Identification of a major protein on the cytosolic face of caveolae

Abstract

Cav-p60, a specific and ubiquitous caveolar protein, was immunoprecipitated from solubilized rat adipocyte plasma membranes and identified as similar to a GeneBank entry annotated mouse polymerase transcript release factor (PTRF) by MALDI-TOF and MS-MS of major fragments. Cloning and virtual translation of the corresponding rat adipocyte cDNA sequence revealed 98.7% identity with mouse PTRF. In vitro translation of this sequence produced a protein, which was recognized by antibodies to both cav-p60 and PTRF. EM gold labeling studies showed that a rabbit antiserum against murine PTRF immunolabeled caveolae specifically in adipocytes from both mouse and rat. In view of the reported function of the protein, which is exerted in the cell nucleus, its subcellular localization was investigated. We found that the protein could be purified by differential solubilization of a plasma membrane fraction followed by SDS-PAGE, and that the protein was as abundant as caveolin in this fraction. We were unable to detect the protein in cell nuclei by subcellular fractionation or fluorescence microscopy. The results show that in a large number of cell types, PTRF is essentially located to caveolae, and that each caveola harbors many copies of the protein. Consequently, we suggest the name Cavin for this protein.

Cellular spelunking: exploring adipocyte caveolae

“…2 to mass spectrometry, and in addition to what we previously identified by sequencing or by Western blotting, we found cavin [also known as polymerase I and transcript release factor (PTRF) (36)] to be a major constituent, in confirmation of the work of Vinten and colleagues (37,38) in rat adipocytes and that of Aboulaich et al (39,40), who used human fat cells. The role of cavin in caveolae structure/ function remains to be determined, but its relative abundance, its tissue distribution that mirrors that of caveolin-1 and -3 (37,41), and its apparent lack of enzymatic activity (36) suggest a possible structural role, although a functional role in adipocytes has been suggested (40) (see lipid trafficking section below).…”

IGF-IR internalizes with CAVEOLIN-1 and PTRF/CAVIN in HACAT cells

“…Subcellular localization of IGF-IR with PTRF/Cavin and Cav-1 was studied by confocal microscopy. Consistently with previous reports [23] in basal condition both Cav-1 and PTRF/Cavin colocalized in plasma membrane showing a distribution typical of caveolae staining-pattern ( Fig.2A). IGF1 induced Cav-1 and PTRF/Cavin internalization as shown by the punctuate staining of the two proteins in the cytoplasm ( Fig.2A).…”

Caveolae at a glance

“…Cavin-1 has also been independently characterized as cav-p60, a protein initially found to be localized to caveolae in adipocytes (Vinten et al, 2005;Vinten et al, 2001) and, subsequently, also in a range of other tissues . This indicates that cavin-1 is not associated with caveolae in a tissue-specific manner and, therefore, could associate with both Cav1 and Cav3.…”