Modulation by vitamin B6 of glucocorticoid receptor-mediated gene expression requires transcription factors in addition to the glucocorticoid receptor.

We have investigated the mechanism by which vitamin B6 acts to modulate steroid hormone-mediated gene expression. We show that the level of glucocorticoid-induced gene expression from simple promoters, containing only hormone response elements and a TATA sequence, was not affected by alterations in intracellular vitamin B6 concentration. However, modulation of hormone-induced gene expression was restored with the inclusion of a binding site for the transcription factor nuclear factor 1 (NF1) within the hormone-responsive promoter; glucocorticoid-induced gene expression was reduced by 44% under conditions of elevated intracellular vitamin B6 concentration and enhanced by 98% in mild vitamin deficiency. Under these conditions, neither glucocorticoid receptor sedimentation characteristics, receptor activation, nor DNA binding capacity was affected. Quantitatively analogous effects were detected with estrogen-induced gene expression when an NF1 binding site was removed from or introduced into an estrogen-responsive promoter. NF1-mediated constitutive transcription was not affected by alterations in vitamin concentration. The modulatory effect of vitamin did not require strict positioning of or spacing between the glucocorticoid response element and NF1 binding site. Moreover, a heterologous transcriptional activator, composed of the viral E1a transactivation domain and the GAL4 DNA binding domain, does not substitute for NF1 in restoring vitamin B6 modulation of hormone-induced gene expression. These results suggest that vitamin B6 modulates steroid hormone-mediated gene expression through its influence on a functional or cooperative interaction between steroid hormone receptors and the transcription factor NF1.