Dominant-negative Rac1 suppresses Ras-induced apoptosis possibly through activation of NFkappaB in Ha-ras oncogene-transformed NIH/3T3 cells.

We investigated the involvement of Rac1 in Ha-ras-overexpression-induced apoptosis using a murine NIH/3T3-derived cell line (designated 7-4), which contains an inducible Ha-ras oncogene under the regulation of Escherichia coli lac operator-repressor system. Ha-ras overexpression was induced by isopropyl beta-D-thiogalactoside (IPTG). To reveal the role of endogenous Rac1, the dominant negative Rac1(Asn17) gene was transfected into the 7-4 cells. Using two cell lines 7-4 Racd2 and 7-4 Racd3 (7-4 derivates) stably expressing Rac1(Asn17), we demonstrate that suppression of Rac1 activity blocked Ha-ras-overexpression-induced apoptosis under a serum-depleted condition, indicating that Rac1 activity is required for a Ras-mediated apoptosis pathway. Cell-cycle analysis revealed that dominant-negative Rac1 partially shifted cell population from S-phase to G0/G1 phase in the cells overexpressing Ha-ras. In contrast to other reports, we showed activation of the transcription factor NFkappaB in the two cell lines expressing dominant-negative Rac1. All together, our results demonstrate that Ha-ras-overexpression- induced apoptosis can be blocked by dominant-negative Rac1, possibly through decreased S-phase accumulation and increased NFkappaB activity.