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Human Apurinic Endonuclease 1 Expression in a Colorectal Adenoma-Carcinoma Sequence¹

Department of Cellular Science [S. K., L. K., K. E., H. T., K. C. G.], Imperial Cancer Research Fund Molecular Oncology Laboratory [I. D. H., A. L. H.], John Radcliffe Hospital, University of Oxford, Oxford OX3 9DU, United Kingdom

Human apurinic endonuclease 1 (HAP1) plays a key role in the repair of baseless sites in DNA. HAP1 is also known to be a potent regulator of the binding activity of a number of transcription factors. We have examined the immunohistochemical expression of the HAP1 protein in normal colorectal mucosa, hyperplastic polyps, tubulovillous adenomas, and carcinomas. In normal colonic mucosa, the predominant staining was nuclear in the less differentiated cells located at the lower part of the crypt, but it was cytoplasmic in the more differentiated superficial colonic epithelium. HAP1 expression was nuclear in 3 of 30 adenomas (10%) and 5 of 44 carcinomas (11%), but it was cytoplasmic in 11 of 30 adenomas (37%) and 22 of 44 carcinomas (50%) and both nuclear and cytoplasmic in 16 of 30 adenomas (53%) and 17 of 44 carcinomas (39%). The observed staining in stromal fibroblasts and endothelial cells was nuclear, whereas that in macrophages was cytoplasmic. Our data indicate that HAP1 is expressed in different subcellular compartments during normal differentiation and that this pattern is disrupted in adenomas and carcinomas. The differential localization may be relevant to the two different proposed functions of HAP1.

¹ The work presented in this paper was funded by the Imperial Cancer Research Fund, London, United Kingdom. The costs for color illustrations were defrayed by Rhone-Poulenc Rorer, Greece.

² To whom requests for reprints should be addressed. Phone: 44-1865-222457; Fax: 44-1865-222431.

Received 9/16/96. Accepted 2/18/97.

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