title: Betulinic acid inhibits colon cancer cell and tumor growth and induces proteasome-dependent and -independent downregulation of specificity proteins (Sp) transcription factors.
abstract: BACKGROUND
  Betulinic acid (BA) inhibits growth of several cancer cell lines and tumors and the effects of BA have been attributed to its mitochondriotoxicity and inhibition of multiple pro-oncogenic factors. Previous studies show that BA induces proteasome-dependent degradation of specificity protein (Sp) transcription factors Sp1, Sp3 and Sp4 in prostate cancer cells and this study focused on the mechanism of action of BA in colon cancer cells.
  
  
  METHODS
  The effects of BA on colon cancer cell proliferation and apoptosis and tumor growth in vivo were determined using standardized assays. The effects of BA on Sp proteins and Sp-regulated gene products were analyzed by western blots, and real time PCR was used to determine microRNA-27a (miR-27a) and ZBTB10 mRNA expression.
  
  
  RESULTS
  BA inhibited growth and induced apoptosis in RKO and SW480 colon cancer cells and inhibited tumor growth in athymic nude mice bearing RKO cells as xenograft. BA also decreased expression of Sp1, Sp3 and Sp4 transcription factors which are overexpressed in colon cancer cells and decreased levels of several Sp-regulated genes including survivin, vascular endothelial growth factor, p65 sub-unit of NFκB, epidermal growth factor receptor, cyclin D1, and pituitary tumor transforming gene-1. The mechanism of action of BA was dependent on cell context, since BA induced proteasome-dependent and proteasome-independent downregulation of Sp1, Sp3 and Sp4 in SW480 and RKO cells, respectively. In RKO cells, the mechanism of BA-induced repression of Sp1, Sp3 and Sp4 was due to induction of reactive oxygen species (ROS), ROS-mediated repression of microRNA-27a, and induction of the Sp repressor gene ZBTB10.
  
  
  CONCLUSIONS
  These results suggest that the anticancer activity of BA in colon cancer cells is due, in part, to downregulation of Sp1, Sp3 and Sp4 transcription factors; however, the mechanism of this response is cell context-dependent.
authors.affiliation: Department of Veterinary Physiology & Pharmacology, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Sudhakar
authors.initials: S
authors.lastname: Chintharlapalli
authors.forename: Sabitha
authors.initials: S
authors.lastname: Papineni
authors.forename: Ping
authors.initials: P
authors.lastname: Lei
authors.forename: Satya
authors.initials: S
authors.lastname: Pathi
authors.forename: Stephen
authors.initials: S
authors.lastname: Safe
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D015536:Down-Regulation / Q000187:drug effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism; D053978:Pentacyclic Triterpenes; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D051703:Sp Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014315:Triterpenes / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays; D000094062:Betulinic Acid
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C531388:MIRN27 microRNA, human; D035683:MicroRNAs; D053978:Pentacyclic Triterpenes; D012097:Repressor Proteins; D051703:Sp Transcription Factors; D014315:Triterpenes; C559929:ZBTB10 protein, human; D046988:Proteasome Endopeptidase Complex; D000094062:Betulinic Acid