title: Podophyllum hexandrum fraction (REC-2006) shows higher radioprotective efficacy in the p53-carrying hepatoma cell line: a role of cell cycle regulatory proteins.
abstract: The present study was carried out to evaluate the radioprotective efficacy of Podophyllum hexandrum fraction (REC-2006) in hepatoma cell lines having different p53 statuses. Higher radioresistance was observed in the HepG2 (p53(++)) cell line in comparison to the Hep3B (p53(-)) cell line, indicating a plausible role of p53 in radioresistance. REC-2006 exhibited nearly twice the survival in p53-expressing HepG2 cells compared with p53-negative Hep3B cells. REC-2006 treatment alone induced p53 expression as compared with untreated controls. However, REC-2006 reduced p53 expression when treated 2 hours before irradiation as compared with the irradiated HepG2 controls, indicating that REC-2006 modulates the expression of p53 to mitigate its apoptotic effect. Induction of p21 in the REC-2006 + radiation treatment group downregulated the expression of cyclin E and CDK2, leading to a delay in the G1 phase of HepG2 cells, which provided time for DNA repair or related processes. However, no significant difference in CDC2 expression in both cell lines suggested that G2 phase arrest might not be the only responsible factor for REC-2006-mediated radioprotection. Significant induction of PCNA and GADD45 expression in HepG2 cells suggested that REC-2006 increased the percentage survival of HepG2 cells by increasing the span of time as well as efficacy for repair processes. In conclusion, REC-2006 modulated the expression of p53 and thereby promoted cell cycle arrest in the G1 phase, encouraging cell proliferation and DNA repair and thus providing significantly higher protection against acute gamma-radiation in the HepG2 cell line.
authors.affiliation: Institute of Nuclear Medicine and Allied Sciences, Delhi, India.
authors.forename: Pankaj Kumar
authors.initials: PK
authors.lastname: Singh
authors.forename: Raj
authors.initials: R
authors.lastname: Kumar
authors.forename: Ashok
authors.initials: A
authors.lastname: Sharma
authors.forename: Rajesh
authors.initials: R
authors.lastname: Arora
authors.forename: Raman
authors.initials: R
authors.lastname: Chawla
authors.forename: Swatantra Kumar
authors.initials: SK
authors.lastname: Jain
authors.forename: Rakesh Kumar
authors.initials: RK
authors.lastname: Sharma
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1 / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D018844:Cyclin-Dependent Kinases; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D005720:Gamma Rays; D056945:Hep G2 Cells; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D010936:Plant Extracts / Q000494:pharmacology*; D011034:Podophyllotoxin / Q000031:analogs & derivatives / Q000494:pharmacology; D011035:Podophyllum / Q000737:chemistry*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D027343:Rhizome / Q000737:chemistry*; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D000097642:GADD45 Proteins
chemical_list: D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D019927:Cyclin E; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases; D009687:Nuclear Proteins; D010936:Plant Extracts; D011034:Podophyllotoxin; D018809:Proliferating Cell Nuclear Antigen; D011837:Radiation-Protective Agents; D016159:Tumor Suppressor Protein p53; C534699:CCNB1 protein, human; C493956:CDKN1A protein, human; C439070:GADD45A protein, human; D000097642:GADD45 Proteins; C528899:CDK1 protein, human; C495894:CDK2 protein, human