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Differential cellular and subcellular expression of the human multifunctional apurinic/apyrimidinic endonuclease
J R Duguid1, J N Eble, T M Wilson
1Department of Neurology and Medical Genetics, Indiana University School of Medicine, Indianapolis 46202, USA.
Abstract:
The multifunctional mammalian apurinic/apyrimidinic endonuclease (APE) is responsible for the repair of apurinic/apyrimidinic sites in DNA. In addition, this enzyme has been shown to function as a redox factor facilitating the DNA-binding capability of JUN and FOS, as well as numerous other transcription factors through the alteration of the transcription factor redox state. Biochemical studies of organ homogenates have shown that APE is present in the different tissues studied at similar concentrations. The present study examines the immunohistochemical distribution of APE in several organs and demonstrates new and unexpected patterns of cellular and subcellular localization of this enzyme. In the hippocampus, the APE protein was highly expressed in neurons of the dentate gyrus and regions CA3 and CA4, and unexpectedly, the staining was primarily cytoplasmic. AP endonuclease immunoreactivity in the cerebellum was found in the granule and Purkinje cells, both cytoplasmic and nuclear. APE staining of the hypoglossal nucleus of the brainstem, where motor neurons that control tongue movement reside, showed reactivity in the cytoplasmic Nissl substance. Skin, liver, and duodenum demonstrated nuclear staining; however, in the duodenum, only the enterocyte nuclei of the proximal villus and the crypts of Lieberkuhn were stained, with no staining of the distal villus. These results suggest that APE has different regulatory and functional roles in different cells and organs of the body. This study shows the importance of correlating in vitro findings in tissue culture cells with the organism as a whole. The cytoplasmic staining seen in parts of the brain and in liver suggests that there may be additional functions for the APE yet to be described.
Insights
The apurinic/apyrimidinic endonuclease (APE) enzyme, crucial for DNA repair, shows varied cellular and subcellular localization across organs. This suggests novel functions beyond DNA repair, particularly in the cytoplasm of certain brain and liver cells.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- The apurinic/apyrimidinic endonuclease (APE) is a multifunctional enzyme vital for DNA repair.
- APE also acts as a redox factor, influencing transcription factor activity.
- Previous studies indicated uniform APE concentrations in various tissues via biochemical analysis.
Purpose of the Study:
- To investigate the immunohistochemical distribution of APE across different organs.
- To identify novel cellular and subcellular localization patterns of APE.
- To explore potential new functions of APE based on its distribution.
Main Methods:
- Immunohistochemistry was employed to visualize APE protein distribution.
- Several organs, including brain regions (hippocampus, cerebellum, brainstem), skin, liver, and duodenum, were analyzed.
- Cellular and subcellular localization (nuclear vs. cytoplasmic) was documented.
Main Results:
- APE exhibited distinct localization patterns in different organs and cell types.
- Unexpected cytoplasmic staining was observed in specific neurons (hippocampus, cerebellum) and liver cells.
- Nuclear staining was noted in skin, liver, and specific duodenal cells (proximal villus enterocytes, crypts).
Conclusions:
- APE's localization varies significantly across tissues, suggesting diverse regulatory and functional roles.
- The presence of cytoplasmic APE indicates functions beyond its established role in DNA repair.
- Correlating in vitro data with in vivo distribution is crucial for understanding APE's complete biological significance.