Post-translational modifications of the regulatory subunits of cAMP-dependent protein kinases during G1/S progression

During the G1/S transition of the cell cycle variations in the labelling by 8-N-3-[P-32]cAMP of the protein kinase A regulatory subunits RI and RII, u sed as a probe to monitor post-translational modifications that may regulat e cAMP binding, were observed in synchronized HeLa cells. A decrease in 8-N -3-[P-32]CAMP labelling of RI, RII and RII phosphorylated by the catalytic subunit of PKA was correlated with the increased percentage of cells in pha ses G1. An increase in 8-N-3-[P-32]cAMP incorporated into the 54-kDa RII su bunit during progression from G1 to S was correlated with an increase in in tracellular cAMP. A transient increase in Mn-SOD activity was detected in c ells arrested at the G1/S transition using two different techniques, sugges ting that oxidative modulation of regulatory subunits by free radicals may modify cAMP binding sites during the cell cycle. Decreased photoaffinity la belling by 8-N-3-[P-32]cAMP of RI, RII and autophosphorylated RII subunits was found to be an inherent characteristic of PKA in the G1/S transition. ( C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.