The Rho family of small guanosine triphosphatases (Rho GTPases: RhoA, Cdc42, and Rac1) regulates many aspects of cell behavior, including actin dynamics and cell migration. The generation of calcium ion (Ca2+) microdomains is critical in promoting cell migration because they control the localized activity of Rho GTPases. We identified receptor-activated TRPC5 and TRPC6 (transient receptor potential canonical type 5 and 6) channels as antagonistic regulators of actin remodeling and cell motility in fibroblasts and kidney podocytes. We show that TRPC5 is in a molecular complex with Rac1, whereas TRPC6 is in a molecular complex with RhoA. TRPC5-mediated Ca2+ influx induces Rac1 activation, thereby promoting cell migration, whereas TRPC6-mediated Ca2+ influx increases RhoA activity, thereby inhibiting cell migration. Our data unveil antagonistic Ca2+ influx pathways as a conserved signaling mechanism for the integrated regulation of cell migration.

The genome of the cnidarian Nematostella vectensis (starlet sea anemone) provides a molecular genetic view into the first nervous systems, which appeared in a late common ancestor of cnidarians and bilaterians. Nematostella has a surprisingly large and diverse set of neuronal signaling genes including paralogs of most neuronal signaling molecules found in higher metazoans. Several ion channel gene families are highly expanded in the sea anemone, including three subfamilies of the Shaker K+ channel gene family: Shaker (Kv1), Shaw (Kv3) and Shal (Kv4). In order to better understand the physiological significance of these voltage-gated K+ channel expansions, we analyzed the function of 18 members of the 20 gene Shaker subfamily in Nematostella. Six of the Nematostella Shaker genes express functional homotetrameric K+ channels in vitro. These include functional orthologs of bilaterian Shakers and channels with an unusually high threshold for voltage activation. We identified 11 Nematostella Shaker genes with a distinct “silent” or “regulatory” phenotype; these encode subunits that function only in heteromeric channels and serve to further diversify Nematostella Shaker channel gating properties. Subunits with the regulatory phenotype have not previously been found in the Shaker subfamily, but have evolved independently in the Shab (Kv2) family in vertebrates and the Shal family in a cnidarian. Phylogenetic analysis indicates that regulatory subunits were present in ancestral cnidarians, but have continued to diversity at a high rate after the split between anthozoans and hydrozoans. Comparison of Shaker family gene complements from diverse metazoan species reveals frequent, large scale duplication has produced highly unique sets of Shaker channels in the major metazoan lineages.

Transmembrane mucins are highly -glycosylated glycoproteins that coat the apical glycocalyx on mucosal surfaces and represent the first line of cellular defense against infection and injury. Relatively low levels of-glycans are found on transmembrane mucins, and their structure and function remain poorly characterized. We previously reported that carbohydrate-dependent interactions of transmembrane mucins with galectin-3 contribute to maintenance of the epithelial barrier at the ocular surface. Now, using MALDI-TOF mass spectrometry, we report that transmembrane mucin -glycans in differentiated human corneal epithelial cells contain primarily complex-type structures with-acetyllactosamine, a preferred galectin ligand. In -glycosylation inhibition experiments, we find that treatment with tunicamycin and siRNA-mediated knockdown of the Golgi-acetylglucosaminyltransferase I gene () induce partial loss of both total and cell-surface levels of the largest mucin, MUC16, and a concomitant reduction in glycocalyx barrier function. Moreover, we identified a distinct role for -glycans in promoting MUC16's binding affinity toward galectin-3 and in causing retention of the lectin on the epithelial cell surface. Taken together, these studies define a role for-linked oligosaccharides in supporting the stability and function of transmembrane mucins on mucosal surfaces.