. Patients having either APC missense mutations or b-catenin nuclear accumulation had less frequent COX-2 overexpression (24% vs. 76%, p = 0.043) and more frequent lymph node involvement (75% vs. 38%, p = 0.023). Patients with either APC mutations or b-catenin accumulation had shorter disease-free interval (13.4 vs. 28 months, p = 0.07), whereas in multivariate analysis they had shorter disease-specific survival (60.5 vs. 20.6 months, p = 0.048). Somatic APC missense mutations are not rare in advanced urothelial neoplasms. Either APC mutations and/or aberrant expression of b-catenin are associated with worse outcome. Further study of the role of the Wnt pathway, potential crosstalk with other pathways and potential candidate therapeutic targets in urothelial cancer is needed.

Molecular markers in bladder cancer

PURPOSE OF REVIEW

Bladder cancer is a diverse disease whose molecular phenotypes are being elucidated. In this review, we summarize currently known molecular pathways and associated markers in bladder cancer.

RECENT FINDINGS

Genetic and epigenetic aberrations have been closely associated with tumor pathogenesis and prognosis. Cell cycle markers have been most extensively studied. More recently, apoptotic and angiogenic pathways are being investigated. Studying the role of multiple concurrent molecular alterations improves the prognostic ability of these markers. The use of tissue microarrays and high-throughput molecular profiling is accelerating the discovery of new markers.

SUMMARY

Molecular biology is paramount to our understanding of bladder cancer pathogenesis. The search for new markers, and elucidating cross-talk between markers in different pathways, is warranted. Molecular markers have the potential benefit of improving detection, prognosis and treatment of bladder cancer. In addition, understanding the molecular profile of the individual patient could usher us into a new era of improving prediction of the natural history of the disease and providing a more personalized and tailored treatment. Prospective trials are still needed, however, to objectively establish the true benefit of these markers in prognostic and therapeutic arenas.

Decreased DOC-2/DAB2 Expression in Urothelial Carcinoma of the Bladder

PURPOSE

DOC-2/DAB2 (differentially expressed in ovarian carcinoma-2/disabled-2), a potential tumor suppressor gene, is underexpressed in several cancers. Little is known about the expression of this gene in urothelial carcinoma of the bladder (UCB). We profiled DOC-2/DAB2 expression in mouse and human normal and neoplastic urothelia.

EXPERIMENTAL DESIGN

Immunohistochemical staining for DOC-2/DAB2 was carried out on tissue specimens from two transgenic mouse models with urothelium-specific molecular alterations and on a tissue microarray containing cores from 9 normal controls, 44 patients who underwent transurethral resection of the bladder tumor (TURBT), 195 patients who underwent radical cystectomy for UCB, and 39 lymph nodes with metastatic UCB.

RESULTS

Normal mouse urothelium stained uniformly with DOC-2/DAB2. Weaker staining was observed in low-grade, superficial papillary bladder tumors from transgenic mice harboring constitutively active Ha-Ras, whereas carcinoma in situ-like lesions and high-grade bladder tumors from transgenic mice expressing a SV40 T antigen completely lacked DOC-2/DAB2 expression. In human tissues, DOC-2/DAB2 expression was decreased in 11% of normal bladder specimens, 59% of TURBT specimens, 65% of radical cystectomy specimens, and 77% of the metastatic lymph node specimens. Decreased DOC-2/DAB2 expression was associated with advanced pathologic stage (P = 0.023), lymph node metastases (P = 0.050), and lymphovascular invasion (P < 0.001). In univariable, but not in multivariable analysis, decreased DOC-2/DAB2 was associated with an increased probability of bladder cancer recurrence (log-rank test, P = 0.020) and bladder cancer-specific mortality (log-rank test, P = 0.023).

CONCLUSIONS

Decreased DOC-2/DAB2 expression seems to occur early in bladder tumorigenesis and becomes more prominent in advanced stages of UCB.

Detection of chromosomal alterations in bladder transitional cell carcinomas from Northern China by comparative genomic hybridization

