Identification of 3α-hs4, a novel Ig heavy chain enhancer element regulated at multiple stages of B cell differentiation

摘要

ABSTRACT In addition to Eμ, several elements downstream of the IgH cluster, i.e. 3' of the C_α gene, areinvolved in regulating IgH gene rearrangement and expression. This entire downstream regulatory region was shown to be deleted in the mutant myeloma cell line, LP1.2. The deletion encompasses ～34 kb and is presumably responsible for the reduced levels of IgH expression in this cell line. An additional regulatory element, included in the LP1.2 deletion, was identified by investigation of a DNase I hypersensitivity site located ?.33 kb downstream of the α gene and present in pre-B and plasma cells. This novel IgH gene enhancer element, termed 3'α-hs4, is capable of activity through out B cell development. Transient transfectlon of 3'α-hs4 in a CAT reporter gene construct shows transcriptional enhancement activity approximating that of Eμ in S194 plasmacytoma and M12.4.1 and A-20 B cell lines; while in apre-B cell line, 18–81, the average activity is 25% that of Eμ. Enhancer activity was localized to an800 bp fragment. The activity of 3'α-hs4 is orientation independent and appears to be B cell specific. Tight regulation of 3'α-hs4 is inferred from its variable activity in different plasmacytoma cell lines and within the pie B cell line, 18–81.