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). Protein modification; protein ubiquitination. Interacts with HIF1AN. Component of an ECS (Elongin BC-CUL2/5-SOCS-box protein) E3 ubiquitin-protein ligase complex formed of CUL2 or CUL5, Elongin BC (ELOB and ELOC), RBX1 and ASB4. The SOCS box domain mediates the interaction with the Elongin BC complex, an adapter module in different E3 ubiquitin-protein ligase complexes. Hydroxylation at Asn-246 by HIF1AN may provide an oxygen-dependent regulation mechanism for the function of ASB4 in promoting vascular differentiation. Belongs to the ankyrin SOCS box (ASB) family.