To identify chromosome alterations in Chinese bladder cancer, forty-six transitional cell carcinomas of the bladder were analyzed by comparative genomic hybridization. Frequent gains of DNA copy number were observed on 1p (13/46), 1q (13/46), 5p (8/46), 6p (9/46), 7p (7/46), 8q (12/46), 11q (8/46), 17q (11/46), 19q (7/46), 20q (8/46) and Yq (8/46), with minimal overlapping regions at 1p32-pter (10/46), 1q21-q24 (12/46), 5p (8/46), 6p22-p23 (7/46), 7p11.2-p14 (7/46), 8q22-q24 (12/46), 11q13-q14 (8/46), 17q22-qter (11/46), 19q11-13.2 (7/46), 20q11-q13.2 (8/46) and Yq11 (8/46). Losses were predominantly found on 2q (16/46), 5q (8/46), 8p (7/46), 9p (8/46), 9q (13/46), 11p (7/46), 13q (7/46), 17p (12/46), 18q (7/46), Xp (18/46) and Xq (19/46), with smallest overlapping regions at 2q32-qter (16/46), 5q12-q31 (8/46), 8p12-pter (7/46), 9p21-pter (10/46), 9q (13/46), 11p (7/46), 13q13-q22 (7/46), 17p (12/46), 18q21-qter (7/46), Xp (18/46) and Xq (19/46). There were significantly higher frequencies of gains of 1q21-q24 and 17q22-qter in moderately differentiated tumors as compared with those in well-differentiated tumors, indicating a possible association of these two abnormalities with the dedifferentiation of tumor cells. Gains of 1p32-pter, 5p, 6p22-p23, 11q13-q14, 17q22-qter and losses of 2q32-qter, 9q, 17p were more frequent in pT1 as compared with those in pTa carcinomas. Gains at 1q21-q24, 7p11.2-p14, 8q22-q24, 19q, 20q11-q13.2 and losses at 5q12-q31, 8p12-pter, 9p21-pter, 11p, 13q13-q22 and 18q21-qter were unique to pT1 and higher stage tumors, suggesting that genes responsible for the invasion and progression of bladder cancer might be located at these chromosomal regions. In multiple tumors from the same patients, consistent alterations such as gains of 8q, 11q13-q14, 12q13-q15, 13q12, 20q and losses of 2q32-qter, 8p, 9, 11p, 11q21-qter, 13q13-qter, X were detected. These abnormalities were possibly earlier events, which might play a critical role during the genesis of the tumors. Further detailed studies to the recurrent aberration regions may lead to the identification of oncogenes and tumor suppressor genes involved in the development and progression of Chinese bladder cancer.

The single-strand DNA binding activity of human PC4 prevents mutagenesis and killing by oxidative DNA damage

Human positive cofactor 4 (PC4) is a transcriptional coactivator with a highly conserved single-strand DNA (ssDNA) binding domain of unknown function. We identified PC4 as a suppressor of the oxidative mutator phenotype of the Escherichia coli fpg mutY mutant and demonstrate that this suppression requires its ssDNA binding activity. Saccharomyces cerevisiae mutants lacking their PC4 ortholog Sub1 are sensitive to hydrogen peroxide and exhibit spontaneous and peroxide-induced hypermutability. PC4 expression suppresses the peroxide sensitivity of the yeast sub1Delta mutant, suggesting that the human protein has a similar function. A role for yeast and human proteins in DNA repair is suggested by the demonstration that Sub1 acts in a peroxide resistance pathway involving Rad2 and by the physical interaction of PC4 with the human Rad2 homolog XPG. We show that XPG recruits PC4 to a bubble-containing DNA substrate with a resulting displacement of XPG and formation of a PC4-DNA complex. We discuss the possible requirement for PC4 in either global or transcription-coupled repair of oxidative DNA damage to mediate the release of XPG bound to its substrate.

High-resolution analysis of genomic copy number alterations in bladder cancer by microarray-based comparative genomic hybridization

We have screened 22 bladder tumour-derived cell lines and one normal urothelium-derived cell line for genome-wide copy number changes using array comparative genomic hybridization (CGH). Comparison of array CGH with existing multiplex-fluorescence in situ hybridization (M-FISH) results revealed excellent concordance. Regions of gain and loss were defined more accurately by array CGH, and several small regions of deletion were detected that were not identified by M-FISH. Numerous genetic changes were identified, many of which were compatible with previous results from conventional CGH and loss of heterozygosity analyses on bladder tumours. The most frequent changes involved complete or partial loss of 4q (83%) and gain of 20q (78%). Other frequent losses were of 18q (65%), 8p (65%), 2q (61%), 6q (61%), 3p (56%), 13q (56%), 4p (52%), 6p (52%), 10p (52%), 10q (52%) and 5p (43%). We have refined the localization of a region of deletion at 8p21.2-p21.3 to an interval of approximately 1 Mb. Five homozygous deletions of tumour suppressor genes were confirmed, and several potentially novel homozygous deletions were identified. In all, 15 high-level amplifications were detected, with a previously reported amplification at 6p22.3 being the most frequent. Real-time PCR analysis revealed a novel candidate gene with consistent overexpression in all cell lines with the 6p22.3 amplicon.

