NADPH oxidase 1 controls the persistence of directed cell migration by a Rho-dependent switch of alpha2/alpha3 integrins.

NADPH oxidase 1 (Nox1) is expressed mainly in colon epithelial cells and produces superoxide ions as a primary function. We showed that Nox1 knockdown inhibits directional persistence of migration on collagen I. This paper dissects the mechanism by which Nox1 affects the direction of colonic epithelial cell migration in a two-dimensional model. Transient activation of Nox1 during cell spreading on collagen 1 temporarily inactivated RhoA and led to efficient exportation of alpha2beta1 integrin to the cell surface, which supported persistent directed migration. Nox1 knockdown led to a loss of directional migration which takes place through a RhoA-dependent alpha2/alpha3 integrin switch. Transient RhoA overactivation upon Nox1 inhibition led to transient cytoskeletal reorganization and increased cell-matrix contact associated with a stable increase in alpha3 integrin cell surface expression. Blocking of alpha3 integrin completely reversed the loss of directional persistence of migration. In this model, Nox1 would represent a switch between random and directional migration through RhoA-dependent integrin cell surface expression modulation.

alphavbeta5/beta6 integrin suppression leads to a stimulation of alpha2beta1 dependent cell migration resistant to PI3K/Akt inhibition.

Crosstalk between integrins is involved in the regulation of various cell functions including cell migration. Here we identify the interplay between the integrins alphavbeta5/beta6 and alpha2beta1 during cell migration toward type I collagen. Human colon cancer cell lines HT29-D4 and SW480 were used as cell models. To improve our understanding of the consequences of alphavbeta5/beta6 function on alpha2beta1, we decreased the expression of alphav integrins by either siRNA or lysosomal targeting strategies or inhibited their function using, as antagonists, blocking antibodies or disintegrins. In all cases, we observed a greatly enhanced alpha2beta1 integrin-dependent cell migration associated with focal adhesion rearrangements and increased outside-in signaling as demonstrated by elevated phosphorylation of focal adhesion kinase and MAPKinase (ERK1 and ERK2). The alphavbeta5/beta6-dependent limitation of alpha2beta1 function could be overridden by TS2/16, an activating anti-beta1 antibody. Interestingly, compared to control cells, the pharmacological inhibition of PI3Kinase or the siRNA-mediated knockdown of AKT had little effect on the high alpha2beta1-mediated cell migration observed in the absence of alphav integrins or following activation of alpha2beta1 integrins by the TS2/16. These results suggest that integrins alphavbeta5/beta6 repress alpha2beta1 possibly by interfering with their activation process and thereby modify the cell signaling regulation of alpha2beta1-mediated migration.

Concomitant cell growth and differentiation are dependent on erbB1 and integrin activation in an autonomously surviving colon adenocarcinoma: involvement of autocrine amphiregulin secretion.

In normal colon epithelium, cell proliferation is followed by cell differentiation. The purpose of this work was to investigate, in the HT29-D4 colon adenocarcinoma cell line, the occurrence of a temporal sequence of changes in cell proliferation and differentiation, the role of autocrine EGF family ligands and to determine which transduction pathway(s) are involved in these processes. In a medium lacking both growth factor and serum, HT29-D4 cells secreted amphiregulin (AR), which was shown to be strongly involved in cell adhesion, growth and differentiation. In the main, integrins alpha2beta1 and alphavbeta6 intervened in these processes. Using tyrphostins, it was demonstrated that AR involvement was mediated through the ErbB1/ERK1,2 and ErbB1/FAK pathways. These signalling molecules were directly involved in pRb inhibition and, thus, in cyclin A expression. Concomitantly, colon differentiation markers were also expressed. Furthermore, terminal cell maturation resulted in a colon absorptive cell with strong polarisation, the growth of which was inhibited by tyrphostin and an ERK1,2 inhibitor. It was concluded that in a colon adenocarcinoma, cell proliferation and differentiation can occur concomitantly and that these deregulated processes are controlled by autocrine secretion through the ErbB1/ERK1,2 and FAK pathways.

HIV-1 Tat protein enhances microtubule polymerization.

BACKGROUND: HIV infection and progression to AIDS is characterized by the depletion of T cells, which could be due, in part, to apoptosis mediated by the extra-cellular HIV-encoded Tat protein as a consequence of Tat binding to tubulin. Microtubules are tubulin polymers that are essential for cell structure and division. Molecules that target microtubules induce apoptosis and are potent anti-cancer drugs. We studied the effect on tubulin polymerization of three Tat variants: Tat HxB2 and Tat Eli from patients who are rapid progressors (RP) and Tat Oyi from highly exposed but persistently seronegative (HEPS) patients. We compared the effect on tubulin polymerization of these Tat variants and peptides corresponding to different parts of the Tat sequence, with paclitaxel, an anti-cancer drug that targets microtubules. RESULTS: We show that Tat, and specifically, residues 38-72, directly enhance tubulin polymerization. We demonstrate that Tat could also directly trigger the mitochondrial pathway to induce T cell apoptosis, as shown in vitro by the release of cytochrome c from isolated mitochondria. CONCLUSIONS: These results show that Tat directly acts on microtubule polymerization and provide insights into the mechanism of T cell apoptosis mediated by extra-cellular Tat.