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Department of Biological and Environmental Sciences and Technologies, Ecotekne, Via Prov.le per Monteroni, 73100 Lecce, Italy

(Requests for offprints should be addressed to S Marsigliante who is now at Laboratorio di Fisiologia Cellulare, Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, Università di Lecce, Via Provinciale per Monteroni, 73100 Lecce, Italy; Email: santo.marsigliante{at}unile.it)

In PC Cl3 cells, a rat thyroid cell line, angiotensin (Ang II) activates the atypical protein kinase C- (PKC-) and the extracellular signal-regulated kinase (ERK) pathways. We here studied the Ang II effects on PC Cl3 cell proliferation. It was found that Ang II: (1) induced the phosphorylation of protein kinase B (PKB), (2) induced the growth-related early gene c-fos expression, (3) enhanced the cyclin E and p27^kip expression, (4) had no effects on Cdk2, and (5) did not affect the transition from G0/G1 to S phase. Inhibition of phosphoinositide-3kinase by LY294002 further increased the effect of Ang II on p27^kip induction, whilst PKCs inhibition by GF109203X decreased such effect. The role of PKC- was recognized by the use of a synthetic myristoylated peptide with sequences based on the endogenous PKC- pseudosubstrate and by PKC- downregulation using the small interfering RNA (siRNA). Insulin had a replicating effect on PC Cl3 cells, induced the phosphorylation of PKB, decreased p27^kip expression and had no effect on the PKC- cytosol-to-membrane translocation. PC Cl3 cell proliferation was induced more potently by simultaneous stimulation with insulin and Ang II than by stimulation with insulin alone, and the effect on p27^kip expression was similar to that obtained with insulin only. These observations demonstrate that in PC Cl3 cells Ang II causes a block in G1 phase, although both ERK and PKB pathways are activated, and this effect may be due to the upregulation of p27^kip and PKC- operativity.