Lasermicrodissection--an important prerequisite for the molecular-genetic analysis of bladder cancer

The past 10 years have shown that a crucial point in the molecular-genetic analysis of malignant tumors is the exact histopathological definition and separation of the investigated lesions. Laser microdissection has become an important tool allowing for the study of specific histological entities and defined preneoplastic lesions. Reliable detection of tumor-specific alterations can be compromised by the presence of normal cells. This requires microdissection of pure tumor cell populations (>80%), necessary for detecting chromosomal alterations by loss of heterozygosity analysis (LOH) and fluorescence in situ hybridization (FISH). The combination of microdissection and molecular methods could also be useful for studying multifocal lesions of the urothelial tract. This article describes in detail the use of laser microdissection, whole genome amplification by Improved Primer Extension Preamplification (I-PEP)-PCR and subsequent LOH, FISH, and sequencing analyses for the investigation of urothelial tumors and their precursors, e.g. dysplasias and hyperplasias. The combination of the described methods allows for a wide spectrum of molecular investigations in lesions with a limited number of tumor cells, and might help to understand the fundamental alterations involved in urothelial carcinogenesis.

Alleviation of PC4-mediated transcriptional repression by the ERCC3 helicase activity of general transcription factor TFIIH

Positive cofactor 4 (PC4), originally identified as a transcriptional coactivator, possesses the ability to suppress promoter-driven as well as nonspecific transcription via its DNA binding activity. Previous studies showed that the repressive activity of PC4 on promoter-driven transcription is alleviated by transcription factor TFIIH, possibly through one of its enzymatic activities. Using recombinant TFIIH, we have analyzed the role of TFIIH for alleviating PC4-mediated transcriptional repression and determined that the excision repair cross complementing (ERCC3) helicase activity of TFIIH is the enzymatic activity that alleviates PC4-mediated repression via beta-gamma bond hydrolysis of ATP. In addition, the alleviation does not require either ERCC2 helicase or cyclin-dependent kinase 7 kinase activity. We also show that, as complexed within TFIIH, the cyclin-dependent kinase 7 kinase does not possess the activity to phosphorylate PC4. Thus, TFIIH appears to protect promoters from PC4-mediated repression by relieving the topological constraint imposed by PC4 through the ERCC3 helicase activity rather than by reducing the repressive activity of PC4 via its phosphorylation.

Loss of heterozygosity on chromosome 5p13-12 predicts adverse prognosis in advanced bladder cancer independent of tumor stage and grade

PURPOSE

The individual prognosis in patients with bladder cancer is only partially predicted by tumor stage and grade. Various molecular markers have been shown to correlate with disease progression and prognosis but few add some predictive capacity beyond that offered by standard clinical and pathological parameters.

MATERIALS AND METHODS

A total of 191 urothelial carcinomas from 157 patients were analyzed. Paired normal and tumor cells were microdissected by manual and microbeam-microdissection of membrane mounted native tissue, and analyzed for loss of heterozygosity (LOH) at a critical region of LOH on chromosome 5p13-12 that is involved in bladder cancer progression. LOH data were correlated with progression-free and tumor specific survival by multivariate analysis.

RESULTS

Informativity of the assay was 60.7%. Log rank analysis of 100 evaluable patients showed a progression-free survival benefit without LOH at 5p13-12 of more than 3 years (p <0.01). Mean followup was 36 months. Multivariate analysis revealed that this benefit was not predicted by tumor stage and grade alone in advanced disease (stages T3/4 and/or N+/M+, stages III/IV).

CONCLUSIONS

LOH at the critical region on chromosome 5p13-12 is a molecular marker of adverse prognosis in advanced bladder carcinoma independent of tumor stage and grade.

Mapping and genome sequence analysis of chromosome 5 regions involved in bladder cancer progression

We studied the evolution of allelic losses on chromosome 5 by whole-organ histologic and genetic mapping in 234 mucosal DNA samples of 5 cystectomy specimens with invasive bladder cancer and preneoplastic changes in adjacent urothelium. The frequency of alterations in individual loci was verified on 32 tumors and 29 voided urine samples from patients with bladder cancer. Finally, deleted regions on chromosome 5 were integrated with the human genome contigs and sequence-based databases. Deleted regions on chromosome 5 involved in intraurothelial phases of bladder neoplasia defined by their nearest flanking markers and predicted size were identified as follows: q13.3-q22 (D5S424-D5S656; 38.8 centimorgan [cM]); q22-q31.1 (D5S656-D5S808; 19.2 cM), q31.1-q32 (D5S816-SPARC; 11.5 cM), and q34 (GABRA1-D5S415; 6.4 cM). The two most frequently deleted neighbor markers (D5S2055 and D5S818) mapping to q22-q31.1 defined a 9 cM region, which may contain genes that play an important role in early phases of urinary bladder carcinogenesis. Human genome database analysis provided an accurate map of deleted regions with positions of 138 known genes and revealed several smaller gene-rich areas representing putative targets for further mapping. The strategic approach presented here, which combines whole-organ histologic and genetic mapping with analysis of the rapidly emerging human genome sequence database, facilitates identification of genes potentially involved in early phases of bladder carcinogenesis.

