title: CRABP I expression and the mediation of the sensitivity of human tumour cells to retinoic acid and irradiation.
abstract: OBJECTIVE
  To examine the role cytoplasmic retinoic acid binding protein type 1 (CRABP I) and retinoic acid receptor beta 2 (RAR-beta 2) in mediating radiosensitization of human tumour cells in vitro by retinoic acid.
  
  
  METHODS
  Human squamous cell carcinoma cell lines of different types were treated with retinoic acid followed by irradiation. Radiation response under drug treatment was detected by colony-formation assay. mRNA and protein expression levels of CRABP I, RAR-beta and cyclin D1 were investigated under different treatment conditions by room temperature polymerase chain reaction and Western blotting. The retinoic acid-sensitive cell line HTB35 was transfected for inducible CRABP I overexpression to test the role of this protein in modulating the sensitivity to retinoic acid and radiation as well as in regulating RAR-beta 2 and cyclin D1 expression.
  
  
  RESULTS
  The basal CRABP I level clearly correlated with the clonogenic survival of tumour cells and normal fibroblasts after treatment with retinoic acid and ionizing irradiation (IR). Cells expressing high basal CRABP I were more resistant to combined retinoic acid radiation treatment than cells with low basal expression. Overexpression of CRABP I in retinoic acid-sensitive HTB35 cells induced a retinoic acid-insensitive phenotype resistant to combined treatment with retinoic acid and radiation. This effect was independent of RAR-beta 2 expression. CRABP I overexpression resulted in stimulated cyclin D1 expression indicating the dependency of this cell cycle control protein on retinoic acid metabolism.
  
  
  CONCLUSIONS
  CRABP I plays an important role not only in mediating the retinoid effects, but also in modulating the radiation sensitivity of tumour cells after combined retinoic acid radiation treatment.
authors.affiliation: Section of Radiobiology and Molecular Environmental Research, Eberhard-Karls-University Tuebingen, Roentgenweg 11, D-72076 Tuebingen, Germany.
authors.forename: M A
authors.initials: MA
authors.lastname: Blaese
authors.forename: L
authors.initials: L
authors.lastname: Santo-Hoeltje
authors.forename: H P
authors.initials: HP
authors.lastname: Rodemann
mesh_terms: D045744:Cell Line, Tumor / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D006801:Humans; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology*; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology*; D014410:Tumor Stem Cell Assay
chemical_list: D011838:Radiation-Sensitizing Agents; D018168:Receptors, Retinoic Acid; C082927:retinoic acid binding protein I, cellular; C082925:retinoic acid receptor beta; D014212:Tretinoin