Tmod3 regulates polarized epithelial cell morphology

Abstract

Although the role of the actin cytoskeleton in morphogenesis of polarized epithelial sheets is generally accepted as centrally important, the regulation of actin dynamics in this process remains unclear. Here, we show that the pointed-end capping protein Tmod3 contributes to epithelial cell shape within confluent monolayers of polarized epithelial cells. Tmod3 localizes to lateral cell membranes in polarized epithelia of several cell types. Reduction of Tmod3 levels by shRNA leads to a loss of F-actin and tropomyosins from lateral cell membranes, and a decrease in epithelial cell height, without effects on localisation of tight junction or adherens junction proteins, or any apparent changes in cell-cell adhesion. Instead, distribution of αII-spectrin on lateral membranes is disrupted upon reduction of Tmod3 levels, suggesting that loss of Tmod3 function leads to destabilization and disassembly of tropomyosin-coated actin filaments followed by disorganization of the spectrin-based membrane skeleton on lateral membranes. These data demonstrate for the first time a role for pointed-end capping in morphology regulation of polarized epithelial cells through stabilization of F-actin on lateral membranes. We propose that Tmod3-capped tropomyosin-actin filaments provide crucial links in the spectrin membrane skeleton of polarized epithelial cells, enabling the membrane skeleton to maintain cell shape.

Palladin, an actin-associated protein, is required for adherens junction formation and intercellular adhesion in HCT116 colorectal cancer cells

“…protein TMOD3, which contributes to the regulation of polarized epithelial cell shape by stabilizing F-actin on lateral membranes, was also down-regulated in the E1 cells, consistent with the loss of polarity markers and epithelial morphology in these cells (46). The changes in mRNA expression of S100A4, DSC2 (Fig.…”

Adducin Promotes Micrometer-Scale Organization of β2-Spectrin in Lateral Membranes of Bronchial Epithelial Cells

“…Interestingly, depletion of tropomodulin 3 from lateral membranes of Caco-2 epithelial cells results in reduced cell height and increased cross-sectional area without a general loss of epithelial polarity (Weber et al, 2007). These results were also attributed to dysfunction of spectrin-actin assembly and suggest a common mechanism to maintaining lateral membrane stability through activities of spectrin-junctional structures.…”

Tropomyosin is required for cardiac morphogenesis, myofibril assembly, and formation of adherens junctions in the developing mouse embryo

“…Alternatively, αTM1 may directly control cell shape and adhesion by stabilizing the circumferential adherens belts of sarcomeric α-actinin and F-actin located at the apical poles of the cardiomyocytes. TM isoforms localize to cell-cell junctions in epithelia (Temm-Grove et al, 1998;Dalby-Payne et al, 2003;Bakin et al, 2004;Weber et al, 2007;Nowak et al, 2009), and other TMs have been implicated in human epithelial cell cancers (Stehn et al, 2006;Helfman et al, 2008), suggesting critical roles for TMs in the stability and function of cell-cell junctions. Lack of adherens belts providing circumferential tension may explain the convoluted contours of the cardiomyocyte membranes evidenced by N-cadherin staining in αTM1-deficient hearts, as well as the large spaces between neighboring cells.…”