Vol. 182, No. 1, 1992 January 15, 1992 BIOCHEMICAL AND BIOPHYSICALRESEARCHCOMMUNICATIONS Pages 318-324 INCREASED EXPRESSION OF RETROVIRAL SEQUENCES IN PROGRESSIONALLY ADVANCED RAT PROSTATIC TUMORS* Marion J.G. Bussemakers, Adrie van Bokhoven, Jan J.M. van Groningen Frans M.J. Debruyne, and Jack A. Schalken 1 Departments of Urology (Urological Research Laboratory) and 1Biochemistry, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands Received November 25, 1991 Summary Differential hybridization analysis revealed two cDNA clones, pBUS19 and pBUS30, to be overexpressed in progressionally advanced rat prostatic tumors. Northern blot analysis suggested the clones to be related although no homology in nucleotide sequence could be shown. Isolation and characterization of a pBUS19- related clone, pJG116, and computer-assisted database comparison showed that all three clones could be mapped within a rat-specific endogenous retrovirus. The importance of overexpression of retroviral sequences in advanced prostatic cancer remains unclear. ® 1992 Academic Press, Inc, In our studies to identify genes that are activated during the proces of prostate tumor progression, we applied the technique of differential hybridization analysis to compare the steady-state mRNA levels of two different tumor stages. Since no well defined human prostate cancer progression model system is available, two sublines of the established Dunning R-3327 rat prostatic cancer model system (1) were used. The serially transplantable Dunning R-3327 sublines represent the various stages of prostate tumor progression. Comparing the steady-state mRNA levels of the most benign Dunning R-3327-H tumor (hormone-dependent, well-differentiated, non- metastasizing), and the aggressive MatLyLu tumor (hormone-independent, anaplastic, metastasizing), three clones that are overexpressed in the metastatic tumors, were isolated (2). Two cDNA clones, pBUS19 and pBUS30, showed a striking homology Sequence data from this article have been deposited with the EMBL/GenBank Data Libraries under Accession Nos. X62950 (R. rattus mRNA (pBUSI9) with repetitive elements), X62951 (R. rattus mRNA (pBUS30) with repetitive ele- ments), and X62952 (R. rattus mRNA (pJGll6) with repetitive elements). 0006-291X/92 $1.50 Copyright © 1992 by Academic Press, Inc. All rights of reproduction in any form reserved. 318