The role of mRNA stability and transcription in O6-methylguanine DNA methyltransferase (MGMT) expression in Mer+ human tumor cells.
We have recently reported that following depletion of O6-methylguanine DNA methyltransferase (MGMT) activity by acute streptozotocin (STZ) treatment to sensitize innately chloroethylnitrosourea (CENU)-resistant HT-29 cells, the eventual repletion of activity occurs with no concommitant alterations in steady-state MGMT mRNA levels. This suggestion of a potentially stable transcript prompted studies to define the relative contributions of MGMT mRNA stability and transcription to cellular MGMT expression. Northern analysis of MGMT mRNA in actinomycin D-treated HT-29, MR-1 and A2182 cells, ranging in relative MGMT expression from high to low respectively, demonstrates relatively long MGMT mRNA half-lives of > 10-12 h. Cell lines with low and moderate levels of MGMT mRNA appear to have longer mRNA half-lives than those with high levels. Run-on transcription in nuclei isolated from cells with low to moderate MGMT mRNA levels demonstrates undetectable basal MGMT transcription rates. Collectively these data suggest that a very low transcription rate, coupled with a stable mRNA molecule, might result in the translation of pre-existing mRNA molecules. This translation may be responsible for the gradual recovery of MGMT and CENU resistance over 24 h following MGMT depletion.
Kroes
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RA
Department of Medicine, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
Erickson
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LC
D004260:DNA Repair; D004355:Drug Stability; D015870:Gene Expression; D019073:HT29 Cells / Q000201:enzymology* / Q000378:metabolism; D006801:Humans; D008745:Methylation; D008780:Methyltransferases / Q000096:biosynthesis* / Q000235:genetics; D019853:O(6)-Methylguanine-DNA Methyltransferase; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic
D012333:RNA, Messenger; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase