Apparent protection from instability of repeat sequences in cancer-related genes in replication error positive gastrointestinal cancers

Pretreatment plasma TGF beta 1 levels are prognostic for survival but not morbidity following radiation therapy of carcinoma of the cervix

PURPOSE

To determine whether pretreatment plasma-transforming growth factor beta 1 (TGF beta 1) levels are prognostic for tumor control and late morbidity following radiation therapy in carcinoma of the cervix.

METHODS AND MATERIALS

The study was comprised of 79 patients undergoing radiotherapy with curative intent for Stage I-III carcinoma of the cervix. TGF beta 1 levels were analyzed using ELISA. Late morbidity was measured using the Franco-Italian glossary. Data were available for the pretreatment levels of circulating tumor markers that represent disease burden, and for peripheral blood lymphocyte radiosensitivity measured as SF2.

RESULTS

Pretreatment TGF beta 1 levels were a significant prognostic factor for survival and local control. There were weak significant correlations of TGF beta 1 levels with disease stage and the levels of circulating tumor markers (CA125, TPA). There was a weak significant correlation between TGF beta 1 levels and normal cell radiosensitivity (lymphocyte SF2). There was no relationship between TGF beta 1 levels and grade of morbidity and pretreatment TGF beta 1 levels were not a significant prognostic factor for the probability of developing late morbidity.

CONCLUSION

In carcinoma of the cervix, pretreatment TGF beta 1 levels reflect tumor burden and are a significant prognostic factor for survival. Despite an underlying weak relationship of TGF beta 1 levels with intrinsic normal cell radiosensitivity, pretreatment levels are not prognostic for the probability of developing late complications. This finding does not rule out the possible usefulness of measurements toward the end of treatment once tumor burden has been reduced.

Hereditary non-polyposis colorectal cancer associated with disseminated superficial porokeratosis. Microsatellite instability in skin tumours

A 73-year-old man presented with typical lesions of disseminated superficial porokeratosis (DSP) and multiple seborrhoeic keratoses on his face, trunk and extremities, and later developed a keratoacanthoma on his lip. He belonged to a cancer-prone pedigree susceptible to colonic, uterine and other internal cancers, and had a personal history of early gastric cancer and advanced adenocarcinoma of the descending colon without adenomatous polyps at age 59 years. Polymerase chain reaction amplification of skin samples for seven separate microsatellite polymorphisms revealed microsatellite instability (MSI) at multiple loci in five of six seborrhoeic keratoses and the keratoacanthoma, strongly suggesting underlying defects in DNA mismatch repair. Although no germline mutations in two mismatch repair genes hMSH2 and hMLH1 were found, our patient was recognized as having hereditary non-polyposis colorectal cancer (HNPCC) based on the family history and the findings of the microsatellite analysis of skin tumours. This confirmed the usefulness of detection of MSI in prevalent and readily accessible skin lesions, including non-sebaceous non-dysplastic tumours such as seborrhoeic keratosis in the screening of HNPCC families. Although DSP may also be inherited as an autosomal dominant condition, this particular skin disease appeared to be sporadic in our patient and, to our knowledge, no association of DSP or other forms of porokeratosis with HNPCC has previously been reported. In contrast to the seborrhoeic keratoses and keratoacanthoma, no MSI was observed in two samples from DSP lesional epidermis examined.

Mutations associated with microsatellite unstable colorectal carcinomas exhibit widespread intratumoral heterogeneity

Although microsatellite instability (MSI) has been shown to be present in 15% of sporadic colorectal carcinomas, the genetic events underlying the development of these tumors have not been well described. By investigating intratumoral heterogeneity, this study attempts to elucidate whether MSI-positive colorectal carcinomas develop as the result of a random accumulation of mutations or as an ordered, stepwise sequence of genetic alterations. Eighty-six regions from 16 MSI-positive sporadic colorectal carcinomas were examined for mutations in repeat nucleotide sequences of the tumour suppressor genes transforming growth factor beta type II receptor (TGFBRII), insulin-like growth factor II receptor (IGFIIR), and BAX, and the mismatch repair genes MSH3 and MSH6. At least 2 and up to 5 of these genes were mutated in each tumour, and widespread intratumoral heterogeneity was observed for each gene. Regions of tumour with TGFBRII mutations were correlated with a poorly differentiated histology. Unlike the situation in microsatellite stable colorectal carcinomas, the findings of the present study did not suggest that a particular sequence of tumour suppressor and mismatch repair genes are mutated during colorectal tumorigenesis. It seems likely that a random accumulation of mutations, as a result of a defect in the mismatch repair pathway, drives tumour progression in this type of colorectal carcinoma.

