T-cadherin Is a Major Glycophosphoinositol-anchored Protein Associated with Noncaveolar Detergent-insoluble Domains of the Cardiac Sarcolemma

Abstract

Sucrose-density flotation analysis of Triton-insoluble membrane domains isolated from highly purified sheep ventricular sarcolemma revealed the presence of two major 120- and 100-kDa proteins. Both species migrated in two-dimensional isoelectric focussing/SDS gels with an apparent pI of approximately 4.3, suggesting that they might be related. Microsequence analysis of peptides derived from the 100-kDa protein yielded amino acid sequences with high homology to T-cadherin, a truncated cadherin lacking a cytoplasmic domain. The similarity was confirmed using antibodies to chicken T-cadherin that reacted with both proteins on immunoblots. T-cadherin was released from the detergent-insoluble sarcolemmal fraction by phospholipase C treatment indicating that it is linked to the membrane by a glycophosphoinositol anchor. T-cadherin could be ADP-ribosylated by a transferase that was also present in the caveolin-enriched Triton-insoluble fraction. T-cadherin-containing membrane fragments cofractionated on sucrose gradients with caveolin-3, a marker protein for myocyte caveolae. However, immunopurified caveolin-3-containing membranes contained no associated T-cadherin. Immunocytochemical analysis of cultured rat atrial myocytes revealed that T-cadherin and caveolin have related but nonoverlapping staining patterns. These results suggest that T-cadherin is a major glycophosphoinositol-linked protein in cardiac myocytes and that it may be located in plasma membrane "rafts" distinct from but possibly adjacent to caveolae.

T-cadherin is a receptor for hexameric and high-molecular-weight forms of Acrp30/adiponectin

“…Tcadherin suppressed the growth of astrocytes and was reduced in a glioblastoma cell line (36), and reexpression of T-cadherin in this cell line induced growth arrest, which depended on p21 (CIP1͞WAF1) expression. T-cadherin may participate in signaling through its association with other membrane proteins and incorporation into specific lipid domains of the cell membrane (37,38), and it may restrict proliferation of the intima through its interactions with adiponectin. T-cadherin is not highly expressed in the hepatocyte, which is one of the major sites of activity of adiponectin in suppressing gluconeogenesis (6, 23); 4, and 6).…”

The differential protein and lipid compositions of noncaveolar lipid microdomains and caveolae

“…The separation of caveolae from noncaveolar lipid microdomains resolves the ambiguity caused by analyzing the lipid microdomains that are isolated with the conventional sucrose density gradient. For example, T-cadherin is reported as a caveolae-associated protein in one study and as a lipid raft-associated protein in another study [37,38]. Aquaporin-1, Thy-1, IGF-1 receptor and N-cadherin, which are reported to co-fractionate with caveolin-1 [5,20,[21][22][23][24][25], are actually noncaveolar lipid microdomain-associated proteins ( Figure 2D).…”

Identification and Characterization of a Soluble Cadherin-7 Isoform Produced by Alternative Splicing

“…The variant protein of cadherin-7 consists of an NH 2 -terminal domain, four CRs (CR1-CR4), a shorter pretransmembrane domain, and a distinct COOH-terminal polypeptide of 14 amino acids but lacks transmembrane and cytoplasmic domains. The variant protein might not be a glycosyl phosphatidylinositol-anchored protein, because it does not have the hydrophobic COOH-terminal domain essential for glycosyl phosphatidylinositol-modification (27), in contrast to T-cadherin (6,7). To investigate whether the variant protein is soluble, we transfected the cDNA of the variant form of cadherin-7 into COS-7 and 293 cells and detected the variant protein in the conditioning medium as a soluble molecule.…”

“…Cadherin-7 shows a partial affinity to cadherin-6B, but the heterophilic interaction is less stable than the homophilic (5). Cadherin-7 is involved in intercellular signaling between homotypic cells and in the sorting of heterotypic cells, but the precise function of cadherin- 7 has not yet been determined (17,18).…”

“…brane domain, and a highly conserved cytoplasmic domain (2,5), except for T-cadherin (6,7). CR1 provides the binding specificity of cadherins (8,9).…”