3'-UNTRANSLATED REGION-MEDIATED REGULATION OF LUTEINIZING-HORMONE HUMAN CHORIONIC-GONADOTROPIN RECEPTOR EXPRESSION

Multiple luteinizing hormone/human chorionic gonadotropin (LH/hCG) rec eptor mRNAs (6.7, 4.4, 2.6, and 1.8 kb) have been identified in the ra t ovary. Our laboratory has previously cloned a 3.5 kb cDNA that corre sponds 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 t he effects of the 3' UTR on receptor expression, we have constructed c DNAs corresponding to the open reading frame of LH/hCG receptor or luc iferase, plus these constructs with the addition of the 3' UTRs associ ated with the short (4.4 kb) and long (6.7 kb) LH/hCG receptor transcr ipts, and measured receptor or luciferase expression in 293 cells tran sformed with large T antigen (293T). Ligand binding analysis with I-12 5-hCG revealed that the 3' UTR inhibited receptor expression, which oc curs through posttranscriptional events, First, the 3' UTRs reduced re ceptor mRNA half-life in actinomycin D-arrested cells, as compared to the open reading frame alone. Second, LH/hCG receptor mRNAs with the l ong 3' UTR associated with significantly fewer ribosomes. The effect o f the LH/hCG receptor 3' UTRs on luciferase expression was also determ ined. 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, sequ ences in the long 3' UTR are sufficient to inhibit both receptor and l uciferase expression in 293T cells.