Role of RhoA activation in the growth and morphology of a murine prostate tumor cell line

Prostate cancer cells derived from transgenic mice with adenocarcinoma of t he prostate (TRAMP cells) were treated with the HMG-CoA reductase inhibitor , lovastatin, This caused inactivation of the small GTPase RhoA, actin stre ss fiber disassembly, cell rounding, growth arrest in the GZ phase of the c ell cycle, cell detachment and apoptosis, Addition of geranylgeraniol (GGOL ) in the presence of lovastatin, to stimulate protein geranylgeranylation, prevented lovastatin's effects. That is, RhoA was activated, actin stress f ibers were assembled, the cells assumed a flat morphology and cell growth r esumed. The following observations support an essential role for RhoA in TR AMP cell growth: (1) TRAMP cells expressing dominant-negative RhoA (T19N) m utant protein displayed few actin stress fibers and grew at a slower rate t han controls (35 h doubling time for cells expressing RhoA (T19N) vs 20 h f or untransfected cells); (2) TRAMP cells expressing constitutively active R hoA. (Q63L) mutant protein displayed a contractile phenotype and grew faste r than controls (13 h doubling time), Interestingly, addition of farnesol ( FOL) with lovastatin, to stimulate protein farnesylation, prevented lovasta tin-induced cell rounding, cell detachment and apoptosis, and stimulated ce ll spreading to a spindle shaped morphology. However, RhoA remained inactiv e and growth arrest persisted. The morphological effects of FOL addition we re prevented in TRAMP cells expressing dominant-negative H-Ras (T17N) mutan t protein. Thus, it appears that H-Ras is capable of inducing cell spreadin g, but incapable of supporting cell proliferation, in the absence of gerany lgeranylated proteins like RhoA.