Vasavada Rupangi C, Wang Lin, Fujinaka Yuichi, Takane Karen K, Rosa Taylor C, Mellado-Gil Jose M D, Friedman Peter A, Garcia-Ocaña Adolfo
Department of Medicine, Division of Endocrinology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Diabetes. 2007 Nov;56(11):2732-43. doi: 10.2337/db07-0461. Epub 2007 Aug 8.
Diabetes results from a deficiency of functional beta-cells. Previous studies have identified hepatocyte growth factor (HGF) and parathyroid hormone-related protein (PTHrP) as two potent beta-cell mitogens. The objective of this study is to determine 1) whether HGF and PTHrP have additive/synergistic effects on beta-cell growth and proliferation; 2) the signaling pathways through which these growth factors mediate beta-cell mitogenesis; and 3) whether activation of this/these signaling pathway(s) enhances human beta-cell replication.
We generated and phenotypically analyzed doubly transgenic mice overexpressing PTHrP and HGF in the beta-cell. INS-1 and primary mouse and human islet cells were used to identify mitogenic signaling pathways activated by HGF and/or PTHrP.
Combined overexpression of HGF and PTHrP in the beta-cell of doubly transgenic mice did not result in additive/synergistic effects on beta-cell growth and proliferation, suggesting potential cross-talk between signaling pathways activated by both growth factors. Examination of these signaling pathways in INS-1 cells revealed atypical protein kinase C (PKC) as a novel intracellular target activated by both HGF and PTHrP in beta-cells. Knockdown of PKC zeta, but not PKC iota/lambda, expression using specific small-interfering RNAs blocked growth factor-induced INS-1 cell proliferation. Furthermore, adenovirus-mediated delivery of kinase-dead PKC zeta completely inhibited beta-cell proliferation in primary islet cells overexpressing PTHrP and/or HGF. Finally, adenovirus-mediated delivery of constitutively active PKC zeta in mouse and human primary islet cells significantly enhanced beta-cell proliferation.
PKC zeta is essential for PTHrP- and HGF-induced beta-cell proliferation. PKC zeta activation could be useful in therapeutic strategies for expanding beta-cell mass in vitro and in vivo.
糖尿病是由功能性β细胞缺乏所致。既往研究已确定肝细胞生长因子（HGF）和甲状旁腺激素相关蛋白（PTHrP）为两种有效的β细胞促有丝分裂原。本研究的目的是确定：1）HGF和PTHrP对β细胞生长和增殖是否具有相加/协同作用；2）这些生长因子介导β细胞有丝分裂的信号通路；3）该信号通路的激活是否能增强人β细胞复制。
我们构建并对在β细胞中过表达PTHrP和HGF的双转基因小鼠进行了表型分析。使用INS-1细胞以及原代小鼠和人胰岛细胞来鉴定由HGF和/或PTHrP激活的促有丝分裂信号通路。
在双转基因小鼠的β细胞中联合过表达HGF和PTHrP并未对β细胞生长和增殖产生相加/协同作用，提示这两种生长因子激活的信号通路之间可能存在相互作用。对INS-1细胞中这些信号通路的研究揭示非典型蛋白激酶C（PKC）是β细胞中由HGF和PTHrP共同激活的一种新的细胞内靶点。使用特异性小干扰RNA敲低PKC ζ而非PKC ι/λ的表达可阻断生长因子诱导的INS-1细胞增殖。此外，腺病毒介导的激酶失活型PKC ζ的递送完全抑制了过表达PTHrP和/或HGF的原代胰岛细胞中的β细胞增殖。最后，腺病毒介导的组成型活性PKC ζ在小鼠和人原代胰岛细胞中的递送显著增强了β细胞增殖。
PKC ζ对于PTHrP和HGF诱导的β细胞增殖至关重要。PKC ζ激活可能有助于在体外和体内扩大β细胞量的治疗策略。
