A novel iron responsive element in the 3′UTR of human MRCKα

Human untranslated region (UTR) databases were searched to identify novel proteins potentially regulated by an iron responsive element (IRE), and found two candidates—cell cycle phosphatase Cdc14A variant 1 and myotonic dystrophy kinase-related Cdc42-binding kinase α (MRCKα), both possessing a putative IRE in their 3′UTR. In further experiments, we focused on MRCKα. Biochemical analyses of the MRCKα IRE revealed that it was functional and mediated the response to iron level in the same way as transferrin receptor 1 IREs (TfR) did. Similarly to TfR mRNA, MRCKα mRNA is stabilized, when iron supply is low, while it is destabilized under iron-rich conditions. The expression of MRCKα mRNA was found to be ubiquitous; the highest levels were noted in testes, the lowest in skeletal muscle. The level of MRCKα mRNA in various tissues strongly positively correlates with the level of TfR mRNA, indicating its possible role in the transferrin iron uptake pathway.