Probable substrate-recognition component of a SCF-like ECS (Elongin-Cullin-SOCS-box protein) E3 ubiquitin-protein ligase complex which mediates the ubiquitination and subsequent proteasomal degradation of target proteins. Promotes differentiation and maturation of the vascular lineage by an oxygen-dependent mechanism (By similarity). Also acts as a negative regulator of GPS1, a component of the COP9 signalosome (CSN) multiprotein complex, thereby inhibiting the serine phosphorylation of IRS1 (By similarity). Regulates IRS4 levels by directing its degradation via ubiquitination and thereby decreases the downstream signal of IRS4 (PubMed:21955513). Plays a critical role during early vascular development and proper placentation. Mechanistically, negatively regulates the transcriptional regulator inhibitor of DNA binding 2/ID2 expression through polyubiquitination and proteasome dependent degradation (PubMed:24586788). {ECO:0000250|UniProtKB:Q9WV71, ECO:0000269|PubMed:21955513, ECO:0000269|PubMed:24586788}. This is the function of ENSG00000005981 (ASB4, ankyrin repeat and SOCS box containing 4).