PUMA (p53 up-regulated modulator of apoptosis, also called Bbc3) was first identified as a BH3-only Bcl-2 family
protein that is transcriptionally up-regulated by p53 and activated upon p53-dependent apoptotic stimuli, such as
treatment with DNA-damaging drugs or UV irradiation. Recently studies have been shown that Puma is also
up-regulated in response to certain p53-independent apoptotic stimuli, such as growth factor deprivation or treatment
with glucocorticoids or STS (staurosporine). However, the molecular mechanisms of PUMA up-regulation and how
PUMA functions in response to p53-independent apoptotic stimuli remain poorly understood. In this study, based on
real-time single cell analysis, flow cytometry and western blotting technique, we investigated the function of PUMA in
living human lung adenocarcinoma cells (ASTC-a-1) after STS treatment. Our results show that FOXO3a was activated
by STS stimulation and then translocated from cytosol to nucleus. The expression of PUMA was up-regulated via a
FOXO3a-dependent manner after STS treatment, while p53 had little function in this process. Moreover, cell apoptosis
and Bax translocation induced by STS were not blocked by Pifithrin-α (p53 inhibitor), which suggested that p53 was not
involved in this signaling pathway. Taken together, these results indicate that PUMA promoted Bax translocation in a
FOXO3a-dependment pathway during STS-induced apoptosis, while p53 was dispensable in this process.
Ultraviolet (UV) irradiation can induce apoptosis through both the membrane death receptor and the intrinsic apoptotic
signaling pathways as DNA-damaging agents. PUMA, a BH3-only Bcl-2 family protein, plays an essential role in
DNA damage-induced apoptosis. Bax, also a Bcl-2 family member, translocates from the cytosol to the mitochondrial
membrane during UV-induced apoptosis. However, the regulation of Bax activation induced by UV irradiation remains
poorly understood. In this study, the FRET (fluorescence resonance energy transfer) technique was used to study the
interactions of Bax, Bcl-Xl, and PUMA in ASTC-a-1 cells. The results show that Bax translocated from the cytosol to the
mitochondrial membrane at about 7 h after UV irradiation, and the translocation can not be blocked completely when
overexpressed Bcl-xl. Moreover, The interaction of Bax and Bcl-Xl weakened markedly. In addition,
Co-immunoprecipitation shows that PUMA released Bax by directly binding to Bcl-XL after UV irradiation in
ASTC-a-1 cells. Taken together, these results indicated that PUMA can promote Bax translocation by binding to
Bcl-Xl during UV-induced apoptosis.
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