Mutant p53 mediated induction of cell cycle arrest and apoptosis at G1 phase by 9-hydroxyellipticine.

Wild-type p53 causes cell-cycle arrest at late G1 phase and induction of apoptosis by up- regulation of waf1 and bax, respectively. Although in many cancer cells p53 is frequently mutated and loses its functions, we have proposed that mutant p53 may be involved in the anticancer mechanism of 9-hydroxy ellipticine (9HE). It was shown using flow cytometry that 9HE (10 microM) caused induction of apoptosis in G1 phase of the cell cycle in mutant p53 (p53ala143, p53his175, orp53his273) transfected Saos-2 cells, but not in p53-deficient parental Saos-2 cells. Similar induction of apoptosis was observed 24-48 h after treatment with 9HE in mutant p53-containing SW480, SK-BR-3 and MKN-1, but not in p53-deficient KATO m cells. Using G1 phase cells isolated by centrifugal elutriation, it was confirmed that 9HE caused cell cycle arrest at G1 phase and subsequently induced G1 phase-restricted apoptosis. In accordance with the induction of arrest and apoptosis in G1 phase, 9HE caused up-regulation of waf1 and bax mRNA in mutant p53-containing cells, but not in p53-deficient parental Saos-2 cells. In control experiments, adriamycin (ADR) showed neither G1-restricted apoptosis nor elevation of bax mRNA. It is suggested that 9HE may cause G1 arrest and induction of G1 phase-restricted apoptosis by restoring the wild-type function of mutant p53 protein.

Negative effects of wild-type p53 and s-Myc on cellular growth and tumorigenicity of glioma cells. Implication of the tumor suppressor genes for gene therapy.

Human (U251, U87, U343) and rat glioma cell lines (C6, 9L) were examined by the reverse transcriptase-polymerase chain reaction and subsequent nucleotide sequencing analysis to see whether they express wild type (wt)-p53 or mutated form (mut)-p53 messages. Results showed that U87, U343, and C6 cells expressed wt-p53 messages whereas U251 and 9L cells expressed mut-p53 messages. All these cell lines were transfected with wt-p53 cDNA or the s-myc gene linked to the mouse mammary tumor virus (MMTV) promoter. Of several G418-resistant clones obtained from each transfection, a few expressed the s-Myc or wt-p53 proteins. Independent of mutations in the intrinsic p53 gene, the cellular growth in vitro and tumorigenicity in nude mice of these clones were drastically suppressed, the extent of suppression being correlated with the expression level of the transfected gene. Flow-cytometric analysis demonstrated that both p53 and s-Myc arrested the cell cycle at the G1/S boundary. These data suggest that these genes having negative effects on tumor cell proliferation could be used in gene therapy of gliomas, which are caused by alteration of the p53 gene or by some other genetic change.