Geranylgeranylated Rho Small GTPase(s) Are Essential for the Degradation of p27 and Facilitate the Progression from G1 to S Phase in Growth-stimulated Rat FRTL-5 Cells

Abstract

Cyclin-dependent kinase (Cdk) enzymes are activated for entry into the S phase of the cell cycle. Elimination of Cdk inhibitor protein p27 Kip1 during the G 1 to S phase is required for the activation process. An inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase prevents its elimination and leads to G 1 arrest. Mevalonate and its metabolite, geranylgeranyl pyrophosphate, but not farnesyl pyrophosphate, restore the inhibitory effect of pravastatin on the degradation of p27 and allow Cdk2 activation. By the addition of geranylgeranyl pyrophosphate, Rho small GTPase(s) are geranylgeranylated and translocated to membranes during G 1 /S progression. The restoring effect of geranylgeranyl pyrophosphate is abolished with botulinum C3 exoenzyme, which specifically inactivates Rho. These results indicate (i) among mevalonate metabolites, geranylgeranyl pyrophosphate is absolutely required for the elimination of p27 followed by Cdk2 activation; (ii) geranylgeranylated Rho small GTPase(s) promote the degradation of p27 during G 1 /S transition in FRTL-5 cells.

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

“…If the cytoskeleton is disassembled prior to a cell reaching the restriction point, growth is arrested (Zhu et al, 1996). Other reports have indicated that RhoA stimulates cell cycle progression through inactivation of the cyclin dependent kinase inhibitors (CKIs) p27 Kip1 (Hirai et al, 1997) or p21 Cip1 (Olson et al, 1998). Our results suggest that, activation of RhoA results in actin stress ®ber assembly, which would provide the signals leading to cell proliferation.…”

“…Our results suggest that, activation of RhoA results in actin stress ®ber assembly, which would provide the signals leading to cell proliferation. These signals may be mediated by the CKIs p27 Kip1 and p21 Cip1 (Hirai et al, 1997;Olson et al, 1998). Under conditions where RhoA might be expected to be active (e.g.…”

“…The farnesylated Ras proteins, on the other hand, are associated with cell proliferation (Khosravi-Far and Der, 1994;Prendergast and Gibbs, 1993;Pronk and Bos, 1994). It has been shown that activation of Rho proteins are also necessary for cell proliferation (Hirai et al, 1997;Hill et al, 1995;Joneson and Bar-Sagi, 1998;Olson et al, 1998). These proteins have also been found to activate the JNK/SAPK signaling pathway in a celltype speci®c manner (Zhang et al, 1995;Coso et al, 1995;Teramoto et al, 1996).…”

Interaction with cyclin-dependent kinases and PCNA modulates proteasome-dependent degradation of p21

“…In addition, the results obtained with lovastatin, an inhibitor of HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase which blocks the posttranslational modi®cation (isoprenylation) of small GTP binding proteins such as Rho and Ras, indicate that small GTP binding proteins are not involved in p21 degradation. In contrast, both Rho and Ras have been suggested to play an important role in the degradation of the related CKI p27 (Hirai et al, 1997;Kawada et al, 1997).…”

Regulation of cell proliferation by G proteins

“…It appears that the signals from Ga 12/13 are translated into growth-promoting signals by the small GTPases Ras, Rac, and Rho. It has been reported that Ras, Rho, Rac, and CDC42 play an essential role in cell cycle progression from G1 to S phase (Aktas et al, 1997;Takuwa and Takuwa, 1997;Olson et al, 1995;Hirai et al, 1997). An additional role for Rac in progression from G2 to M phase has been also identi®ed (Moore et al, 1997).…”