Identification of novel cAMP responsive element modulator (CREM) isoforms expressed by osteoblasts.

CREM, the cyclic adenosine monophosphate (cAMP) responsive element modulator, belongs to a multigene family of cAMP-responsive transcription factors. CREM encodes a variety of different isoforms by utilizing four promoters and a complex pattern of alternative messenger ribonucleic acid (mRNA) splicing. We showed previously that parathyroid hormone induces the CREM P2 promoter products known as ICER (inducible cAMP early repressor) in osteoblasts. Herein we report that osteoblasts also express at least 15 CREM transcripts initiated from the P1 promoter, including 7 novel transcripts that result from alternative splicing. It is of interest that we found that CREM-X contains both exon theta1, previously identified only in P3 promoter products, and a new exon termed L, which is located upstream of exon theta1.