title: Stable alterations of CD44 isoform expression in prostate cancer cells decrease invasion and growth and alter ligand binding and chemosensitivity.
abstract: BACKGROUND
  Dysregulated CD44 expression characterizes most human cancers, including prostate cancer (PCa). PCa loses expression of CD44 standard (CD44s) that is present in benign epithelium, and overexpresses the novel splice variant isoform, CD44v7-10.
  
  
  METHODS
  Using retroviral gene delivery to PC-3M PCa cells, we expressed luciferase-only, enforced CD44s re-expression as a fusion protein with luciferase at its C-terminus or as a protein separate from luciferase, or knocked down CD44v7-10 by RNAi. Invasion, migration, proliferation, soft agar colony formation, adhesion, Docetaxel sensitivity, and xenograft growth assays were carried out. Expression responses of merlin, a CD44 binding partner, and growth-permissive phospho-merlin, were assessed by western blot.
  
  
  RESULTS
  Compared to luciferase-only PC-3M cells, all three treatments reduced invasion and migration. Growth and soft agar colony formation were reduced only by re-expression of CD44s as a separate or fusion protein but not CD44v7-10 RNAi. Hyaluronan and osteopontin binding were greatly strengthened by CD44s expression as a separate protein, but not a fusion protein. CD44v7-10 RNAi in PC-3M cells caused marked sensitization to Docetaxel; the two CD44s re-expression approaches caused minimal sensitization. In limited numbers of mouse subcutaneous xenografts, all three alterations produced only nonsignificant trends toward slower growth compared with luciferase-only controls. The expression of CD44s as a separate protein, but not a fusion protein, caused emergence of a strongly-expressed, hypophosphorylated species of phospho-merlin.
  
  
  CONCLUSIONS
  Stable re-expression of CD44s reduces PCa growth and invasion in vitro, and possibly in vivo, suggesting CD44 alterations have potential as gene therapy. When the C-terminus of CD44s is fused to another protein, most phenotypic effects are lessened, particularly hyaluronan adhesion. Finally, CD44v7-10, although it was not functionally significant for growth, may be a target for chemosensitization.
authors.affiliation: Department of Pathology, University of Colorado Denver Health Science Center, Aurora, Colorado, USA.
authors.forename: Kui
authors.initials: K
authors.lastname: Yang
authors.forename: Yaqiong
authors.initials: Y
authors.lastname: Tang
authors.forename: Gabriel K
authors.initials: GK
authors.lastname: Habermehl
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Iczkowski
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002448:Cell Adhesion; D002465:Cell Movement; D000077143:Docetaxel; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018960:Hyaluronan Receptors / Q000096:biosynthesis* / Q000737:chemistry; D008024:Ligands; D008297:Male; D051379:Mice; D009361:Neoplasm Invasiveness; D009368:Neoplasm Transplantation; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000378:metabolism*; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D043823:Taxoids / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D018960:Hyaluronan Receptors; D008024:Ligands; D020033:Protein Isoforms; D043823:Taxoids; D000077143:Docetaxel