Differential effects of protein kinase a sub‐units on chinese‐hamster‐ovary cell cycle and proliferation

It has been shown that a marked increase in the levels of Rlα sub‐units and a decrease in RIIβ sub‐unit levels correlate with neoplastic transformation or with the mitogenic response of normal cells to hormones and growth factors. The selective down‐regulation of RIα and the following induction of RIIβ determine cell‐growth arrest and differentiation of several cancer cells. To directly address the question whether the 2 protein‐kinase‐A(PKA) isoforms play different roles in the control of proliferation and cell‐cycle distribution, we introduced and over‐expressed the different PKA sub‐units in Chinese‐hamster‐ovary (CHO) cells via retroviral‐vector‐mediated gene transfer. Whereas CHO cells treated with RIα anti‐sense oligodeoxynucleotides were growth arrested and accumulated in the G0/G1 phases of the cell cycle, infection of CHO cells with a retroviral vector in order to over‐express RIα determined growth advantages in monolayer conditions and substantially increased their cloning efficiency in soft agar. These events correlated with a sustained percentage of cells in S phase induced by RIα over‐expression in the infected cells. In contrast, CHO cells infected with retroviral vectors over‐expressing either a RIIβ sub‐unit or a Cα catalytic sub‐unit of PKA exhibited growth arrest within a few days of culture and accumulated in the G2‐M phase of the cell cycle. The results of our study demonstrate that the different PKA sub‐units play different and specific roles in the control of cell growth and cell‐cycle distribution.