Arteriovenous malformations (AVM) are benign vascular anomalies prone to pain, bleeding, and progressive growth. AVM are mainly caused by mosaic pathogenic variants of the RAS-MAPK pathway. However, a causative variant is not identified in all patients. Using ultra-deep sequencing, we identified novel somatic RIT1 delins variants in lesional tissue of three AVM patients. RIT1 encodes a RAS-like protein that can modulate RAS-MAPK signaling. We expressed RIT1 variants in HEK293T cells, which led to a strong increase in ERK1/2 phosphorylation. Endothelial-specific mosaic overexpression of RIT1 delins in zebrafish embryos induced AVM formation, highlighting their functional importance in vascular development. Both ERK1/2 hyperactivation in vitro and AVM formation in vivo could be suppressed by pharmacological MEK inhibition. Treatment with the MEK inhibitor trametinib led to a significant decrease in bleeding episodes and AVM size in one patient. Our findings implicate RIT1 in AVM formation and provide a rationale for clinical trials with targeted treatments.

BACKGROUND: As a small G protein of Ras family, Ras-like-without-CAAX-1 (RIT1) plays a critical role in various tumors. Our previous study has demonstrated the involvement of RIT1 in promoting malignant progression of hepatocellular carcinoma (HCC). However, its underlying mechanism remains unclear.
METHODS: Gene set enrichment analysis (GSEA) was conducted in the TCGA LIHC cohort to investigate the underlying biological mechanism of RIT1. Live cell imaging, immunofluorescence (IF) and flow cytometry assays were used to verify biological function of RIT1 in HCC mitosis. Subcutaneous xenografting of human HCC cells in BALB/c nude mice was utilized to assess tumor proliferation in vivo. RNA-seq, co-immunoprecipitation (Co-IP), mass spectrometry analyses, western blot and IF assays were employed to elucidate the mechanisms by which RIT1 regulates mitosis and promotes proliferation in HCC.
RESULTS: Our findings demonstrate that RIT1 plays a crucial role in regulating mitosis in HCC. Knockdown of RIT1 disrupts cell division, leading to G2/M phase arrest, mitotic catastrophe, and apoptosis in HCC cells. SMC3 is found to interact with RIT1 and knockdown of SMC3 attenuates the proliferative effects mediated by RIT1 both in vitro and in vivo. Mechanistically, RIT1 protects and maintains SMC3 acetylation by binding to SMC3 and PDS5 during mitosis, thereby promoting rapid cell division and proliferation in HCC. Notably, we have observed an upregulation of SMC3 expression in HCC tissues, which is associated with poor patient survival and promotion of HCC cell proliferation. Furthermore, there is a significant positive correlation between the expression levels of RIT1, SMC3, and PDS5. Importantly, HCC patients with high expression of both RIT1 and SMC3 exhibit worse prognosis compared to those with high RIT1 but low SMC3 expression.
CONCLUSIONS: Our findings underscore the crucial role of RIT1 in regulating mitosis in HCC and further demonstrate its potential as a promising therapeutic target for HCC treatment.

Liver cancer is a prevalent malignant tumor with high mortality worldwide, making it urgent to explore new targets for liver cancer therapy. N-terminal EF-hand calcium binding protein 3 (NECAB3) is a new recognized regulator of cancer, while its role in liver cancer remained elusive. Thus, the study clarified the action of NECAB3 on liver cancer development and explored the detailed mechanism. We found that NECAB3 was enhanced in liver cancer. Knockdown of NECAB3 restrained liver cancer cell migration and invasion. Besides, knockdown of NECAB3 suppressed the activation of the hypoxia-inducible factor 1-alpha (HIF-1α)/Ras like without CAAX 1 (RIT1) pathway. Furthermore, NECAB3 regulated liver cancer migration and invasion through modulating RIT1 expression. Moreover, downregulation of NECAB3 suppressed liver cancer tumor growth in vivo. In conclusion, NECAB3 was upregulated in liver cancer. Knockdown of NECAB3 suppressed aggressive phenotype of liver cancer via modulating the HIF-1α/RIT1 axis, providing a possible target for liver cancer therapy.

