Hsp72 mediates TAp73α anti-apoptotic effects in small cell lung carcinoma cells.
Bottom Line: However, the precise mechanism by which TAp73α exerts its pro-survival effect is yet unclear.Finally, we revealed that TAp73β counteracts the anti-apoptotic effect of TAp73α by preventing Hsp72 induction.Our results thus provide additional evidence for the potential oncogenic role of TAp73α, and extend the understanding of the mechanism for its anti-apoptotic effect.
Affiliation: Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden.Show MeSH
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Mentions: Significant activation of Bax in H82 cells upon VP16 treatment is observed by FACS analysis at 18–24 hrs after exposure (Fig. S1B). We have previously shown that the anti-apoptotic effect of TAp73α in SCLC cells is exerted upstream of mitochondria, at the level of Bax activation . In addition, Hsp72 has been shown to exert some of its protective effects at the same level, inhibiting apoptosis via the prevention of Bax activation and its translocation to the mitochondria . To investigate whether the simultaneous expression of TAp73α and depletion of Hsp72 could affect the apoptotic process at the level or upstream of mitochondria, H82 cells were co-transfected with TAp73α and asHsp72, and treated with VP16. Indeed, TAp73α was able to prevent VP16-induced disruption of mitochondrial membrane potential (ΔΨm) as shown both by microscopic count of TMRE– cells (Fig. 4A, black bars) and FACS analysis (Fig. 4B, black bars). However, upon co-transfection of TAp73α with asHsp72 the protective effect disappeared leading to a drop in ΔΨm upon VP16 treatment (Fig. 4A and B, TAp73α black and dark grey bars). Moreover, TAp73α-mediated inhibition of Bax activation was eliminated by co-transfection with asHsp72, as depicted by immunofluorescent staining (Fig. 4C) and FACS analysis on percentage of cells staining positive for active Bax (Fig. 4D, black and dark grey bars). Thus, depletion of Hsp72 leads to a loss of TAp73α anti-apoptotic effect upon drug-treatment and favours Bax activation and mitochondrial dysfunctions.
Affiliation: Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden.