Junctional Adhesion Molecule 1 Regulates Epithelial Cell Morphology through Effects on β1 Integrins and Rap1 Activity

Abstract

Here we have used small interfering RNA to investigate the effect of the loss of JAM1 expression on epithelial cell function. Consistent with our previous study, knockdown of JAM1 was observed to increase paracellular permeability in epithelial monolayers. Interestingly, knockdown of JAM1 also produced dramatic changes in cell morphology, and a similar effect was observed with expression of a JAM1 mutant lacking the putative homodimer interface. Further studies revealed that JAM1 knockdown decreased cell-matrix adhesion and spreading on matrix proteins that are ligands of ␤1 integrins. These changes were characterized by a decrease in ␤1 integrin protein levels and loss of ␤1 integrin staining at the cell surface. Immunolabeling of cells for the small GTPase Rap1, a known activator of ␤1 integrins, revealed colocalization of Rap1 with JAM1 at intercellular junctions, and knockdown of JAM1 resulted in decreased Rap1 activity. Lastly, knockdown of Rap1b resulted in diminished ␤1 integrin expression and altered cell morphology analogous to that observed with knockdown of JAM1. Together, these results suggest that JAM1 regulates epithelial cell morphology and ␤1 integrin expression by modulating activity of the small GTPase Rap1.

Junctional Adhesion Molecule A Interacts with Afadin and PDZ-GEF2 to Activate Rap1A, Regulate β1 Integrin Levels, and Enhance Cell Migration

“…In in vitro studies, Rap1 has been reported to regulate integrin levels in epithelial cells (Mandell et al, 2005) as well as integrin activation in leukocytes (Reedquist et al, 2000). To verify these results in vivo, we determined the influence of JAM-A on ␤1 integrin protein levels and Rap1 activation in intestinal epithelial cells derived from JAM-A knockout mice.…”

“…Recently, it was shown that decreased JAM-A expression results in reduced activation of the small GTPase Rap1 (Mandell et al, 2005;Severson et al, 2008). In in vitro studies, Rap1 has been reported to regulate integrin levels in epithelial cells (Mandell et al, 2005) as well as integrin activation in leukocytes (Reedquist et al, 2000).…”

“…In these cells, JAM-A has been reported to play a role in the regulation of epithelial barrier function (Mandell et al, 2005;Laukoetter et al, 2007), endothelial cell migration (Naik et al, 2003a;Bazzoni et al, 2005), angiogenesis (Naik et al, 2003a), platelet aggregation (Babinska et al, 2002), and leukocyte adhesion (Martin-Padura et al, 1998;Del Maschio et al, 1999). Recent reports suggest that JAM-A not only directly decreases paracellular permeability (Mandell et al, 2005;Laukoetter et al, 2007) but also promotes epithelial cell migration (Severson et al, 2008), which is critical for the maintenance of intestinal barrier in health and disease (Lacy, 1988;Fenteany et al, 2000). The relationship between these functions and JAM-A structure remains poorly understood.…”

Junctional adhesion molecule-A is co-expressed with HER2 in breast tumors and acts as a novel regulator of HER2 protein degradation and signaling

“…Of primary interest in our study is the TJ protein JAM-A, which has important functions in cellular adhesive processes including TJ assembly (Liang et al, 2000), cellular polarity (Ebnet et al, 2001), the regulation of cell morphology (Mandell et al, 2005), angiogenesis (Cooke et al, 2006), platelet activation (Babinska et al, 2002) and leukocyte migration (Ostermann et al, 2002). We (McSherry et al, 2009) and others (Murakami et al, 2011) recently identified a significant association between JAM-A over-expression and poor prognosis of breast cancer patients.…”

Neutrophil-Epithelial Interactions

“…65e67 An interesting feature of this family of proteins are the tissue-specific functions that seem to be governed by protein distribution patterns and may account for the wide variety of observed functions attributed to various JAMs. A few of the reported functions include regulation of epithelial barrier, 68,69 endothelial and epithelial cell migration, 70,71 spermatogenesis, 72 angiogenesis, 73 and leukocyte adhesion. 74 In addition, JAMs have been linked to roles in the pathophysiology of several disease processes, such as atherosclerosis, 75,76 cancer metastasis, 77 and IBD.…”