Showing papers on "Smoothelin published in 1997"

Differentiation of Smooth Muscle Cells in Human Blood Vessels as Defined by Smoothelin, a Novel Marker for the Contractile Phenotype

Abstract: Smoothelin is a constituent of the cytoskeleton specific for smooth muscle cells (SMCs) in a broad range of species. It has been postulated that smoothelin represents a marker of highly differentiated, contractile SMCs. Here, we present data on the presence of smoothelin in the human vascular system that support this hypothesis. For this purpose, smoothelin distribution was studied (1) during vasculogenesis of the placenta, (2) in normal adult blood vessels, and (3) in atherosclerotic lesions. Smoothelin was first observed in placental tissue at approximately week 10 to 11 of gestation. In full-term placenta, it was found in the SMCs of vessels in the large stem villi and in the chorionic plate. Furthermore, it was present in the fetal arteries of smaller stem villi, but it was not found in the veins. In adult blood vessels, a small population of aortic (≈10%) and large muscular artery (≈30% to 50%) SMCs was positive for smoothelin. In general, smoothelin and desmin were coexpressed in the same S...

Smoothelin expression characteristics: development of a smooth muscle cell in vitro system and identification of a vascular variant

Abstract: Recently we described a protein, smoothelin, that has been exclusively found in smooth muscle cells (SMC). The human cDNA has been cloned from a colon cDNA library and the putative protein sequence was deduced. Smoothelin does not belong to a known protein family but shows a partial homology with members of the spectrin family. Transfection studies revealed that smoothelin has an affinity for actin and is either capable of forming filamentous structures or colocalizes with such structures. The protein is expressed in visceral as well as vascular tissues of all vertebrate classes. A study on the distribution of smoothelin in the vascular and placental system showed that smoothelin expression was largely restricted to the muscular pulsating blood vessels. Therefore, we hypothesized that smoothelin is expressed in contractile SMC only (36, 37). No expression of smoothelin was observed in established cell lines of SMC. In tissue explants smoothelin mRNA concentration decreases to undetectable levels within 12 hours after dissection as was in general the case in primary cell cultures. Here we report on continued smoothelin expression for several passages observed in a human prostate primary cell culture system. Smoothelin was demonstrated to colocalize with actin stress fibers but not with desmin filaments. This culture system offers opportunities to study the cytological localization of smoothelin, interactions with other proteins and should provide a system to test the promoter of the smoothelin gene. On immunoblots the molecular weight of smoothelin differed between visceral and vascular smooth muscle tissue with apparent molecular weights of respectively 59 kDa and 94 kDa. There is no evidence for the existence of another gene coding for the 94 kDa smoothelin. Thus, posttranslational modification, alternative splicing and dual promoter control are the alternatives for the expression of two isoforms of smoothelin.

Cytoskeletal characterization of arteriovenous epithelioid cells.

Abstract: Data on the cytoskeleton of epithelioid cells in arteriovenous anastomosis (AVA) are sparse, but there is evidence that the (myo)-epithelioid cells of the AVAs represent a specialized smooth muscle cell type with less contractile properties. We demonstrated the expression of α-smooth muscle actin, smooth muscle myosin, calponin, caldesmon, and caveolin in epithelioid cells of rabbit ear and in human toes, finger tips, and glomus tumors by means of indirect immunofluorescence techniques and immunoelectron microscopy. Epithelioid cells in rabbit ear did not express vimentin, but it was present in human toes, finger tips, and glomus tumors. Epithelioid cells in human toes, finger tips, and glomus tumors did not express desmin, but it was present in rabbit ear. Epithelioid cells did not express cytokeratins. The epithelioid cells examined showed only a weak expression of the protein smoothelin, which occurs exclusively in contractile smooth muscle cells. Immunoelectron microscopical demonstration of α-smooth muscle actin revealed a striking difference in the arrangement of actin filaments in the epithelioid cells as compared to that in the smooth muscle cells of blood vessels. The epithelioid cells contained a loose array of actin filaments, whereas the smooth muscle cells contained tightly packed parallel actin bundles. In the present study we observed a correlation between the lack of contractile marker protein expression in epithelioid cells and the presence of only a few filaments, although the epithelioid cells are α-smooth muscle actin positive. The reduced number of contractile elements in the epithelioid cells of rabbit and human anastomoses suggests a lower contractility of epithelioid cells compared to that of the surrounding smooth muscle cells in anastomoses. A second interesting difference between both cell types is the high number of caveolae in epithelioid cells. Immunoelectron microscopy showed a compact distribution of caveolae at the epithelioid cell border, but a more dispersed distribution of caveolae in the cytoplasm of the blood vessel endothelium. The benign glomus tumor was characterized by an expression pattern of cytoskeletal proteins similar to that of epithelioid cells, confirming its description as a benign tumor.