title: Alternative splicing of the cell fate determinant Numb in hepatocellular carcinoma.
abstract: The cell fate determinant Numb is aberrantly expressed in cancer. Numb is alternatively spliced, with one isoform containing a long proline-rich region (PRR(L) ) compared to the other with a short PRR (PRR(S) ). Recently, PRR(L) was reported to enhance proliferation of breast and lung cancer cells. However, the importance of Numb alternative splicing in hepatocellular carcinoma (HCC) remains unexplored. We report here that Numb PRR(L) expression is increased in HCC and associated with early recurrence and reduced overall survival after surgery. In a panel of HCC cell lines, PRR(L) generally promotes and PRR(S) suppresses proliferation, migration, invasion, and colony formation. Knockdown of PRR(S) leads to increased Akt phosphorylation and c-Myc expression, and Akt inhibition or c-Myc silencing dampens the proliferative impact of Numb PRR(S) knockdown. In the cell models explored in this study, alternative splicing of Numb PRR isoforms is coordinately regulated by the splicing factor RNA-binding Fox domain containing 2 (RbFox2) and the kinase serine/arginine protein-specific kinase 2 (SRPK2). Knockdown of the former causes accumulation of PRR(L) , while SRPK2 knockdown causes accumulation of PRR(S) . The subcellular location of SRPK2 is regulated by the molecular chaperone heat shock protein 90, and heat shock protein 90 inhibition or knockdown phenocopies SRPK2 knockdown in promoting accumulation of Numb PRR(S) . Finally, HCC cell lines that predominantly express PRR(L) are differentially sensitive to heat shock protein 90 inhibition.
  
  
  CONCLUSIONS
  Alternative splicing of Numb may provide a useful prognostic biomarker in HCC and is pharmacologically tractable.
authors.affiliation: Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, Beijing, China.|Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Yinying
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Wanping
authors.initials: W
authors.lastname: Xu
authors.affiliation: Liver Carcinogenesis Section, Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Junfang
authors.initials: J
authors.lastname: Ji
authors.affiliation: Laboratory of Liver Diseases, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD.
authors.forename: Dechun
authors.initials: D
authors.lastname: Feng
authors.affiliation: Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Carole
authors.initials: C
authors.lastname: Sourbier
authors.affiliation: Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Youfeng
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, Beijing, China.
authors.forename: Jianhui
authors.initials: J
authors.lastname: Qu
authors.affiliation: Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, Beijing, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zeng
authors.affiliation: Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, Beijing, China.
authors.forename: Chunping
authors.initials: C
authors.lastname: Wang
authors.affiliation: Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, Beijing, China.
authors.forename: Xiujuan
authors.initials: X
authors.lastname: Chang
authors.affiliation: Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, Beijing, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Alok
authors.initials: A
authors.lastname: Mishra
authors.affiliation: Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Max
authors.initials: M
authors.lastname: Xu
authors.affiliation: Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Min-Jung
authors.initials: MJ
authors.lastname: Lee
authors.affiliation: Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Sunmin
authors.initials: S
authors.lastname: Lee
authors.affiliation: Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Jane
authors.initials: J
authors.lastname: Trepel
authors.affiliation: Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: W Marston
authors.initials: WM
authors.lastname: Linehan
authors.affiliation: Liver Carcinogenesis Section, Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Xinwei
authors.initials: X
authors.lastname: Wang
authors.affiliation: Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, Beijing, China.
authors.forename: Yongping
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD.
authors.forename: Len
authors.initials: L
authors.lastname: Neckers
mesh_terms: D017398:Alternative Splicing; D006528:Carcinoma, Hepatocellular / Q000235:genetics*; D002454:Cell Differentiation / Q000235:genetics*; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D014407:Tumor Cells, Cultured
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C113026:NUMB protein, human