Overexpression of the small heat shock protein 27 (hsp27) concomitant with elevated estrogen receptor levels are correlated with increased doxorubicin resistance, increased metastatic behavior and reduced disease free survival in breast cancer patients. In human breast cancer cells overexpressing hsp27 the tyrosine kinase c-Yes is downregulated at the RNA and protein level. This downregulation is associated with increased invasive and metastatic behavior of human breast cancer cells, and can be abrogated by reconstituting c-Yes expression. Sequence analysis of the c-Yes mRNA revealed that its 3′-untranslated region (3′-UTR) contains several stretches resembling adenine/ uridine-rich elements (AREs) involved in accelerated mRNA degradation of highly regulated genes, such as oncogenes and cytokines. The decay of mRNAs containing AREs is mediated by a multi-protein complex containing the RNA-binding protein ARE binding factor 1 (AUF1). Another constituent of this complex is the translation initiation factor eIF4G, that is reported to also be a binding partner of hsp27. Therefore, we propose that hsp27 is involved in the ARE-mediated downregulation of c-Yes levels, which could provide a mechanism of hsp27 signaling in human breast cancer cells leading to metastatic behavior. Methods: We screened the 3′-UTR of the c-Yes mRNA for putative AREs using RNA-protein gel-shifts with extracts from MDA-MB 231 human breast cancer cells overexpressing hsp27 as well as control cells. Results: We found that at least three regions in the c-Yes mRNA 3′-UTR contain binding sites for factors present in both hsp27-overexpressing and control human breast cancer cells. Supershift experiments with polyclonal antibodies against AUF1 suggest that one of these factors is identical with AUF1. Conclusion: We conclude that the c-Yes mRNA 3′-UTR contains at least three AREs, which are bound by AUF1 in MDA-MB 231 cells. These regions probably are involved in the regulation of c-Yes mRNA turnover, which may be accelerated in human breast cancer cells overexpressing hsp27. We hypothesize that hsp27 signals through the c-Yes tyrosine kinase pathway during hsp27-induced metastasis formation and this hypothesis will be investigated in other model systems.
|Original language||English (US)|
|Number of pages||1|
|Journal||Breast Cancer Research and Treatment|
|State||Published - 2001|
All Science Journal Classification (ASJC) codes
- Cancer Research