ENHANCED EXPRESSION OF THE MAREKS-DISEASE VIRUS-SPECIFIC PHOSPHOPROTEINS AFTER STABLE TRANSFECTION OF MSB-1 CELLS WITH THE MAREKS-DISEASE VIRUS HOMOLOG OF ICP4

Phosphoprotein pp38, coded for by the BamHI-H fragment of the Marek's disease herpesvirus (MDV) genome is expressed in tumor cells and tumor cell lines. pp38 is associated with two other phosphoproteins, pp41 a nd pp24, and can be detected in a small percentage of tumor cells by i ndirect immunofluorescence assays (IIFA). The importance of MDV ICP4 f or the regulation of pp38 expression was examined in the following MSB -1-derived cell lines stably transfected with the selection plasmid pN L1 [MDCC-CU221 (CU221)], pNL1 and the BamHI-A fragment of MDV DNA cont aining ICP4 (CU224), MDV ICP4 inserted in antisense direction in the e ukaryotic expression vector pXT1 (CU222), or ICP4 in sense direction i n pXT1 (CU223) or cotransfected with pNL1 and EcoRI-linearized BamHI-A MDV DNA (CU225, -237, -243, -244). IIFA analysis showed that CU223 ha d a markedly increased expression of pp38, while CU224 had a slightly increased expression. No changes were noted in CU221 or CU222, while e xpression of pp38 was decreased in CU225, -237, -243, and -244. Radioi mmunoprecipitation assays demonstrated that the expression of all thre e phosphoproteins was enhanced in CU223. Steady-state transcriptional analysis showed that CU223 had increased levels of pp38-specific (1.9 and 3.3 kb) and ICP4-specific (10.0 kb) transcripts. (C) 1994 Academic Press, Inc.