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Identification of additional cancer-associated genes and secondary mutations driving the metastatic progression in pheochromocytoma and paraganglioma (PPGL) is important for subtyping, and may provide optimization of therapeutic regimens. We recently reported novel recurrent nonsynonymous mutations in the MYO5B gene in metastatic PPGL. Here, we explored the functional impact of these MYO5B mutations, and analyzed MYO5B expression in primary PPGL tumor cases in relation to mutation status. Immunohistochemistry and mRNA expression analysis in 30 PPGL tumors revealed an increased MYO5B expression in metastatic compared to non-metastatic cases. In addition, subcellular localization of MYO5B protein was altered from cytoplasmic to membranous in some metastatic tumors, and the strongest and most abnormal expression pattern was observed in a paraganglioma harboring a somatic MYO5B:p.G1611S mutation. In addition to five previously discovered MYO5B mutations, the present study of 30 PPGL (8 previous and 22 new samples) also revealed two, and hence recurrent, mutations in the gene paralog MYO5A. The three MYO5B missense mutations with the highest prediction scores (p.L587P, p.G1611S and p.R1641C) were selected and functionally validated using site directed mutagenesis and stable transfection into human neuroblastoma cells (SK-N-AS) and embryonic kidney cells (HEK293). In vitro analysis showed a significant increased proliferation rate in all three MYO5B mutated clones. The two somatically derived mutations, p.L587P and p.G1611S, were also found to increase the migration rate. Expression analysis of MYO5B mutants compared to wild type clones, demonstrated a significant enrichment of genes involved in migration, proliferation, cell adhesion, glucose metabolism, and cellular homeostasis. Our study validates the functional role of novel MYO5B mutations in proliferation and migration, and suggest the MYO5-pathway to be involved in the malignant progression in some PPGL tumors.

We performed a genome-wide association scan in 1461 patients with bipolar (BP) 1 disorder, 2008 controls drawn from the Systematic Treatment Enhancement Program for Bipolar Disorder and the University College London sample collections with successful genotyping for 372 193 single nucleotide polymorphisms (SNPs). Our strongest single SNP results are found in myosin5B ( MYO5B ; P =1.66 × 10 −7 ) and tetraspanin-8 ( TSPAN8 ; P =6.11 × 10 −7 ). Haplotype analysis further supported single SNP results highlighting MYO5B, TSPAN8 and the epidermal growth factor receptor ( MYO5B ; P =2.04 × 10 −8 , TSPAN8 ; P =7.57 × 10 −7 and EGFR ; P =8.36 × 10 −8 ). For replication, we genotyped 304 SNPs in family-based NIMH samples ( n =409 trios) and University of Edinburgh case–control samples ( n =365 cases, 351 controls) that did not provide independent replication after correction for multiple testing. A comparison of our strongest associations with the genome-wide scan of 1868 patients with BP disorder and 2938 controls who completed the scan as part of the Wellcome Trust Case–Control Consortium indicates concordant signals for SNPs within the voltage-dependent calcium channel, L-type, alpha 1C subunit ( CACNA1C) gene. Given the heritability of BP disorder, the lack of agreement between studies emphasizes that susceptibility alleles are likely to be modest in effect size and require even larger samples for detection.

Background: Selecting the most beneficial treatment regimens for colorectal cancer (CRC) patients remains challenging due to a lack of prognostic markers. Members of the Myosin family, proteins recognised to have a major role in trafficking and polarisation of cells, have recently been reported to be closely associated with several types of cancer and might thus serve as potential prognostic markers in the context of CRC. Methods: We used a previously established meta-analysis of publicly available gene expression data to analyse the expression of different members of the Myosin V family, namely MYO5A , 5B , and 5C , in CRC. Using laser-microdissected material as well as tissue microarrays from paired human CRC samples, we validated both RNA and protein expression of Myosin Vb (MYO5B) and its known adapter proteins (RAB8A and RAB25) in an independent patient cohort. Finally, we assessed the prognostic value of both MYO5B and its adapter-coupled combinatorial gene expression signatures. Results: The meta-analysis as well as an independent patient cohort study revealed a methylation-independent loss of MYO5B expression in CRC that matched disease progression. Although MYO5B mutations were identified in a small number of patients, these cannot be solely responsible for the common downregulation observed in CRC patients. Significantly, CRC patients with low MYO5B expression displayed shorter overall, disease-, and metastasis-free survival, a trend that was further reinforced when RAB8A expression was also taken into account. Conclusions: Our data identify MYO5B as a powerful prognostic biomarker in CRC, especially in early stages (stages I and II), which might help stratifying patients with stage II for adjuvant chemotherapy.

Myosin Vb (MYO5B) is a motor protein that facilitates protein trafficking and recycling in polarized cells by RAB11- and RAB8-dependent mechanisms. Biallelic MYO5B mutations are identified in the majority of patients with microvillus inclusion disease (MVID). MVID is an intractable diarrhea of infantile onset with characteristic histopathologic findings that requires life-long parenteral nutrition or intestinal transplantation. A large number of such patients eventually develop cholestatic liver disease. Bi-allelic MYO5B mutations are also identified in a subset of patients with predominant early-onset cholestatic liver disease. We present here the compilation of 114 patients with disease-causing MYO5B genotypes, including 44 novel patients as well as 35 novel MYO5B mutations, and an analysis of MYO5B mutations with regard to functional consequences. Our data support the concept that (1) a complete lack of MYO5B protein or early MYO5B truncation causes predominant intestinal disease (MYO5B-MVID), (2) the expression of full-length mutant MYO5B proteins with residual function causes predominant cholestatic liver disease (MYO5B-PFIC), and (3) the expression of mutant MYO5B proteins without residual function causes both intestinal and hepatic disease (MYO5B-MIXED). Genotype-phenotype data are deposited in the existing open MYO5B database in order to improve disease diagnosis, prognosis, and genetic counseling.

