Abstract
To elucidate the molecular events associated with the regulation of luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor mRNA stability during hCG-induced receptor down-regulation, we have identified an LH/hCG receptor-specific mRNA binding protein. Proteins were isolated from control and down-regulated rat ovary and were incubated with in vitro transcribed RNAs corresponding to the full-length LH/hCG receptor, as well as 5'- and 3'-truncated receptor forms. Resultant ribonucleoprotein complexes were analyzed by RNA gel mobility shift. A prominent Mr 50,000 ribonucleoprotein complex was identified with the following characteristics: 1) specificity for LH/hCG receptor open reading frame sequences located between nucleotides 102 and 282; 2) lack of competition by nonspecific RNAs; 3) a 3-fold increase in RNA binding activity during hCG-induced receptor down-regulation; and 4) limited tissue expression. This report describes the first evidence of an LH/hCG receptor mRNA binding protein, which we term LRBP-1, for luteinizing hormone receptor RNA binding protein-1. This protein is a candidate for a trans-acting factor involved in the hormonal regulation of LH/hCG receptor mRNA stability in rat ovary.
Highlights
§ To whom correspondence should be addressed: 6428 Medical Sciences Bldg
Since specific mRNA binding proteins have been implicated in selective mRNA degradation, we investigated whether any LH/human chorionic gonadotropin (hCG) receptor mRNA binding proteins were expressed in rat ovary
Our previous studies have shown that hCG-induced downregulation of the LH/hCG receptor is accompanied by a dramatic decline of receptor mRNA [3, 4]
Summary
§ To whom correspondence should be addressed: 6428 Medical Sciences Bldg. I, 1300 Catherine, Ann Arbor, MI 48109-0617. Following the injection of a pharmacological dose of hCG in female rat, a rapid decline in the steady state levels of all four of the LH/hCG receptor mRNAs (6.7, 4.4, 2.6, and 1.8 kb) is seen within 12 h, with complete loss of detectable receptor mRNAs by 24 h [3]. This selective loss is followed by a recovery of mRNA expression between 24 and 48 h [3]. This study describes the characterization of this mRNA binding protein with respect to LH/hCG receptor mRNA sequence recognition, hormonal regulation, and tissue specificity
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