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TP Meehan, D Puett, and P Narayan

We have previously reported the construction of a constitutively active luteinizing hormone receptor by covalently linking a fused heterodimeric hormone to the extracellular domain of the G protein-coupled receptor. This yoked hormone-receptor complex (YHR) was found to produce high levels of cAMP in the absence of exogenous hormone. Stable lines expressing YHR were generated in HEK 293 cells to obtain lines with different expression levels; however, in a relatively short time of continued passage, it was found that YHR expression was greatly reduced. Herein, we describe the development of clonal lines of HEK 293 cells in which the expression of YHR is under the control of a tetracycline-regulated system. Characterization of clonal lines revealed tight control of YHR expression both by dose and time of incubation with doxycycline. These experiments demonstrated a good correlation between expression levels of the receptor and basal cAMP production. Moreover, the reduction in receptor expression following doxycycline removal revealed that YHR mRNA and protein decayed at similar rates, again suggesting a strong linkage between mRNA and protein levels. The controlled expression of YHR in this cell system will allow for a more detailed analysis of the signaling properties associated with constitutive receptor activation and may prove to be advantageous in developmental studies with transgenic animals.

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L Shen, H Xia, N Bhowmick, P Narayan, and D Puett


The Arg68-Leu69 sequence is invariant in the β subunits of chorionic gonadotrophin and luteinizing hormone from a variety of species. Using site-directed mutagenesis of the human chorionic gonadotrophin (hCG)-β cDNA, several replacements of Arg68, an Ala replacement of Leu69, and a multiple replacement with Ala-Ala-Ala-Ala of the tetrapeptide sequence, Arg68-Leu69-Pro70-Gly71, were prepared and characterized. The wild-type and mutant cDNAs were subcloned into a pRSV expression vector and transiently transfected into CHO cells containing a stably integrated gene for bovine a. Concentrations of secreted wild-type and mutant hCG-β subunit and holoprotein were determined using radioimmunoassays; potencies, i.e. the ratio of biologic to immunologic activity, of several of the mutant heterodimers were measured in vitro via gonadotrophin-mediated steroidogenesis in transformed murine Leydig cells (MA-10). The Leu69→Ala mutant formed a mutant holoprotein that was essentially equipotent with wild-type hormone in the steroidogenesis assay. The Arg68 replacements with Lys, Ala, and Leu were poorly secreted by the cells, e.g. <10% that of wild-type hCG; however, sufficient quantities of mutant holoproteins containing Lys68 and Ala68 were obtained for biological assays, and both exhibited greater apparent potencies than wild-type hormone. Likewise, a mutant holoprotein containing the Arg68-Leu69-Pro70-Gly71→Ala-Ala-Ala-Ala multiple replacement was apparently more potent than wild-type hormone, but it too was secreted at lower levels than wild-type. These results establish that replacements of Arg68 in hCG-β diminish secretion, but the small amount of holoprotein that is formed and secreted appears to be of somewhat greater potency than wild-type hormone.

Free access

Thomas P Meehan, Barry G Harmon, Megan E Overcast, Kristine K Yu, Sally A Camper, David Puett, and Prema Narayan

To study the effects of premature and chronic ligand-mediated luteinizing hormone receptor (LHR) activation on reproductive development, we have generated transgenic mice expressing a genetically engineered, constitutively active yoked hormone–receptor complex (YHR), in which a fusion protein of human chorionic gonadotropin (hCG) is covalently linked to the N-terminus of rat LHR. YHR-expressing mice (YHR+) were analyzed at pre- and post-pubertal ages. Relative to wild type (WT) controls, male mice exhibited prepubertal increases in testosterone levels and seminal vesicle weights, and decreases in serum FSH, serum LH, testes weight, and the size of the seminiferous tubules. In adult male YHR+ mice, testosterone and LH levels are not significantly different from WT controls. However, FSH levels and testes weights remain decreased. Female YHR+ mice undergo precocious puberty with early vaginal opening, accelerated uterine development, enhanced follicular development, including the presence of corpora lutea, and an increase in serum progesterone. At 12 weeks of age, the ovary exhibits a relative increase in the amount of interstitial tissue, comprised of cells that are hypertrophic and luteinized, as well as follicles that are degenerating. Additionally, hemorrhagic cysts develop in approximately 25% of the transgenic mice. These degenerative changes are consistent with an aging ovary suggesting that CG-induced LHR activation in female mice leads to precocious sexual development and ovarian lesions. Taken together, these data indicate that the single chain YHR is functional in vivo and demonstrate that YHR+ mice provide a novel system to further understand the reproductive consequences of aberrant LHR activation.