The Switch in Alternative Splicing of Cyclic AMP-response Element Modulator Protein CREMτ₂α (Activator) to CREMα (Repressor) in Human Myometrial Cells Is Mediated by SRp40*

Abstract

The transcription factor cAMP-response element modulator (CREM) protein, plays a major role in cAMP-responsive gene regulation. Biological consequences resulting from the transcriptional stimuli of CREM are dictated by the expression of multiple protein isoforms generated by extensive alternative splicing of its precursor mRNA. We have previously shown that alternative splicing enables the expression of the CREM gene to be “switched” within the human myometrium during pregnancy from the production of CREMτ_2α, a potent transcriptional activator to the synthesis of CREMα, a transcriptional repressor. Furthermore we have recently reported that this change in the expression of CREM spliced variants is likely to have important ramifications on the regulation of downstream cAMP-response element-responsive target genes involved in uterine activity during gestation. We have investigated the splicing factors involved in controlling the expression of myometrial CREM splice variants. Data presented here from transient transfections indicate that the switch in the synthesis of CREMτ₂α to CREMα that occurs during pregnancy is regulated primarily by an SR protein family member, SRp40. We also show that expression of this splicing factor is tightly regulated in the myometrium during pregnancy. SRp40 regulates the splicing of CREM via its interactions with multiple ESE motifs present in the alternatively exons of CREM. In vitro splicing and electrophoretic mobility shift assays were employed to confirm the functionality of the SRp40-binding ESEs, thus providing a mechanistic explanation of how SRp40 regulates the switch in splicing from production of CREMτ₂α to CREMα.