Chromosome location of genes encoding human blood groups

In this study the transactivation potential and DNA binding activities of p53 protein were examined following exposure of A2780 cells, a human ovarian carcinoma cell line, to the DNA damaging agent, cis-diamminedichloroplatinum II (cisplatin). The endogenous murine double minute-2 gene (mdm-2) was used to monitor the ability of p53 to transactivate genes. Northern analysis showed an induction of mdm-2 mRNA upon cisplatin treatment. It was further demonstrated, using an RNase protection assay, that the p53-responsive, mdm-2 promoter (P2) was activated in cisplatin-treated A2780 cells. However, when p53 protein DNA binding activity was analyzed, there was no detectable increase in p53 sequence-specific DNA binding activity during the period of time following DNA damage when mdm-2 mRNA was induced. Instead the increase in p53 protein observed in nuclear, cytoplasmic, and whole cell extracts correlated with a latent conformation of p53 that lacked sequence-specific DNA binding activity. At low doses of cisplatin, these latent pools of p53 increased in parallel with mdm-2 gene activation and were detectable as early as 4 h following cisplatin treatment. In vitro attempts to convert the latent p53 into an active, sequence-specific DNA binding conformation were unsuccessful. Even though cisplatin-induced p53 lacked sequence-specific DNA binding activity, it does possess an increased affinity for cisplatin-damaged duplex DNA molecules. This represents the first identification where cisplatin treatment induces a p53 protein, lacking sequence-specific DNA binding but with an increased affinity for platinated DNA molecules.     

WAF1/p21 regulates proliferation, but does not mediate p53-dependent apoptosis in urothelial carcinoma cell lines

The WAF1/p21 gene product is an inhibitor of cyclin-dependent kinases which can be induced by the tumor suppressor p53 and mediate some of its effects, or function in p53-independent pathways of cell cycle regulation. Although a potential tumor suppressor gene, WAF1/p21 is expressed in bladder cancer. To elucidate the function of p21 in tumor cells we have investigated in urothelial carcinoma cell lines: i) WAF1/p21 mRNA and protein expression, ii) the biological effects of p21 overexpression or down-regulation and (iii) whether p21 can be induced by p53. WAF1/p21 mRNA levels examined in four cell lines were comparable to bladder mucosa. One cell line, HT1376, failed to express p21 protein due to a frame shift mutation. Overexpression of WAF1/p21 cDNA inhibited clone formation in three cell lines, whereas transfection with antisense WAF1 increased clone sizes and numbers. WAF1 sense clones showed diminished cell proliferation compared to the parental cell line. Apoptosis- induced wild-type p53 was not inhibited by overexpression of antisense WAF1/p21. In a cell clone derived from line VMCub1 by stable transfection with wild-type p53 under the control of a metallothionein promotor, p21 was induced along with p53 upon activation of the promoter with zinc chloride. This induction was accompanied by a decrease in cell proliferation but by little apoptosis. These data suggest that p21 inhibits proliferation in a p53-dependent or independent manner but does not mediate p53-induced apoptosis in urothelial carcinoma cells.     

Regulation of Myc-dependent apoptosis by p53, c-Jun N-terminal kinases/stress-activated protein kinases, and Mdm-2

Deregulated overexpression of c-Myc (Myc) confers susceptibility to apoptosis in several cell types, but the molecular regulation of these processes has not been well established. Here we have characterized several molecular changes that may modulate Myc-dependent apoptosis. Ectopic overexpression of Myc in both Rat1 fibroblasts and human osteosarcoma cells causes a dramatic increase of cellular p53 mRNA and protein, and this induction of p53 correlates with apoptosis triggered by withdrawal of serum. Stable transfection of a wild-type human p53 gene into Myc-transformed cells further potentiates apoptosis. Anticancer agents vinblastine and nocodazole also induce apoptosis in Myc-transformed Rat1 fibroblasts but are cytostatic to the same cells without Myc overexpression. We demonstrate that induction of Myc-dependent apoptosis in these cells is specifically associated with an activation of p46 c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) activity, whereas this JNK/SAPK activation is absent in stress-treated cells without Myc overexpression. Moreover, overexpression of the Mdm-2 gene in Rat1-myc cells significantly inhibits apoptosis induced by low serum but has little effect on apoptosis triggered by chemotherapeutic drugs. Interestingly, differential inhibition by Mdm-2 paralleled differential activation of p46 JNK/SAPK. Thus, our data support a functional involvement of p53 in Myc-dependent apoptosis and implicate potential regulatory roles for JNK/SAPK and Mdm-2 pathways in the regulation of apoptosis in Myc-transformed tumor cells.