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The sequence of human caveolin reveals identity with VIP21, a component of transport vesicles.

Caveolin is a protein present in membrane specializations termed caveolae where it may play a structural role. Previous studies on the cDNA sequence of chicken caveolin demonstrated that it is an integral membrane protein without significant homology to any known protein. The cDNA sequence of human lung caveolin is presented here. A striking sequence homology is observed with the chicken protein, as well as a very recently reported protein termed VIP21 [(1992) J. Cell Biol. 118, 1003-1014], a putative vesicle transport protein isolated from MDCK cells. Genomic Southern blots suggest that caveolin is present in a single copy, and Northern blots confirm that the caveolin mRNA is elevated in muscle.

Amino Acid Sequence

Sequence and expression of caveolin, a protein component of caveolae plasma membrane domains phosphorylated on tyrosine in Rous sarcoma virus-transformed fibroblasts.

Caveolae are flask-shaped plasma membrane invaginations abundant in endothelium and muscle but may be present in all cells. They contain a filamentous coat material thought to be important in their structure and function. Recent studies have demonstrated that a 22-kDa protein (caveolin) phosphorylated on tyrosine in Rous sarcoma virus-transformed chicken fibroblasts is a component of the caveolae coat on the inner aspect of the membrane. We now report the deduced protein sequence of chicken caveolin derived from cDNA PCR products and genomic DNA clones. Caveolin is a unique protein of 178 amino acids and displays little sequence similarity to other proteins in the GenBank data base. Hydrophobicity predictions indicate an unusual 40-amino acid hydrophobic region near the C terminus that may be used to anchor the protein to the membrane. When chicken caveolin was expressed in mouse 3T3 cells and detected by immunofluorescence microscopy, the typical caveolae pattern was observed. This includes brightly fluorescent membrane patches in many cases concentrated at the margin of cells and in arrays. Caveolae may be distinct from other membrane domains due at least in part to caveolin.

3T3 Cells

Desmoplakin Mutations in Cardiac Fibroblasts Cause TGFβ1-Mediated Pathological Fibrogenesis in Desmoplakin Cardiomyopathy Via Beclin-1 Regulation.

BACKGROUND: Pathological fibrosis is a major finding in cardiovascular diseases and can result in arrhythmia and heart failure. Desmosome gene mutations can lead to arrhythmogenic cardiomyopathy. Among arrhythmogenic cardiomyopathies, pathogenic DSP (desmoplakin) variants cause a distinctive cardiomyopathy with excessive cardiac fibrosis that could precede ventricular dysfunction. DSP variants are also linked to other fibrotic diseases. Whether DSP plays any role in pathological fibrosis remains unknown. METHODS: Mesenchymal stromal cells (MSCs) are resident fibroblast-like cells that are responsible for fibrogenesis in most organs, including the heart. We first used RNA-seq genome-wide analyses to generate cardiac fibroblast-like, induced pluripotent stem cell-derived MSCs from normal donors and patients with arrhythmogenic cardiomyopathy and DSP mutations. We then studied the fibrogenic responses of cardiac MSCs to TGFβ1 (transforming growth factor β1) using Western/Co-IP, autophagy assays, gene knockdowns/over-expressions, genomic analyses, mouse DSP knockdown models, immunostaining, and qPCR. RESULTS: TGFβ1 induced excessive accumulation of VIM (vimentin)/fibrillar collagens and over-activated fibrotic genes in DSP-mutant MSCs when compared with normal MSCs. In normal MSCs, VIMs bind to wild-type DSP during normal fibrogenesis after TGFβ1. DSP-mutant MSCs exhibited a haplo-insufficient phenotype with increased DSP-unbound VIMs that sequestered BECN1 (beclin-1) from activating autophagy and CAV1 (caveolin-1)-mediated endocytosis. Decreased autophagy caused collagen accumulation, and diminished CAV1 endocytosis resulted in abnormal CAV1 plaque formation that over-activated fibrotic genes (COL1A1, COL3A1, and fibronectin [FN]) via heightened p38 activity after TGFβ1. Genome-wide analysis and DSP knockdown in mouse fibroblasts confirmed this novel role of DSP mutations in pathological fibrosis. Overexpression of VIM-binding domains of DSP could suppress pathological fibrosis by increasing collagen autophagic degradation and decreasing fibrotic gene expression. CONCLUSIONS: Our data reveal that DSP deficiency in MSCs/fibroblasts leads to exaggerated fibrogenesis in DSP-cardiomyopathy by decreasing BECN1 availability for autophagy and CAV1-endocytosis. Overexpression of VIM binding domains of DSP could be a new strategy to treat pathological fibrosis.

Animals

Desmoplakin mutations in cardiac fibroblasts cause TGFβ1-mediated pathological fibrogenesis in desmoplakin cardiomyopathy via beclin-1 regulation.

BACKGROUND: Pathological fibrosis is a major finding in cardiovascular diseases and can result in arrhythmia and heart failure. Desmosome gene mutations can lead to arrhythmogenic cardiomyopathy (ACM). Among ACM, pathogenic desmoplakin ( DSP ) variants cause a distinctive cardiomyopathy with excessive cardiac fibrosis that could precede ventricular dysfunction. DSP variants are also linked to other fibrotic diseases. Whether DSP plays any role in pathological fibrosis remain unknown. METHODS: Mesenchymal stromal cells (MSCs) are resident fibroblast-like cells that are responsible for fibrogenesis in most organs, including hearts. We first used unbiased genome-wide analyses to generate cardiac fibroblasts-like, induced pluripotent stem cell-derived MSCs from normal donors and ACM patients with DSP mutations. We then studied the fibrogenic responses of cardiac MSCs to transforming growth factor beta-1 (TGF-β1) using Western/Co-IP, autophagy assay, gene knockdowns/over-expressions, genomic analyses, mouse DSP knockdown models, immunostaining, and qPCR. RESULTS: TGFβ1 induced excessive accumulations of vimentin (VIM)/fibrillar collagens, and over-activated fibrotic genes in DSP- mutant MSCs when compared to normal MSCs. In normal MSCs, VIMs bind to wild-type DSP during normal fibrogenesis after TGFβ1. DSP- mutant MSCs exhibited a haplo-insufficient phenotype with increased DSP-unbound VIMs that sequestered beclin-1 (BECN1) from activating autophagy and caveolin-1 (CAV1)-mediated endocytosis. Decreased autophagy caused collagen accumulations and diminished CAV1 endocytosis resulted in abnormal CAV1 plaque formation that over-activated fibrotic genes [ COL1A1, COL3A1, and fibronectin ( FN )] via heightened p38 activities after TGFβ1. Genome-wide analysis and DSP knockdown in mouse fibroblasts confirmed this novel role of DSP mutations in pathological fibrosis. Overexpression of VIM-binding domains of DSP could suppress pathological fibrosis by increasing collagen autophagic degradation and decreasing fibrotic gene expressions. CONCLUSIONS: Our data reveal that DSP deficiency in MSCs/fibroblasts leads to exaggerated fibrogenesis in DSP-cardiomyopathy by decreasing BECN1 availability for autophagy and CAV1-endocytosis. Overexpression of VIM binding domains of DSP could be a new strategy to treat pathological fibrosis.

Journal Article