[Molecular biology in bladder cancer]

Progress of molecular biology with regard to etiopathogeny of tumours in general, and cancer of the bladder in particular, is taking place at such a vertiginous pace that practising urologists find themselves overwhelmed in terms of their ability to learn and keep updated in so complex a subject. The understanding of certain molecular factors with critical influence on the formation, growth and progression of a tumour of the bladder, is forcing us to make unbiased assessments on the role they will play in the evolution and survival of this neoplasia. It is anticipate they will be much more reliable than traditionally established morphological factors such as grade and stage. We also include a literature review with an analysis and elucidation of the role played by oncogenes, tumor suppressor genes, vascular density markers, telomerase etc., in the formation and growth of cancer of the bladder and their likely relationships with already established clinico-pathological factors.

Allelic changes at multiple regions of chromosome 5 are associated with progression of urinary bladder cancer

This study has analysed 65 urothelial carcinomas for allelic imbalance at 22 loci of chromosome 5 and has determined three regions of interest. A commonly duplicated region was mapped to chromosome 5p between loci D5S1473 and D5S819, one region of deletion to chromosome 5q22-23 between loci D5S2055 and D5S659, and another to chromosome 5q33-34 between loci D5S1456 and D5S1465. An allelic imbalance was detected in 54% of the cases. Only 10% of grade 1 tumours showed allelic changes at chromosome 5, whereas 60% and 63% of grade 2 and grade 3 cancers, respectively, had alterations of chromosome 5. The frequency of chromosome 5 changes increased from 24% in pTa tumours up to 72% in pT3-4 tumours. Of particular interest, ten out of 12 urothelial carcinomas showing metastatic growth in regional lymph nodes at the time of cystectomy had alterations at chromosome 5. No specific region, but genetic changes in general were associated with the grading and staging of bladder cancers.

Isolation of DICE1: a gene frequently affected by LOH and downregulated in lung carcinomas

In the development and progression of sporadic tumors multiple tumor suppressor genes are inactivated that may be distinct from predisposing cancer genes. Previously, a tumor suppressor locus on human chromosome 13q14 that is distinct from the retinoblastoma predisposing gene 1 (RB1) has been identified in lung, head and neck, breast, ovarian and prostate tumors. By an approach that combines genomic difference cloning and positional cloning we isolated the cDNA of a novel gene (DICE1) located at 13q14.12-14.2. The DICE1 gene is highly conserved in evolution and its mRNA is expressed in a wide variety of fetal and adult tissues. The DICE1 cDNA encodes a predicted protein of 887 amino acids corresponding to an 100 kD protein that shows 92.9% identity to the carboxy-terminal half of the mouse EGF repeat transmembrane protein DBI-1. The DBI-1 protein interferes with the mitogenic response to insulin-like growth factor 1 (IGF-I) and is presumably involved in anchorage-dependent growth. When compared to normal lung tissue expression of the DICE1 mRNA was reduced or undetectable in the majority of non-small cell lung carcinomas analysed. The location of the DICE1 gene in the region of allelic loss, its high evolutionary conservation and the downregulation of expression in carcinoma cells suggests that DICE1 is a candidate tumor suppressor gene in non-small cell lung carcinomas and possibly in other sporadic carcinomas.

Coactivator PC4 mediates AP-2 transcriptional activity and suppresses ras-induced transformation dependent on AP-2 transcriptional interference

ras oncogene-transformed PA-1 human teratocarcinoma cells have abundant AP-2 mRNA but, paradoxically, little AP-2 transcriptional activity. We have previously shown that overexpression of AP-2 in nontumorigenic variants of PA-1 cells results in inhibition of AP-2 activity and induction of tumorigenicity similar to that caused by ras transformation of PA-1 cells. Evidence indicated the existence of a novel mechanism of inhibition of AP-2 activity involving sequestering of transcriptional coactivators. In this study, we found that PC4 is a positive coactivator of AP-2 and can restore AP-2 activity in ras-transformed PA-1 cells. Relative to vector-transfected ras cell lines, ras cell lines stably transfected with and expressing the PC4 cDNA have a diminished growth rate and exhibit a loss of anchorage-independent growth, and they are unable to induce the formation of tumors in nude mice. These data suggest that a transcriptional coactivator, like a tumor suppressor, can have a growth-suppressive effect on cells. Our experiments are the first to show that ras oncogenes and oncogenic transcription factors can induce transformation through effects on the transcription machinery rather than through specific programs of gene expression.

