Doing cell biology in embryos: regulated membrane traffic and its implications for cadherin biology

Regulated trafficking of cadherin adhesion molecules is often invoked as a mechanism to generate dynamic adhesive cell-cell contacts for tissue modeling and morphogenesis. The past 2-3 years have seen several important papers that tackle the cell biology of cadherin trafficking in organismal systems to provide new insights into both mechanism and morphogenetic impact

Drosophila TNF modulates tissue tension in the embryo to facilitate macrophage invasive migration

Migrating cells penetrate tissue barriers during development, inflammatory responses, and tumor metastasis. We study if migration in vivo in such three-dimensionally confined environments requires changes in the mechanical properties of the surrounding cells using embryonic Drosophila melanogaster hemocytes, also called macrophages, as a model. We find that macrophage invasion into the germband through transient separation of the apposing ectoderm and mesoderm requires cell deformations and reductions in apical tension in the ectoderm. Interestingly, the genetic pathway governing these mechanical shifts acts downstream of the only known tumor necrosis factor superfamily member in Drosophila, Eiger, and its receptor, Grindelwald. Eiger-Grindelwald signaling reduces levels of active Myosin in the germband ectodermal cortex through the localization of a Crumbs complex component, Patj (Pals-1-associated tight junction protein). We therefore elucidate a distinct molecular pathway that controls tissue tension and demonstrate the importance of such regulation for invasive migration in vivo

A conserved major facilitator superfamily member orchestrates a subset of O-glycosylation to aid macrophage tissue invasion

Aberrant display of the truncated core1 O-glycan T-antigen is a common feature of human cancer cells that correlates with metastasis. Here we show that T-antigen in Drosophila melanogaster macrophages is involved in their developmentally programmed tissue invasion. Higher macrophage T-antigen levels require an atypical major facilitator superfamily (MFS) member that we named Minerva which enables macrophage dissemination and invasion. We characterize for the first time the T and Tn glycoform O-glycoproteome of the Drosophila melanogaster embryo, and determine that Minerva increases the presence of T-antigen on proteins in pathways previously linked to cancer, most strongly on the sulfhydryl oxidase Qsox1 which we show is required for macrophage tissue entry. Minerva’s vertebrate ortholog, MFSD1, rescues the minerva mutant’s migration and T-antigen glycosylation defects. We thus identify a key conserved regulator that orchestrates O-glycosylation on a protein subset to activate a program governing migration steps important for both development and cancer metastasis

Coordinating Rho and Rac: the regulation of Rho GTPase signaling and cadherin junctions

Cadherin-based cell-cell adhesions are dynamic structures that mediate tissue organization and morphogenesis. They link cells together, mediate cell-cell recognition, and influence cell shape, motility, proliferation, and differentiation. At the cellular level, moperation of classical cadherin adhesion systems is coordinated with cytoskeletal dynamics, contractility, and membrane trafficking to support productive interactions. Cadherin-based cell signaling is critical for the coordination of these many cellular processes. Here, we discuss the role of Rho family GTPases in cadherin signaling. We focus on understanding the pathways that utilize Rae and Rho in junctional biology, aiming to identify the mechanisms of upstream regulation and define how the effects of these activated GTPases might regulate the actin cytoskeleton to modulate the cellular processes involved in cadherin-based cell-cell interactions

Pentoxifylline modulates cell surface integrin expression and integrin mediated adhesion of B16F10 cells to extracellular matrix components

Our previous studies demonstrated that Pentoxifylline (PTX), a phosphodiesterase inhibitor could inhibit the lung homing of B16-F10 melanoma cells in C57BL/6 mice. In this study we have looked at the effect of PTX on cell surface integrin expression and integrin mediated adhesion of B16-F10 melanoma cells. B16F10 cells treated with PTX when injected through the tail vein of mice showed a 75% reduction in pulmonary nodules as compared to control untreated cells. PTX brought about a significant reduction in the integrin mediated adhesion of F10 cells to Fibronectin and Vitronectin (58.75% + 3.4 S.E and 60% + 1.7 S.E respectively if control was considered as 100 %). This inhibition in adhesion was evident upto 4 hours only and treatment for 24 hours brought about an increase in adhesion (135.5 % + 0.5 S.E). Flow cytometric analysis showed higher surface expressions of αv, α5 and αIIb integrin subunits in B16-F10 as compared to the low metastatic cell line B16-F1 suggesting a role for these integrins in determining the metastatic potential. PTX brought about a significant decrease in the cell surface expression of α5, αIIb and β1integrin subunits but not that of the αv subunit on B16-F10 cells. PTX also brought about a reduction in the total cellular protein levels of β1 and αv integrin subunits. Various isoforms of Protein Kinase C (PKC) has been shown to regulate integrin expression, localization and activity. Hence we looked at the effect of PTX on total cellular PKC activity. PTX brought about a significant reduction in total cellular PKC activity (82.66 + 0.593). Collectively our results indicate that the antimetastatic action of PTX is mediated, at least in part through its effects on adhesion and the surface expression of specific integrin receptors

