SYNERGISTIC ANTIPROLIFERATIVE ACTIONS OF CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE, INTERLEUKIN-1-BETA, AND ACTIVATORS OF CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE IN PRIMARY HEPATOCYTES/
G. Mellgren et al., SYNERGISTIC ANTIPROLIFERATIVE ACTIONS OF CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE, INTERLEUKIN-1-BETA, AND ACTIVATORS OF CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE IN PRIMARY HEPATOCYTES/, Endocrinology, 138(10), 1997, pp. 4373-4383
cAMP and Ca2+ acted together with the acute phase cytokine interleukin
-1 beta (IL-1 beta) to inhibit hepatocyte DNA replication. At sub-basa
l activity of cAMP-dependent protein kinase (PKA), neither IL-1 beta n
or the Ca2+-elevating hormone vasopressin affected hepatocyte prolifer
ation. Basal level of PKA activity permitted IL-1 beta action. Increas
ed PKA activity also permitted vasopressin action and sensitized furth
er towards IL-1 beta, which acted at 10-50 pM concentrations. Vasopres
sin acted via Ca2+/calmodulin-dependent protein kinase II (CaMKII), an
d its action was mimicked by the serine/threonine phosphatase inhibito
r microcystin, which activates CaMKII. Inhibitors (KN93 and KT5926) of
CaMKII selectively counteracted the effects of vasopressin and microc
ystin on hepatocyte proliferation at concentrations similar to those r
equired to inhibit CaMKII in vitro. Two-dimensional gel electrophoresi
s of P-32-prelabeled hepatocytes revealed a common set of proteins pho
sphorylated in response to vasopressin and microcystin. Their phosphor
ylation was counteracted by CaMKII inhibitor (KT5926). Phosphorylation
of the CaMKII substrate phenylalanine hydroxylase (PAH; EC 1.14.16.1)
was used as an endogenous marker of CaMKII activation. It was found t
hat treatment of the cells with vasopressin or microcystin increased t
he phosphorylation of PAH, and that the vasopressin-induced PAH phosph
orylation was inhibited by KT5926. In conclusion, the Ca2+-elevating h
ormone vasopressin potentiated the antiproliferative effects of cAMP a
nd IL-1 beta through CaMKII activation.