Catalyzes the addition of GlcNAc or GlcUA monosaccharides to the nascent hyaluronan polymer (PubMed:20507985, PubMed:32993960, PubMed:23303191, PubMed:21228273) (Probable). Therefore, it is essential to hyaluronan synthesis a major component of most extracellular matrices that has a structural role in tissues architectures and regulates cell adhesion, migration and differentiation (PubMed:8798477, PubMed:21228273, PubMed:20507985). This is one of three isoenzymes responsible for cellular hyaluronan synthesis and it is particularly responsible for the synthesis of high molecular mass hyaluronan (By similarity). [hyaluronan](n) + UDP-N-acetyl-alpha-D-glucosamine = H(+) + N-acetyl-beta-D-glucosaminyl-(1->4)-[hyaluronan](n) + UDP N-acetyl-beta-D-glucosaminyl-(1->4)-[hyaluronan](n) + UDP-alpha-D-glucuronate = [hyaluronan](n+1) + H(+) + UDP Regulated by several post-translational modifications such as ubiquitination/deubiquitination, phosphorylation and O-GlcNAcylation (PubMed:32993960, PubMed:30394292, PubMed:28604766, PubMed:22887999, PubMed:20507985, PubMed:21228273). The enzymatic activity depends on the availability of UDP-GlcUA and UDP-GlcNAc (PubMed:23303191, PubMed:22887999). Glycan biosynthesis; hyaluronan biosynthesis. Homodimer; dimerization promotes enzymatic activity (PubMed:20507985, PubMed:25795779). Forms heterodimer with HAS3 (PubMed:20507985, PubMed:25795779). Forms heterodimer with HAS1 (PubMed:25795779). Travels from endoplasmic reticulum (ER), Golgi to plasma membrane and either back to endosomes and lysosomes, or out into extracellular vesicles (PubMed:30394292). Post-translational modifications control HAS2 trafficking (PubMed:30394292). Expressed in fibroblasts. During cell cycle progression is induced at the G1-S and G2-M transitions. Up-regulated in a panel of cancer cell lines. Phosphorylation at Thr-328 is essential for hyaluronan synthase activity (PubMed:32993960). Phosphorylation at Thr-110 is required for transport from ER to Golgi (PubMed:30394292). O-GlcNAcylation at Ser-221 increases the stability of HAS2 and plasma membrane localization. Ubiquitination at Lys-190; this ubiquitination is essential for hyaluronan synthase activity and homo- or hetero-oligomerization. Can also be poly-ubiquitinated (PubMed:20507985). Deubiquitinated by USP17 and USP4. USP17 efficiently removes 'Lys-63'- and 'Lys-48'-linked polyubiquitin chains, whereas USP4 preferentially removes monoubiquitination and, partially, both 'Lys-63'- and 'Lys-48'-linked polyubiquitin chain (PubMed:28604766). A chromosomal aberration involving HAS2 may be a cause of lipoblastomas, which are benign tumors resulting from transformation of adipocytes, usually diagnosed in children. 8q12.1 to 8q24.1 intrachromosomal rearrangement with PLAG1. Belongs to the NodC/HAS family.