Noonan Syndrome is caused by variants in a variety of genes found in the RAS/MAPK pathway. As more causative genes for Noonan Syndrome have been identified, more phenotype variability has been found, particularly congenital heart defects. Here, we report a case of dilated coronary arteries in a pediatric patient with a RIT1 variant to add to the body of literature around this rare presentation of Noonan Syndrome.  CASE PRESENTATION: A 2-month-old female was admitted due to increasing coronary artery dilation and elevated inflammatory markers. Rapid whole genome sequencing was performed and a likely pathogenic RIT1 variant was detected. This gene has been associated with a rare form of Noonan Syndrome and associated heart defects. Diagnosis of the RIT1 variant also gave reassurance about the patient\'s cardiac findings and allowed for more timely discharge as she was discharged to home the following day.  CONCLUSIONS: This case highlights the importance of the association between dilated coronary arteries and Noonan syndrome and that careful cardiac screening should be advised in patients diagnosed with Noonan syndrome. In addition, this case emphasizes the importance of involvement of other subspecialities to determine a diagnosis. Through multidisciplinary medicine, the patient was able to return home in a timely manner with a diagnosis and the reassurance that despite her dilated coronary arteries and elevated inflammatory markers there was no immediate concern to her health.

Non-immune hydrops fetalis (NIHF) indicates the risk for stillbirth. Although the causes vary and most NIHFs have no identifiable cause, recent advances in exome sequencing have increased diagnostic rates. We report a case of NIHF that developed into a giant cystic hygroma complicated by maternal mirror syndrome. Trio-based exome sequencing showed a de novo heterozygous missense variant in the RIT1 (NM_006912: c.246 T > G [p.F82L]). The RIT1 variants are known causative variants of Noonan syndrome (NS; OMIM #163950). The location of the RIT1 variants in the previously reported NS cases with NIHF or/and maternal mirror syndrome was mainly in the switch II region, including the present case. While a further accumulation of cases is needed, exome sequencing, which can identify the variant type in detail, might help predict the phenotype and severity of NIHF.

UNASSIGNED: Noonan syndrome (NS), an autosomal dominant disease known as a RASopathy, is caused by germline mutations in mitogen-activated protein kinase pathway genes. A RIT1 gene mutation has been found to cause NS. The present study summarizes RIT1 gene mutation sites and associated clinical phenotypes.
UNASSIGNED: We retrospectively analyzed the clinical characteristics of a case of NS caused by RIT1 mutation in our hospital, and searched the PubMed database, China National Knowledge Infrastructure (CNKI) database and Wanfang database with the keywords Noonan syndrome and RIT1. Studies published between May 1, 2014 and July 1, 2021 were retrieved. By reviewing the abstracts and full text of the studies, we screened NS cases associated with RIT1 mutation in children 0-18 years of age. The clinical characteristics of these cases were summarized.
UNASSIGNED: A total of 41 cases were analyzed, including 13 boys and 28 girls. There were 14 premature cases. The age at diagnosis was 4 days to 18 years, and 10 cases were diagnosed at 0-1 years of age. Common amino acid substitution positions included 57 (13/41), 95 (7/41), 82 (8/41), and 90 (4/41). A total of 63.63% cases had abnormal prenatal examination results, manifesting mainly as fetal neck edema, polyhydramnios and cardiac malformation. With respect to abnormal conditions after birth, 70-80% of patients had typical developmental malformations of the face, neck and thorax; 19/35 patients had abnormal lymphatic development; and a portion of patients had short stature and motor development disorders. A total of 87.80% (36/41) patients had cardiac dysplasia, among which hypertrophic cardiomyopathy (HCM) accounted for 58.53%. A total of 84.62% of patients carrying the p.A57G mutation had HCM, but no HCM was found in patients with the p.G95A mutation. A total of 34.15% of patients had pulmonary artery or pulmonary valve stenosis (PVS). In patients with the p.M90I mutation, 75% had PVS. Patients with concurrent HCM and PVS accounted for 19.51 and 48.78% of patients had supraventricular tachycardia.
UNASSIGNED: A RIT1 gene mutation causing NS was associated with a high rate of abnormal prenatal examination findings. Most patients had typical NS craniofacial deformities, and some have short stature and motor development disorders. The cardiac deformity rate was high, and HCM was common. Some patients had supraventricular arrhythmias. Heart abnormalities showed high heterogeneity, given the various mutation loci.

