Role of the Suppressor, Rsu-1, in Regulation of Ras Signal Transduction in Breast Cancer Cells.

摘要

Rsu-1 is a cDNA previously identified as an inhibitor of Ras-induced transformation. An HA-epitope tagged Rsu-1 cDNA was introduced into the MCF7 breast carcinoma cell line. Stable transfectants were selected for analysis of effects of Rsu-1 expression on growth control and Ras-dependent kinase pathways. Assessment of biological activity of HA-Rsu-1 transfectants revealed slower anchorage dependent growth rates , a significant reduction in anchorage independent growth and increased apoptosis compared to control MCF7 cell lines. Analysis of cell cycle regulatory proteins required for transit through 61 revealed that HA-Rsu-1 transfectant cell lines expressed elevated levels of p21 (CIP) CDK inhibitor but not cyclin D or p27 KIP, This appears to be due to stabilization of P53 by Rsu-1 expression as revealed by pulse-chase experiments. Moreover, Rsu-1 transfectants exhibited reduced levels of cyclin D- associated kinase and cdk2 kinase activity. Perturbations in signal transduction pathways which can be activated by Ras were detected in the Ha-Rsu- 1 transfectants including activation of Jun kinase, Rho kinase and c-myc transcription. Growth inhibition was not observed in Rsu-1 transfectants of the p53 mutant cell lines MDA-MB-231 and MDA-MB-468. Hence, Rsu-I expression critically altered cell cycle regulation and growth of MCF7 cells as well as signaling pathways required for malignant growth.