Comparison of O⁶-alkylguanine-DNA alkyltransferase activity based on cellular DNA content in human, rat and mouse tissues

Abstract

O6-Alkylguanine-DNA alkyltransferase (alkyltransferase) is the repair protein for O6-alkylguanine, a pre-mutagenic adduct formed by a variety of alkylating agents. Previous comparisons of the repair capacity of O6-alkylguanine in different tissues have expressed the alkyltransferase activity relative to total protein, and have asserted that tissues with low levels of activity were at greater risk for mutagenic damage than tissues with higher levels of activity. Because the alkyltransferase uses DNA as substrate, and because tissues vary greatly in protein content, comparisons of tissue alkyltransferase activity may be more appropriately based on cellular DNA content. We compared alkyltransferase activity relative to tissue DNA content with the activity related to protein content in human, rat and mouse tissues. In each species, liver containing the highest level of activity using either method. In agreement with the findings of others, low levels of alkyltransferase activity relative to protein were seen in human brain, rat brain and small intestine, and mouse kidney. However, based on alkyltransferase activity relative to DNA content, low levels of activity were seen in human bone marrow myeloid precursors, rat bone marrow, brain and intestine, and mouse spleen and bone marrow. The range of activity between tissues was 18-fold in human, 15-fold in rat and 8-fold in mouse. In general, the rank of alkyltransferase activity relative to DNA for each tissue was human greater than rat greater than mouse. These results suggest that the mouse is more susceptible to nitrosoureas than rat or human. In each species, the organs with low levels of alkyltransferase activity relative to tissue DNA content would appear to be targets for mutagenic damage following nitrosourea exposure.

High Expression of a New Marker PCA-1 in Human Prostate Carcinoma

“…However, among tissues, the activities of these repair enzymes are somewhat different. For example, the highest activity of AGT is detected in the liver, followed by the lung and kidney, with much lower activity in the pancreas, hematopoietic cells, and lymphoid tissues (37,38). In normal human tissues, the expression of pca-1 mRNA is also ubiquitous and variable, with the highest expression being in the testis, pancreas, and ovary.…”

The detection of alkylation damage in the DNA of human gastrointestinal tissues

“…After treatment, nuclear reactions can repair alkylation injury to DNA to a variable extent, thereby adding further to this heterogeneity (O'Connor et al, 1991). In human tissue, similar factors would be expected to operate since in man and the rat, similar systems are responsible for the metabolism of environmental nitrosamines such as NDMA (Yoo et al, 1988) and for the repair of O6-MeG (Pegg, 1983;Gerson et al, 1986).…”

CpG methylation of MGMT and hMLH1 promoter in hepatocellular carcinoma associated with hepatitis viral infection

“…Since ubiquitous and environmental alkylating agents such as N-nitroso compounds are principally metabolised and activated in mammalian hepatocytes, liver tissue is persistently exposed to activated alkylating agents (Gerson et al, 1986). It was demonstrated that Mgmt-targeted mice (Mgmt À/À ) treated with alkylating agents generated hepatocellular carcinoma (Iwakuma et al, 1997).…”