This report describes Noonan syndrome 5 (NS5), which is a subtype of Noonan syndrome; NS5 exhibits autosomal dominant inheritance. The human gene implicated in this disease is RAF1, which encodes Raf-1 proto-oncogene, serine/threonine kinase, a kinase that acts within the RAS-RAF-MEK-ERK pathway. RAF1 is also associated with the diseases Noonan syndrome with multiple lentigines 2 (OMIM:611554, FBhh0000132) and dilated cardiomyopathy-1NN (OMIM:615916, FBhh0000156). See, in addition, FBhh0000558, a fly model of RAS-RAF-MEK-ERK-pathway-related cancer using RAF1. There is one high-scoring fly ortholog, Raf, for which RNAi targeting constructs, alleles caused by insertional mutagenesis, and classical amorphic alleles have been generated. Dmel\Raf is orthologous to two additional human genes, ARAF and BRAF.
Multiple transgenic constructs of the human Hsap\RAF1 gene have been introduced into flies, including wild-type RAF1, gain-of-function RAF1, UAS and heat-shock promoter constructs, and genes carrying an N-terminal deletion. Functional conservation between the human and fly genes has been demonstrated in fly several systems; for example, an activated form of the human gene has been shown to recapitulate phenotypes observed for an activated form of, or overexpression of, the fly gene.
Cardiomyopathy, which is observed in over 90% of NS5 patients, has been investigated in the fly model using both the human Hsap\RAF1 gene and the fly Raf gene (FBhh0000737).
Animals homozygous for amorphic mutations of Dmel\Raf exhibit lethality in the late larval stage; imaginal discs are undeveloped. Embryos lacking all Dmel\Raf activity (derived from homozygous null germline clones in the mother and not rescued by paternal contribution) die in early embryogenesis. Many physical and genetic interactions have been described for Dmel\Raf; see below and in the gene report for Raf.
[updated Aug. 2020 by FlyBase; FBrf0222196]
Noonan syndrome (NS) is an autosomal dominant disorder characterized by short stature, facial dysmorphism, and a wide spectrum of congenital heart defects. The distinctive facial features consist of a broad forehead, hypertelorism, downslanting palpebral fissures, a high-arched palate, and low-set, posteriorly rotated ears. Cardiac involvement is present in up to 90% of patients. Pulmonic stenosis and hypertrophic cardiomyopathy are the most common forms of cardiac disease, but a variety of other lesions are also observed. Additional relatively frequent features include multiple skeletal defects (chest and spine deformities), webbed neck, mental retardation, cryptorchidism, and bleeding diathesis (summary by Tartaglia et al., 2002 pubmed:11992261). [from OMIM:163950, 2015.04.14]
Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. [Gene Reviews, Noonan Syndrome, 2020.08.21]
[NOONAN SYNDROME 5; NS5](https://omim.org/entry/611553)
[RAF1 PROTOONCOGENE, SERINE/THREONINE KINASE ; RAF1](https://omim.org/entry/164760)
Of 17 Noonan syndrome patients with a RAF1 mutation in either of two hotspots (clustering around ser259 or ser612), 16 (94%) had hypertrophic cardiomyopathy (CMH; see OMIM:192600), compared with an 18% prevalence of CMH among Noonan syndrome patients in general (Pandit et al., 2007, pubmed:17603483). Pandit et al. (2007) also scanned RAF1 exons mutated in Noonan and LEOPARD syndrome patients in 241 unrelated individuals with nonsyndromic CMH who did not have mutations in 8 myofilament genes known to cause CMH, and the authors identified a thr260-to-ile mutation in the RAF1 gene in one patient (Pandit et al., 2007, pubmed:17603483). [from OMIM:164760, 2016.01.19]
The studies reported to date emphasize a striking correlation with hypertrophic cardiomyopathy, with 95% of affected individuals with a RAF1 mutation showing this feature, in comparison with the overall prevalence in Noonan syndrome of 18%. This suggests that pathologic cardiomyocyte hypertrophy occurs because of increased Ras signaling. Multiple nevi, lentigines, and/or café au lait spots were reported in one third of people with RAF1-associated Noonan syndrome. [from GeneReviews, Noonan Syndrome, pubmed:20301303 2016.01.20]
Noonan syndrome 5 (NS5) is caused by mutation in the RAF1 gene. LEOPARD syndrome-2 (OMIM:611554) is also caused by mutation in RAF1, indicating that the 2 disorders are allelic. [From OMIM:611553, 2016.01.15]
RAF1 is a serine-threonine kinase that activates MEK1 (OMIM:176872) and MEK2 (OMIM:601263). Ectopically expressed RAF1 mutants from the two hypertrophic cardiomyopathy (CMH; see OMIM:192600) hotspots (around ser259 or ser612) linked to LEOPARD syndrome 2 and/or Noonan syndrome 5 had increased kinase activity and enhanced ERK (see 176948) activation, whereas non-CMH-associated mutants were kinase impaired. (Pandit et al., 2007, pubmed:17603483). Mutations in the CR2 domain, but not the CR3 domain, of RAF1 are associated with hypertrophic cardiomyopathy (Razzaque et al., 2007, pubmed:17603482). [From OMIM:611553 and OMIM:164760, 2016.01.19]
RAF1 is ubiquitously expressed and encodes a protein of 648 amino acids with three conserved regions (CR). CR1 contains a Ras-binding domain; CR2 is a site of regulatory phosphorylation and association with the 14-3-3 protein. CR1 and CR2 both have negative regulatory function, removal of which results in oncogenic activity. The kinase domain, CR3, also associates with 14-3-3. The protein is highly regulated with numerous serine and threonine residues that can be phosphorylated, resulting in activation or inactivation. The serine at residue 259, which is in CR2, is particularly important. In the inactive state, the N-terminus of RAF1 interacts with and inactivates the kinase domain at the C-terminus. This conformation is stabilized by 14-3-3 protein dimers that bind to phosphorylated Ser259 and Ser261. Dephosphorylation of Ser259 facilitates binding of RAF1 to RAS-GTP and propagation of the signal through the RAS-MAPK cascade via RAF1 MEK kinase activity. [from GeneReviews, Noonan Syndrome with Multiple Lentigines, pubmed:20301557 2016.01.20]
Many to one: 3 human to 1 Drosophila.
Ortholog of human BRAF, ARAF, and RAF1 (1 Drosophila to 3 human).
Dmel\Raf shares 43% identity and 54% similarity with human BRAF, 44% identity and 58% similarity with human ARAF, and 47% identity and 60% similarity with human RAF1.
