IDENTIFICATION OF 3'ALPHA-HS4, A NOVEL IG HEAVY-CHAIN ENHANCER ELEMENT REGULATED AT MULTIPLE STAGES OF B-CELL DIFFERENTIATION

In addition to E mu, several elements downstream of the IgH cluster, i .e, 3' of the C alpha gene, are involved in regulating IgH gene rearra ngement and expression. This entire downstream regulatory region was s hown to be deleted in the mutant myeloma cell line, LP1.2. The deletio n encompasses similar to 34 kb and is presumably responsible for the r educed levels of IgH expression in this cell line. An additional regul atory element, included in the LP1.2 deletion, was identified by inves tigation of a DNase I hypersensitivity site located similar to 33 kb d ownstream of the alpha gene and present in pre-B and plasma cells. Thi s novel IgH gene enhancer element, termed 3' alpha-hs4, is capable of activity throughout B cell development. Transient transfection of 3'al pha-hs4 in a CAT reporter gene construct shows transcriptional enhance ment activity approximating that of E mu in S194 plasmacytoma and M12. 4.1 and A-20 B cell lines; while in a pre-B cell line, 18-81,the avera ge activity is 25% that of E mu. Enhancer activity was localized to an 800 bp fragment. The activity of 3' alpha-hs4 is orientation independ ent and appears to be B cell specific. Tight regulation of 3' alpha-hs 4 is inferred from its variable activity in different plasmacytoma cel l lines and within the pre B cell line, 18-81.