Pro-oncogenic Roles of HLXB9 Protein in Insulinoma Cells through Interaction with Nono Protein and Down-regulation of the c-Met Inhibitor Cblb (Casitas B-lineage Lymphoma b).
Pancreatic islet β-cells that lack the MEN1-encoded protein menin develop into tumors. Such tumors express the phosphorylated isoform of the β-cell differentiation transcription factor HLXB9. It is not known how phospho-HLXB9 acts as an oncogenic factor in insulin-secreting β-cell tumors (insulinomas). In this study we investigated the binding partners and target genes of phospho-HLXB9 in mouse insulinoma MIN6 β-cells. Co-immunoprecipitation coupled with mass spectrometry showed a significant association of phospho-HLXB9 with the survival factor p54nrb/Nono (54-kDa nuclear RNA-binding protein, non-POU-domain-containing octamer). Endogenous phospho-HLXB9 co-localized with endogenous Nono in the nucleus. Overexpression of HLXB9 decreased the level of overexpressed Nono but not endogenous Nono. Anti-phospho-HLXB9 chromatin immunoprecipitation followed by deep sequencing (ChIP-Seq) identified the c-Met inhibitor, Cblb, as a direct phospho-HLXB9 target gene. Phospho-HLXB9 occupied the promoter of Cblb and reduced the expression of Cblb mRNA. Cblb overexpression or HLXB9 knockdown decreased c-Met protein and reduced cell migration. Also, increased phospho-HLXB9 coincided with reduced Cblb and increased c-Met in insulinomas of two mouse models of menin loss. These data provide mechanistic insights into the role of phospho-HLXB9 as a pro-oncogenic factor by interacting with a survival factor and by promoting the oncogenic c-Met pathway. These mechanisms have therapeutic implications for reducing β-cell proliferation in insulinomas by inhibiting phospho-HLXB9 or its interaction with Nono and modulating the expression of its direct (Cblb) or indirect (c-Met) targets. Our data also implicate the use of pro-oncogenic activities of phospho-HLXB9 in β-cell expansion strategies to alleviate β-cell loss in diabetes.
From the Metabolic Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Shruti S
SS
Desai
From the Metabolic Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Sampada S
SS
Kharade
From the Metabolic Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Vaishali I
VI
Parekh
From the Metabolic Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Sucharitha
S
Iyer
From the Metabolic Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892 sunitaa@mail.nih.gov.
Sunita K
SK
Agarwal
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D007340:Insulinoma / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D009857:Oncogenes; D011485:Protein Binding; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D016601:RNA-Binding Proteins; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; C118387:Cblb protein, mouse; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; C500331:Nono protein, mouse; D016601:RNA-Binding Proteins; D014157:Transcription Factors; C084059:Hb9 protein, mouse; D050721:Proto-Oncogene Proteins c-cbl
PNET; c-Met; gene regulation; menin (MEN1); neuroendocrine; p54nrb/Nono; pancreatic islet; pathogenesis; phospho-HLXB9; tumor