Deciphering the Mammary Stem Cell Niche: A Role for Laminin-Binding Integrins

Summary: Integrins, which bind laminin, a major component of the mammary basement membrane, are strongly expressed in basal stem cell-enriched populations, but their role in controlling mammary stem cell function remains unclear. We found that stem cell activity, as evaluated in transplantation and mammosphere assays, was reduced in mammary basal cells depleted of laminin receptors containing α3- and α6-integrin subunits. This was accompanied by low MDM2 levels, p53 stabilization, and diminished proliferative capacity. Importantly, disruption of p53 function restored the clonogenicity of α3/α6-integrin-depleted mammary basal stem cells, while inhibition of RHO or myosin II, leading to decreased p53 activity, rescued the mammosphere formation. These data suggest that α3/α6-integrin-mediated adhesion plays an essential role in controlling the proliferative potential of mammary basal stem/progenitor cells through myosin II-mediated regulation of p53 and indicate that laminins might be important components of the mammary stem cell niche. : Faraldo and colleagues report that major cellular receptors for laminins, α3-and α6-subunit-containing integrins play an important role in the control of the proliferative potential of mammary basal stem/progenitor cells regulating the p53 activity through an RHOA/myosin II-dependent mechanism. These findings indicate that laminins might be essential components of the mammary stem cell niche. Key words: mammary gland, cre-lox gene deletion, integrin, laminin, stem cells