cDNA cloning and gene mapping of human homologs for Schizosaccharomyces pombe rad17, rad1, and hus1 and cloning of homologs from mouse, Caenorhabditis elegans, and Drosophila melanogaster

Mutations in DNA repair/cell cycle checkpoint genes can lead to the development of cancer. The cloning of human homologs of yeast DNA repair/cell cycle checkpoint genes should yield candidates for human tumor suppressor genes as well as identifying potential targets for cancer therapy. The Schizosaccharomyces pombe genes rad17, rad1, and hus1 have been identified as playing roles in DNA repair and cell cycle checkpoint control pathways. We have cloned the cDNA for the human homolog of S. pombe rad17, RAD17, which localizes to chromosomal location 5q13 by fluorescence in situ hybridization and radiation hybrid mapping; the cDNA for the human homolog of S. pombe rad1, RAD1, which maps to 5p14-p13.2; and the cDNA for the human homolog of S. pombe hus1, HUS1, which maps to 7p13-p12. The human gene loci have previously been identified as regions containing tumor suppressor genes. In addition, we report the cloning of the cDNAs for genes related to S. pombe rad17, rad9, rad1, and hus1 from mouse, Caenorhabditis elegans, and Drosophila melanogaster. These include Rad17 and Rad9 from D. melanogaster, hpr-17 and hpr-1 from C. elegans, and RAD1 and HUS1 from mouse. The identification of homologs of the S. pombe rad checkpoint genes from mammals, arthropods, and nematodes indicates that this cell cycle checkpoint pathway is conserved throughout eukaryotes.

RAD1, a human structural homolog of the Schizosaccharomyces pombe RAD1 cell cycle checkpoint gene

Cell cycle checkpoints are gating mechanisms that govern cell cycle progression in the presence of DNA damage and incomplete DNA replication. The Schizosaccharomyces pombe Rad1 protein is an essential component of cell cycle checkpoints activated by both types of genomic stress. In this study, we report the isolation of a human homolog of the S. pombe RAD1 gene. The hRAD1 protein is also similar to the Saccharomyces cerevisiae cell cycle checkpoint protein Rad17 and the Ustilago maydis 3' --> 5' exonuclease, Rec1. We show that human RAD1 partially complements the hydroxyurea and ionizing radiation hypersensitivities of a S. pombe rad1 mutant, suggesting phylogenetic conservation of the DNA damage and replication checkpoints. The human RAD1 locus was mapped to human chromosome 5p13.2, a locus frequently altered in non-small-cell lung cancer and bladder cancer.

Human and mouse homologs of Schizosaccharomyces pombe rad1(+) and Saccharomyces cerevisiae RAD17: linkage to checkpoint control and mammalian meiosis

Preventing or delaying progress through the cell cycle in response to DNA damage is crucial for eukaryotic cells to allow the damage to be repaired and not incorporated irrevocably into daughter cells. Several genes involved in this process have been discovered in fission and budding yeast. Here, we report the identification of human and mouse homologs of the Schizosaccharomyces pombe DNA damage checkpoint control gene rad1(+) and its Saccharomyces cerevisiae homolog RAD17. The human gene HRAD1 is located on chromosome 5p13 and is most homologous to S. pombe rad1(+). This gene encodes a 382-amino-acid residue protein that is localized mainly in the nucleus and is expressed at high levels in proliferative tissues. This human gene significantly complements the sensitivity to UV light of a S. pombe strain mutated in rad1(+). Moreover, HRAD1 complements the checkpoint control defect of this strain after UV exposure. In addition to functioning in DNA repair checkpoints, S. cerevisiae RAD17 plays a role during meiosis to prevent progress through prophase I when recombination is interrupted. Consistent with a similar role in mammals, Rad1 protein is abundant in testis, and is associated with both synapsed and unsynapsed chromosomes during meiotic prophase I of spermatogenesis, with a staining pattern distinct from that of the recombination proteins Rad51 and Dmc1. Together, these data imply an important role for hRad1 both in the mitotic DNA damage checkpoint and in meiotic checkpoint mechanisms, and suggest that these events are highly conserved from yeast to humans.