O(6)-methylguanine-DNA methyltransferase activity, p53 gene status and BCNU resistance in mouse astrocytes.
We observed previously that wild-type p53 rendered neonatal mouse astrocytes resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in a gene dose-dependent fashion. This effect of p53 appeared to be unrelated to its cell cycle regulation or apoptotic functions. Because in many cell types O(6)-methylguanine-DNA methyltransferase (MGMT)-mediated DNA repair is an important mechanism of resistance to nitrosoureas, we measured MGMT activity in wild-type, heterozygous and p53 knockout neonatal mouse astrocytes. Wild-type p53 astrocytes had significantly greater MGMT activity than either heterozygous or p53 knockout astrocytes: MGMT activity was approximately 5-fold greater in wild-type p53 astrocytes than in p53 knockout cells. However, despite successful depletion of MGMT activity in wild-type astrocytes by O(6)-benzylguanine (BG), resistance to BCNU persisted unchanged. Moreover, we excluded the possibility that continued resistance to BCNU at the concentrations used could be explained by a compensatory induction of MGMT triggered by exposure to either BCNU or BG. Although these studies support a role for p53 regulation of MGMT in neonatal mouse astrocytes, BCNU resistance in wild-type cells appears to be mediated by a non-MGMT mechanism. Nevertheless, regulation of DNA repair by MGMT may be another mechanism by which alterations of the p53 gene promote tumor initiation or progression.
Nutt
C L
CL
Department of Oncology, University of Western Ontario and London Regional Cancer Centre, London, Ontario N6A 4L6, Canada.
Loktionova
N A
NA
Pegg
A E
AE
Chambers
A F
AF
Cairncross
J G
JG
D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D001253:Astrocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D001483:Base Sequence; D002330:Carmustine / Q000494:pharmacology*; D017931:DNA Primers; D004351:Drug Resistance; D004790:Enzyme Induction; D016158:Genes, p53; D051379:Mice; D018345:Mice, Knockout; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000096:biosynthesis / Q000378:metabolism*
D018906:Antineoplastic Agents, Alkylating; D017931:DNA Primers; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002330:Carmustine