Long-time expression of DNA repair enzymes MGMT and APE in human peripheral blood mononuclear cells

Abstract

The DNA repair enzymes O6-methylguanine-DNA methyltransferase (MGMT) and apurinic/apyrimidinic endonuclease (APE, also known as Ref-1) play an important role in cellular defense against the mutagenic and carcinogenic effects of DNA-damaging agents. Cells with low enzyme activity are more sensitive to induced DNA damage and may confer a higher carcinogenic risk to the individuals in question. To study the level of variability of MGMT and APE expression in human, we analyzed in a long-time study MGMT and APE expression in peripheral blood mononuclear cells (PBMC) from healthy individuals. The data revealed high inter- and intraindividual variability of MGMT but not of APE. For MGMT, the interindividual levels ranged from 27 to 204 fmol/10(6) cells (7.6-fold, 40 healthy individuals). The intraindividual variation was determined by measuring MGMT repeatedly over 42 days, and was found to vary from 1.4-fold to 3.5-fold. Averaging over the measurement period, some individuals displayed low MGMT activity compared to others. In contrast, APE expression showed only a 2.9-fold difference between individuals and a 1.2 to 2.3-fold intra-individual long-time variation, and thus was less variable than MGMT. MGMT and APE expression were not correlated. Overall the results showed variable MGMT and rather constant APE levels in PBMC of healthy individuals measured over a long period.

Smoking is associated with a decrease of O6‐alkylguanine‐DNA alkyltransferase activity in bronchial epithelial cells

“…Such a lack of association has been reported for several tissues by several authors in different tissues. 11,12,15 In our study material, there was also no significant correlation with age. Previous studies using surgically resected lung tissues 12,15 or lymphocytes 25,26 have also failed to find an association between age and activity.…”

“…The causes underlying differences in MGMT activity have been the focus of several studies. 8,10,11 Studies attempting to show whether in humans exposure to cigarette smoke causes an increase of MGMT activity in normal tissues have led to contradictory results. Some reports describe such increases, 12 while other studies report no association.…”

Apoptosis triggered by DNA damage O6-methylguanine in human lymphocytes requires DNA replication and is mediated by p53 and Fas/CD95/Apo-1

“…Using this approach, we were able to compare resting and proliferating lymphocytes with respect to their apoptotic response upon the treatment with the O 6 MeG-generating model agent MNNG. Human lymphocytes express MGMT (average expression level B700 fmol/mg protein (Janssen et al, 2001 and unpublished data) that would repair O 6 MeG in (Moschel et al, 1992) prior to MNNG exposure. Apoptosis was quantified by determining subG1 fraction (for an example, see Figure 1c,d).…”

“…To determine the contribution of MGMT on apoptosis, cells were pretreated with 10 mM O 6 BG 1 h before MNNG treatment. This concentration of O 6 BG was highly effective in depleting cells completely with respect to MGMT activity, which in undepleted cells was in the range of 400-600 fmol/mg protein (Janssen et al, 2001). Cells were stimulated with anti-CD3 and anti-CD28 for 24 h before mutagen treatment.…”

Inhibition of O6-Methylguanine-DNA Methyltransferase by Glucose-Conjugated Inhibitors: Comparison with Nonconjugated Inhibitors and Effect on Fotemustine and Temozolomide-Induced Cell Death

“…For instance, in human lymphocytes it ranges in expression between 27 and 204 fmol/10 6 cells (i.e., 7.6-fold). A given expression level in lymphocytes seems to be stable and therefore may reflect the personal situation (Janssen et al, 2001), although various environmental factors exert influence on MGMT expression (for review, see Margison et al, 2003). In tumors, MGMT is tumor type-specific, expressed with low expression in brain and malignant melanomas and high expression in ovarian and breast tumors (Preuss et al, 1996a;Hengstler et al, 1999;Margison et al, 2003).…”