DIFFERENTIAL RESPONSE OF NF-KAPPA-B1 P105 AND NF-KAPPA-B2 P100 TO HTLV-I ENCODED TAX

In a previous study we found that HTLV-I encoded Tax transactivator, which binds to NF-kappa B1 p105, suppresses p105-mediated I kappa B activity, thereby allowing entry of NF-kappa B p65 (RelA) and p50 into the nucleus. In the present report, we compared the effect of Tax on NF-kappa B2 p100, which also binds to Tax, with that of p105 in transfected COS7 cells. While p105 is processed to the DNA binding form, p50, processing of p100 was much less efficient both in the presence and absence of Tax. Both p105 and p100 showed I kappa B activity in sequestering NF-kappa B p65 into the cytoplasm. However, only p105-mediated I kappa B activity, and not that of p100, was inhibited by Tax. Chimeric molecules between p100 and p105 suggested that inefficient processing of p100 can be attributed to the Rel homologous domain, rather than to the ankyrin repeat domain. p100, but not p105, potently suppressed Tax- and p65-induced transactivation of a GM-CSF promoter in Jurkat cells. Taken together, these results suggest that p105 and p100 may have distinct effects on Tax-induced transactivation events.