Prostaglandin F2alpha induces the normoxic activation of the hypoxia-inducible factor-1 transcription factor in differentiating 3T3-L1 preadipocytes: Potential role in the regulation of adipogenesis.

Prostaglandin F2alpha (PGF2alpha) is a potent paracrine inhibitor of adipocyte differentiation. Here we show that treatment of differentiating 3T3-L1 preadipocytes with PGF2alpha induces the expression of DEC1, a transcriptional repressor that has previously been implicated in the inhibition of adipogenesis in response to hypoxia as a downstream effector of the hypoxia-inducible factor-1 (HIF-1) transcription factor. Surprisingly, despite performing our experiments under normal ambient oxygen conditions, we find that treatment of differentiating 3T3-L1 preadipocytes with PGF2alpha also results in the marked activation of HIF-1, as measured by an increase in the accumulation of the HIF-1alpha regulatory subunit. However, unlike the effects of hypoxia, this PGF2alpha-induced normoxic increase in HIF-1alpha is not mediated by an increase in the stability of the HIF-1alpha polypeptide, rather we find that PGF2alpha selectively increases the expression of the alternatively spliced HIF-1alpha I.1 mRNA isoform. Significantly, we demonstrate that the shRNA-mediated knockdown of endogenous HIF-1alpha expression attenuates the PGF2alpha-induced expression of DEC1, overcomes the inhibitory effects of PGF2alpha on the expression of proadipogenic transcription factors C/EBPalpha and PPARgamma and partially rescues the PGF2alpha-induced inhibition of adipogenesis. Taken together, these results indicate that PGF2alpha promotes the activation of the HIF-1 transcription factor pathway under normal oxygen conditions, and highlight a potential role for the normoxic activation of the HIF-1/DEC1-pathway in mediating the inhibitory effects of PGF2alpha on adipocyte differentiation.