Mécanisme et régulation de l'interaction entre molécules de cadhérines

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Rôle des protéases des entérocytes dans les dernières étapes de digestion et dans le phénomène d'absorption

International audienc

Aspects moléculaires de l’adhérence cellulaire cadhérine-dépendante : les premiers moments de l’interaction

Les cadhérines représentent une des principales familles de molécules d’adhérence cellulaire et jouent un rôle crucial dans la mise en place des tissus au stade embryonnaire et dans leur cohésion à l’âge adulte. Ces glycoprotéines réalisent des interactions de type homophile dépendantes du calcium. Ces dernières années, différentes approches expérimentales ont été utilisées pour résoudre les bases moléculaires de ces interactions. Les données de la littérature sont relativement confuses en ce qui concerne le mode d’interaction de ces molécules. Différents modèles ont été proposés, et le mécanisme d’adhérence est encore soumis à controverses. De récentes approches biophysiques conjuguées aux techniques classiques de biologie nous permettront de progresser vers une meilleure compréhension du mécanisme par lequel les cadhérines régulent l’adhérence cellulaire. La prise en compte des propriétés cinétiques de ces interactions au niveau unimoléculaire apporte ainsi un éclairage nouveau sur ces régulations moléculaires

Activated Rac1 requires gp130 for Stat3 activation, cell proliferation and migration

Rac1 (Rac) is a member of the Rho family of small GTPases which controls cell migration by regulating the organization of actin filaments. Previous results suggested that mutationally activated forms of the Rho GTPases can activate the Signal Transducer and Activator of Transcription-3 (Stat3), but the exact mechanism is a matter of controversy. We recently demonstrated that Stat3 activity of cultured cells increases dramatically following E-cadherin engagement. To better understand this pathway, we now compared Stat3 activity levels in mouse HC11 cells before and after expression of the mutationally activated Rac1 (RacV12), at different cell densities. The results revealed for the first time a dramatic increase in protein levels and activity of both the endogenous Rac and RacV12 with cell density, which was due to inhibition of proteasomal degradation. In addition, RacV12-expressing cells had higher Stat3, tyrosine-705 phosphorylation and activity levels at all densities, indicating that RacV12 is able to activate Stat3. Further examination of the mechanism of Stat3 activation showed that RacV12 expression caused a surge in mRNA of Interleukin-6 (IL6) family cytokines, known potent Stat3 activators. Knockdown of gp130, the common subunit of this family reduced Stat3 activity, indicating that these cytokines may be responsible for the Stat3 activation by RacV12. The upregulation of IL6 family cytokines was required for cell migration and proliferation induced by RacV12, as shown by gp130 knockdown experiments, thus demonstrating that the gp130/Stat3 axis represents an essential effector of activated Rac for the regulation of key cellular functions

Beyond structure, to survival: activation of Stat3 by cadherin engagement

Cells in normal tissues or in tumors have extensive opportunities for adhesion to their neighbors and the importance of cell to cell contact in the study of fundamental cellular processes in beginning to emerge. In this review, we discuss recent evidence of dramatic changes in the activity of an important signal transducer found to be profoundly affected by cell to cell adhesion, the signal trasducerand activator of transcription-3 (Stat3). Direct cadherin engagement, growth of cells to postconfluence, or formation of multicellular aggregates were found to induce a striking increase in the levels of Stat3 activity, Rac1/Cdc42, and members of the IL6 receptor family in different settings. This activation was specific to Stat3, in that the levels of the extracellular signal regulated kinase (Erk1/2)), a signal transducer often coodinately activated with Stat3 by a number of growth factors or oncogenes, remained unaffected by cell density. Density-dependent Stat3 activation may play a key role in survival, and could contribute to the establishment of cell polarity. It is clear that at any given time the total Stat3 activity levels in a cell are the sum of the effects of cell to cell adhesion plus the conventional Stat3 ac tivating factors present

Fast dissociation kinetics between individual E-cadherin fragments revealed by flow chamber analysis

E-cadherin is the predominant adhesion molecule of epithelia. The interaction between extracellular segments of E-cadherin in the membrane of opposing cells is homophilic and calcium dependent. Whereas it is widely accepted that the specificity of the adhesive interaction is localized to the N-terminal domain, the kinetics of the recognition process are unknown. We report the first quantitative data describing the dissociation kinetics of individual E-cadherin interactions. Aggregation assays indicate that the two outermost domains of E-cadherin (E/EC1–2) retain biological activity when chemically immobilized on glass beads. Cadherin fragment trans-interaction was analysed using a flow chamber technique. Transient tethers had first-order kinetics, suggesting a unimolecular interaction. The unstressed lifetime of individual E-cadherin interactions was as brief as 2 s. A fast off rate and the low tensile strength of the E-cadherin bond may be necessary to support the high selectivity and plasticity of epithelial cell interactions

Dynamique de l'interaction homophile de la E-cadhérine (étude biophysique à l'échelle unimoléculaire)

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Cadherin-Cadherin Engagement Promotes Cell Survival via Rac1/Cdc42 and Signal Transducer and Activator of Transcription-3

Signal transducer and activator of transcription-3 (Stat3) is activated by a number of receptor and nonreceptor tyrosine kinases, whereas a constitutively active form of Stat3 alone is sufficient to induce neoplastic transformation. In the present report, we show that Stat3 can also be activated through homophilic interactions by the epithelial (E)-cadherin. Indeed, by plating cells onto surfaces coated with fragments encompassing the two outermost domains of this cadherin, we clearly show that cadherin engagement can activate Stat3, even in the absence of direct cell-to-cell contact. Most importantly, our results also reveal for the first time an unexpected and dramatic surge in total Rac1 and Cdc42 protein levels triggered by cadherin engagement and an increase in Rac1 and Cdc42 activity, which is responsible for the Stat3 stimulation observed. Inhibition of cadherin interactions using a peptide, a soluble cadherin fragment, or genetic ablation induced apoptosis, points to a significant role of this pathway in cell survival signaling, a finding that could also have important therapeutic implications