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

We used adenoviral gene transfer methods to evaluate the role of atypical p rotein kinase Cs (PKCs) during insulin stimulation of glucose transport in L6 myotubes. Expression of wild-type PKC-lambda potentiated maximal and hal f-maximal effects of insulin on a-deoxyglucose uptake, but did not alter ba sal uptake. Expression of constitutively active PKC-lambda enhanced basal a -deoxyglucose uptake to virtually the same extent as that observed during i nsulin treatment. In contrast, expression of kinase-defective PKC-lambda co mpletely blocked insulin-stimulated, but not basal, a-deoxyglucose uptake. Similar to alterations in glucose transport, constitutively active PKC-lamb da mimicked, and kinase-defective PKC-lambda completely inhibited, insulin effects on GLUT4 glucose transporter translocation to the plasma membrane. Expression of kinase-defective PKC-lambda, in addition to inhibition of aty pical PKC enzyme activity, was attended by paradoxical increases in GLUT4 a nd GLUT1 glucose transporter levels and insulin-stimulated protein kinase B enzyme activity. Our findings suggest that in L6 myotubes, 1) atypical PKC s are required and sufficient for insulin-stimulated GLUT4 translocation an d glucose transport; and 2) activation of protein kinase B in the absence o f activation of atypical PKCs is insufficient for insulin-induced activatio n of glucose transport.