DIFFERENTIAL EXPRESSION OF REL FAMILY MEMBERS IN HUMAN T-CELL LEUKEMIA-VIRUS TYPE I-INFECTED CELLS - TRANSCRIPTIONAL ACTIVATION OF C-REL BY TAX PROTEIN

The Tax protein of the human T-cell leukemia virus type I (HTLV-I) has been shown to induce nuclear expression of Rel family NF-kappaB-binding proteins. However, under different experimental conditions, different members of the Rel family were induced (N. Arima, J. A. Molitor, M. R. Smith, J. H. Kim, Y. Daitoku, and W. G. Greene, J. Virol. 65:6892-6899, 1991). In this study, using specific immunological reagents capable of distinguishing individual members of the Rel family proteins, we show that only c-Rel, not NF-kappaB p50 or p65, is induced in HTLV-I-infected cells. Preferential c-rel induction by HTLV-1 infection was detected at the protein and RNA levels as well as in the nuclear NF-kappaB-binding form. Induced c-rel expression was also detected in cells stably transfected with tax cDNA, further correlating the c-rel induction with viral Tax expression. An increase in c-rel mRNA was detected within 3 h after induction of Tax expression, suggesting that this effect is at least partially regulated at the level of transcription. Furthermore, using a particle bombardment method for gene cotransfection, we show that Tax can transcriptionally activate the c-rel promoter in a T-cell line, Jurkat.