14-3-3 protein zeta/delta
regulation of ERK1 and ERK2 cascade
A YWHAZ Variant Associated With Cardiofaciocutaneous Syndrome Activates the RAF-ERK Pathway.
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 <i>KRAS, BRAF, MEK1</i>, and <i>MEK2</i>. 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 <i>YWHAZ</i>, 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 <i>Xenopus laevis</i> to analyze the functional consequence of a particular <i>YWHAZ</i> variant, S230W, and investigate the molecular mechanisms underlying its activity. We show that compared with wild type <i>YWHAZ</i>, the S230W variant induces severe embryonic defects when ectopically expressed in early <i>Xenopus</i> 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 <i>YWHAZ</i>. Although neither <i>YWHAZ</i> 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 <i>YWHAZ</i> is a gain-of-function mutation in the RAS-ERK pathway and may underlie a CFC phenotype.