CD151 restricts α6 integrin diffusion mode

Abstract

Laminin-binding integrins (α3β1, α6β1, α6β4, α7β1) are almost always expressed together with tetraspanin CD151. In every co-expressing cell analyzed to date, CD151 makes a fundamental contribution towards 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 α6 integrin clustering and functions without decreasing α6 expression or activation. Furthermore, CD151 knockdown minimally affects α6 diffusion magnitude, as measured using single particle tracking. Instead, CD151 knockdown has a novel and unexpected dysregulating effect on α6 integrin diffusion mode. Control cell α6 shows mostly random/confined diffusion (RCD) and some directed motion (DMO). In sharp contrast, CD151 knockdown cell α6 shows mostly DMO. Control α6 diffusion mode is sensitive to actin disruption, talin knockdown, and phorbol ester stimulation. In contrast, CD151 knockdown cell α6 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 α6 RCD in control cells. In contrast, CD151-ablated cells retain EGF effects but lose phorbol ester-stimulated spreading and α6 RCD. For α6 integrins, physical association with CD151 promotes α6 RCD, in support of α6-mediated cable formation and adhesion. By comparison, for integrins not associated with CD151 (e.g. αv integrins), CD151 affects neither diffusion mode, nor αv function. Hence, CD151 support of α6 RCD is specific and functionally relevant, and likely underlies diverse CD151 functions in skin, kidney, and cancer cells.