Inducible transcription of the unrearranged kappa constant region locus is a common feature of pre-B cells and does not require DNA or protein synthesis.

Abstract

Transcription of unrearranged K constant region (KO) loci is dramatically induced in pre-B cells transformed by the Abelson murine leukemia virus when the cells are exposed to bacterial lipopolysaccharide (LPS). Transcriptional activity, detected both by accumulation of the 8-kilobase ic" RNA product and by nuclear run-on measurements, is evident within a few hours after exposure to LPS and continues to increase over a 24-hr period. CK (5,6). Like its viral counterparts, the C,. enhancer can increase transcription from distal promoters in either orientation and appears to influence local chromatin structure (7,8). A notable feature of the enhancer is its role in helping to define tissue-specific expression of K genes. When productively rearranged K genes are transfected into cell lines or are introduced into transgenic mice, they are efficiently and accurately expressed only in cells of lymphoid origin (5, 9). Other genes linked to the K enhancer also exhibit such tissue specificity (6). These observations suggest that the ability of the K enhancer to regulate transcriptional activity may require interaction with a trans-acting soluble factor(s) found only in lymphoid cells. Indeed, recent studies of the immunoglobulin heavy-chain enhancer have identified protein binding sites in a region containing a sequence motif that is shared by the K enhancer (10). Although promoter elements are also clearly important in determining the transcriptional activity of K genes, the enhancer seems to have a dominant role in the regulatory hierarchy, at least in mature plasma cells (11).In earlier studies of a B-cell-lymphoma line, 70Z/3, which has the unusual property of being inducible for K light-chain synthesis by the mitogen bacterial lipopolysaccharide (LPS), it was shown that LPS treatment elicits a dramatic increase in transcriptional activity and a concomitant alteration in the chromatin structure encompassing the K enhancer element (7,12). Both the productively rearranged K gene and the germline K allele exhibited transcriptional activation and altered chromatin structure, leading us to speculate that the inductive effect is directed at the K enhancer rather than the V1K promoter.In this report, we demonstrate that LPS-inducible transcriptional competence of the K locus is not a peculiarity of the 70Z/3 line, but rather is a characteristic of a discrete stage of B-cell ontogeny near the pre-B-cell to B-cell transition. Moreover, we show that the induction of transcription can occur in the absence of DNA or protein synthesis. These results suggest a model for B-cell development in which an external signal may initiate expression of the K locus by modifying or overriding the activity of an enhancer-specific factor. MATERIALS AND METHODSThe Abelson murine leukemia virus (A-MuLV)-transformed cell lines were obtained from David Baltimore and propagated in RPMI 1640 medium (GIBCO) supplemented with 10% heat-inactivated fetal calf serum. LPS (Difco; Escherichia coli 0111:B4) was used at a final concentration of 10 Ag/...

The coupling between enhancer activity and hypomethylation of kappa immunoglobulin genes is developmentally regulated.

“…One possibility is that the enhancer function is superseded by developmentally controlled structural alterations of the immunoglobulin genes. Indeed, a previous comparison of constitutively expressed and LPS-induced K genes indicated that such an alteration might include a propensity for hypomethylation (19,20). These observations also indicated that enhancer activation alone might not be sufficient to alter the methylation pattern, suggesting that the coupling of such structural alterations to enhancer activity might itself be a developmentally regulated phenomenon.…”

“…In fact, the enhancer may serve not only to establish transcriptional competence at the K locus, but also to render the JK region accessible to the DNA recombinases that catalyze K gene rearrangements. Direct evidence implicating the enhancer in the developmental activation of the K locus was provided by studies of its role in mediating lipopolysac-charide (LPS)-induced precocious K transcription in a variety of pre-B-cell lines (3,19). After transcription is established at the K locus, the importance of the K enhancer would presumably diminish during further maturation of the B lymphocyte.…”

The Igκ3′ Enhancer Is Activated by Gradients of Chromatin Accessibility and Protein Association

“…To test this possibility, we took advantage of the demonstration that the locus can be activated by LPS in 3-1 cells, as measured by 0 transcript production (16). ChIP specific for acetylated H3/3Ј association demonstrated that LPS treatment increases association between acetylated H3 and the enhancer ϳ4.3-fold (Fig.…”

The v-abl tyrosine kinase negatively regulates NF-kappa B/Rel factors and blocks kappa gene transcription in pre-B lymphocytes.

“…In almost every case, these cell lines have initiated or completed rearrangements at a transcriptionally active heavy-chain locus but contain germ-line K alleles that are transcriptionally inactive (Alt et al 1981;Nelson et al 1985). A long-standing question has been whether transformation by the virus actively blocks transcription and/or rearrangement of the K lo cus.…”