Mediates depolymerization of hyaluronic acid (HA) via the cell membrane-associated clathrin-coated pit endocytic pathway. Binds to hyaluronic acid. Hydrolyzes high molecular weight hyaluronic acid to produce an intermediate-sized product, a process that may occur through rapid vesicle endocytosis and recycling without intracytoplasmic accumulation or digestion in lysosomes. Involved in hyaluronan catabolism in the dermis of the skin and arthritic synovium. Positively regulates epithelial-mesenchymal transition (EMT), and hence tumor cell growth, invasion and cancer dissemination. In collaboration with HSPA5/BIP, promotes cancer cell migration in a calcium and PKC-dependent manner. May be involved in hearing. Random hydrolysis of (1->4)-linkages between N-acetyl-beta-D-glucosamine and D-glucuronate residues in hyaluronate. Activity is up-regulated by histamine. Interacts with EPHA2 and ITPR3. Interacts with HSPA5/BIP; the interaction induces calcium leakage from the endoplasmic reticulum and cell migration. Interacts with clathrin heavy chain/CLTC (By similarity). Retained in the endoplasmic reticulum (ER) in a HSPA5/BIP-dependent manner. Strongly detected in the cytoplasm of breast carcinoma cells, whereas poorly detected in adjacent normal epithelial cells, stromal cells, or benign breast tissues. Localized in the nucleus and cytoplasm of colon adenocarcinomas (By similarity). Colocalized with clathrin heavy chain/CLTC in clathrin-coated vesicles. Expressed in Deiters' cells and various supporting cells in the organ of Corti including inner phalangeal, border, inner and outer pillar cells (at protein level). Weakly expressed in brain and testis. In ear, it is specifically expressed in inner ear. Expressed in Deiters' cells in the organ of Corti at P0 (postnatal day zero) before the onset of hearing, but disappears by day P7. Also expressed in fibrocytes of the spiral ligament and the spiral limbus through to P21, when the cochlea matures. Expressed throughout development. The signal sequence is essential in mediating its proper translocation, hyaluronic acid (HA) degradation activity and secretion. N-glycosylated; glycosylation is not necessary for HA-binding. Belongs to the CEMIP family.