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The Oct-2 gene appears to encode a developmental regulator of immunoglobulin gene transcription. We demonstrate that the Oct-2 gene is expressed at low levels in a variety of transformed pre-B-cell lines and is induced specifically in these cells by lipopolysaccharide signalling. This work extends an earlier observation in the pre-B-cell line 70Z/3 and therefore suggests that the inducible expression of the Oct-2 gene, like that of the kappa gene, is a characteristic feature of the pre-B stage of B-cell development. In 70Z/3 cells, the lymphokine interleukin-1 also induces the expression of the Oct-2 and kappa loci. Interestingly, expression of the Oct-2 gene is rapidly induced at the transcriptional level and may not require de novo protein synthesis. Since the changes in the activity of the Oct-2 locus completely correlate with the changes of the activity of the kappa locus, the two genes may be transcriptionally regulated by a common trans-acting factor. In 70Z/3 cells, transforming growth factor beta, an inhibitor of kappa-gene induction, blocks the upregulation of Oct-2 but not the activation of NF-kappa B. These results suggest that the combinatorial action of increased levels of Oct-2 and activated NF-kappa B may be necessary for the proper stage-specific expression of the kappa locus.

NM23-H2/NDP kinase B has been identified as a sequence-specific DNA-binding protein with affinity for a nuclease-hypersensitive element of the c-MYC gene promoter (Postel et al., 1993). The ability of Nm23-H2 to activate c-MYC transcription in vitro and in vivo via the same element demonstrates the biological significance of this interaction. Mutational analyses have identified Arg34, Asn69 and Lys135 as critical for DNA binding, but not required for the NDP kinase reaction. However, the catalytically important His118 residue is dispensible for sequence-specific DNA binding, suggesting that sequence-specific DNA recognition and phosphoryl transfer are independent properties. Nm23-H2 also has an activity that cleaves DNA site-specifically, involving a covalent protein-DNA complex. In a DNA sequence-dependent manner, Nm23-H2 recognizes additional target genes for activation, including myeloperoxidase, CD11b, and CCR5, all involved in myeloid-specific differentiation. Moreover, both NM23-H1 and Nm23-H2 bind to nuclease hypersensitive elements in the platelet-derived growth factor PDGF-A gene promoter sequence-specifically, correlating with either positive or negative transcriptional regulation. These data support a model in which NM23/NDP kinase modulates gene expression through DNA binding and subsequent structural transactions.

Transforming growth factor beta 1 (TGF-beta 1) is a pleiotropic cytokine that decreases the expression of class II MHC Ag in the melanoma cell line Hs294T(c). To investigate the mechanism of this repression, we have examined the effect of TGF-beta 1 on expression of the HLA-DR alpha gene. Both the constitutive level of HLA-DR protein and DR alpha mRNA were repressed by treatment with TGF-beta 1. The proximal 176 bp of the DR alpha promoter were sufficient to confer TGF-beta 1 repression on a reporter gene. Deletional and mutational analysis of the DR alpha promoter revealed that the conserved S and X1 promoter elements were important for basal expression of DR alpha and also mediated the down-regulation by TGF-beta 1. Mobility shift assays and in vivo footprinting showed no change in occupancy of the proximal DR alpha promoter after TGF-beta 1 treatment. These results identify the DNA elements that mediate repression of the HLA-DR alpha gene by TGF-beta 1 and suggest that TGF-beta 1 acts at these sites without causing a change in promoter occupancy.