Involvement of both phosphatidylinositol 3-kinase and p44/p42 mitogen-activated protein kinase pathways in the short-term regulation of pyruvate kinase L by insulin
Jj. Carrillo et al., Involvement of both phosphatidylinositol 3-kinase and p44/p42 mitogen-activated protein kinase pathways in the short-term regulation of pyruvate kinase L by insulin, ENDOCRINOL, 142(3), 2001, pp. 1057-1064
Pyruvate kinase L (PK-L) is a key regulatory enzyme of the hepatic glycolyt
ic/gluconeogenic pathway that can be dephosphorylated and activated in resp
onse to insulin. However, the signaling cascades involved in this insulin e
ffect have not been established. In this work we have investigated the pote
ntial involvement of phosphatidylinositol 3-kinase (PI 3-K) and p44/p42 mit
ogen-activated protein kinase (MAPK) pathways in the short-term modulation
of PK-L by insulin in primary cultures of rat hepatocytes. Wortmannin, at a
concentration of 100 nM, caused a marked inhibition of the PI 3-K/protein
kinase B pathway, which became complete at 500 nw wortmannin. Likewise, wor
tmannin at 100 and 500 nM, elicited partial and total inhibitions of insuli
n-mediated activation of PK-L, respectively. However, this PI 3-K inhibitor
also reduced insulin-mediated phosphorylation of p44/ p42 MAPK in cultured
rat hepatocytes, indicating that both the PI 3-K and MAPK pathways could b
e involved in PK-L activation by insulin. Three facts appear to reinforce t
his hypothesis: 1) the selective and complete inhibition of the PI 3-K/prot
ein kinase B pathway by LY294002 (50 muM) was accompanied by a partial bloc
kade of insulin-induced PK-L activation; 2) when signaling through the MAPK
cascade was selectively suppressed by the presence of PD98059 (50 mum), a
50% reduction of insulin-induced activation of PK-L was observed; and 3) th
e effect of PD98059 (50 muM) on PK-L activation was reinforced by the addit
ional presence of 100 nM wortmannin. We also observed that the blockade of
p70 S6-kinase by rapamycin did not affect the activation of PK-L by insulin
. From these findings it can be concluded that both PI 3-K and MAPK pathway
s, but not p70 S6-kinase, are involved in the short-term activation of PK-L
by insulin in rat hepatocytes.