Background With recent advances in gene sequencing technology, more than 60 genetic mutations associated with very early onset inflammatory bowel disease (VEO-IBD) have been reported. Most of the genes are associated with immune deficiencies. The Myosin 5B ( MYO5B ) gene is primarily involved in cell motility and material transport which is associated with congenital intractable diarrhea and cholestasis. No studies have examined the relationship between the MYO5B gene and VEO-IBD. We report a case of a child with a mutation in the MYO5B gene who was diagnosed with VEO-IBD, then we investigated the association between the MYO5B gene and VEO-IBD. Case presentation A 7-month-old baby girl with a chief complaint of “blood in the stool for more than 4 months and vaginal pus and blood discharge for 3 weeks” was diagnosed with VEO-IBD, and her symptoms improved after treatment with mesalazine. The whole-exome sequencing was performed with peripheral blood. Immunohistochemistry was performed on the terminal ileal tissue. Western blotting, quantitative polymerase chain reaction (Q-PCR) and immunofluorescence were performed with cultured organoid tissue from the terminal ileum. Whole-exome sequencing identified heterozygous missense of MYO5B variant of unknown significance (p. [I769N]; [T1546M]). Immunohistochemistry revealed a significant decrease in the expression of MYO5B protein in the terminal ileum of the child with MYO5B mutation; Q-PCR revealed a decrease in the mRNA levels of occludin and ZO-1 and both the mRNA levels and protein levels of MYO5B was downregulated in the patient. Immunofluorescence images showed that MYO5B gene mutation disrupted the apical delivery of transporters SGLT1, NHE3 and AQP7. Conclusions MYO5B gene mutation leading to the downregulation of MYO5B protein may promote the occurrence of VEO-IBD by decreasing mRNA and protein levels of intestinal tight junction genes and dislocating the apical transporters.

Intrahepatic cholestasis is characterized by the accumulation of compounds in the serum that are normally secreted by hepatocytes into the bile. Genes associated with familial intrahepatic cholestasis (FIC) include ATP8B1 (FIC1), ABCB11 (FIC2), ABCB4 (FIC3), TJP2 (FIC4), NR1H4 (FIC5) and MYO5B (FIC6). With advanced genome sequencing methodologies, additional mutated genes are rapidly identified in patients presenting with idiopathic FIC. Notably, several of these genes, VPS33B, VIPAS39, SCYL1, and AP1S1, together with MYO5B, are functionally associated with recycling endosomes and/or the Golgi apparatus. These are components of a complex process that controls the sorting and trafficking of proteins, including those involved in bile secretion. These gene variants therefore suggest that defects in intracellular trafficking take a prominent place in FIC. Here we review these FIC-associated trafficking genes and their variants, their contribution to biliary transporter and canalicular protein trafficking, and, when perturbed, to cholestatic liver disease. Published variants for each of these genes have been summarized in table format, providing a convenient reference for those who work in the intrahepatic cholestasis field.

Background Our previous study has shown that MYO5B is downregulated in gastric cancer. However, the mechanism by which the expression of MYO5B was inhibited remains unknown. Methods Inspection of the human MYO5B locus uncovered a large and dense CpG island within the 5′ region of this gene. Methylation-specific PCR (MSP) and bisulfite sequencing (BSP) were used for determination of MYO5B promoter methylation in gastric cancer cell lines and gastric cancer samples. Involvement of histone H3 methylation in those cell lines were examined by ChIP assay. Results The densely methylated MYO5B promoter region was confirmed by MSP and BSP. Enhanced gene expression was detected when the cells were treated with the DNA-demethylating agent 5-aza-2′-deoxycytidine (DAC) and trichostatin A (TSA), a histone deacetylase inhibitor. Knockdown of MYO5B expression in gastric cancer cells expressing endogenous MYO5B inhibits HGF-stimulated MET degradation, concomitant with sustained c-MET levels and signaling. Conclusion The results of our study showed for the first time that MYO5B is epigenetically silenced in gastric cancer cells by aberrant DNA methylation and histone modification. Inactivation of MYO5B expression in gastric cancer cells expressing endogenous MYO5B inhibits HGF-stimulated MET degradation, concomitant with sustained c-MET levels and signaling.

Background Loss of cell polarity and tissue disorganisation are hallmarks of cancer. MYO5B mutations disrupt epithelial cell polarity, suggesting that MYO5B may be involved in tumorigenesis. Methods We analyzed MYO5B expression in 70 gastric cancer tissues by immunohistochemistry using a tissue microarray method. Two related proteins, Rab11a and TfR, were also investigated. Results We found that the negative rate of MYO5B was 78.6 and 17.1% in gastric cancer and normal gastric tissues ( P  < 0.001), respectively. The MYO5B expression had a strong relationship with Rab11a expression ( P  = 0.002). We also found that inactivation by siRNA against MYO5B promoted the proliferation, invasion and migration of gastric cancer cells. Conclusion The expression of MYO5B was downregulated in gastric cancer and inactivation of MYO5B may contribute to tumorigenesis. Therefore, MYO5B may become an important biomarker for gastric cancer in the future.