M-Ras/Shoc2 signaling modulates E-cadherin turnover and cell–cell adhesion during collective cell migration

Significance Noonan syndrome belongs to a group of related developmental disorders termed the RASopathies, and both the M-Ras GTPase and its effector Shoc2 are signaling proteins mutated in specific subtypes of this disorder. Previously, the M-Ras/Shoc2 complex has been shown to act as a positive regulator of growth factor-mediated ERK cascade activation, and, here, we demonstrate a function for M-Ras/Shoc2/ERK cascade signaling in the dynamic control of cell–cell adhesion that is required for collective cell migration. Given the essential role of collective cell migration in human embryogenesis and organ development, our elucidation of M-Ras/Shoc2 function in this highly regulated process may provide insight regarding the cellular basis of defects associated with Noonan syndrome and other RASopathies.
Collective cell migration is required for normal embryonic development and contributes to various biological processes, including wound healing and cancer cell invasion. The M-Ras GTPase and its effector, the Shoc2 scaffold, are proteins mutated in the developmental RASopathy Noonan syndrome, and, here, we report that activated M-Ras recruits Shoc2 to cell surface junctions where M-Ras/Shoc2 signaling contributes to the dynamic regulation of cell–cell junction turnover required for collective cell migration. MCF10A cells expressing the dominant-inhibitory M-RasS27N variant or those lacking Shoc2 exhibited reduced junction turnover and were unable to migrate effectively as a group. Through further depletion/reconstitution studies, we found that M-Ras/Shoc2 signaling contributes to junction turnover by modulating the E-cadherin/p120-catenin interaction and, in turn, the junctional expression of E-cadherin. The regulatory effect of the M-Ras/Shoc2 complex was mediated at least in part through the phosphoregulation of p120-catenin and required downstream ERK cascade activation. Strikingly, cells rescued with the Noonan-associated, myristoylated-Shoc2 mutant (Myr-Shoc2) displayed a gain-of-function (GOF) phenotype, with the cells exhibiting increased junction turnover and reduced E-cadherin/p120-catenin binding and migrating as a faster but less cohesive group. Consistent with these results, Noonan-associated C-Raf mutants that bypass the need for M-Ras/Shoc2 signaling exhibited a similar GOF phenotype when expressed in Shoc2-depleted MCF10A cells. Finally, expression of the Noonan-associated Myr-Shoc2 or C-Raf mutants, but not their WT counterparts, induced gastrulation defects indicative of aberrant cell migration in zebrafish embryos, further demonstrating the function of the M-Ras/Shoc2/ERK cascade signaling axis in the dynamic control of coordinated cell movement.