Selective alterations in biosynthetic and endocytic protein traffic in Madin-Darby canine kidney epithelial cells expressing mutants of the small GTPase Rac1

Madin-Darby canine kidney (MDCK) cells expressing constitutively active Rac1 (Rac1V12) accumulate a large central aggregate of membranes beneath the apical membrane that contains filamentous actin, Rac1V12, rab11, and the resident apical membrane protein GP-135. To examine the roles of Rac1 in membrane traffic and the formation of this aggregate, we analyzed endocytic and biosynthetic trafficking pathways in MDCK cells expressing Rac1V12 and dominant inactive Rac1 (Rac1N17). Rac1V12 expression decreased the rates of apical and basolateral endocytosis, whereas Rac1N17 expression increased those rates from both membrane domains. Basolateral-to-apical transcytosis of immunoglobulin A (IgA) (a ligand for the polymeric immunoglobulin receptor [pIgR]), apical recycling of pIgR-IgA, and accumulation of newly synthesized GP-135 at the apical plasma membrane were all decreased in cells expressing Rac1V12. These effects of Rac1V12 on trafficking pathways to the apical membrane were the result of the delivery and trapping of these proteins in the central aggregate. In contrast to abnormalities in apical trafficking events, basolateral recycling of transferrin, degradation of EGF internalized from the basolateral membrane, and delivery of newly synthesized pIgR from the Golgi to the basolateral membrane were all relatively unaffected by Rac1V12 expression. Rac1N17 expression had little or no effect on these postendocytic or biosynthetic trafficking pathways. These results show that in polarized MDCK cells activated Rac1 may regulate the rate of endocytosis from both membrane domains and that expression of dominant active Rac1V12 specifically alters postendocytic and biosynthetic membrane traffic directed to the apical, but not the basolateral, membrane.     

Beta1-integrin orients epithelial polarity via Rac1 and laminin

Epithelial cells polarize and orient polarity in response to cell-cell and cell-matrix adhesion. Although there has been much recent progress in understanding the general polarizing machinery of epithelia, it is largely unclear how this machinery is controlled by the extracellular environment. To explore the signals from cell-matrix interactions that control orientation of cell polarity, we have used three-dimensional culture systems in which Madin-Darby canine kidney (MDCK) cells form polarized, lumen-containing structures. We show that interaction of collagen I with apical beta1-integrins after collagen overlay of a polarized MDCK monolayer induces activation of Rac1, which is required for collagen overlay-induced tubulocyst formation. Cysts, comprised of a monolayer enclosing a central lumen, form after embedding single cells in collagen. In those cultures, addition of a beta1-integrin function-blocking antibody to the collagen matrix gives rise to cysts that have defects in the organization of laminin into the basement membrane and have inverted polarity. Normal polarity is restored by either expression of activated Rac1, or the inclusion of excess laminin-1 (LN-1). Together, our results suggest a signaling pathway in which the activation of beta1-integrins orients the apical pole of polarized cysts via a mechanism that requires Rac1 activation and laminin organization into the basement membrane.     

Cdc42-dependent modulation of tight junctions and membrane protein traffic in polarized Madin-Darby canine kidney cells

Polarized epithelial cells maintain the asymmetric composition of their apical and basolateral membrane domains by at least two different processes. These include the regulated trafficking of macromolecules from the biosynthetic and endocytic pathway to the appropriate membrane domain and the ability of the tight junction to prevent free mixing of membrane domain-specific proteins and lipids. Cdc42, a Rho family GTPase, is known to govern cellular polarity and membrane traffic in several cell types. We examined whether this protein regulated tight junction function in Madin-Darby canine kidney cells and pathways that direct proteins to the apical and basolateral surface of these cells. We used Madin-Darby canine kidney cells that expressed dominant-active or dominant-negative mutants of Cdc42 under the control of a tetracycline-repressible system. Here we report that expression of dominant-active Cdc42V12 or dominant-negative Cdc42N17 altered tight junction function. Expression of Cdc42V12 slowed endocytic and biosynthetic traffic, and expression of Cdc42N17 slowed apical endocytosis and basolateral to apical transcytosis but stimulated biosynthetic traffic. These results indicate that Cdc42 may modulate multiple cellular pathways required for the maintenance of epithelial cell polarity.     

