Bcl-2 accelerates retinoic acid-induced growth arrest and recovery in human gastric cancer cells

The role of Bcl-2 as an anti-apoptotic protein has been well documented. In the present work, we present evidence that Bcl-2 may also be involved in c ell growth regulation. SC-Mi is an unique cell line which responds to retin oic acid (RA) treatment with reversible growth arrest [Shyu, Jiang, Huang, Chang, Wu, Roffler and Yeh (1995) Eur. J. Cancer 31, 237-243]. In this stud y, when treated with RA, SC-M1/Bcl2 cells, which were generated by transfec ting SC-Mi cells with bcl-2 DNA, were growth-arrested two days earlier than SC-M1/neo cells, which were generated by transfecting SC-M1 cells with vec tor DNA. This indicates that Bcl-2 accelerates RA-induced growth arrest. In addition to the accelerated growth arrest, RA-treated SC-M1/Bcl2 cells als o recovered from growth arrest two days faster than SC-M1/neo cells after t he removal of RA. Previously, we had identified the cyclin-dependent kinase inhibitor p21((WAF1/C1P1)) (p21) as a mediator of RA-induced growth arrest [Tsao, Li, Kuo, Liu and Chen (1996) Biochem. J, 317, 707-711]. In a search for the mechanism by which Bcl-2 affects growth regulation, we found that p21 gene expression was more prominent in SC-M1/Bcl2 cells than in SC-M1/ne o cells in the presence of RA, but when RA was removed, p21 gene expression levels in SC-M1/Bcl2 cells were also reduced earlier than in SC-M1/neo cel ls. The present report is the first to show that Bcl-2 accelerates not only growth arrest but also recovery from growth arrest. Moreover, the close co rrelation between the effect of Bcl-2 on both RA-induced growth arrest and RA-induced p21 gene expression suggests the possibility that Bcl-2 affects cell growth through the mechanism of p21.