A novel sensitive method to detect frameshift mutations in exonic repeat sequences of cancer-related genes

We have investigated frameshift mutations in exonic repeats in the ATR, BRCA1, BRCA2, PTCH, CTCF, Cx26, NuMa and TGFbetaRII genes, using human tumor samples from stomach, esophagus, breast and skin and melanoma, as well as colon cancer and endometrial cancer cell lines (125 samples in total). We developed a sensitive method to detect mutations in the repeats, using the introduction of an artificial restriction site into a repeat. The method detects a single mutant among 10(3) normal genes. Thus, an alteration in a repeated sequence can be detected unambiguously. The (A)(8) repeat of BRCA2 was found mutated in only two of five colon cell lines with microsatellite instability (MI(+)). The ATR gene has an (A)(10) repeat which was altered in two of three MI(+) stomach cancer samples and one of three MI(+) endometrial cell lines. The TGFbetaRII gene [with an (A)(10) repeat] had the maximal frequency of mutations: 10 out of 13 MI(+) samples. At least one sample from all types of cancers, except melanomas, was positive for TGFbetaRII gene mutations. No mutations were found in repeats in the BRCA1, PTCH, CTCF, NuMA and Cx26 genes in any types of tumors examined. In conclusion, our study indicates that repeats were altered only in MI(+) cells and that the mutation frequencies in the genes studied differ among tumor types. Based on these results, we discuss meaningful and meaningless alterations in exonic repeats.

Mismatch repair and drug responses in cancer

Defects in mismatch repair contribute to development of approximately 15% of colon cancers and to origination of endometrial, gastric and other cancers. Tumors with defects in mismatch repair exhibit marked resistance to alkylators and a variety of anticancer agents that modify DNA to create substrates for the mismatch repair system. These altered drug responses appear to derive from requirements for mismatch repair proteins in signalling apoptosis, altered cell cycle checkpoint behaviour and/or loss of mismatch repair dependent toxicity arising from futile repair cycling. Altered repair mechanisms for mismatched substrates in mismatch repair defective tumors provide both challenges for development of tumor-phenotype-screening methodologies to assure appropriate therapy is administered for these cancers and foci for development of new therapy approaches that capitalize on modified drug responses in mismatch repair- defective cells. Copyright 1999 Harcourt Publishers Ltd.

Expression of Bcl-2 protein is decreased in colorectal adenocarcinomas with microsatellite instability

Bcl-2 is known to inhibit apoptosis and is thought to play a role in colorectal tumour development. Studies of the promoter region of bcl-2 have indicated the presence of a p53 responsive element which downregulates bcl-2 expression. Since p53 is commonly mutated in colorectal cancers, but rarely in those tumours showing microsatellite instability (MSI), the aim of this study was to examine the relationship of bcl-2 protein expression to MSI, as well as to other clinicopathological and molecular variables, in colorectal adenocarcinomas. Expression of bcl-2 was analysed by immunohistochemistry in 71 colorectal cancers which had been previously assigned to three classes depending upon their levels of MSI. MSI-high tumours demonstrated instability in three or more of six microsatellite markers tested, MSI-low tumours in one or two of six, and MSI-null in none of six. Bcl-2 expression in tumours was quantified independently by two pathologists and assigned to one of five categories, with respect to the number of cells which showed positive staining: 0, up to 5%; 1, 6-25%; 2, 26-50%; 3, 51-75%; and 4, > or =76%. Bcl-2 negative tumours were defined as those with a score of 0. Bcl-2 protein expression was tested for association with clinicopathological stage, differentiation level, tumour site, age, sex, survival, evidence of p53 inactivation and MSI level. A significant association was found between bcl-2 expression and patient survival (P = 0.012, Gehan Wilcoxon test). Further, a significant reciprocal relationship was found between bcl-2 expression and the presence of MSI (P = 0.012, Wilcoxon rank sum test). We conclude that bcl-2 expressing colorectal cancers are more likely to be MSI-null, and to be associated with improved patient survival.

Mutational analyses of multiple target genes in histologically heterogeneous gastric cancer with microsatellite instability

It has been recognized that gastric cancer often shows histological heterogeneity in a single tumor. Although microsatellite instability (MSI) has been reported in gastric cancer, the significance of genomic instability in gastric cancers with histological heterogeneity within a single tumor has never been addressed. We investigated MSI at 8 microsatellite loci in 40 normal/tumor DNA pairs from 20 gastric cancers with histological heterogeneity. Six of 20 patients (10 DNAs of 40 tumor DNAs) had severe MSI in more than 3 loci. Four of the MSI-positive cases had frameshift mutations in the poly(A)10 tract of the TGF beta RII gene. This mutation was found only in the MSI-positive component in the 2 cases (cases 4 and 5) in which only 1 component exhibited MSI. The other 4 cases demonstrated homozygous or heteroclonal mutations (1 and 2 base deletions) in the poly(A)8 tract of the hMSH3 gene; no mutation was detected in the poly(C)8 tract of the hMSH6 gene in any of the MSI-positive cases. The profile of alterations in multiple targets was different between the 2 components in most of the cases (5/6). These findings suggest that mismatch repair deficiency in MSI-positive tumors causes multiple gene inactivations through frameshift mutations in short repetitive sequences in a heterogeneous way within a histologically heterogeneous tumor.

