Myosin 1e is a component of the glomerular slit diaphragm complex that regulates actin reorganization during cell-cell contact formation in podocytes

Abstract

Glomerular visceral epithelial cells, also known as podocytes, are critical to both normal kidney function and the development of kidney disease. Podocyte actin cytoskeleton and their highly specialized cell-cell junctions (also called slit diaphragm complexes) play key roles in controlling glomerular filtration. Myosin 1e (myo1e) is an actin-based molecular motor that is expressed in renal glomeruli. Disruption of the Myo1e gene in mice and humans promotes podocyte injury and results in the loss of the integrity of the glomerular filtration barrier. Here, we have used biochemical and microscopic approaches to determine whether myo1e is associated with the slit diaphragm complexes in glomerular podocytes. Myo1e was consistently enriched in the slit diaphragm fraction during subcellular fractionation of renal glomeruli and colocalized with the slit diaphragm markers in mouse kidney. Live cell imaging studies showed that myo1e was recruited to the newly formed cell-cell junctions in cultured podocytes, where it colocalized with the actin filament cables aligned with the nascent contacts. Myo1e-null podocytes expressing FSGS-associated myo1e mutant (A159P) did not efficiently assemble actin cables along new cell-cell junctions. We have mapped domains in myo1e that were critical for its localization to cell-cell junctions and determined that the SH3 domain of myo1e tail interacts with ZO-1, a component of the slit diaphragm complex and tight junctions. These findings suggest that myo1e represents a component of the slit diaphragm complex and may contribute to regulating junctional integrity in kidney podocytes.

Injury-induced actin cytoskeleton reorganization in podocytes revealed by super-resolution microscopy

“…This suggests that synaptopodin and α-actinin-4 are contained within the thick actin cable in the center of the foot process. We also detected focal clusters of α-actinin-4 (data not shown) and synaptopodin along the apical podocyte plasma membrane ( Figure 2, A and B, arrowheads), suggesting the presence of circumferential actin filaments near the apical plasma membrane, as reported in cultured podocytes (29).…”

Myosin-I molecular motors at a glance

“…Myo1c, Myo1d and Myo1e have been found to contribute to the stability of cell-cell adhesion at adherens junctions, and Myo1e has been found at focal adhesions (Bi et al, 2013;Gupta et al, 2013;Hegan et al, 2015;Oh et al, 2013;Petzoldt et al, 2012;Spéder et al, 2006;Stöffler and Bähler, 1998;Stöffler et al, 1995;Tokuo and Coluccio, 2013). Myo1c localizes to E-cadherin-rich areas in cell-cell contacts between Madin-Darby canine kidney epithelial (MDCK) cells and contributes to the stability of these junctions, although it is unclear how Myo1c functionally establishes and/or maintains this stability (Tokuo and Coluccio, 2013).…”

“…Myo1e localizes to sites of actin polymerization and adhesion in lamellipodia, thereby influencing adhesion formation and actin dynamics through localization of its binding partners (Gupta et al, 2013;Stöffler et al, 1995). Myo1e also localizes to and regulates slit junctions, the highly specialized cell-cell contacts found in the glomerulus of kidney podocyte cells, suggesting why its absence results in kidney disease (Bi et al, 2013;Mele et al, 2011). Overall, it is still unclear whether these myosin-Imediated adhesion functions can be separated from the roles of the same isoforms in the generation and maintenance of membrane and/ or cortical tension.…”

“…Myo1b, Myo1c, and Myo1e are widely expressed and found in most cell types (Krendel et al, 2009;Ruppert et al, 1993;Sherr et al, 1993;Sielski et al, 2014;Skowron et al, 1998;Tyska et al, 2005). Loss of Myo1c or Myo1e is associated with kidney disease (Arif et al, 2011;Bi et al, 2013;Krendel et al, 2009;Mele et al, 2011;Wagner et al, 2005), in addition to deafness associated with Myo1c loss (Batters et al, 2004;Holt et al, 2002) and arteriosclerosis upon loss of Myo1e (Inouye et al, 2012). Mutations in Myo1a are also associated with hearing loss (Donaudy et al, 2003), although Myo1a is most highly expressed in the small intestines and colon where it is associated with colon cancer (Mazzolini et al, 2012(Mazzolini et al, , 2013Skowron et al, 1998).…”

Mechanisms of Glucocorticoid Resistance in Idiopathic Nephrotic Syndrome

“…The N-terminal domain is responsible for actin binding and ATPase activity. The tail domain contains three tail homology (TH) regions that bind acidic phopholipids and prolin-rich proteins[98]. Myo1e-null mice exhibit glomerular filtration defects and, consequently, extensive proteinuria, of which the mechanism may involve changes of podocyte adhesion and cytoskeletal organization rather than loss of other podocyte-related molecules [99,100].…”