title: Relationship between cyclin D1 expression and poor radioresponse of murine carcinomas.
abstract: OBJECTIVE
  We recently reported that overexpression of epidermal growth factor receptor (EGFR) positively correlated with radioresistance of murine carcinomas. Because cyclin D1 is a downstream sensor of EGFR activation, the present study investigated whether a relationship exists between the extent of cyclin D1 expression and in vivo radiocurability of murine tumors. We further investigated the influence of radiation on cyclin D1 expression and the expression of p27, an inhibitor of the cyclin D1 downstream pathway, as well as the relationship of these molecular determinants to cell proliferation and induced apoptosis in tumors exposed to radiation.
  
  
  METHODS
  Cyclin D1 expression was assayed in nine carcinomas syngeneic to C3Hf/Kam mice using Western blot analysis. These tumors greatly differed in their radioresponse as assessed by TCD(50). The expression of cyclin D1 and p27 proteins was determined by Western blotting. Cell proliferative activity in tumors was determined by proliferating cell nuclear antigen (PCNA) immunochemistry. The effect of irradiation on the expression of cyclin D1 or p27 proteins and on PCNA positivity was determined in the radiosensitive OCa-I and in the radioresistant SCC-VII tumors.
  
  
  RESULTS
  Cyclin D1 expression varied among tumors by 40-fold, and its magnitude positively correlated with poorer tumor radioresponse (higher TCD(50) values). The level of cyclin D1 expression paralleled that of EGFR. A 15-Gy dose reduced constitutive expression of cyclin D1 in the radiosensitive OCa-I tumors, but had no influence on expression of cyclin D1 in the radioresistant SCC-VII tumors. In contrast, 15 Gy increased the expression of p27 in radiosensitive tumors and reduced it in radioresistant tumors. Radiation induced no significant apoptosis or change in the percentage of PCNA-positive (proliferating) cells in SCC-VII tumors with high cyclin D1 levels, but it induced significant apoptosis and a decrease in the percentage of proliferating cells in OCa-I tumors with low cyclin D1 expression.
  
  
  CONCLUSIONS
  Our findings show a positive correlation between cyclin D1 expression and tumor radioresistance. The expression of cyclin D1 and p27 was modified by radiation and was associated with cellular response to radiation, but this depended on the pretreatment level of cyclin D1 expression. These findings may have important clinical implications: The pretreatment assessment of cyclin D1 expression could serve as a useful predictor of radiotherapy outcome and assist in selecting an effective treatment modality.
authors.affiliation: Department of Experimental Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030-4009, USA. lmilas@mdanderson.org
authors.forename: Luka
authors.initials: L
authors.lastname: Milas
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Akimoto
authors.forename: Nancy R
authors.initials: NR
authors.lastname: Hunter
authors.forename: Kathyrn A
authors.initials: KA
authors.lastname: Mason
authors.forename: Lara
authors.initials: L
authors.lastname: Buchmiller
authors.forename: Michitaka
authors.initials: M
authors.lastname: Yamakawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Muramatsu
authors.forename: K Kian
authors.initials: KK
authors.lastname: Ang
mesh_terms: D000818:Animals; D017209:Apoptosis; D015415:Biomarkers; D015153:Blotting, Western; D002455:Cell Division; D019938:Cyclin D1 / Q000378:metabolism* / Q000528:radiation effects; D066246:ErbB Receptors / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D051379:Mice; D008809:Mice, Inbred C3H; D008840:Microfilament Proteins / Q000378:metabolism* / Q000528:radiation effects; D009124:Muscle Proteins; D009363:Neoplasm Proteins / Q000378:metabolism* / Q000528:radiation effects; D009369:Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism / Q000528:radiation effects; D011836:Radiation Tolerance / Q000502:physiology*; D011853:Radiobiology
chemical_list: D015415:Biomarkers; D008840:Microfilament Proteins; D009124:Muscle Proteins; D009363:Neoplasm Proteins; D018809:Proliferating Cell Nuclear Antigen; C058992:Tagln protein, mouse; D019938:Cyclin D1; D066246:ErbB Receptors