T-antigen of sv40 blocks p53 transactivation but not p53 specific binding to DNA

The p53 is a DNA binding phosphoprotein that can act as a transcriptional activator through high affinity DNA binding sequences (HBS). The large T antigen (LT-ag) of SV40 virus can bind p53 and their association is considered important for transforming activities of the virus. In this study, we investigated the effects of LT-ag on transcriptional transactivating function of p53 using cotransfection assays and DNA-binding electrophoretic mobility shift assays. A reporter gene containing a minimal TK promoter and two copies of HBS for p53 was cotransfected with p53 and LT-ag expression vector into human SKOV3 cells (p53 non-expressor). The LT-ag inhibited in a dose-dependent fashion transactivation by wild-type p53. The LT-ag was unable to inhibit transactivation of a reporter gene containing a similar promoter (TK). The LT-ag mutants defective for binding to p53, failed to inhibit transactivation. The LT-ag inhibited the transactivation of a CAT reporter gene containing the GAL4-DNA recognition sequences by the p53 protein which was fused to the heterologous DNA binding domain (amino acids 1-147 of GAL4) in cotransfected cells showing that inhibition of p53 activities by LT-ag was not restricted to the p53 HBS-dependent reporter. LT-ag failed to inhibit GAL4-p53 fragment containing the transactivating, but non-LT-ag binding region of p53, showing the importance of LT-ag binding to p53 in order to restrict p53 transactivation. Immunohistochemical analysis showed that in SKOV3, nuclear localization of wild type p53 was unaffected by coexpressed LT-ag. Gel shift analysis determined that nuclear extract from cells cotransfected with p53 and LT-ag expression vectors contained p53 not associated with LT-ag; this free p53 was able to bind to the HBS. These results suggest that LT-ag of SV40 preferentially binds the transcriptionally active p53, preventing it from transactivating through p53-HBS; the transcriptionally inactive p53 in these cells can still bind p53-HBS.

Molecular analysis of INK4 genes in breast carcinomas

Cell cycle regulators have recently been implicated in oncogenic transformation of cells, including the cyclins active in the G1 phase of the cell cycle and their respective cyclin-dependent kinases (CDK) whose activities are regulated by a set of inhibitors of CDK (CDKI). Since CDKIs can inhibit cell proliferation, they may have a role as tumor suppressor genes. To determine if alterations of CDKI genes may be involved in tumorigenesis of breast cancer, we examined the mutational status of p16(INK4A), p15(INK4B), p18(INK4C), p19(INK4D) CDKI genes in 36 primary breast carcinomas and 9 breast cancer cell lines using polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP), direct DNA sequencing, and Southern blot analysis. Furthermore, amplification of cyclin D1, D2, D3 genes were also examined in these samples. One mutation of p15(INK4B) gene occurred, resulting in change of aspartic acid to asparagine at codon 85. Since aspartic acid at this position is conserved between all four human and murine INK4 proteins, this missense mutation may have functional significance. The sample with a p15(INK4B) point mutation was accompanied by amplification of the cyclin D1 gene. A deletion of the p18(INK4C) gene was found in a primary tumor. Three deletions of the p16(INK4A) gene and two deletions of the p15(INK4B) gene were found in the cell lines. Also, we found amplification of the p15(INK4B) and p16(INK4A) loci in a clinical sample as well as amplification of the p19(INK4D) in another sample, and amplification of the myeloperoxidase (MPO) gene in one cell line and two primary tumors. We suspect that a critical gene for breast cancer is amplified near the MPO gene. These data indicate that CDKI mutations are moderately rare in breast cancer and are often associated with the simultaneous alteration of more than one cell-cycle regulatory gene.

