Induction of hypoxia-inducible factor 1 activity by muscarinic acetylcholine receptor signaling

Abstract

Hypoxia-inducible factor-1 (HIF-1) is a master regulator of cellular adaptive responses to hypoxia. Levels of the HIF-1α subunit increase under hypoxic conditions. Exposure of cells to growth factors, prostaglandin, and certain nitric oxide donors also induces HIF-1α expression under non-hypoxic conditions. We demonstrate that muscarinic acetylcholine signals induce HIF-1α expression and transcriptional activity in a receptor subtype-specific manner using HEK293 cells transiently overexpressing each of M1-M4 muscarinic acetylcholine receptors. The muscarinic signaling pathways inhibited HIF-1α hydroxylation and degradation and induced HIF-1α protein synthesis that was confirmed by pulse labeling studies. Muscarinic signal-induced HIF-1α protein and HIF-1-dependent gene expression were blocked by treating cells with inhibitors of phosphatidylinositol 3-kinase, MAP kinase kinase, or tyrosine kinase signaling pathways. Dominant-negative forms of Ras and/or Rac-1 significantly suppressed HIF-1 activation by muscarinic signaling. Signaling via M1- and M3- but not M2-or M4-AchRs promote accumulation and transcriptional activation of HIF-1α. We conclude that muscarinic acetylcholine signals activate HIF-1 by both stabilization and synthesis of HIF-1α and by inducing the transcriptional activity of HIF-1α.