Activating transcription factor 1 and cyclic AMP response element modulator can modulate the activity of the immunoglobulin κ 3' enhancer

Abstract

Previously we determined that the immunoglobulin kappa 3' enhancer (κE3') contains at least two functional DNA sequences (PU.1/NF-EM5 and 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 linker scan mutagenesis across the core fragment we identified several additional functional sequences. We used one of these functional sequences to screen a χt11 cDNA expression library resulting in the isolation of cDNA clones encoding the transcription factors ATF-1 (activating transcription factor) and CREM (cyclic AMP response element modulator). Because ATF-1 and CREM are known to bind to cAMP response elements (CRE), this functional sequence was named the κE3'-CRE. We show that dibutyryl cAMP can increase κE3' enhancer activity, and in transient expression assays ATF-1 caused a 4-5-fold increase in the activity of the core enhancer while CREM-α expression resulted in repression of enhancer activity. RNA analyses showed increased levels of ATF-1 mRNA during B cell development and some changes in CREM transcript processing. By joining various fragments of the κE3' enhancer to the κE3'-CRE, we observed that the κE3'-CRE can synergistically increase transcription in association with the PU.1/NF-EM5 binding sites, suggesting a functional interaction between the proteins 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 κE3'-CRE may relate to previous conflicting results concerning the role of the cAMP signal transduction pathway in κ gene transcription.