Nd. Perkins et al., A COOPERATIVE INTERACTION BETWEEN NF-KAPPA-B AND SP1 IS REQUIRED FOR HIV-1 ENHANCER ACTIVATION, EMBO journal, 12(9), 1993, pp. 3551-3558
The human immunodeficiency virus (HIV-1) long terminal repeat (LTR) co
ntains two binding sites for NF-chiB in close proximity to three bindi
ng sites for the constitutive transcription factor, Spl. Previously, s
timulation of the HIV enhancer in response to mitogens has been attrib
uted to the binding of NF-chiB to the viral enhancer. In this report,
we show that the binding of NF-chiB is not by itself sufficient to ind
uce HIV gene expression. Instead, a protein - protein interaction must
occur between NF-chiB and Sp1 bound to an adjacent site. Cooperativit
y both in DNA binding and in transcriptional activation of NF-chiB and
Sp1 was confirmed by electrophoretic mobility shift gel analysis, DNa
se footprinting, chemical cross-linking and transfection studies in vi
vo. With a heterologous promoter, we find that the interaction of NF-c
hiB with Sp1 is dependent on orientation and position, and is not obse
rved with other elements, including GATA, CCAAT or octamer. An increas
e in the spacing between the chiB and Sp1 elements virtually abolishes
this functional interaction, which is not restored when these sites a
re brought back into the same helical position. Several other promoter
s regulated by NF-chiB also contain chiB in proximity to Spl binding s
ites. These findings suggest that an interaction between NF-chiB and S
p1 is required for inducible HIV-1 gene expression and may serve as a
regulatory mechanism to activate specific viral and cellular genes.