Tsuru Masatoshi, Katagiri Hideki, Asano Tomoichiro, Yamada Tetsuya, Ohno Shigeo, Ogihara Takehide, Oka Yoshitomo
Third Department of Internal Medicine, Yamaguchi University School of Medicine, Ube, Yamaguchi 755-8505, Japan.
Am J Physiol Endocrinol Metab. 2002 Aug;283(2):E338-45. doi: 10.1152/ajpendo.00457.2001.
To elucidate the involvement of protein kinase C (PKC) isoforms in insulin-induced and phorbol ester-induced glucose transport, we expressed several PKC isoforms, conventional PKC-alpha, novel PKC-delta, and atypical PKC isoforms of PKC-lambda and PKC-zeta, and their mutants in 3T3-L1 adipocytes using an adenovirus-mediated gene transduction system. Endogenous expression and the activities of PKC-alpha and PKC-lambda/zeta, but not of PKC-delta, were detected in 3T3-L1 adipocytes. Overexpression of each wild-type PKC isoform induced a large amount of PKC activity in 3T3-L1 adipocytes. Phorbol 12-myristrate 13-acetate (PMA) activated PKC-alpha and exogenous PKC-delta but not atypical PKC-lambda/zeta. Insulin also activated the overexpressed PKC-delta but not PKC-alpha. Expression of the wild-type PKC-alpha or PKC-delta resulted in significant increases in glucose transport activity in the basal and PMA-stimulated states. Dominant-negative PKC-alpha expression, which inhibited the PMA activation of PKC-alpha, decreased in PMA-stimulated glucose transport. Glucose transport activity in the insulin-stimulated state was increased by the expression of PKC-delta but not of PKC-alpha. These findings demonstrate that both conventional and novel PKC isoforms are involved in PMA-stimulated glucose transport and that other novel PKC isoforms could participate in PMA-stimulated and insulin-stimulated glucose transport. Atypical PKC-lambda/zeta was not significantly activated by insulin, and expression of the wild-type, constitutively active, and dominant-negative mutants of atypical PKC did not affect either basal or insulin-stimulated glucose transport. Thus atypical PKC enzymes do not play a major role in insulin-stimulated glucose transport in 3T3-L1 adipocytes.
为阐明蛋白激酶C（PKC）亚型在胰岛素诱导及佛波酯诱导的葡萄糖转运中的作用，我们利用腺病毒介导的基因转导系统，在3T3-L1脂肪细胞中表达了几种PKC亚型，即传统型PKC-α、新型PKC-δ以及非典型PKC亚型PKC-λ和PKC-ζ及其突变体。在3T3-L1脂肪细胞中检测到了内源性PKC-α和PKC-λ/ζ的表达及活性，但未检测到PKC-δ的表达及活性。每种野生型PKC亚型的过表达均在3T3-L1脂肪细胞中诱导产生了大量的PKC活性。佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）激活了PKC-α和外源性PKC-δ，但未激活非典型PKC-λ/ζ。胰岛素也激活了过表达的PKC-δ，但未激活PKC-α。野生型PKC-α或PKC-δ的表达导致基础状态及PMA刺激状态下的葡萄糖转运活性显著增加。抑制PKC-α的PMA激活的显性负性PKC-α表达降低了PMA刺激的葡萄糖转运。PKC-δ的表达增加了胰岛素刺激状态下的葡萄糖转运活性，但PKC-α的表达未产生此作用。这些发现表明，传统型和新型PKC亚型均参与PMA刺激的葡萄糖转运，且其他新型PKC亚型可能参与PMA刺激及胰岛素刺激的葡萄糖转运。非典型PKC-λ/ζ未被胰岛素显著激活，非典型PKC的野生型、组成型激活型及显性负性突变体的表达均未影响基础或胰岛素刺激的葡萄糖转运。因此，非典型PKC酶在3T3-L1脂肪细胞的胰岛素刺激的葡萄糖转运中不发挥主要作用。
