b2-adrenergic stimulation blunts the hypoxia effects on alveolar epithelial cells indicating opposing effects of HIF and CREB signaling. We studied here, whether hypoxia and terbutaline affect the expression of HIF, and tested for dependency on CREB.

Primary rat lung alveolar epithelial cells were exposed to hypoxia (1.5% O₂) and terbutaline for 24h. HIF-1a and HIF-2a were measured by qRT-PCR and Western blot. Involvement of CREB was tested by silencing CREB1 and ATF-2 after introducing shRNAs using adenoviral infection.

Hypoxia decreased HIF-1a but not HIF-2a mRNA but increased their protein levels in nuclear extracts. Terbutaline increased the mRNA and protein expression of both HIF-1a and HIF-2a in normoxia, and prevented the decrease in HIF-1a mRNA by hypoxia. Terbutaline also increased GAPDH expression, a HIF-dependent gene. Silencing of CREB-1 and CREB-2 (ATF-2) did not affect HIF mRNAs in normoxia and hypoxia, and prevented the terbutaline effects on HIF-1a mRNA expression at both oxygenation levels. Terbutaline-induced HIF-2a expression in hypoxia was prevented by CREB-2 silencing. CREB silencing also prevented the increase in GAPD mRNA.

These results indicate that 24h stimulation with terbutaline increases HIF-1a and HIF-2a expression and activity in normoxia and hypoxia by mechanisms depending on CREB.

(Supported by DFG (Ma 1503/28-1) to HM).