Basu A, Akkaraju G R
Department of Molecular Biology & Immunology, University of North Texas Health Science Center, Fort Worth 76107, USA.
Biochemistry. 1999 Apr 6;38(14):4245-51. doi: 10.1021/bi982854q.
Activation of caspases is critical for the induction of apoptosis. We have shown previously that cell death mediated by the anticancer agent cis-diamminedichloroplatinum(II) (cDDP) is influenced by the protein kinase C (PKC) signal transduction pathway. In the present study, we have examined whether regulation of cDDP sensitivity by PKC involves caspase activation. cDDP caused a time- and concentration-dependent increase in the generation of the catalytic fragment (CF) of novel (n) PKCdelta, nPKCepsilon, and atypical (a) PKCzeta but had little effect on conventional (c) PKCalpha. Cleavage of PKC isozymes was associated with the activation of caspase-3 and -7 but not of caspase-2. PKC activators enhanced cDDP-induced cleavage of these isozymes and activation of caspase-3. Rottlerin, an inhibitor of nPKCdelta, blocked caspase-3 activation and proteolytic cleavage of nPKCdelta by cDDP. Bryostatin 1, which elicits a biphasic concentration-response in potentiating cell death by cDDP, exhibited a similar biphasic effect on cDDP-induced activation of caspase-3 and caspase-7 and the cleavage of poly(ADP-ribose) polymerase; while 1 nM bryostatin 1 induced maximum activation of these caspases, 1 microM bryostatin 1 had little effect. z-DEVD-fmk, an inhibitor of caspase-3-like proteases, prevented cDDP-induced cell death. Bryostatin 1 also induced a similar biphasic down-regulation of nPKCdelta but not of cPKCalpha or nPKCepsilon. These results suggest that nPKCdelta not only acts downstream of caspases but also regulates the activation of caspases and that the biphasic concentration response of bryostatin 1 on cDDP-induced cell death could be explained by its distinct effect on nPKCdelta down-regulation and caspase activation.
半胱天冬酶的激活对于细胞凋亡的诱导至关重要。我们之前已经表明，抗癌药物顺二氯二氨铂（II）（cDDP）介导的细胞死亡受蛋白激酶C（PKC）信号转导途径的影响。在本研究中，我们检测了PKC对cDDP敏感性的调节是否涉及半胱天冬酶的激活。cDDP导致新型（n）PKCδ、nPKCε和非典型（a）PKCζ的催化片段（CF）生成呈时间和浓度依赖性增加，但对传统（c）PKCα影响很小。PKC同工酶的切割与半胱天冬酶-3和-7的激活相关，但与半胱天冬酶-2的激活无关。PKC激活剂增强了cDDP诱导的这些同工酶的切割和半胱天冬酶-3的激活。nPKCδ抑制剂罗特lerin阻断了半胱天冬酶-3的激活以及cDDP对nPKCδ的蛋白水解切割。苔藓抑素1在增强cDDP诱导的细胞死亡方面呈现双相浓度反应，对cDDP诱导的半胱天冬酶-3和半胱天冬酶-7的激活以及聚（ADP-核糖）聚合酶的切割也表现出类似的双相效应；虽然1 nM苔藓抑素1诱导这些半胱天冬酶的最大激活，但1 μM苔藓抑素1几乎没有作用。半胱天冬酶-3样蛋白酶抑制剂z-DEVD-fmk可防止cDDP诱导的细胞死亡。苔藓抑素-1还诱导了nPKCδ的类似双相下调，但对cPKCα或nPKCε没有影响。这些结果表明，nPKCδ不仅在半胱天冬酶下游起作用，还调节半胱天冬酶的激活，并且苔藓抑素1对cDDP诱导的细胞死亡的双相浓度反应可以通过其对nPKCδ下调和半胱天冬酶激活的不同作用来解释。
