title: Knockdown of RNA binding protein musashi-1 leads to tumor regression in vivo.
abstract: OBJECTIVE
  In the gut, tumorigenesis is thought to arise from the stem cell population located near the base of intestinal and colonic crypts. The RNA binding protein musashi-1 (Msi-1) is a putative intestinal and progenitor/stem cell marker. Msi-1 expression is increased during rat brain development and in APC(min/+) mice tumors. This study examined a potential role of Msi-1 in tumorigenesis.
  
  
  METHODS
  Msi-1 small interfering RNA (siRNA) was administered as a liposomal preparation to HCT116 colon adenocarcinoma xenografts in athymic nude mice and tumor volume was measured. Cell proliferation was assessed by hexosaminidase and 3-(4,5-dimethylthiazol 2-yl)-2,5-diphenyltetrazolium bromide MTT assays. siRNA-transfected cells were subjected to 12 Gy gamma-irradiation. Apoptosis was assessed by immunoreactive activated caspase-3 and mitosis was assessed by phosphorylated histone H3 staining. The tumor xenografts were stained similarly for phosphorylated histone H3, activated caspase-3, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, Notch-1, and p21(WAF1). Furthermore, siRNA-transfected cells were subjected to cell-cycle analysis and Western blot analyses for Notch-1 and p21(WAF1).
  
  
  RESULTS
  Knockdown of Msi-1 resulted in tumor growth arrest in xenografts, reduced cancer cell proliferation, and increased apoptosis alone and in combination with radiation injury. siRNA-mediated reduction of Msi-1 lead to mitotic catastrophe in tumor cells. Moreover, there was inhibition of Notch-1 and up-regulation of p21(WAF1) after knockdown of Msi-1.
  
  
  CONCLUSIONS
  Our results show the involvement of Msi-1 in cancer cell proliferation, inhibition of apoptosis, and mitotic catastrophe, suggesting an important potential mechanism for its role in tumorigenesis.
authors.affiliation: Department of Medicine, Division of Digestive Diseases and Nutrition, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
authors.forename: Sripathi M
authors.initials: SM
authors.lastname: Sureban
authors.forename: Randal
authors.initials: R
authors.lastname: May
authors.forename: Robert J
authors.initials: RJ
authors.lastname: George
authors.forename: Brian K
authors.initials: BK
authors.lastname: Dieckgraefe
authors.forename: Howard L
authors.initials: HL
authors.lastname: McLeod
authors.forename: Satish
authors.initials: S
authors.lastname: Ramalingam
authors.forename: Kumar S
authors.initials: KS
authors.lastname: Bishnupuri
authors.forename: Gopalan
authors.initials: G
authors.lastname: Natarajan
authors.forename: Shrikant
authors.initials: S
authors.lastname: Anant
authors.forename: Courtney W
authors.initials: CW
authors.lastname: Houchen
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D017209:Apoptosis; D014408:Biomarkers, Tumor; D015153:Blotting, Western; D049109:Cell Proliferation; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D018450:Disease Progression; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014183:Transplantation, Heterologous
chemical_list: D014408:Biomarkers, Tumor; C491297:MSI1 protein, human; C104786:Msi1h protein, mouse; D009419:Nerve Tissue Proteins; D012334:RNA, Neoplasm; D016601:RNA-Binding Proteins