RESUMEN
Stimulation of cultured epithelial cells with scatter factor/hepatocyte growth factor (HGF) results in individual cells detaching and assuming a migratory and invasive phenotype. Epithelial scattering recapitulates cancer progression and studies have implicated HGF signaling as a driver of cancer metastasis. Inhibitors of HGF signaling have been proposed to act as anti-cancer agents. We previously screened a small molecule library for compounds that block HGF-induced epithelial scattering. Most hits identified in this screen exhibit anti-mitotic properties. Here we assess the biological mechanism of a compound that blocks HGF-induced scattering with limited anti-mitotic activity. Analogs of this compound have one of two distinct activities: inhibiting either cell migration or cell proliferation with cell cycle arrest in G2/M. Each activity bears unique structure-activity relationships. The mechanism of action of anti-mitotic compounds is by inhibition of microtubule polymerization; these compounds entropically and enthalpically bind tubulin in the colchicine binding site, generating a conformational change in the tubulin dimer.
Asunto(s)
Amidas/farmacología , Antineoplásicos/farmacología , Células Epiteliales/efectos de los fármacos , Factor de Crecimiento de Hepatocito/antagonistas & inhibidores , Piridinas/farmacología , Pirimidinas/farmacología , Amidas/síntesis química , Amidas/química , Antineoplásicos/síntesis química , Antineoplásicos/química , Línea Celular Tumoral , Movimiento Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Ensayos de Selección de Medicamentos Antitumorales , Células Epiteliales/metabolismo , Factor de Crecimiento de Hepatocito/metabolismo , Humanos , Células MCF-7 , Estructura Molecular , Piridinas/síntesis química , Piridinas/química , Pirimidinas/síntesis química , Pirimidinas/química , Relación Estructura-ActividadRESUMEN
Epithelial scattering occurs when cells disassemble cell-cell junctions, allowing individual epithelial cells to act in a solitary manner. Epithelial scattering occurs frequently in development, where it accompanies epithelial-mesenchymal transitions and is required for individual cells to migrate and invade. While migration and invasion have received extensive research focus, how cell-cell junctions are detached remains poorly understood. An open debate has been whether disruption of cell-cell interactions occurs by remodeling of cell-cell adhesions, increased traction forces through cell substrate adhesions, or some combination of both processes. Here we seek to examine how changes in adhesion and contractility are coupled to drive detachment of individual epithelial cells during hepatocyte growth factor (HGF)/scatter factor-induced EMT. We find that HGF signaling does not alter the strength of cell-cell adhesion between cells in suspension, suggesting that changes in cell-cell adhesion strength might not accompany epithelial scattering. Instead, cell-substrate adhesion seems to play a bigger role, as cell-substrate adhesions are stronger in cells treated with HGF and since rapid scattering in cells treated with HGF and TGFß is associated with a dramatic increase in focal adhesions. Increases in the pliability of the substratum, reducing cells ability to generate traction on the substrate, alter cells׳ ability to scatter. Further consistent with changes in substrate adhesion being required for cell-cell detachment during EMT, scattering is impaired in cells expressing both active and inactive RhoA mutants, though in different ways. In addition to its roles in driving assembly of both stress fibers and focal adhesions, RhoA also generates myosin-based contractility in cells. We therefore sought to examine how RhoA-dependent contractility contributes to cell-cell detachment. Inhibition of Rho kinase or myosin II induces the same effect on cells, namely an inhibition of cell scattering following HGF treatment. Interestingly, restoration of myosin-based contractility in blebbistatin-treated cells results in cell scattering, including global actin rearrangements. Scattering is reminiscent of HGF-induced epithelial scattering without a concomitant increase in cell migration or decrease in adhesion strength. This scattering is dependent on RhoA, as blebbistatin-induced scattering is reduced in cells expressing dominant-negative RhoA mutants. This suggests that induction of myosin-based cellular contractility may be sufficient for cell-cell detachment during epithelial scattering.
Asunto(s)
Movimiento Celular/fisiología , Células Epiteliales/fisiología , Actinas/metabolismo , Animales , Adhesión Celular/fisiología , Línea Celular , Perros , Células Epiteliales/efectos de los fármacos , Transición Epitelial-Mesenquimal/fisiología , Adhesiones Focales/fisiología , Factor de Crecimiento de Hepatocito/fisiología , Compuestos Heterocíclicos de 4 o más Anillos/farmacología , Uniones Intercelulares/fisiología , Mutación , Miosina Tipo II/metabolismo , Transducción de Señal , Fibras de Estrés/fisiología , Proteína de Unión al GTP rhoA/genética , Proteína de Unión al GTP rhoA/metabolismoRESUMEN
Cell-cell junction remodeling is associated with dramatic actin reorganizations. Several actin regulatory systems have been implicated in actin remodeling events as cell-cell contacts are assembled and disassembled, including zyxin/LPP-VASP complexes. These complexes facilitate strong cell-cell adhesion by maintaining actin-membrane connections. It has been proposed that zyxin and LPP localize to cell-cell junctions via a well-defined interaction with alpha-actinin. This was recently confirmed for LPP, but zyxin localization at cell-cell contacts occurs independently of alpha-actinin binding. Here we seek to map the zyxin sequence responsible for localization to cell-cell contacts and identify the protein that docks zyxin at this cellular location. Previous results have shown that a zyxin fragment excluding the alpha-actin binding site and the LIM domains (amino acids 51-392) can independently localize to cell-cell contacts. Here, expression of smaller zyxin fragments show that zyxin localization requires amino acids 230-280. A yeast-two-hybrid screen, using the central region of zyxin as bait, resulted in the identification of the cell-cell adhesion receptor nectin-4 as a zyxin binding partner. Further demonstrating zyxin-nectin interactions, zyxin binds the intracellular domain of nectin-2 in vitro. Depletion of nectin-2 from L cells expressing E-cadherin results in a loss of zyxin localization to cell-cell contacts, demonstrating that the zyxin-nectin interaction plays a critical role in zyxin targeting to these sites.