Biallelic loss of FAM46C triggers tumor growth with concomitant activation of Akt signaling in multiple myeloma cells

Loss of heterozygosity or mutation of the family with sequence similarity 46, member C (FAM46C) gene on chromosome band 1p12 is associated with shorter overall survival of patients with multiple myeloma (MM). In this study, using human MM cell lines (KMS-11, OCI-My5, and ANBL-6), we generated FAM46C^−/− cell clones and examined the effect of disruption of FAM46C on cell survival and cellular signaling. Cell proliferation assays showed increased clonogenicity of FAM46C^−/− KMS-11 cells compared to WT cells. Xenograft experiments showed significantly shorter overall survival of mice harboring the FAM46C^−/− cell-derived tumors than mice with the FAM46C^WT cell-derived tumors. Notably, levels of phosphorylated Akt and its substrates increased both in vitro and in vivo in the FAM46C^−/− cells compared to WT cells. In addition, caspase activities decreased in the FAM46C^−/− cells. Results of gene set enrichment analysis showed that loss of FAM46C significantly activated serum-responsive genes while inactivating phosphatase and tensin homolog (PTEN)-related genes. Mechanistically, loss of FAM46C decreased the PTEN activity, number of apoptotic cells, and caspase activities. PF-04691502, a selective PI3K inhibitor, suppressed the augmented phosphorylation of Akt and its substrate FoxO3a. Treatment with afuresertib (a specific Akt inhibitor) in combination with bortezomib additively decreased FAM46C^−/− MM cell survival. Collectively, this study is the first to report that loss of FAM46C triggers the concomitant activation of the PI3K-Akt signaling pathway, which might be a therapeutic target for MM with abnormalities in the FAM46C gene.