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[摘要]：Laminin-binding integrins (alpha 3 beta 1, alpha 6 beta 1, alpha 6 beta 4, alpha 7 beta 1) are almost always expressed together with tetraspanin CD151. In every coexpressing cell analyzed to date, CD151 makes a fundamental contribution to integrin-dependent motility, invasion, morphology, adhesion and/or signaling. However, there has been minimal mechanistic insight into how CD151 affects integrin functions. In MDA-MB-231 mammary cells, tetraspanin CD151 knockdown impairs alpha 6 integrin clustering and functions without decreasing alpha 6 integrin expression or activation. Furthermore, CD151 knockdown minimally affects the magnitude of a6 integrin diffusion, as measured using single particle tracking. Instead, CD151 knockdown has a novel and unexpected dysregulating effect on the mode of alpha 6 integrin diffusion. In control cells alpha 6 integrin shows mostly random-confined diffusion (RCD) and some directed motion (DMO). In sharp contrast, in CD151-knockdown cells alpha 6 integrin shows mostly DMO. In control cells alpha 6 diffusion mode is sensitive to actin disruption, talin knockdown and phorbol ester stimulation. By contrast, CD151 knockdown cell alpha 6 integrin is sensitive to actin disruption but desensitized to talin knockdown or phorbol ester stimulation, indicating dysregulation. Both phorbol ester and EGF stimulate cell spreading and promote alpha 6 RCD in control cells. By contrast, CD151-ablated cells retain EGF effects but lose phorbol-ester-stimulated spreading and alpha 6 RCD. For alpha 6 integrins, physical association with CD151 promotes alpha 6 RCD, in support of alpha 6-mediated cable formation and adhesion. By comparison, for integrins not associated with CD151 (e.g. av integrins), CD151 affects neither diffusion mode nor alpha v function. Hence, CD151 support of alpha 6 RCD is specific and functionally relevant, and probably underlies diverse CD151 functions in skin, kidney and cancer cells. |
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