title: 5-fluorouracil mediates apoptosis and G1/S arrest in laryngeal squamous cell carcinoma via a p53-independent pathway.
abstract: OBJECTIVE
  5-Fluorouracil (5-FU) is a commonly used chemotherapeutic agent in the treatment of laryngeal squamous cell carcinoma. 5-FU can induce cell cycle arrest or apoptosis in various cancers via either a p53-dependent or a p53-independent pathway; however, its pathway of action in laryngeal carcinoma is unknown. In this study, we aim to investigate the role that p53 plays in the cytotoxic effect of 5-FU on laryngeal squamous carcinoma cells.
  
  
  METHODS
  We employed two human laryngeal squamous carcinoma cell lines with different p53 statuses-one (UMSCC12) had truncated non-functional p53 and the other (UMSCC11A) had mutant but functional p53. Cell death was detected using cytotoxicity assay and Annexin V staining. Cell cycles were analyzed by flow cytometry. Western blot was used to analyze the protein expression.
  
  
  RESULTS
  5-FU induces apoptosis in both UMSCC12 and UMSCC11A cells in a dose- and time-dependent manner, suggesting that the pathway was p53-independent. 5-FU induced the accumulation of retinoblastoma protein and a cyclin dependent kinase inhibitor, p21WAF1/CIP1, in both UMSCC12 and UMSCC11A cells. However, 5-FU did not induce p53 expression in either UMSCC12 or UMSCC11A cells. In addition, G1/S cell cycle phase arrest was associated with antiproliferative activity of 5-FU in both cell lines. In order to gain an insight into the role p53 plays in response to 5-FU treatment in laryngeal carcinoma, we further transfected either a wildtype p53 plasmid or an empty pcDNA3.1 vector into UMSCC12 cells. We found that 5-FU increased pRb and p21WAF1/CIP1 expression in both p53-transfected and vector-transfected cells without the significant accumulation of p53.
  
  
  CONCLUSIONS
  Our results suggest that 5-FU mediates apoptosis and G1/S cell cycle phase arrest in laryngeal carcinoma via a p53-independent but p21WAF1/CIP1-dependent or p21WAF1/CIP1-Rb-dependent pathway. While p53 does not seem to be involved in 5-FU induced apoptosis and cell cycle arrest in laryngeal carcinoma, further studies are needed to examine the roles of retinoblastoma protein and p21WAF1/CIP1 in laryngeal carcinoma receiving chemotherapy.
authors.affiliation: Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Han Ching
authors.initials: HC
authors.lastname: Liu
authors.forename: George G
authors.initials: GG
authors.lastname: Chen
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Vlantis
authors.forename: Billy C S
authors.initials: BC
authors.lastname: Leung
authors.forename: Michael C F
authors.initials: MC
authors.lastname: Tong
authors.forename: C Andrew
authors.initials: CA
authors.lastname: van Hasselt
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy*; D045744:Cell Line, Tumor; D004261:DNA Replication / Q000187:drug effects*; D005472:Fluorouracil / Q000494:pharmacology*; D016193:G1 Phase / Q000187:drug effects*; D006801:Humans; D007822:Laryngeal Neoplasms / Q000188:drug therapy*; D015398:Signal Transduction / Q000187:drug effects*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics
chemical_list: D000964:Antimetabolites, Antineoplastic; D016159:Tumor Suppressor Protein p53; D005472:Fluorouracil