Inmolecular biology,caveolins are a family ofintegral membrane proteins that are the principal components ofcaveolae membranes and involved in receptor-independentendocytosis.^[1][2][3] Caveolins may act asscaffolding proteins within caveolar membranes by compartmentalizing and concentrating signaling molecules. They also induce positive (inward) membrane curvature by way of oligomerization, and hairpin insertion. Various classes of signaling molecules, includingG-protein subunits, receptor and non-receptortyrosine kinases, endothelialnitric oxide synthase (eNOS), and smallGTPases, bind Cav-1 through its 'caveolin-scaffolding domain'.

The caveolingene family has three members invertebrates: CAV1, CAV2, and CAV3, coding for the proteins caveolin-1, caveolin-2, and caveolin-3, respectively. All three members aremembrane proteins with similar structure. Caveolin formsoligomers and associates with cholesterol and sphingolipids in certain areas of thecell membrane, leading to the formation ofcaveolae.

The caveolins are similar in structure. They all form hairpin loops that are inserted into the cell membrane. Both theC-terminus and theN-terminus face thecytoplasmic side of the membrane. There are twoisoforms of caveolin-1: caveolin-1α and caveolin-1β, the latter lacking a part of the N-terminus.

Caveolins are found in the majority ofadherent,mammalian cells.

• Caveolin-1 is most prominently expressed inendothelial,fibrous, andadipose tissue.
• The expression pattern of caveolin-2 is similar to that of caveolin-1; it seems to beco-expressed with caveolin-1.
• The expression of caveolin-3 is restricted tostriated and smooth muscle.

The functions of caveolins are still under intensive investigation. They are best known for their role in the formation of 50-nanometer-sizeinvaginations of the plasma membrane, called caveolae.Oligomers of caveolin form the coat of these domains. Cells that lack caveolins also lack caveolae. Many functions are ascribed to these domains, ranging fromendocytosis andtranscytosis tosignal transduction.

Caveolin-1 has also been shown to play a role in theintegrin signaling. Thetyrosinephosphorylated form of caveolin-1 colocalizes withfocal adhesions, suggesting a role for caveolin-1 inmigration. Indeed, downregulation of caveolin-1 leads to less efficient migrationin vitro.

Genetically engineered mice that lack caveolin-1 and caveolin-2 are viable and fertile, showing that neither the caveolins nor the caveolae are essential in embryonic development or reproduction of these animals. However,knock-out animals do develop abnormal, hypertrophic lungs, and cardiac myopathy, leading to a reduction in lifespan. Mice lacking caveolins also suffer from impairedangiogenic responses as well as abnormal responses tovasoconstrictive stimuli. Inzebrafish, lack of caveolins leads to embryoniclethality, suggesting that highervertebrates (as exemplified by mice) have developed compensation or redundancy for the functions of caveolins.

Caveolins have a paradoxical role in the development of this disease. They have been implicated in bothtumor suppression andoncogenesis.^[4] Highexpression of caveolins leads to inhibition of cancer-related pathways, such asgrowth factorsignaling pathways. However, certain cancer cells that express caveolins have been shown to be more aggressive andmetastatic, because of a potential for anchorage-independent growth.

Caveolins are thought to play an important role during the development of atherosclerosis.^[5] Furthermore, caveolin-3 has been associated withlong QT syndrome.^[6]

Caveolin-3 has been implicated in the development of certain types of muscular dystrophy (limb-girdle muscular dystrophy).^[7]

• The Caveolin Protein
• Caveolins at the U.S. National Library of MedicineMedical Subject Headings (MeSH)
• Caveolin-3 page

• Genes on human chromosome 7
• Genes on human chromosome 3
• Integral membrane proteins

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