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FAM46C controls antibody production by the polyadenylation of immunoglobulin mRNAs and inhibits cell migration in multiple myeloma.

ABSTRACT: FAM46C, frequently mutated in multiple myeloma (MM), has recently been shown to encode a non-canonical poly(A) polymerase (ncPAP). However, its target mRNAs and its role in MM pathogenesis remain mostly unknown. Using CRISPR-Cas9 technology and gene expression analysis, we found that the inactivation of FAM46C in MM down-regulates immunoglobulins (Igs) and several mRNAs encoding ER-resident proteins, including some involved in unfolded protein response and others that affect glycosylation. Interestingly, we show that FAM46C expression is induced during plasma cell (PC) differentiation and that Ig mRNAs encoding heavy and light chains are substrates of the ncPAP, as revealed by poly(A) tail-length determination assays. The absence of the ncPAP results in Ig mRNA poly(A) tail-shortening, leading to a reduction in mRNA and protein abundance. On the other hand, loss of FAM46C up-regulates metastasis-associated lncRNA MALAT1 and results in a sharp increase in the migration ability. This phenotype depends mainly on the activation of PI3K/Rac1 signalling, which might have significant therapeutic implications. In conclusion, our results identify Ig mRNAs as targets of FAM46C, reveal an important function of this protein during PC maturation to increase antibody production and suggest that its role as a tumour suppressor might be related to the inhibition of myeloma cell migration.

SUBMITTER: Herrero AB

PROVIDER: S-EPMC7171423 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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FAM46C controls antibody production by the polyadenylation of immunoglobulin mRNAs and inhibits cell migration in multiple myeloma.

Herrero Ana Belén AB Quwaider Dalia D Corchete Luis Antonio LA Mateos Maria Victoria MV García-Sanz Ramón R Gutiérrez Norma C NC

Journal of cellular and molecular medicine 20200306 7

FAM46C, frequently mutated in multiple myeloma (MM), has recently been shown to encode a non-canonical poly(A) polymerase (ncPAP). However, its target mRNAs and its role in MM pathogenesis remain mostly unknown. Using CRISPR-Cas9 technology and gene expression analysis, we found that the inactivation of FAM46C in MM down-regulates immunoglobulins (Igs) and several mRNAs encoding ER-resident proteins, including some involved in unfolded protein response and others that affect glycosylation. Inter ...[more]

PMID: 32141701

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Project description:FAM46C is a multiple myeloma (MM) tumor suppressor whose function is only starting to be elucidated. We recently showed that in MM cells FAM46C triggers apoptosis by inhibiting autophagy and altering intracellular trafficking and protein secretion. To date, both a physiological characterization of FAM46C role and an assessment of FAM46C-induced phenotypes outside of MM are lacking. Preliminary reports suggested an involvement of FAM46C with regulation of viral replication, but this was never confirmed. Here, we show that FAM46C is an interferon-stimulated gene and that the expression of wild-type FAM46C in HEK-293T cells, but not of its most frequently found mutant variants, inhibits the production of both HIV-1-derived and HIV-1 lentiviruses. We demonstrate that this effect does not require transcriptional regulation and does not depend on inhibition of either global or virus-specific translation but rather mostly relies on FAM46C-induced deregulation of autophagy, a pathway that we show to be required for efficient lentiviral particle production. These studies not only provide new insights on the physiological role of the FAM46C protein but also could help in implementing more efficient antiviral strategies on one side and lentiviral particle production approaches on the other. IMPORTANCE FAM46C role has been thoroughly investigated in MM, but studies characterizing its role outside of the tumoral environment are still lacking. Despite the success of antiretroviral therapy in suppressing HIV load to undetectable levels, there is currently no HIV cure, and treatment is lifelong. Indeed, HIV continues to be a major global public health issue. Here, we show that FAM46C expression in HEK-293T cells inhibits the production of both HIV and HIV-derived lentiviruses. We also demonstrate that such inhibitory effect relies, at least in part, on the well-established regulatory role that FAM46C exerts on autophagy. Deciphering the molecular mechanism underlying this regulation will not only facilitate the understanding of FAM46C physiological role but also give new insights on the interplay between HIV and the cellular environment.

Project description:BackgroundMultiple myeloma (MM) is a hematologic malignancy characterized by the accumulation of aberrant plasma cells within the bone marrow. The high frequent mutation of family with sequence similarity 46, member C (FAM46C) is closely related with the occurrence and progression of MM. Recently, FAM46C has been identified as a non-canonical poly(A) polymerase (PAP) that functions as a tumor suppressor in MM. This study aimed to elucidate the structural features of this novel non-canonical PAP and how MM-related mutations affect the structural and biochemical properties of FAM46C, eventually advancing our understandings towards FAM46C mutation-related MM occurrence.MethodsWe purified and crystallized a mammalian FAM46C construct, and solved its structure. Next, we characterized the property of FAM46C as a PAP through a combination of structural analysis, site-directed mutagenesis and biochemical assays, and by comparison with its homolog FAM46B. Finally, we structurally analyzed MM-related FAM46C mutations and tested the enzymatic activity of corresponding mutants.ResultsWe determined the crystal structure of a mammalian FAM46C protein at 2.35 Å, and confirmed that FAM46C preferentially consumed adenosine triphosphate (ATP) and extended A-rich RNA substrates. FAM46C showed a weaker PAP activity than its homolog FAM46B, and this difference was largely dependent on the residue variance at particular sites. Of them, residues at positions 77, 290, and 298 of mouse FAM46C were most important for the divergence in enzymatic activity. Among the MM-associated FAM46C mutants, those residing at the catalytic site (D90G and D90H) or putative RNA-binding site (I155L, S156F, D182Y, F184L, Y247V, and M270V) showed abolished or compromised PAP activity of FAM46C, while N72A and S248A did not severely affect the PAP activity. FAM46C mutants D90G, D90H, I155L, S156F, F184L, Y247V, and M270V had significantly lower inhibitory effect on apoptosis of RPMI-8226 cells as compared to wild-type FAM46C.ConclusionsFAM46C is a prokaryotic-like PAP with preference for A-rich RNA substrates, and showed distinct enzymatic efficiency with its homolog FAM46B. The MM-related missense mutations of FAM46C lead to various structural and biochemical outcomes to the protein.

Dataset Information

FAM46C controls antibody production by the polyadenylation of immunoglobulin mRNAs and inhibits cell migration in multiple myeloma.

Publications

FAM46C controls antibody production by the polyadenylation of immunoglobulin mRNAs and inhibits cell migration in multiple myeloma.

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