Tumor suppressor protein CYLD regulates morphogenesis of dendrites and spines.

Cylindromatosis tumor suppressor protein (CYLD) was initially identified as a tumor suppressor deubiquitylating protein in familial cylindromatosis patients. Proteomic analyses using rodent brain samples revealed enrichment of CYLD in purified postsynaptic density fractions. Here, we report that CYLD regulates dendritic growth and postsynaptic differentiation in mouse hippocampal neurons. CYLD showed diffuse localization in rapidly growing dendrites, but was gradually concentrated in spines. Overexpression and knockdown of CYLD in the early stage of cultured neurons demonstrated that CYLD positively regulated dendritic growth. Phenotypes in dendritic morphogenesis induced by CYLD overexpression and knockdown could be reversed by manipulation of the critical acetylation site of α-tubulin, suggesting tubulin acetylation is a downstream pathway of CYLD-dependent dendritic growth. Overexpression and knockdown of CYLD in the later stage of cultured neurons revealed that CYLD promoted formation of postsynaptic spines. Influence of CYLD on spines was not affected by co-expression of acetylation mutant forms of α-tubulin, indicating that CYLD regulates dendritic growth and spine formation through different molecular mechanisms. Analyses with the truncated and mutated forms of CYLD demonstrated that the first microtubule-binding domain of CYLD was critical for spine formation. These results suggest important roles of CYLD in sequential promotion of dendritic growth and postsynaptic spine maturation.

mDia1 targets v-Src to the cell periphery and facilitates cell transformation, tumorigenesis, and invasion.

The small GTPase Rho regulates cell morphogenesis through remodeling of the actin cytoskeleton. While Rho is overexpressed in many clinical cancers, the role of Rho signaling in oncogenesis remains unknown. mDia1 is a Rho effector producing straight actin filaments. Here we transduced mouse embryonic fibroblasts from mDia1-deficient mice with temperature-sensitive v-Src and examined the involvement and mechanism of the Rho-mDia1 pathway in Src-induced oncogenesis. We showed that in v-Src-transduced mDia1-deficient cells, formation of actin filaments is suppressed, and v-Src in the perinuclear region does not move to focal adhesions upon a temperature shift. Consequently, membrane translocation of v-Src, v-Src-induced morphological transformation, and podosome formation are all suppressed in mDia1-deficient cells with impaired tyrosine phosphorylation. mDia1-deficient cells show reduced transformation in vitro as examined by focus formation and colony formation in soft agar and exhibit suppressed tumorigenesis and invasion when implanted in nude mice in vivo. Given overexpression of c-Src in various cancers, these findings suggest that Rho-mDia1 signaling facilitates malignant transformation and invasion by manipulating the actin cytoskeleton and targeting Src to the cell periphery.