ACTIVATING TRANSCRIPTION FACTOR-1 AND CYCLIC-AMP RESPONSE ELEMENT MODULATOR CAN MODULATE THE ACTIVITY OF THE IMMUNOGLOBULIN-KAPPA 3' ENHANCER

Previously we determined that the immunoglobulin kappa 3' enhancer (ka ppa E3') contains at least two functional DNA sequences (PU.1/NF-EM5 a nd E2A) within its 132-base pair active core. We have determined that the activities of these two sequences are insufficient to account for the entire activity of the 132-base pair core. Using site-directed lin ker scan mutagenesis across the core fragment we identified several ad ditional functional sequences. We used one of these functional sequenc es to screen a lambda gt11 cDNA expression library resulting in the is olation of cDNA clones encoding the transcription factors ATF-1 (activ ating transcription factor) and CREM. (cyclic AMP response element mod ulator). Because ATF-1 and CREM are known to bind to cAMP response ele ments (CRE), this functional sequence was named the kappa E3'-CRE. We show that dibutyryl cAMP can increase kappa E3' enhancer activity, and in transient expression assays ATF-1 caused a 4-5-fold increase in th e activity of the core enhancer while CREM-alpha expression resulted i n repression of enhancer activity. RNA analyses showed increased level s of ATF-1 mRNA during B cell development and some changes in CREIM tr anscript processing. By joining various fragments of the kappa E3' enh ancer to the kappa E3'-CRE, we observed that the kappa E3'-CRE can syn ergistically increase transcription in association with the PU.1/NF-EM 5 binding sites, suggesting a functional interaction between the prote ins that bind to these DNA sequences. Consistent with this possibility , we found that ATF-1 and CREM can physically interact with PU.1. The isolation of activator and repressor proteins that bind to the kappa E 3'-CRE may relate to previous conflicting results concerning the role of the cAMP signal transduction pathway in kappa gene transcription.