Protein expression of the alpha, gamma, delta and epsilon subspecies of protein kinase C changes as C6 glioma cells become contact inhibited and quiescent in the presence of serum.

Total protein kinase C (PKC) activity and protein expression of the alpha and delta subspecies of PKC increases markedly as C6 glioma cells grow from low cell density to the contact-inhibited quiescent state (also known as G(o)) in the presence of serum. At the same time protein expression of PKC subspecies gamma and epsilon decreases while the beta I, beta II, iota and zeta subspecies did not change. Serum deprivation of growing C6 glioma cells does not induce the same changes in PKC subspecies protein expression. The findings support the growing view that there are significant differences between the G(o) states brought about by contact inhibition or serum deprivation.