Mammalian sprouty 2 protein accumulates during mild and prolonged hypoxic exposure

Oxygen‐sensing mechanisms allow eukaryotic cells to adapt to fluctuating oxygen levels caused by cellular stresses like hypoxia. Mammalian sprouty 2 protein, a modulator of receptor tyrosine kinase activity, participates in the formation of an iron‐sulfur complex through its conserved cysteine residues. As iron‐sulfur complexes can act as sensors of oxygen as well as form the catalytic centers of enzymes, we asked the question of whether altered oxygen concentrations would affect the function, localization, and/or expression of human sprouty 2 (hSPRY2). Herein, we report that hSPRY2 protein levels were dramatically increased in stably transfected Hela cells exposed to mild hypoxic condition (3% O 2 ) for 24 and 48 hours. While transient expression of hSPRY2 in Hela cells also yielded similar results, expression of proteins like GFP or RSK1, did not show similar increases in protein levels under hypoxia. Degradation studies indicate that the half‐life of hSPRY2 is extended during hypoxic exposure in stably transfected Hela cells. The ability of EGF to stimulate phosphorylation of ERK1/2 in hSPRY2 expressing cells remained unchanged when cells were exposed to hypoxia. However, stimulation with FGF under hypoxic conditions resulted in a shift of the peak of ERK1/2 phosphorylation to an earlier time point in hSPRY2 expressing cells. Exposing cells to the hypoxia mimetics, DMOG, DFO, and CoCl 2 , for 24 hrs also resulted in increased hSPRY2 levels. Moreover, incubation of cells in DMOG with the lysosomal inhibitor chloroquine resulted in an additional accumulation of hSPRY2 in these cells, suggesting that these two inhibitors additively increase hSPRY2 levels by different mechanisms.