Cell apoptosis induced by UV irradiation is a highly complex process in which different molecular signaling pathways
are involved. JNK has been proposed as an important regulator in UV irradiation-induced apoptosis. However, the
molecular mechanism through which JNK regulates apoptosis, especially how JNK activates Bax in response to UV
irradiation is still controversial. In this study, using real-time single-cell analysis, we studied the machinery of Bax
activation during UV-induced apoptosis. UV treatment resulted in a series of events: phosphorylation of JNK,
mitochondrial translocation of Bim, and subsequent activation of Bax. The activation of Bim and Bax could be inhibited
in the presence of SP600125 (a specific inhibitor of JNK), suggesting that UV irradiation activated the JNK/Bim/Bax
Mitochondria are dynamic structures that frequently divide and fuse with one another to form interconnecting network.
This network disintegrates into punctiform organelles during apoptosis. However, it remains unclear whether this event
has a significant impact on the rate of cell death or only accompanies apoptosis as an epiphenomenon. In this study, we
investigate the role of dynamin-related protein 1 (Drp1), a large GTPase that mediates outer mitochondrial membrane
fission, in mitochondrial morphology and apoptosis in response to UV irradiation in human lung adenocarcinoma cells
(ASTC-a-1) and HeLa cells. Using time-lapse fluorescent imaging, we find that Drp1 primarily distributes in cytosol
under physiological conditions. After UV treatment, Drp1 translocates from cytosol to mitochondria, indicating the
enhancement of Drp1 mitochondrial accumulation. Down-regulation of Drp1 by shRNA inhibits UV-induced apoptosis.
Our results suggest that Drp1 is involved in the regulation of transition from a reticulo-tubular to a punctiform
mitochondrial phenotype and mitochondrial fission plays an important role in UV-induced apoptosis.
Photodynamic therapy (PDT) employing photosensiter N-aspartyl chlorin e6 (NPe6) can induce
lysosome disruption and initiate apoptotic pathway. Apoptosis signal-regulating kinase (ASK1) is an
important regulator of apoptosis in response to various stresses, such as reactive oxygen species (ROS),
endoplasmic reticulum (ER) stress, lipopolysaccharide (LPS) and calcium influx. In this study, we
investigated the molecular mechanisms of apoptosis induced by
NPe6-PDT in ASTC-a-1 cells. The
results showed that the activities of ASK1 increased in response to NPe6-PDT. Over-expression of
wild-type or activated mutant of ASK1 could obviously decrease cell viability and increase cell death;
while inhibition of ASK1 significantly decreased cell apoptosis. These results suggested that ASK1
plays an important role in apoptosis induced by NPe6-PDT.