3' untranslated region-mediated regulation of luteinizing hormone/human chorionic gonadotropin receptor expression

Multiple luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor mRNAs (6.7, 4.4, 2.6, and 1.8 kb) have been identified in the rat ovary. Our laboratory has previously cloned a 3.5 kb cDNA that corresponds to the 3' untranslated region (3' UTR) of the 6.7 kb transcript, the major LH/hCG receptor mRNA in rat ovary. In order to determine the effects of the 3' UTR on receptor expression, we have constructed cDNAs corresponding to the open reading frame of LH/hCG receptor or luciferase, plus these constructs with the addition of the 3' UTRs associated with the short (4.4 kb) and long (6.7 kb) LH/hCG receptor transcripts, and measured receptor or luciferase expression in 293 cells transformed with large T antigen (293T). Ligand binding analysis with 125I-hCG revealed that the 3' UTR inhibited receptor expression, which occurs through posttranscriptional events. First, the 3' UTRs reduced receptor mRNA half-life in actinomycin D-arrested cells, as compared to the open reading frame alone. Second, LH/hCG receptor mRNAs with the long 3' UTR associated with significantly fewer ribosomes. The effect of the LH/hCG receptor 3' UTRs on luciferase expression was also determined. The short 3' UTR increased luciferase activity, whereas the long 3' UTR decreased luciferase expression. Thus, the short 3' UTR exerts opposite effects on receptor and luciferase expression. However, sequences in the long 3' UTR are sufficient to inhibit both receptor and luciferase expression in 293T cells.