Characterization of the EMS1 gene and its product, human Cortactin

We have identified a novel gene, EMS1, that is consistently amplified and overexpressed in human carcinomas with an amplification of the chromosome 11q13 region. Comparisons of the EMS1 sequences with those present in the GenBank databases revealed a high identity with chicken cortactin. Southern and western blot analyses confirm the high sequence conservation during evolution. An antiserum specific for human cortactin, showed in gene transfer experiments that both human p80 and p85 isoforms are encoded by the EMS1 cDNA. Further comparisons demonstrated an high sequence and structural homology with HS1 that is implicated in signal transduction in lymphoid cells only. Expression of EMS1/cortactin mRNA was restricted to tumor cell lines derived from non-lymphoid origin. Cortactin contains (i) a filamentous actin binding tandem repeat domain, (ii) a proline-rich SH3-binding and (iii) a SH3 domain that is common in proteins involved in signal transduction. Our data suggest that human EMS1/cortactin has a function in signal transmission between cell-matrix contact sites and the cytoskeleton and, as such, its overexpression due to 11q13 amplification might effect adhesive properties of human carcinomas.

Accumulated clonal genetic alterations in familial and sporadic colorectal carcinomas with widespread instability in microsatellite sequences

A subset of hereditary and sporadic colorectal carcinomas is defined by microsatellite instability (MSI), but the spectra of gene mutations have not been characterized extensively. Thirty-nine hereditary nonpolyposis colorectal cancer syndrome carcinomas (HNPCCa) and 57 sporadic right-sided colonic carcinomas (SRSCCa) were evaluated. Of HNPCCa, 95% (37/39) were MSI-positive as contrasted with 31% (18/57) of SRSCCa (P < 0.000001), but instability tended to be more widespread in SRSCCa (P = 0.08). Absence of nuclear hMSH2 mismatch repair gene product by immunohistochemistry was associated with germline hMSH2 mutation (P = 0.0007). The prevalence of K-ras proto-oncogene mutations was similar in HNPCCa and SRSCCa (30% (11/37) and 30% (16/54)), but no HNPCCa from patients with germline hMSH2 mutation had codon 13 mutation (P = 0.02), and two other HNPCCa had multiple K-ras mutations attributable to subclones. 18q allelic deletion and p53 gene product overexpression were inversely related to MSI (P = 0.0004 and P = 0.0001, respectively). Frameshift mutation of the transforming growth factor beta type II receptor gene was frequent in all MSI-positive cancers (85%, 46/54), but mutation of the E2F-4 transcription factor gene was more common in HNPCCa of patients with germline hMSH2 mutation than in those with germline bMLH1 mutation (100% (8/8) versus 40% (2/5), P = 0.04), and mutation of the Bax proapoptotic gene was more frequent in HNPCCa than in MSI-positive SRSCCa (55% (17/31) versus 13% (2/15), P = 0.01). The most common combination of mutations occurred in only 23% (8/35) of evaluable MSI-positive cancers. Our findings suggest that the accumulation of specific genetic alterations in MSI-positive colorectal cancers is markedly heterogeneous, because the occurrence of some mutations (eg, ras, E2F-4, and Bax genes), but not others (eg, transforming growth factor beta type II receptor gene), depends on the underlying basis of the mismatch repair deficiency. This genetic heterogeneity may contribute to the heterogeneous clinical and pathological features of MSI-positive cancers.

Microsatellite instability in ductal carcinoma in situ of the breast

Microsatellite instability (MI+) is associated with defects in mismatch repair, resulting in a 'mutator' phenotype and the development and progression of cancer. MI+ has been documented in invasive breast carcinomas. This study was undertaken to determine whether MI+ is found in the early non-invasive form of breast cancer, ductal carcinoma in situ (DCIS). We examined microdissected ducts from 23 cases of DCIS with 11 markers comprising mono-, di-, and trinucleotide repeats from six chromosomal regions. Five tumours (22 per cent) displayed MI+ at two or more loci, in all ducts examined. A further seven (30 per cent) tumours showed alterations at a single locus (the DM-1 trinucleotide), and for two of these, heterogeneity between ducts was observed. Alterations at microsatellite repeat motifs in the coding regions of four cancer-associated genes (TGF beta RII, IGFIIR, BAX, and E2F-4) were not observed. Immunohistochemistry revealed that there was no loss of reactivity for the mismatch repair proteins, MLH1, MSH2, and PMS2, in the DCIS cases. In general, MI+ tumours and those with alterations at the DM-1 microsatellite were predominantly of higher nuclear grade and expressing c-erbB-2, suggesting that aberrations in DNA repair functions may lead to the acquisition of a more aggressive phenotype in breast cancer.