Related Experiment Videos
Affinity purification and characterization of human O6-alkylguanine-DNA alkyltransferase complexed with BCNU-treated,
1Department of Biochemical and Clinical Pharmacology, St. Jude Children's Research Hospital, Memphis, TN 38101.
Abstract:
Tumor cells resistant to chloroethylnitrosourea (CENU) therapy contain high levels of O6-alkylguanine DNA-alkyltransferase (GATase), a DNA repair enzyme that aborts DNA interstrand cross-linking by removing CENU-induced O6-alkylguanine adducts. Because the transferase binds covalently to CENU-treated oligonucleotides, we reacted partially purified GATase from cultured human lymphoblasts with a BCNU-treated, 35S-5'-end-labeled, synthetic oligonucleotide designed to have a polyadenylated 3' terminus. Immunoprobing Western blots of this reaction mixture with GATase-specific monoclonal antibody indicated that 25-30% of the transferase became complexed. We purified this complex by affinity chromatography with oligo(dT) cellulose, recovering homogenous material that appeared as a discrete 35-kDa Coomassie blue or silver-stained band after SDS-polyacrylamide gel electrophoresis. Autoradiography and Western immunoblotting confirmed that this band contained both the radiolabeled oligonucleotide and the GATase protein.
Insights
Tumor cells resistant to chloroethylnitrosourea (CENU) therapy have high levels of O6-alkylguanine DNA-alkyltransferase (GATase). This study purified a complex of GATase bound to CENU-treated DNA, aiding in understanding CENU resistance mechanisms.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Tumor cells resistant to chloroethylnitrosourea (CENU) therapy exhibit elevated levels of O6-alkylguanine DNA-alkyltransferase (GATase).
- GATase is a DNA repair enzyme crucial for removing CENU-induced O6-alkylguanine adducts, thereby preventing DNA interstrand cross-linking and conferring resistance.
- Understanding the interaction between GATase and CENU-treated DNA is vital for developing strategies to overcome therapeutic resistance.
Purpose of the Study:
- To investigate the interaction between O6-alkylguanine DNA-alkyltransferase (GATase) and chloroethylnitrosourea (CENU)-treated DNA.
- To purify and characterize the complex formed between GATase and CENU-modified oligonucleotides.
- To provide insights into the molecular mechanisms underlying CENU resistance in tumor cells.
Main Methods:
- Partially purified GATase from cultured human lymphoblasts was reacted with a 35S-5'-end-labeled, synthetic oligonucleotide treated with BCNU (a type of CENU).
- The reaction mixture was analyzed using immunoprobing with a GATase-specific monoclonal antibody and Western blotting.
- Complexes were purified using oligo(dT) cellulose affinity chromatography and analyzed by SDS-polyacrylamide gel electrophoresis, autoradiography, and Western immunoblotting.
Main Results:
- Immunoprobing and Western blotting indicated that 25-30% of the GATase formed complexes with the CENU-treated oligonucleotide.
- Affinity chromatography successfully purified a homogenous complex, appearing as a distinct 35-kDa band on SDS-PAGE.
- Autoradiography and Western immunoblotting confirmed the presence of both the radiolabeled oligonucleotide and GATase protein within the purified complex.
Conclusions:
- O6-alkylguanine DNA-alkyltransferase (GATase) forms a covalent complex with chloroethylnitrosourea (CENU)-treated DNA.
- The purification of this complex provides a method for studying the interaction between GATase and its DNA adducts.
- These findings contribute to understanding the mechanism of CENU resistance and may inform future therapeutic strategies.