N. Nakaigawa et al., DIFFERENTIAL-EFFECTS OF OVEREXPRESSION OF PKC-ALPHA AND PKC-DELTA EPSILON ON CELLULAR E2F ACTIVITY IN LATE G1 PHASE/, Biochemical and biophysical research communications, 222(1), 1996, pp. 95-100
Introduction of a reporter gene containing E2F binding sites linked to
the luciferase gene permitted us to detect transient cellular E2F act
ivity in late G1 phase rat 3Y1 fibroblasts. Overexpression of three ma
jor protein kinase C (PKC) isozymes expressed in 3Y1 cells caused diff
ering effects on E2F activity depending on the isozymes overexpressed.
Overexpression of PKC alpha inhibited E2F activity while the overexpr
ession of PKC delta or PKC epsilon enhanced it, suggesting that these
PKC isozymes play different roles in the regulation of E2F activity. C
onsistent with previous findings that the activation of PKC by TPA in
late G1 phase results in the inhibition of DNA synthesis (Huang, C., a
nd Ives, H.E., 1987, Nature 329, 849-850), the addition of TPA in late
G1 phase specifically inhibited E2F activity. Overexpression of PKC i
sozymes resulted in an enhancement of the TPA-induced inhibition of E2
F in late G1 phase. This enhancement was observed for all three PKC is
ozymes examined, suggesting that these PKC isozymes all are potent med
iators of the TPA-induced inhibition of E2F activity in late G1 phase.
(C) 1996 Academic Press, Inc.