The Proteasome Inhibitor Bortezomib Is a Potent Inducer of Zinc Finger AN1-type Domain 2a Gene Expression

Background: AIRAP is a recently identified heat shock protein whose function and regulation are still not well defined. Results: Proteasome inhibition causes abundant AIRAP expression in human primary cells. Conclusion: The anticancer drug bortezomib regulates AIRAP expression through HSF1-HSF2 interplay. Significance: This study reveals how persistent proteasomal inhibition by clinically relevant concentrations of bortezomib affects heat shock response regulation and HSF-mediated AIRAP induction. The zinc finger AN1-type domain 2a gene, also known as arsenite-inducible RNA-associated protein (AIRAP), was recently identified as a novel human canonical heat shock gene strictly controlled by heat shock factor (HSF) 1. Little is known about AIRAP gene regulation in human cells. Here we report that bortezomib, a proteasome inhibitor with anticancer and antiangiogenic properties used in the clinic for treatment of multiple myeloma, is a potent inducer of AIRAP expression in human cells. Using endothelial cells as a model, we unraveled the molecular mechanism regulating AIRAP expression during proteasome inhibition. Bortezomib induces AIRAP expression at the transcriptional level early after treatment, concomitantly with polyubiquitinated protein accumulation and HSF activation. AIRAP protein is detected at high levels for at least 48 h after bortezomib exposure, together with the accumulation of HSF2, a factor implicated in differentiation and development regulation. Different from heat-mediated induction, in bortezomib-treated cells, HSF1 and HSF2 interact directly, forming HSF1-HSF2 heterotrimeric complexes recruited to a specific heat shock element in the AIRAP promoter. Interestingly, whereas HSF1 has been confirmed to be critical for AIRAP gene transcription, HSF2 was found to negatively regulate AIRAP expression after bortezomib treatment, further emphasizing an important modulatory role of this transcription factor under stress conditions. AIRAP function is still not defined. However, the fact that AIRAP is expressed abundantly in primary human cells at bortezomib concentrations comparable with plasma levels in treated patients suggests that AIRAP may participate in the regulatory network controlling proteotoxic stress during bortezomib treatment.