Effects of adenoviral gene transfer of wild-type, constitutively active, and kinase-defective protein kinase C-λ on insulin-stimulated glucose transport in L6 myotubes

Abstract

We used adenoviral gene transfer methods to evaluate the role of atypical protein kinase Cs (PKCs) during insulin stimulation of glucose transport in L6 myotubes. Expression of wild-type PKC-λ potentiated maximal and half-maximal effects of insulin on 2-deoxyglucose uptake, but did not alter basal uptake. Expression of constitutively active PKC-λ enhanced basal 2-deoxyglucose uptake to virtually the same extent as that observed during insulin treatment. In contrast, expression of kinase-defective PKC-λ completely blocked insulin-stimulated, but not basal, 2-deoxyglucose uptake. Similar to alterations in glucose transport, constitutively active PKC-λ mimicked, and kinase-defective PKC-λ completely inhibited, insulin effects on GLUT4 glucose transporter translocation to the plasma membrane. Expression of kinase-defective PKC-λ, in addition to inhibition of atypical PKC enzyme activity, was attended by paradoxical increases in GLUT4 and GLUT1 glucose transporter levels and insulin-stimulated protein kinase B enzyme activity. Our findings suggest that in L6 myotubes, 1) atypical PKCs are required and sufficient for insulin-stimulated GLUT4 translocation and glucose transport; and 2) activation of protein kinase B in the absence of activation of atypical PKCs is insufficient for insulin-induced activation of glucose transport.