MAREKS-DISEASE VIRUS (MDV) ICP4, PP38, AND MEQ GENES ARE INVOLVED IN THE MAINTENANCE OF TRANSFORMATION OF MDCC-MSB1 MDV-TRANSFORMED LYMPHOBLASTOID-CELLS

An antisense strategy has been used to identify genes important for th e maintenance of transformation of MDCC-MSB1 (MSB1) Marek's disease vi rus-transformed lymphoblastoid cells, Oligodeoxynucleotides antisense to the predicted translation initiation regions of ICP4 and pp38 mRNAs inhibited proliferation of MSB1 cells but not MDCC-CU91 (CU98) reticu loendotheliosis virus-transformed cells, Control oligodeoxynucleotides having the same base composition but a different sequence did not inh ibit MSB1 cell proliferation, In addition, ICP4 and pp38 antisense oli godeoxynucleotides resulted in 77- and 100-fold reductions in colony f ormation by MSB1 cells in soft agar, respectively, To extend and corro borate these results, a novel system based on efficiently regulated ex pression of eukaryotic genes by a chimeric mammalian transactivator, L AP267 (S. B. Palm, M. A. Labow, A. J. Levine, and T. Shenk, Proc. Natl . Acad. Sci. USA 88:5072-5076, 1991), was used, MSB1-derived stably tr ansfected cell lines in which RNA antisense to Marek's disease virus I CP4, pp38, or meq could be induced by treatment of the cells with isop ropyl-beta-D-thiogalactopyranoside (IPTG) were constructed, Control ce ll lines in which expression of ICP4 sense or pUC19 sequences could be induced by IPTG were also constructed, Induction of the fell lines in dicated that ICP4 antisense RNA, but not ICP4 sense RNA or pUC19 RNA, inhibited proliferation of MSB1 cells, Induction of ICP4, meg, or pp38 antisense RNAs, but not ICP4 sense or pUC19 RNAs, had a dramatic effe ct on relative colony formation by MSB1 cells in soft agar, These resu lts indicate that ICP4, pp38, and Meq are all involved in the maintena nce of transformation of MSB1 cells.