Role of stress-induced alternative splicing of hdm2 in human tumor and non-tumorigenic cell lines

Hdm2, an oncogene, regulates the function of various cellular proteins that have critical roles in cell cycle regulation. One of the most important regulatory targets of HDM2 is p53, a tumor suppressor protein. Precise regulation of the p53-HDM2 circuit is paramount for coordinated malignant suppression and cell survival. To explore the role of post-transcriptional regulation of hdm2 on this circuit, the effects of various damaging agents on hdm2 were examined in human tumor and non-tumorigenic cell lines using nested RT-PCR. Hdm2 was alternatively spliced to hdm2alt1 after certain levels of radiation- and cisplatin-induced damage. Protein analysis, using immunoprecipitation and western blot analysis showed that HDM2ALT1 interacted with full-length HDM2 after damage and its presence correlated with increased p53 and decreased HDM2 protein levels. This corresponded with decreased p53-HDM2 interaction, as detected by immunofluoresence and immunoprecipitation studies. Interestingly, real time RT-PCR analyses revealed a decrease in hdm2 RNA levels after UV radiation, when hdm2alt1 was detected. This implies that induction of hdm2 alt1 is a cellular response to certain stress signals tailored mainly to decrease hdm2 RNA and protein levels, in turn decreasing p53-HDM2 interaction or the oncogenic properties of hdm2 . This mechanism may function in concert with other endogenous stress-induced processes to facilitate a more potent damage response.