Electrophoretic Characterization of Ribosomal Subunits and Proteins in Apotosis: Specific Downregulation of S 11 in Staurosporine-Treated Human Breast Carcinoma Cells

摘要

Stimulation of death receptors (Fas on human T-cell leukemia Jurkat cells and tumor necrosis factor receptor- 1 on human monoblastic leukemia U937 cells) triggers the specific degradation of 285 ribosomal RNA, and this process may contribute to cell death through the inhibition of protein synthesis. We have developed an analytical method using a polyacrylamide—agarose composite gel to evaluate ribosomal subunits in apoptotic cells (human breast carcinoma MCF-7 cells treated with staurosporine and human 2931 cells irradiated with ultraviolet light were used in addition to the two apoptosis systems described above). No alterations were detected by this method, suggesting that apoptosis, including the process of ribosomal RNA degradation, does not cause fragmentation or extensive conformational changes in the ribosome. We also examined the status of 21 different ribosomal proteins in apoptotic cells by immunoblotting with polyclonal antibodies. 811 was specifically downregulated in apoptotic MCF-7 cells and in other apoptotic breast carcinoma cells. Previous studies have shown that SIi is heterogeneously expressed in cancer cells. Taken together, it appears that particular intracellular environments regulate the expression of SIl protein. However, the mechanism by which this process is modulated is as yet unknown. Furthermore, we have demonstrated that our composite gel electrophoresis system can efficiently detect ubiquitination of ribosomal subunits.