Raf-1-induced cell cycle arrest in LNCaP human prostate cancer cells

Prostate cancer is the most commonly diagnosed neoplasm in men. LNCaP cells continue to possess many of the molecular characteristics of in situ prost ate cancer. These cells lack ras mutations, and nitogen-activated protein k inase (MAPK) is not extensively phosphorylated in these cells. To determine the effects of ras/raf/MAPK pathway activation in these cells, we transfec ted LNCaP cells with an activatable form of c-raf-1(Delta Raf-1:ER). Activa tion of Delta Raf-1:ER, with resultant MAPK activation, reduced plating eff iciency and soft agarose cloning efficiency 30-fold in LNCaP cells. Cell cy cle distribution showed an accumulation of cells in G1 and was associated w ith the induction of CDK inhibitor p21(WAF1/CIP1) at the protein and mRNA l evels. p21(WAF1/CIP1) mRNA stability was increased after Delta Raf-1:ER act ivation. in addition, activated Delta Raf-1:ER induced the senescence assoc iated-beta-galactosidase in LNCaP cells. These data demonstrate that rat ac tivation can activate growth inhibitory pathways leading to growth suppress ion in prostate carcinoma cells and also suggest that raf/MEK/MAPK pathway activation, rather than inhibition, may be a therapeutic target tor some hu man prostate cancer cells. J. Cell. Biochem. 72:458-469, 1999. (C) 1999 Wil ey-Liss, Inc.