Mutational analysis of the hMSH2 gene in a wide variety of tumors

The hMSH2 gene participates in DNA mismatch repair and its mutation can result in genetic instability of the human genome which is an important feature of tumorigenesis. In this study, genetic alterations of the hMSH2 gene were examined in 43 ovarian, 36 non-small cell lung (NSCL), 31 poorly differentiated gastric, 15 endometrial, and 11 colon cancers, nine gastric cancer cell lines, 41 adult T-cell leukemias (ATLs), two ATL cell lines, and 37 non-Hodgkin's lymphomas (NHLs), using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique. Microsatellite instability (MSI) was also investigated for ovarian, NSCL, and colon cancers. The incidence of MSI was 1/36 (3%) for NSCL, 2/23 (9%) for ovarian, and 1/11 (9%) for colon cancers. Missense base changes of the hMSH2 gene were identified in two gastric cancer patients (ATG to ATA resulting in Met changing to Ile at codon 688 in exon 13 and ACA to GCA resulting in Thr changing to Ala at codon 803 in exon 14). These mutations were found in samples with no MSI. One ovarian and one gastric cancer, and six ATL samples showed two types of polymorphisms of hMSH2 (CTT to TTT resulting in Leu changing to Phe at codon 390 in exon 7 and CAG to AAG resulting in Gin to Arg at codon 419 in exon 7). Our data suggest that MSI and hMSH2 mutations are uncommon in sporadic tumors.

Potent tumoricidal effects of a human cytotoxic T-cell line (TALL-104) against prostate cancer

The human TALL-104 cell line possesses major histocompatibility complex non-restricted cytotoxic activity against a large variety of tumor targets. Adequate therapies for prostate cancer that has spread outside its capsule are lacking. In order to identify effective therapies for this problem, we investigated the antiproliferative effects of TALL-104 cells against three prostate cancer cell lines (LNCaP, PC-3, DU-145). A Cr-51-release: cytotoxicity assay showed that TALL-104 cells were very cytotoxic against the prostate cancer cells. For example, at a 1:1 ratio of TALL-104 cells to prostate cancer cells, the percent release of Cr-51 at 18 h were 50, 40, and 45% for LNCaP, PC-3, and DU-145, respectively. Analysis by inhibition of clonogenic growth of prostate cancer cells also showed that TALL-104 cells were extremely effective. For instance, a short-term (4 h or 18 h) pre-incubation of TALL-104 cells with these tumor cells at the effector to target ratio of 10:1 prior to clonogenic assay resulted in a substantial reduction in clonogenic tumor growth (90%, 65%, and 50% clonal growth inhibition for LNCaP, PC-3, and DU-145, respectively). Further experiments using both Cr-51 release and clonogenic assays showed that irradiated TALL-104 cells were also effective in their anti-prostatic cancer activities. We also examined if TALL-104 cells plus a chemotherapeutic agent might complement each other in their cytotoxic effects. Preincubation of prostate cancer cell targets with etoposide (0.2-20 mu g/ml) for 18 h markedly increased their susceptibility to TALL-104 lysis. The anti-tumor efficacy of TALL-104 cells was also demonstrated in vivo utilizing the BNX murine model engrafted with subcutaneous PC-3 prostate cancer cells. A substantial reduction in PC-3 tumor cell progression was observed in mice injected with irradiated TALL-104 cells (1x10(7) cells intraperitoneally or intratumorally for 5 days beginning on days 24 and 45 after implantation) as compared to mice injected with tumors only. Taken together, these findings suggest that TALL-104 cells may be utilized as a potent anti-tumor agent, either alone or in combination with other agents (such as etoposide) in metastatic prostate cancer.

DPC 4/SMAD 4 in non-pancreatic tumors with frequent LOH 18q21 and in hematological malignancies

Recently, a novel candidate tumor suppressor gene, DPC 4/SMAD 4, has been implicated in the development of pancreatic cancers. Its location at human chromosome 18q21 prompted us to investigate this gene in a large series of primary tumors located outside the gastrointestinal tract which have been associated with loss of heterozygocity (LOH) at this locus. One hundred and thirty primary solid tumor samples (28 breast, 34 non-small cell lung, and 20 prostate cancers, and 40 osteosarcomas), 32 cell lines as well as 162 leukemia and lymphoma cases were analysed by Southern blotting and PCR-SSCP for deletions and mutations of the DPC 4 gene. In the breast cancer cell line MDA-MB-468, the gene was found to be homozygously deleted. Neither the primary solid tumor samples nor hematological malignancies had detectable abnormalities. Our study suggests that alterations of the DPC 4 gene, unlike in pancreatic cancer, are rare in breast, nonsmall cell lung and prostate cancers, osteosarcomas and hematopoietic malignancies.