OBJECTIVE: We aimed to identify the genetic cause of one hydrops fetalis with Noonan syndrome (NS) manifestations including increased nuchal translucency (INT) and ascites through prenatal whole exome sequencing (WES).
METHODS: The case is a gestational age (GA) 18 fetus of two healthy parents with a normal child. We proceeded the genomic DNA from both fetus amniotic cells and parents to WES and identified a RIT1 mutation (c.268A>G) as the pathogenic cause of the hydrops fetalis by automatic prioritization algorithm after array-comparative genomic hybridization results showing negative.
CONCLUSIONS: Mutations in RIT1 have been reported as the causes for different fetus structural abnormities in the recent years. This case contributes to the summary delineations of the prenatal NS phenotypes related to RIT1 mutation. In addition, the fast WES application, in this case, has demonstrated its advantage in prenatal disorder diagnosis when conventional karyotyping or chromosomal microarray testing result is negative.

BACKGROUND: Cardiovascular disease is one of the most important problems in long-term follow-up for Noonan syndrome. We examined cardiovascular issues and clinical manifestations, with a focus on the cardiovascular disease and prognosis of patients with Noonan syndrome.
METHODS: This single-centre study evaluated patients who were clinically and genetically diagnosed with Noonan syndrome.
RESULTS: Forty-three patients diagnosed with Noonan syndrome were analysed. The most prevalent responsible mutation was found in PTPN11 (25/43). The second and third most prevalent causative genes were SOS1 (6/43) and RIT1 (5/43), respectively, and 67.4% of genetically diagnosed patients with Noonan syndrome had structural cardiovascular abnormalities. Pulmonary valve stenosis was prevalent in patients with mutations in PTPN11 (8/25), SOS1 (4/6), and RIT1 (4/5). Hypertrophic cardiomyopathy was found in two of three patients with mutations in RAF1. There was no difference in the cardiovascular events or cardiovascular disease prevalence in patients with or without PTPN11 mutations. The proportion of RIT1 mutation-positive patients who underwent intervention due to cardiovascular disease was significantly higher than that of patients with PTPN11 mutations. Patients who underwent any intervention for pulmonary valve stenosis exhibited significantly higher pulmonary flow velocity than patients who did not undergo intervention, when they visited our hospital for the first time. All patients who underwent intervention for pulmonary valve stenosis had a pulmonary flow velocity of more than 3.0 m/s at first visit.
CONCLUSIONS: These findings suggest that genetic information can provide a clinical prognosis for cardiovascular disease and may be part of genotype-based follow-up in Noonan syndrome.

RAS GTPases are highly conserved proteins involved in the regulation of mitogenic signaling. We have previously described a novel Cullin 3 RING E3 ubiquitin ligase complex formed by the substrate adaptor protein LZTR1 that binds, ubiquitinates, and promotes proteasomal degradation of the RAS GTPase RIT1. In addition, others have described that this complex is also responsible for the ubiquitination of classical RAS GTPases. Here, we have analyzed the phenotypes of Lztr1 loss-of-function mutants in both fruit flies and mice and have demonstrated a biochemical preference for their RIT1 orthologs. Moreover, we show that Lztr1 is haplosufficient in mice and that embryonic lethality of the homozygous null allele can be rescued by deletion of Rit1. Overall, our results indicate that, in model organisms, RIT1 orthologs are the preferred substrates of LZTR1.

In recent work, we performed CRISPR/Cas9 screening in RIT1 (Ras-like in all tissues)-mutant cancer cells. We found that RIT1-mutant cells are vulnerable to loss of mitotic regulators, and mutant RIT1 synergizes with YAP1 (yes-associated protein 1) in oncogenesis. These findings can be leveraged to identify targeted therapies for RIT1-mutant cancer.