An isoform of transcription factor CREM expressed during spermatogenesis lacks the phosphorylation domain and represses cAMP-induced transcription.

Abstract

ABSTRACTcAMP response element-binding protein (CREB) and modulator protein (CREM) regulate the transcription of cAMP-responsive genes via phosphorylation by cAMP-dependent protein kinase A. Reverse transcription and polymerase chain amplification of RNA from male germ cells identify an alternatively spliced CREM isoform, CREMAC-G, lacking four exons including those encoding the protein kinase A-regulated phosphorylation domain and the flanking glutamine-rich transcriptional activation domains. CREMAC-G retains exons that encode the basic-eucine zipper (bZIP) DNA-binding domain, binds to cAMP response elements (CREs), and competitively inhibits binding of CREB and CREM to CREs. Expression ofCREMAC-G inhibits transcription of a CRE-containing chloramphenicol acetyltransferase reporter plasmid induced by endogenous CREB. Antiserum to CREM detects CREMAC-G in elongated spermatids from rat testis. These observations indicate that CREMAC-G is a unique form of a competitive negative regulator of CREB-mediated gene transcription expressed in a maturation-dependent manner in haploid germ cells. The developmental specificity of CREMAC-G suggests that it may play a role in transcriptional regulation during spermatogenesis.One mechanism for the mediation of the cAMP-dependent regulation of gene transcription is via phosphorylation by protein kinase A (PKA) of a single serine in the structurally similar transcription factors CREB, CREM, and ATF-1 (1-6). CREB and CREM in particular share several structural motifs, including the carboxyl-terminal DNA-binding bZIP domain, which consists of a positively charged DNA-binding region (b) and an adjacent leucine zipper (ZIP) dimerization region. In addition, CREB and CREM contain a unique amino-terminal phosphorylation domain (P-box, kinaseinducible domain) flanked by two glutamine-rich transcription activation domains. Alternative exon splicing of CREB and CREM RNA transcripts and alternative translational start sites for CREM account for proteins ranging from full-length transcriptional activators to truncated transcriptional repressors. Repressor forms of CREM are generated in the testis by alternative deletion of the glutamine-rich (Qrich) exons that mediate transcriptional activation (7,8), in the brain by internal translation that deletes one of the Q-rich exons and the P-box (9), and in neuroendocrine cells by alternative utilization of an internal promoter and translational start site between the Q-rich/P-box domains and the DNA-binding (bZIP) domain (10, 11).In the rat and mouse testis, alternatively spliced forms of CREB and CREM are expressed in stage-and cell-specific patterns during spermatogenesis, the generation of spermatozoa from germ cells. In the process of spermatogenesis, stem cells give rise to spermatogonia that further develop into diploid primary spermatocytes. As a result of two meiotic divisions, spermatocytes give rise to haploid round spermatids which shed their cytoplasm and elongate to become spermatozoa (12,13). In germ cells and Sertoli cells that sur...

Developmentally distinct in vivo effects of FSH on proliferation and apoptosis during testis maturation

“…References for those genes previously reported to be in the rat testis and/or regulated by FSH are in parentheses. Yes; (Walker et al 1994, West et al 1994, Monaco et al 1995 (Wolgemuth et al 1998, Buemer et al 2000, Strothmann et al 2004 Yes Androgen Binding Protein (ABP); sex hormone binding globulin…”

Differential Activation of Viral and Cellular Promoters by Human T-cell Lymphotropic Virus-1 Tax and cAMP-responsive Element Modulator Isoforms

“…Moreover, CREM␣-mediated activation of the HTLV-1 LTR should occur in the absence of PKA, in a manner similar to that reported previously for CREB. The CREM⌬(C-G) isoform lacks both the glutamine-rich regions and the KID (19). This form is predicted to be incapable of mediating Tax activation of the cellular CRE, but because it contains a CREB-like basic/zipper region, it should still be able to contribute to activation of the viral LTR.…”

The Administration of Retinoic Acid Down-Regulates cAMP-Responsive Element Modulator (CREM) mRNA in Vitamin A-Deficient Testes

“…[26][27][28] Interestingly, the CREM gene generates both activators (CREM, 1, 2) and repressors (CREM, , ) by alternative splicing in both germ and somatic cells of the testes. [29][30][31][32][33] More importantly, previous reports have found a developmental change in the expression pattern of CREM isoforms from repressor to activator during spermatogenesis. 30,31) Repressor CREM isoforms are expressed at the premeiotic stage of spermatogenesis.…”

“…Since the CREM gene encodes multiple CREM isoforms, including both activators and repressors, 27,[29][30][31][32] we examined which mRNA level of CREM isoforms was regulated in VAD testes by ATRA. To compare the expression ratio of multiple CREM isoforms in VAD testes before and after administration of ATRA, we performed a semi-quantitative RT-PCR using two primers that enable discrimination of various isoforms, as previously described.…”

“…30,31) Repressor CREM isoforms are expressed at the premeiotic stage of spermatogenesis. [30][31][32] In contrast, CREM, an activator CREM isoform, is highly expressed in post-meiotic cells, activating the transcription of post-meiotic stage-specific genes, including RT7, protamine, and transition protein 1. 30,[34][35][36] In addition, mutant mice that carry a defective CREM gene show y To whom correspondence should be addressed.…”