Phosphorylation of serine residues S252, S268/S269, and S879 in p120 catenin activates migration of presomitic mesoderm in gastrulating zebrafish embryos.

BACKGROUND: Cadherin-associated protein p120 catenin regulates cell adhesion and migration in cell cultures and is required for axial elongation in embryos. Its roles in adhesion and cell migration are regulated by phosphorylation. We determined the effects of phosphorylation of six serine and three threonine residues in p120 catenin during zebrafish (Danio rerio) embryogenesis. RESULTS: We knocked down endogenous p120 catenin-δ1 with an antisense RNA-splice-site morpholino (Sp-MO) causing defects in axis elongation. These defects were rescued by co-injections of mRNAs for wildtype mouse p120 catenin-δ1-3A or various mutated forms. Several mRNAs containing serine or threonine codons singly or doubly mutated to phosphomimetic glutamic acid rescued, and some nonphosphorylatable mutants did not. CONCLUSIONS: We discovered that phosphorylation of serine residue S252 or S879 is required for convergent extension of zebrafish embryos, since rescue occurred only when these residues were mutated to glutamic acid. In addition, the phosphorylation of either S268 or S269 is required, not both, consistent with the presence of only a single one of these residues in two isoforms of zebrafish and Xenopus laevis. In summary, phosphorylation of multiple serine and threonine residues of p120 catenin activates migration of presomitic mesoderm of zebrafish embryos facilitating elongation of the dorsal axis.

Functional proteomics of patient derived head and neck squamous cell carcinoma cells reveal novel applications of trametinib.

In this study, we report a differential response of mitogen-activated protein kinase-kinase (MEK) inhibitor trametinib in 20 head and neck squamous cell carcinoma (HNSCC) patients' tumor-derived cell cultures. Relatively sensitive and resistant cases to trametinib were identified using high throughput metabolic assays and validated in extended dose response studies in vitro. High throughput metabolic assays exploring combination therapies with trametinib were subjected to synergy models and maximal synergistic dose analyses. These yielded several candidates, including axtinib, GDC-0032, GSK-690693, and SGX-523. The combination regimen of trametinib and AXL/MET/VEGFR inhibitor glesatinib showed initial efficacy both in vitro and in vivo (92% reduction in tumor volume). Sensitivity was validated in vivo in a patient-derived xenograft (PDX) model in which trametinib as a single agent effected reduction in tumor volume up to 72%. Reverse Phase Protein Arrays (RPPA) demonstrated differentially expressed proteins and phosphoproteins upon trametinib treatment. Furthermore, resistant cell lines showed a compensatory mechanism via increases in MAPK and non-MAPK pathway proteins that may represent targets for future combination regimens. Intrinsic-targeted options have potential to address paucity of medical treatment options for HNSCC cancer patients, enhance response to extrinsic targeted agents, and/or reduce morbidity as neoadjuvant to surgical treatments.