A YWHAZ Variant Associated With Cardiofaciocutaneous Syndrome Activates the RAF-ERK Pathway

Abstract

Cardiofaciocutaneous (CFC) syndrome is a genetic disorder characterized by distinctive facial features, congenital heart defects, and skin abnormalities. Several germline gain-of-function mutations in the RAS/RAF/MEK/ERK pathway are associated with the disease, including KRAS, BRAF, MEK1 , and MEK2 . CFC syndrome thus belongs to a group of disorders known as RASopathies, which are all caused by pathogenic mutations in various genes encoding components of the RAS pathway. We recently identified novel variants in YWHAZ , a 14-3-3 family member, in individuals with a phenotype consistent with CFC that may potentially be deleterious and disease-causing. In the current study, we take advantage of the vertebrate model Xenopus laevis to analyze the functional consequence of a particular YWHAZ variant, S230W, and investigate the molecular mechanisms underlying its activity. We show that compared with wild type YWHAZ , the S230W variant induces severe embryonic defects when ectopically expressed in early Xenopus embryos. The S230W variant also rescues the defects induced by a dominant negative FGF receptor more efficiently and enhances Raf-stimulated Erk phosphorylation to a higher level than wild type YWHAZ . Although neither YWHAZ nor the variant promotes membrane recruitment of Raf proteins, the variant binds to more Raf and escapes phosphorylation by casein kinase 1a. Our data provide strong support to the hypothesis that the S230W variant of YWHAZ is a gain-of-function mutation in the RAS-ERK pathway and may underlie a CFC phenotype.

The RASopathies: from pathogenetics to therapeutics

“…Recently, a germline variant in 14-3-3zeta ( YWHAZ ) was identified in a patient with a clinical diagnosis of CFC. Expression of this variant in Xenopus tropicalis increased BRAF and RAF1 binding, ERK phosphorylation and decreased body length, consistent with YWHAZ functioning as a RASopathy gene ( Popov et al, 2019 ).…”

Affinity Purification of NF1 Protein–Protein Interactors Identifies Keratins and Neurofibromin Itself as Binding Partners

“…In our proteomics study, we showed that 14-3-3σ is up-regulated when NF1 is deleted in HEK293 cells and that restoration of neurofibromin expression leads to decreased/normalization of expression [19]. 14-3-3 proteins have also been implicated in other Rasopathy phenotypes, including cardio-facio-cutaneous syndrome [20] and Noonan syndrome [21].…”

Cystic Fibrosis: Systems Biology Analysis from Homozygous p.Phe508del Variant Patients’ Samples Reveals Perturbations in Tissue-Specific Pathways

“…YWHAZ, a member of 14-3-3 proteins, is a conserved regulatory protein that maintains multiple types of signals via binding to several partner proteins. The binding of 14-3-3 proteins can lead to conformational changes in their partners, masking specific sequences or structural features in the partner proteins that promote the formation of complex [ 93 ]. No previous data has reported YWHAZ interaction with CFTR.…”