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Isolation and Characterization of a Novel trans-Factor for Luteinizing Hormone Receptor mRNA from Ovary*
Anil K. Nair, and
K. M. J. Menon
Departments of Biological Chemistry and Obstetrics/Gynecology, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0617
Post-transcriptional mechanisms play a major role in regulatingluteinizing hormone (LH) receptor mRNA expression in the ovary.An ovarian cytosolic protein that we have identified in ratsand humans, which binds to a polypyrimidine-rich bipartitatesequence in the coding region of LHR mRNA, acts as a trans-actingfactor in this process. In the present study, we isolated andcharacterized this LH receptor mRNA-binding protein (LRBP) fromrat ovary. LRBP was purified to homogeneity by cation exchangechromatography followed by Northwestern analysis and subsequentelution of the single protein band from SDS-polyacrylamide gel.Purified LRBP was subjected to N-terminal microsequencing followedby homology search, which revealed its identity as mevalonatekinase. Purified rat mevalonate kinase antibody recognized thegel-purified LRBP on Western blots performed with one- and two-dimensionalSDS-polyacrylamide gels. When recombinant mevalonate kinaseproduced in human embryonic kidney cells (293 cells) was tested,it showed all of the characteristics of LRBP with respect tospecificity of LHR mRNA binding sequence, as examined by gelmobility shift analysis. Inhibition of LHR mRNA binding activityof mevalonate kinase in the presence of ATP and mevalonate indicatesthat the RNA recognition site of mevalonate kinase might involvethe ATP/mevalonate binding region of the protein. Treatmentof 293 cells with mevastatin to deplete cellular mevalonateresulted in an increase in LHR mRNA binding activity of mevalonatekinase. Collectively, the data support the novel function ofrat mevalonate kinase as a LHR mRNA-binding protein in the post-transcriptionalregulation of LH receptor expression in the ovary.
Received for publication August 26, 2003.
Revision received December 26, 2003.
* This work was supported by National Institutes of Health GrantHD-06656. The costs of publication of this article were defrayedin part by the payment of page charges. This article must thereforebe hereby marked "advertisement" in accordance with 18 U.S.C.Section 1734 solely to indicate this fact.
To whom all correspondence should be addressed: 6428 Medical Science Bldg. 1, 1301 Catherine, Ann Arbor, MI 48109-0617. Tel.: 734-764-8142; Fax: 734-936-8617.
The editors suggest the following Related Resources on Science sites:
Regulation of Luteinizing Hormone Receptor Expression: EVIDENCE OF TRANSLATIONAL SUPPRESSION IN VITRO BY A HORMONALLY REGULATED mRNA-BINDING PROTEIN AND ITS ENDOGENOUS ASSOCIATION WITH LUTEINIZING HORMONE RECEPTOR mRNA IN THE OVARY.