Regulates the traffic and/or budding of caveolae (By similarity). Plays a role in caveola formation in a tissue-specific manner. Required for the formation of caveolae in smooth muscle but not in the lung and heart endothelial cells (PubMed: 28285351, PubMed:23652019). Regulates the equilibrium between cell surface-associated and cell surface-dissociated caveolae by promoting the rapid release of caveolae from the cell surface (PubMed:25588833). Plays a role in the regulation of the circadian clock. Modulates the period length and phase of circadian gene expression and also regulates expression and interaction of the core clock components PER1/2 and CRY1/2 (PubMed:23079727). Component of the CAVIN complex composed of CAVIN1, CAVIN2, CAVIN3 and CAVIN4 (PubMed:19546242). Interacts with PRKCD and with phosphatidylserine. Phosphatidylserine may form a bridge between PKC and PKC-binding partners and stabilize the binding (PubMed:9054438). Interacts with PER2 (PubMed:23079727). Interacts with CAVIN1 (PubMed:19546242, PubMed:25588833). Interacts (via leucine-zipper domain) with CAV1 in a cholesterol-sensitive manner (PubMed:25588833). Interacts with EPS15L1 (By similarity). Localizes in the caveolae in a caveolin-dependent manner. Lung, heart, skeletal muscle, liver, brain, vascular and urinary bladder smooth muscle (at protein level). Strongly expressed in uterus, ovary, mammary and epithelial cells. Also expressed in spleen, intestine, kidney and testis. Up-regulated in serum-starvated cells or during cell growth arrest. The leucine-zipper domain is essential for its localization in the caveolae and for its interaction with CAV1 and EPS15L1. In vitro, phosphorylated by PRKCD. Mice show reduced density of membrane caveolae in the arterial smooth muscle and the urinary bladder but show no loss of endothelial caveolae in lung and heart. Belongs to the CAVIN family.