Protein OS-9 is a protein that in humans is encoded by the OS9 gene.

This gene encodes a protein that is highly expressed in osteosarcomas. This protein binds to the hypoxia-inducible factor 1 (HIF-1), a key regulator of the hypoxic response and angiogenesis, and promotes the degradation of one of its subunits. Alternate transcriptional splice variants, encoding different isoforms, have been characterized. [provided by RefSeq, Jul 2008].
Function: Lectin which functions in endoplasmic reticulum (ER) quality control and ER-associated degradation (ERAD). May bind terminally misfolded non-glycosylated proteins as well as improperly folded glycoproteins, retain them in the ER, and possibly transfer them to the ubiquitination machinery and promote their degradation. Possible targets include TRPV4.