Rho GTPase activity modulates Pseudomonas aeruginosa internalization by epithelial cells

The Gram-negative pathogen Pseudomonas aeruginosa invades epithelial cells in vivo and in vitro . We have examined the pathway(s) by which epithelial cells internalize P. aeruginosa strain PA103 using Madin-Darby canine kidney (MDCK) cells. We have recently demonstrated that P. aeruginosa internalization occurs by an actin-dependent Toxin B-inhibited pathway which becomes downregulated as epithelial cells become polarized, suggesting that one or more of the Rho family GTPases is involved in bacterial internalization. Here, we demonstrate that activation of the Rho family GTPases by cytotoxic necrotizing factor 1 (CNF-1) stimulates P. aeruginosa internalization. Examination of the roles of the individual Rho family GTPases in internalization shows that expression of a constitutively active allele of RhoA (RhoAV14), but not of constitutively active Rac1 (Rac1V12) or Cdc42 (Cdc42V12), is sufficient to increase uptake of PA103 pscJ . This relative increase persists when bacterial infection is established at the basolateral surface of polarized cells, suggesting that the effect of RhoAV14 is not simply due to its known ability to disrupt tight junction integrity in polarized cells. RhoAV14-mediated stimulation of bacterial uptake is actin dependent as it is abrogated by exposure to latrunculin A. We also find that endogenous Rho GTP levels in epithelial cells are increased by infection with an internalized strain of P. aeruginosa; conversely, a poorly internalized isogenic strain expressing the bacterial anti-internalization protein ExoT causes decreased Rho GTP levels. Experimental inhibition of Rho, either by expressing dominant negative RhoAN19 or by inhibiting native Rho using a membrane permeable fusion construct of a Rho-specific inhibitor, C3 ADP-ribosyltransferase, does not inhibit PA103 pscJ internalization in MDCK or HeLa cells. Models consistent with these data are presented.     

Rac1 orientates epithelial apical polarity through effects on basolateral laminin assembly

Cellular polarization involves the generation of asymmetry along an intracellular axis. In a multicellular tissue, the asymmetry of individual cells must conform to the overlying architecture of the tissue. However, the mechanisms that couple cellular polarization to tissue morphogenesis are poorly understood. Here, we report that orientation of apical polarity in developing Madin-Darby canine kidney (MDCK) epithelial cysts requires the small GTPase Rac1 and the basement membrane component laminin. Dominant-negative Rac1 alters the supramolecular assembly of endogenous MDCK laminin and causes a striking inversion of apical polarity. Exogenous laminin is recruited to the surface of these cysts and rescues apical polarity. These findings implicate Rac1-mediated laminin assembly in apical pole orientation. By linking apical orientation to generation of the basement membrane, epithelial cells ensure the coordination of polarity with tissue architecture.     

De novo formation of focal complex-like structures in host cells by invading Streptococci

Group A streptococcus (GAS) induces its own entry into eukaryotic cells in vitro and in vivo. Fibronectin (Fn) bound to protein F1, a GAS surface protein, acts as a bridge connecting the bacterium to host cell integrins. This triggers clustering of integrins, which acquire a polar pattern of distribution similar to that of protein F1 on the GAS surface. A unique and transient adhesion complex is formed at the site of GAS entry, which does not contain alpha-actinin. Vinculin is recruited to the site of GAS entry but is not required for uptake. The invading GAS recruits focal adhesion kinase (FAK), which is required for uptake and is tyrosine phosphorylated. The Src kinases, Src, Yes and Fyn, enhance the efficiency of GAS uptake but are not absolutely required for GAS entry. In addition, Rac and Cdc42, but not Rho, are required for the entry process. We suggest a model in which integrin engagement by Fn-occupied protein F1 triggers two independent signalling pathways. One is initiated by FAK recruitment and tyrosine phosphorylation, whereas the other is initiated by the recruitment and activation of Rac. The two pathways subsequently converge to trigger actin rearrangement leading to bacterial uptake.     

