Takasawa R, Tanuma S
Genome & Drug Research Center, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-0022, Japan.
Apoptosis. 2003 Jun;8(3):291-9. doi: 10.1023/a:1023629023696.
Apoptotic response of keratinocytes to UVB irradiation has physiological significance on photocarcinogenesis. Here, we show that the sustained release of Smac/DIABLO from mitochondria is an important event for the onset of apoptosis in keratinocytes exposed to UVB irradiation. In human keratinocyte HaCaT cells, UVB irradiation at 500 J/m(2), but not at 150 J/m(2), induces apoptosis. Significant activations of caspases-9 and -3, and slight activation of caspase-7 were observed only in 500 J/m(2) UVB irradiated HaCaT cells. Correspondingly, the cleavage of PARP, a substrate of caspases-3 and -7, was detected in cells irradiated at 500 J/m(2) UVB, but not at 150 J/m(2). However, with both 150 and 500 J/m(2) UVB irradiation, cytochrome c, an activator of caspase-9 via the formation of apoptosome, was released from mitochondria to the cytosol at the same extent. In contrast, significant amounts of Smac/DIABLO are released from mitochondria to the cytosol only with 500 J/m(2) UVB irradiation, and that the level of XIAP is decreased. These results suggest that the extent of Smac/DIABLO efflux from mitochondria is a determinant whether a cell will undergo apoptosis or survival.
角质形成细胞对紫外线B照射的凋亡反应在光致癌过程中具有生理意义。在此，我们表明Smac/DIABLO从线粒体的持续释放是暴露于紫外线B照射的角质形成细胞凋亡起始的一个重要事件。在人角质形成细胞HaCaT细胞中，500 J/m(2)的紫外线B照射可诱导凋亡，但150 J/m(2)的照射则不会。仅在接受500 J/m(2)紫外线B照射的HaCaT细胞中观察到半胱天冬酶-9和-3的显著激活以及半胱天冬酶-7的轻微激活。相应地，在接受500 J/m(2)紫外线B照射的细胞中检测到了半胱天冬酶-3和-7的底物PARP的切割，但在150 J/m(2)照射的细胞中未检测到。然而，在150和500 J/m(2)的紫外线B照射下，细胞色素c（通过形成凋亡小体激活半胱天冬酶-9）从线粒体释放到细胞质中的程度相同。相比之下，只有在500 J/m(2)紫外线B照射下，大量的Smac/DIABLO才从线粒体释放到细胞质中，并且XIAP的水平降低。这些结果表明，Smac/DIABLO从线粒体流出的程度是决定细胞是发生凋亡还是存活的一个因素。
