Heart 6-phosphofructo-2-kinase activation by insulin requires PKB (protein kinase B), but not SGK3 (serum- and glucocorticoid-induced protein kinase 3)

Abstract

On the basis of transfection experiments using a dominant-negative approach, our previous studies suggested that PKB (protein kinase B) was not involved in heart PFK-2 (6-phosphofructo2-kinase) activation by insulin. Therefore we first tested whether SGK3 (serum- and glucocorticoid-induced protein kinase 3) might be involved in this effect. Treatment of recombinant heart PFK-2 with [γ-32P]ATP and SGK3 in vitro led to PFK-2 activation and phosphorylation at Ser466 and Ser483. However, in HEK-293T cells [HEK (human embryonic kidney)-293 cells expressing the large T-antigen of SV40 (simian virus 40)] co-transfected with SGK3 siRNA (small interfering RNA) and heart PFK-2, insulin-induced heart PFK-2 activation was unaffected. The involvement of PKB in heart PFK-2 activation by insulin was re-evaluated using different models: (i) hearts from transgenic mice with a muscle/heart-specific mutation in the PDK1 (phosphoinositide-dependent protein kinase 1)-substrate-docking site injected with insulin; (ii) hearts from PKBβ-deficient mice injected with insulin; (iii) freshly isolated rat cardiomyocytes and perfused hearts treated with the selective Akti-1/2 PKB inhibitor prior to insulin treatment; and (iv) HEK-293T cells co-transfected with heart PFK-2, and PKBα/β siRNA or PKBα siRNA, incubated with insulin. Together, the results indicated that SGK3 is not required for insulin-induced PFK-2 activation and that this effect is likely mediated by PKBα.

Akt-dependent Activation of the Heart 6-Phosphofructo-2-kinase/Fructose-2,6-bisphosphatase (PFKFB2) Isoenzyme by Amino Acids

“…Thus, Akt activation is required for the increase in Fru-2,6-P 2 content and the activation of PFKFB2 after amino acid addition. In agreement with these data, the phosphorylation and activation of PFKFB2 by insulin also require Akt (4,10).…”

“…PFKFB2 activity is regulated by phosphorylation of its C-terminal domain by protein kinases such as 3-phosphoinositide-dependent kinase-1 (PDK-1), cAMP-dependent protein kinase (protein kinase A), protein kinase B (also known as Akt), p70 ribosomal S6 kinase (S6K1), and mitogen-activated protein kinase 1 (MAPK-1). Insulin-induced PFKFB2 activation requires the protein kinase Akt (4).…”

Mondo/ChREBP-Mlx-Regulated Transcriptional Network Is Essential for Dietary Sugar Tolerance in Drosophila

“…Exploring the contribution of Mondo and Mlx proteins in this setting is therefore warranted. In addition to being regulated transcriptionally, PFK2 activity in mammals is known to be posttranslationally regulated by insulin signalling through protein kinase AKT [41], [42]. It will be interesting to learn, what is the contribution of insulin signalling pathway activity on the dietary sugar tolerance.…”

Glucose Uptake and Its Consequence on Cardiomyocyte Function

“…Indeed, PKB/Akt phosphorylates and activates the cardiac PFK-2 [30,31]. In addition to stimulate glucose use for ATP production, insulin also blocks fatty acid oxidation [8] (Figure 12.1).…”