Rab7 Activation by Growth Factor Withdrawal Contributes to the Induction of Apoptosis
Rab7 Activation by Growth Factor Withdrawal Contributes to the Induction of Apoptosis
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DOI：
10.1091/mbc.e08-09-0911
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发表时间：
2009-06-15
影响因子：
3.3
通讯作者：
Edinger, Aimee L.
中科院分区：
文献类型：
--
作者：
Rosales, Kimberly Romero;Peralta, Eigen R.;Edinger, Aimee L.
Rab7 GTPase促进晚期核内体和溶酶体之间的膜融合反应。在之前的研究中，我们证实Rab7失活可阻断生长因子戒断诱导的细胞死亡。这些结果使我们假设生长因子戒断激活Rab7。在这里，我们发现生长因子剥夺增加了与细胞膜相关的Rab7的比例和与三磷酸鸟苷（GTP）结合的Rab7的百分比。此外，表达Rab7的组成型gtp结合突变体Rab7- q67l，即使在生长因子存在的情况下也足以引发细胞死亡。这种活化的Rab7突变体也能够逆转由蛋白激酶C (PKC) δ抑制所赋予的生长因子无关的细胞存活。PKC δ是生长因子停用后最易诱导的蛋白之一，参与诱导细胞凋亡。为了评估PKC δ是否调节Rab7，我们首先检测了PKC δ活性降低的细胞的溶酶体形态。与Rab7激活剂的潜在作用一致，阻断PKC δ函数导致与Rab7直接抑制时观察到的相似的溶酶体断裂。有趣的是，PKC δ抑制使溶酶体破碎，而不降低Rab7-GTP水平。综上所述，这些结果表明，生长因子停用激活Rab7有助于诱导细胞凋亡，Rab7依赖的融合反应可能是限制生长因子不依赖型细胞存活的信号通路的靶标。
The Rab7 GTPase promotes membrane fusion reactions between late endosomes and lysosomes. In previous studies, we demonstrated that Rab7 inactivation blocks growth factor withdrawal-induced cell death. These results led us to hypothesize that growth factor withdrawal activates Rab7. Here, we show that growth factor deprivation increased both the fraction of Rab7 that was associated with cellular membranes and the percentage of Rab7 bound to guanosine triphosphate (GTP). Moreover, expressing a constitutively GTP-bound mutant of Rab7, Rab7-Q67L, was sufficient to trigger cell death even in the presence of growth factors. This activated Rab7 mutant was also able to reverse the growth factor-independent cell survival conferred by protein kinase C (PKC) delta inhibition. PKC delta is one of the most highly induced proteins after growth factor withdrawal and contributes to the induction of apoptosis. To evaluate whether PKC delta regulates Rab7, we first examined lysosomal morphology in cells with reduced PKC delta activity. Consistent with a potential role as a Rab7 activator, blocking PKC delta function caused profound lysosomal fragmentation comparable to that observed when Rab7 was directly inhibited. Interestingly, PKC delta inhibition fragmented the lysosome without decreasing Rab7-GTP levels. Taken together, these results suggest that Rab7 activation by growth factor withdrawal contributes to the induction of apoptosis and that Rab7-dependent fusion reactions may be targeted by signaling pathways that limit growth factor-independent cell survival.