Hypoxia Associated Proteolytic Processing of OS-9 by the Metalloproteinase Meprin beta

Meprin metalloproteases play a role in the pathology of ischemia/reperfusion-(IR-) induced renal injury. The endoplasmic reticulum-associated protein, osteosarcoma-9 (OS-9), has been shown to interact with the carboxyl-terminal tail of meprin beta. More importantly, OS-9 interacts with the hypoxia inducible factor-1 alpha (HIF-1 alpha) and the prolyl-hydroxylase, proteins which mediate the cell's response to hypoxia. To determine if OS-9 is a meprin substrate, kidney proteins from meprin alpha beta knockout mice (alpha beta KO) (which lack endogenous meprins) and purified human OS-9 were incubated with activated forms of meprin A and meprin B, and Western blot analysis was used to evaluate proteolytic processing of OS-9. Fragmentation of OS-9 was observed in reactions with meprin B, but not meprin A. To determine whether meprin B cleaves OS-9 in vivo, wild-type (WT) and meprin alpha beta KO mice were subjected to IR-induced renal injury. Fragmentation of OS-9 was observed in kidney proteins fromWT mice subjected to IR, but not in meprin alpha beta KO counterparts. Transfection of kidney cells (MDCK and HEK293) with meprin beta cDNA prevented accumulation of OS-9 following exposure to the hypoxia mimic, CoCl2. These data suggest that meprin beta interaction with OS-9 plays a role in the hypoxia response associated with IR-induced renal injury.