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: We suggested that since TAp73α is a potent inducer of Hsp72 expression, the anti-apoptotic effect of TAp73α might depend on the induction of Hsp72 protein. To investigate whether depletion of Hsp72 affects the anti-apoptotic activity of TAp73α we took advantage of an antisense Hsp72 vector (asHsp72). Transfection of cells with asHsp72 lead to a reduction in Hsp72 protein levels as shown both by Western blot (Fig. 2A) and confocal imaging (Fig. 2B). However, expression of the asHsp72 vector did not affect levels of Hsp72-related proteins HSF1, Hsp90, Hsc70 (as shown by Western blot, Fig. 2C) or Hsp27 (as shown by immunofluorescent staining, Fig. 2C). Subsequently, H82 cells were co-transfected with EGFP, p73 isoforms and asHsp72 vector, and treated with VP16 for 24 hrs. TAp73α and ΔNp73α are able to repress drug-induced apoptosis, whereas TAp73β enhances it (Fig. 2D, and as previously reported ). Upon co-transfection of ΔNp73α with asHsp72, ΔNp73α still exhibits an anti-apoptotic effect upon VP16 treatment (Fig. 2D, ΔNp73α black and grey bars). These data were further confirmed using a siRNA targeting HSP72/HSPA1A mRNA (Fig. 2E and F). This indicates the anti-apoptotic effect of ΔNp73α being independent on induction of Hsp72, consistent with the data described above (Fig. 1) where, in H82 cells, ΔNp73α do not show any induction of Hsp72, neither on the level of the promoter nor on mRNA and protein levels. The pro-apoptotic activity of TAp73β was unaffected by the co-expression of asHsp72. However, co-transfection of TAp73α together with asHsp72 significantly reduced the anti-apoptotic effect of TAp73α (Fig. 2D, TAp73α black and grey bars). Hence, the anti-apoptotic activity of TAp73α in SCLC H82 cells treated with chemotherapeutic drugs seems to depend on the induction of Hsp72.
Affiliation: Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, Stockholm, Sweden.