Vanadate increases oxygen affinity and affects enzyme activities and membrane properties of erythrocytes

Incubation of blood with vanadate markedly increases the affinity of hemoglobin for oxygen, decreases the deformability of erythrocytes, reduces their osmotic fragility and alters their morphology, determining the appearance of equinocytic forms. Since vanadate is easily taken up by the erythrocytes and binds hemoglobin, these effects might result from interactions of vanadate with hemoglobin and with membrane proteins at the glycerate-2, 3-P₂ and/or ATP binding site. In addition, vanadate inhibits phosphoglycerate mutase, phosphoglucomutase and adenylate-kinase activities from hemolysates, suggesting a possible inhibitory effect on erythrocyte metabolism     

Safety,Effectiveness and Acceptability of the PrePex Device for Adult Male Circumcision in Kenya

Objective

To assess the safety, effectiveness and acceptability of the PrePex device for adult medical male circumcision (MMC) in routine service delivery in Kenya.

Methods

We enrolled 427 men ages 18–49 at one fixed and two outreach clinics. Procedures were performed by trained clinical officers and nurses. The first 50 enrollees were scheduled for six follow-up visits, and remaining men were followed at Days 7 and 42. We recorded adverse events (AEs) and time to complete healing, and interviewed men about acceptability and pain.

Results

Placement and removal procedures each averaged between 3 and 4 minutes. Self-reported pain was minimal during placement but was fleetingly intense during removal. The rate of moderate/severe AEs was 5.9% overall (95% confidence interval [CI] 3.8%–8.5%), all of which resolved without sequelae. AEs included 5 device displacements, 2 spontaneous foreskin detachments, and 9 cases of insufficient foreskin removal. Surgical completion of MMC was required for 9 men (2.1%). Among the closely monitored first 50 participants, the probability of complete healing by Day 42 was 0.44 (95% CI 0.30–0.58), and 0.90 by Day 56. A large majority of men was favorable about their MMC procedure and would recommend PrePex to friends and family.

Conclusions

The PrePex device was effective for MMC in Kenya, and well-accepted. The AE rate was higher than reported for surgical procedures there, or in previous PrePex studies. Healing time is longer than following surgical circumcision. Provider experience and clearer counseling on post-placement and post-removal care should lead to lower AE rates.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT01711411","term_id":"NCT01711411"}}NCT01711411     

The exocyst protein Sec10 interacts with Polycystin-2 and knockdown causes PKD-phenotypes

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by formation of renal cysts that destroy the kidney. Mutations in PKD1 and PKD2, encoding polycystins-1 and -2, cause ADPKD. Polycystins are thought to function in primary cilia, but it is not well understood how these and other proteins are targeted to cilia. Here, we provide the first genetic and biochemical link between polycystins and the exocyst, a highly-conserved eight-protein membrane trafficking complex. We show that knockdown of exocyst component Sec10 yields cellular phenotypes associated with ADPKD, including loss of flow-generated calcium increases, hyperproliferation, and abnormal activation of MAPK. Sec10 knockdown in zebrafish phenocopies many aspects of polycystin-2 knockdown-including curly tail up, left-right patterning defects, glomerular expansion, and MAPK activation-suggesting that the exocyst is required for pkd2 function in vivo. We observe a synergistic genetic interaction between zebrafish sec10 and pkd2 for many of these cilia-related phenotypes. Importantly, we demonstrate a biochemical interaction between Sec10 and the ciliary proteins polycystin-2, IFT88, and IFT20 and co-localization of the exocyst and polycystin-2 at the primary cilium. Our work supports a model in which the exocyst is required for the ciliary localization of polycystin-2, thus allowing for polycystin-2 function in cellular processes.