The effects of hypoxia on hemocyanin regulation in Cancer magister: Possible role of Hypoxia-Inducible Factor-1

Aquatic organisms routinely experience fluctuations in oxygen levels. In response to oxygen deprivation, many organisms increase the oxygen carrying capacity of their blood to restore balance to hypoxic cells and tissues. This response has been well described in vertebrate as well as invertebrate systems. The respiratory pigment found in decapod crustaceans, hemocyanin (Hc), increases in concentration and is differentially regulated in response to decreases in oxygen tension. To test the effects of hypoxia on Hc regulation in Cancer magister, adult crabs were exposed to hypoxic conditions (6.4 kPa) for 12 days. Total protein and oxyhemocyanin were significantly higher in crabs that had been exposed to hypoxic conditions. Hemocyanin analyzed by pH7.4 PAGE showed that the concentration of both the 16S and 25S conformations of Hc significantly increased in hypoxic crabs. We also show that C. magister differentially regulates Hc subunits 3 and 6 when challenged by hypoxia. As Hypoxia-Inducible Factor-1 (HIF-1) is considered to be the global regulator for oxygen homeostasis, we have also identified putative HIF-1α binding sites in the promoter and intronic sequence of several Hc subunits. The presence of these potential hypoxia response elements, the conservation of physiological responses, and the discovery of a HIF-1α homologue in C. magister and several other crustacean species, suggest a role for HIF-1 in regulating crustacean responses to hypoxia.