Cooper, Lisa M.

Abstract Plekha7 associates with p120 catenin and localizes at apical cell-cell junctions where it has been implicated in junction stabilization. However, it’s in vivo function and underlying mechanisms of action remain unclear. Here, we show that constitutive Plekha7 loss in mice disrupts retinal organization, reduces retinal thickness, and induces RPE multinucleation, microglia infiltration, and photoreceptor loss. Plekha7 deficiency reduces the accumulation of cadherin–catenin complexes at apical junctions without altering overall cadherin levels, indicating a defect in junctional maintenance. Mechanistically, PLEKHA7 regulates cadherin trafficking by limiting levels of endocytosed E-cadherin, thereby maintaining junctional cadherin pools. Notably, these effects are largely independent of p120 catenin. In addition, further Plekha7 roles in the regulation of centrosome, cilia, microtubule dynamics, and cytokinesis, likely contribute to the phenotypic changes induced by Plekha7 knockout. These findings establish Plekha7 as a key regulator of cadherin trafficking and epithelial organization with relevance to retinal disease.

Glioblastomas (GBM) are aggressive tumors that lack effective treatments. Here, we show that the Rho family guanine nucleotide exchange factor Syx promotes GBM cell growth both in vitro and in orthotopic xenografts derived from patients with GBM. Growth defects upon Syx depletion are attributed to prolonged mitosis, increased DNA damage, G2/M cell cycle arrest, and cell apoptosis, mediated by altered mRNA and protein expression of various cell cycle regulators. These effects are phenocopied by depletion of the Rho downstream effector Dia1 and are due, at least in part, to increased phosphorylation, cytoplasmic retention, and reduced activity of the YAP/TAZ transcriptional coactivators. Furthermore, targeting Syx signaling cooperates with radiation treatment and temozolomide (TMZ) to decrease viability in GBM cells, irrespective of their inherent response to TMZ. The data indicate that a Syx-RhoA-Dia1-YAP/TAZ signaling axis regulates cell cycle progression, DNA damage, and therapy resistance in GBM and argue for its targeting for cancer treatment.