Role of Apg-1 in HSF1 activation and bortezomib sensitivity in myeloma cells

Abstract

Exposure of cells to bortezomib (BTZ) could activate heat shock protein (HSP) expression, which is regulated mainly by heat shock factor 1 (HSF1). We determined the role of Apg-1 (HSPA4L, a member of the HSP110 family) in HSF1 activation and bortezomib sensitivity by silencing HSF1 in multiple myeloma (MM) cells. We observed that the Apg-1 protein level was upregulated as BTZ concentration increased. To investigate the mechanism underlying Apg-1 induction, we evaluated the HSF1 translocation and found BTZ-inducible transposition to the nucleus of HSF1. In addition, cleaved caspase 3 and PARP might account for increased BTZ sensitivity on Apg-1 silencing. Furthermore, silencing HSF1 with shRNA or triptolide resulted in significant BTZ sensitivity. It had a more profound effect on cell death caused by BTZ when myeloma cells were adherent to bone marrow stromal cell lines (Hs-5). In summary, we found that Apg-1 knockdown sensitized myeloma cells to bortezomib treatment, which may provide a new approach in multiple myeloma treatment.