Antimetastatic action of Pentoxifylline, a methyl xanthine derivative, through its effect on PKC Mediated integrin transport in B16F10 melanoma cells

Integrins are adhesion molecules known to regulate cellular processes like adhesion, migration and proliferation. At the same time role of integrin in progress of cancer metastasis is well established, increased integrin expression is reported to be linked to high metastasis potential of cells. Pentoxifylline a methyl xanthine derivative is a potent antimetastatic agent. Studies on the mechanism of inhibition of lung homing of B16F10 melanoma cells by PTX shows that it can inhibit cell- Extracellular Matrix adhesion, cell surface integrin expression as well as Protein kinase C activity. Previous study from our laboratory have shown PTX treatment can selectively inhibit the cell surface expression of α5 integrin in B16F10 cells without affecting its total cellular protein levels. Numerous studies have documented that differences in surface expression and distribution of integrins affects metastasis. The purpose of present study is to observe the effect of PTX on cellular distribution/ redistribution of integrins and to study the underlying molecular mechanism of PTX action

Drosophila immune cell migration and adhesion during embryonic development and larval immune responses

The majority of immune cells in Drosophila melanogaster are plasmatocytes; they carry out similar functions to vertebrate macrophages, influencing development as well as protecting against infection and cancer. Plasmatocytes, sometimes referred to with the broader term of hemocytes, migrate widely during embryonic development and cycle in the larvae between sessile and circulating positions. Here we discuss the similarities of plasmatocyte developmental migration and its functions to that of vertebrate macrophages, considering the recent controversy regarding the functions of Drosophila PDGF/VEGF related ligands. We also examine recent findings on the significance of adhesion for plasmatocyte migration in the embryo, as well as proliferation, trans-differentiation, and tumor responses in the larva. We spotlight parallels throughout to vertebrate immune responses

Resveratrol inhibits type II phosphatidylinositol 4-kinase: a key component in pathways of phosphoinositide turn over

Resveratrol has anti-inflammatory, cardio protective and cancer chemopreventive properties. The molecular targets for resveratrol in early signaling cascades are not well understood. Resveratrol inhibits type II PtdIns 4-kinase but not PtdIns 3-kinase activity in vitro. Resveratrol directly binds to the enzyme with a Kd of 7.2 μM. Kinetic studies show that resveratrol competes with PtdIns binding. Inhibition of PtdIns 4-kinase activity by resveratrol/phenylarsine oxide reduces Jurkat cell adhesion to matrigel/fibronectin coated surfaces, suggesting a role for type II PtdIns 4-kinase in lymphocyte infiltration to the sites of inflammation.© Elsevie

Resveratrol inhibits type II phosphatidylinositol 4-kinase : a key component in pathways of phosphoinositide turn over

Resveratrol has anti-inflammatory, cardio protective and cancer chemopreventive properties. The molecular targets for resveratrol in early signaling cascades are not well understood. Resveratrol inhibits type II PtdIns 4-kinase but not PtdIns 3-kinase activity in vitro. Resveratrol directly binds to the enzyme with a Kd of 7.2 μM. Kinetic studies show that resveratrol competes with PtdIns binding. Inhibition of PtdIns 4-kinase activity by resveratrol/phenylarsine oxide reduces Jurkat cell adhesion to matrigel/fibronectin coated surfaces, suggesting a role for type II PtdIns 4-kinase in lymphocyte infiltration to the sites of inflammation

Type II phosphatidylinositol 4-kinase β is an integral signaling component of early T cell activation mechanisms

The early signaling events in T cell activation through CD3 receptor include a rapid change in intra cellular free calcium concentration and reorganization of actin cytoskeleton. Phosphatidylinositol 4-kinases (PtdIns 4-kinases) are implicated as key components in these early signaling events. The role of type II PtdIns 4-kinase β in CD3 receptor signaling was investigated with the help of short hairpin RNA sequences. Cross-linking of CD3 receptors on Jurkat T Cells with monoclonal antibodies showed an early increase in type II PtdIns 4-kinase activity and co-localization of type II PtdIns 4-kinase β with CD3 ζ. Transfection of Jurkat T Cells with shRNAs inhibited CD3 receptor mediated type II PtdIns 4-kinase activation with a concomitant reduction in intra cellular calcium release, suggesting a role for type II PtdIns 4-kinase β in CD3 receptor signal transduction. Knock-down of type II PtdIns 4-kinase β with shRNAs also correlated with a decrease in PtdIns 4-kinase activity in cytoskeleton fractions and reduced adhesion to matrigel surfaces. These results indicate that type II PtdIns 4-kinase β is a key component in early T cell activation signaling cascades