title: Involvement of cyclin D1-cdk5 overexpression and MCM3 cleavage in bax-associated spontaneous apoptosis and differentiation in an A253 human head and neck carcinoma xenograft model.
abstract: Time-dependent ladder-type DNA fragmentation and morphological alterations consistent with apoptosis were observed among A253 human head and neck squamous cell carcinoma (HNSCC) cells in nude mice from 15 to 18 days after transplantation, without any drug treatment. No evidence of ladder-type DNA fragmentation was detected in A253 cells in vitro or in normal nude mouse tissues (skin and muscle). Our aim was to explore molecular factors associated with such spontaneous apoptosis. Bcl-2 protein expression decreased, while bax protein expression increased from day 9 after transplantation. Moreover, altered expression of bcl-2 and bax was accompanied by the increased proteolytic cleavage of poly(ADP-ribose) polymerase (PARP). Time-dependent dephosphorylation of Rb, followed by proteolytic cleavage, was also observed from day 9 after transplantation. The data indicate that the caspase-3 activation and cleavage of Rb protein may represent important steps in the regulation pathway of bax-mediated spontaneous apoptosis. Interestingly, the time-dependent activation of spontaneous apoptosis was almost simultaneous with the induction of differentiation and increased expression of several differentiation-associated regulatory proteins. An increased expression of cyclin D1 and cyclin-dependent kinase-5 (cdk5) was observed from day 9 after transplantation, whereas only slight alteration of cdk4 expression was found. The time-dependent activation of cyclin D1 and cdk5 preceded both the induction of ladder-type DNA fragmentation and increased keratin pearl formation. Furthermore, MCM3 was cleaved early in spontaneous apoptosis and differentiation. Our observations suggest the involvement of cyclin D1-cdk5 overexpression and MCM3 cleavage in bax-mediated spontaneous apoptosis and differentiation in A253 xenografts. P53 and WAF1 proteins were not expressed in the xenografts, indicating that the changes in the regulatory proteins during apoptosis and differentiation were not p53 or WAF1 dependent.
authors.affiliation: Department of Pharmacology and Therapeutics, Grace Cancer Drug Center, Roswell Park Cancer Institute, Buffalo, NY, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Yin
authors.forename: K
authors.initials: K
authors.lastname: Tóth
authors.forename: S
authors.initials: S
authors.lastname: Cao
authors.forename: B
authors.initials: B
authors.lastname: Guo
authors.forename: C
authors.initials: C
authors.lastname: Frank
authors.forename: H K
authors.initials: HK
authors.lastname: Slocum
authors.forename: Y M
authors.initials: YM
authors.lastname: Rustum
mesh_terms: D000818:Animals; D017209:Apoptosis; D020170:Caspase 1 / Q000502:physiology; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D019938:Cyclin D1 / Q000502:physiology*; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D053938:DNA Fragmentation; D004268:DNA-Binding Proteins; D005260:Female; D006258:Head and Neck Neoplasms / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008819:Mice, Nude; D064126:Minichromosome Maintenance Complex Component 3; D009368:Neoplasm Transplantation; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
chemical_list: C494826:BAX protein, human; C494827:Bax protein, mouse; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C066470:MCM3 protein, human; C513269:Mcm3 protein, mouse; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D019938:Cyclin D1; D051360:Cyclin-Dependent Kinase 5; C495905:CDK5 protein, human; C495906:Cdk5 protein, mouse; D018844:Cyclin-Dependent Kinases; D020170:Caspase 1; D064126:Minichromosome Maintenance Complex Component 3