Stub1 acetylation by CBP/p300 attenuates chronic hypoxia-induced pulmonary hypertension by suppressing HIF-2a transcriptional activity

Chronic hypoxia induces pulmonary vascular remodeling and pulmonary hypertension (PH). While it is established that transcription factors, hypoxia-inducible factors (HIF-1a/HIF-2a) activate gene programs that drive hypoxia-induced PH, the mechanism of HIF-1/2 activation is less clear. Here, we report that carboxylterminus of Hsp70-interacting protein (CHIP or Stub1) modulates HIF-1a and HIF-2a transcription rather than reducing their stability. Knocking-down Stub1 reduced hypoxic activation of HIF-1a mRNA, protein, and activity while enhancing hypoxic induction of HIF-2a mRNA, protein, and target genes in pulmonary vascular cells. Mechanistically, CBP/p300-mediated acetylation of lysine (K287) inactivates the ubiquitin ligase activity of Stub1 and triggers its translocation from the cytoplasm into the nucleus. There, it recognizes the HIF promoter and hypoxia response elements (HREs) in target genes. Expression of Stub1-K287Q mutant (mimicking acetylation) enhanced hypoxia-induced HIF-1a expression, while acetyl-deficient Stub1-K287R mutant had the opposite effect on HIF-a but enhanced hypoxia-induced HIF-2a transcriptional activity. Endothelial-Stub1 transgenic mice tolerated chronic hypoxia better, had less pulmonary vascular remodeling, reduced pulmonary vascular resistance, and greater cardioprotection. Thus, Stub1 nuclear translocation enhances hypoxic induction of HIF-1a activity while suppressing deleterious effects of HIF-2a. These observations indicate that nuclear-Stub1 synergizes with HIF-1a to promote transcriptional responses and antagonizes HIF2a-driven PH in chronic hypoxia. Overall design: Examination of the effect of nuclear localization or exclusion of STUB1 protein on downstream gene expression.