title: Rad5 template switch pathway of DNA damage tolerance determines synergism between cisplatin and NSC109268 in Saccharomyces cerevisiae.
abstract: The success of cisplatin (CP) based therapy is often hindered by acquisition of CP resistance. We isolated NSC109268 as a compound altering cellular sensitivity to DNA damaging agents. Previous investigation revealed an enhancement of CP sensitivity by NSC109268 in wild-type Saccharomyces cerevisiae and CP-sensitive and -resistant cancer cell lines that correlated with a slower S phase traversal. Here, we extended these studies to determine the target pathway(s) of NSC109268 in mediating CP sensitization, using yeast as a model. We reasoned that mutants defective in the relevant target of NSC109268 should be hypersensitive to CP and the sensitization effect by NSC109268 should be absent or strongly reduced. A survey of various yeast deletion mutants converged on the Rad5 pathway of DNA damage tolerance by template switching as the likely target pathway of NSC109268 in mediating cellular sensitization to CP. Additionally, cell cycle delays following CP treatment were not synergistically influenced by NSC109268 in the CP hypersensitive rad5Δ mutant. The involvement of the known inhibitory activities of NSC109268 on 20S proteasome and phosphatases 2Cα and 2A was tested. In the CP hypersensitive ptc2Δptc3Δpph3Δ yeast strain, deficient for 2C and 2A-type phosphatases, cellular sensitization to CP by NSC109268 was greatly reduced. It is therefore suggested that NSC109268 affects CP sensitivity by inhibiting the activity of unknown protein(s) whose dephosphorylation is required for the template switch pathway.
authors.affiliation: Department of Cell Biology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States of America.
authors.forename: Dilip
authors.initials: D
authors.lastname: Jain
authors.forename: Wolfram
authors.initials: W
authors.lastname: Siede
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D002945:Cisplatin / Q000494:pharmacology*; D056831:Coordination Complexes / Q000494:pharmacology*; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004249:DNA Damage / Q000187:drug effects*; D004265:DNA Helicases / Q000235:genetics*; D026141:Drug Resistance, Multiple, Fungal / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D017353:Gene Deletion; D006801:Humans; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*
chemical_list: D000970:Antineoplastic Agents; D056831:Coordination Complexes; D003432:Cross-Linking Reagents; C551925:NSC 109268; D029701:Saccharomyces cerevisiae Proteins; C076225:RAD5 protein, S cerevisiae; D004265:DNA Helicases; D002945:Cisplatin