Enhancement of Epstein-Barr virus membrane protein (LMP) expression by serum, TPA, or n-butyrate in latently infected Raji cells.

The BamHI Nhet region of the EBV DNA is known to code for two proteins. One is a membrane protein (LMP) with an apparent molecular weight of 60,000 on SDS-PAGE which is expressed in latently EBV infected cells. The second protein, so far unidentified, is presumably a late protein with a calculated molecular weight of 28,000 Da. Antisera against both proteins were generated by immunizing rabbits with either a fusion protein containing 155 amino acids of the C-terminus of LMP and a 37,000 mol wt piece of the bacterial anthranilate synthase or with a C-terminal synthetic peptide of 7 amino acids. These sera reacted with a protein varying in size between 60,000 and 65,000 mol wt on SDS-PAGE, found in all cell lines harboring EBV. In addition, these sera identified a second protein with an apparent molecular weight of 49,000 on SDS-PAGE in B95-8, P3HR-1, and M-ABA cells, which is presumably identical with the 28,000-Da protein mentioned above. Furthermore, with these sera a positive cytoplasmic immunofluorescence in 1 to 10% of the cells was obtained, depending on the cell line examined. Analyzing the nonproducer Raji cell line, the number of immunofluorescence-positive cells and the amount of the 60,000 protein, as judged by immunoblotting, was rapidly increased by addition of fresh medium with 10% fetal calf serum as well as by the tumor promoter TPA or to an even higher extend by n-butyrate. The kinetics of induction reached a maximum 24 hr after addition of medium plus 10% fresh serum or TPA or n-butyrate and decreased after 24 to 48 hr. Since the induction of the EBV early antigen (EA) associated proteins by TPA or n-butyrate exhibits a diverse kinetic with a maximum at 72 hr, the regulation of the 60,000 protein synthesis appears to be different from known EA-associated proteins.