The CD34-Related Molecule Podocalyxin Is a Potent Inducer of Microvillus Formation

Abstract

BackgroundPodocalyxin is a CD34-related transmembrane protein involved in hematopoietic cell homing, kidney morphogenesis, breast cancer progression, and epithelial cell polarization. Although this sialomucin has been shown to block cell adhesion, the mechanisms involved remain enigmatic. It has, however, been postulated that the adaptor proteins NHERF-1 and 2 could regulate apical targeting of Podocalyxin by linking it to the actin cytoskeleton.Principal FindingsHere, in contrast, we find that full-length Podocalyxin acts to recruit NHERF-1 to the apical domain. Moreover, we show that ectopic expression of Podocalyxin in epithelial cells leads to microvillus formation along an expanded apical domain that extends laterally to the junctional complexes. Removal of the C-terminal PDZ-binding domain of Podocalyxin abolishes NHERF-1 recruitment but, surprisingly, has no effect on the formation of microvilli. Instead, we find that the extracellular domain and transmembrane region of Podocalyxin are sufficient to direct recruitment of filamentous actin and ezrin to the plasma membrane and induce microvillus formation.Conclusions/SignificanceOur data suggest that this single molecule can modulate NHERF localization and, independently, act as a key orchestrator of apical cell morphology, thereby lending mechanistic insights into its multiple roles as a polarity regulator, tumor progression marker, and anti-adhesin.

The periciliary ring in polarized epithelial cells is a hot spot for delivery of the apical protein gp135

“…We never observed delivery of Crumbs3a to the periciliary region. Crumbs3a forms stable attachments with a submembranous anchoring complex that includes the proteins PALS and PATJ (Makarova et al, 2003), and transmembrane gp135 has been shown to interact directly with cytoskeletal components (Ojakian and Schwimmer, 1988;Li et al, 2002;Nielsen et al, 2007;Yu et al, 2007;Francis et al, 2011). Thus, we next wished to examine the behavior of a membrane protein that cannot participate in such interactions.…”

Podocalyxin in the Diagnosis and Treatment of Cancer

“…1); by western blotting and immunofluorescence confocal microscopy, expression of PC is low or not detected, respectively (Nielsen et al, 2007;Sizemore et al, 2007;Somasiri et al, 2004). In order to study the molecular function of PC in breast epithelial cells, others and we have ectopically expressed full-length PC and a series of structural mutants in MCF7 (Fig.…”

“…Overexpression of full-length PC (FL) in MCF7 results in apical bulging of monolayers, reduced transepithelial resistance (i.e., disrupted cell junctions), delamination and shedding of cells from monolayers in vitro (Nielsen et al, 2007;Somasiri et al, 2004). Strikingly, expression of PC in MCF7 (and MDCK) potently induces formation of apical microvilli.…”

“…As we anticipated, full-length, exogenously expressed PC recruits NHERF-1, ezrin and Factin to apical membrane domains and forms microvilli in MCF7 cells. However, surprisingly, the intracellular domain of PC is dispensable for the formation of microvilli since the transmembrane-anchored extracellular domain alone (CT) is sufficient to drive morphogenesis and the recruitment of ezrin and F-actin to apical membranes and microvilli in MCF7 (Nielsen et al, 2007). Notably, NHERF-1 is not recruited to apical domains or microvilli in the absence of PC's C-terminal DTHL domain (DTHL or CT).…”

Podocalyxin-Targeting Comparative Glycan Profiling Reveals Difference between Human Embryonic Stem Cells and Embryonal Carcinoma Cells

“…Podocalyxin is a member of the CD-34-related family of sialomucins [3][4][5][6][7][8]. Podocalyxin was originally cloned from the human kidney as a component of the podocyte cell glycocalyx, while it was also identified on vascular endothelium and hematopoietic cells [3,4,[9][10][11].…”