Ps. Backlund, POSTTRANSLATIONAL PROCESSING OF RHOA - CARBOXYL METHYLATION OF THE CARBOXYL-TERMINAL PRENYLCYSTEINE INCREASES THE HALF-LIFE OF RHOA, The Journal of biological chemistry, 272(52), 1997, pp. 33175-33180
RhoA and related GTP-binding proteins are modified post-translationall
y at their carboxyl terminus to form a prenylcysteine methyl ester. Th
e synthesis and posttranslational modification of RhoA and Cdc42 were
examined in the RAW264 macrophage cell line, and the effect of carboxy
l methylation on protein turnover was determined. Cells were labeled w
ith [S-35]cysteine, and RhoA or Cdc42 was immunoprecipitated with spec
ific antibodies. Both RhoA and Cdc42 were methylated rapidly in contro
l cells, with little accumulation of unmethylated protein. Carboxyl me
thylation of RhoA was inhibited by incubation of cells with a carbocyc
lic adenosine analog, 3-deazaaristeromycin, resulting in the accumulat
ion of unmethylated RhoA. Under these conditions, Cdc42 methylation wa
s inhibited only partially, When methylation was inhibited, the RhoA h
alf-life decreased from 31 to 12 h, and the Cdc42 half-life decreased
from 15 to 11 h. The increased degradation of unmethylated RhoA demons
trates a novel function for carboxyl-terminal prenylcysteine carboxyl
methylation in protecting RhoA and related proteins from degradation.