Thyroid-stimulating hormone (TSH) is one of a family of pituitary glycoprotein hormones that include luteinizing hormone (LH), follicle-stimulating hormone (FSH), as well as placental chorionic gonadotropin (CG). These hormones act togther to regulate the metabolic processes required for normal growth, reproduction and development. The hormones consist of two non-covalenty linked, dissimilar subunits, alpha and beta. In a given species, the structures of the alpha subunits are similar, if not identical. Beta subunits differ greatly in structure and confer biologic specificities to the hormones. We wish to understand gene structure, organization and regulation, and the cellular mechanisms of post-translational processing of the alpha and beta subunits; particularly how the expression of the alpha and beta subunit genes are coordinately regulated. As a first step in these studies, we have cloned and sequenced the cDNAs encoding both mouse and rat alpha and TSH-beta as well as rat LH beta subunits. We have isolated and sequencedd the gene encoding rat LH beta and are presently sequencing the genes encoding rat alpha and TSH beta subunits. Using both the recombinant cDNAs encoding the alpha and beta subunits have been used in conjunction with synthetic oligonucleotide cDNAs to analyze the effects of endocrine manipulations on rat pituitary alpha, LH beta, and TSH beta subunit mRNA levels. In addition, we have determined the effects of thyroid hormones on the rates of TSH gene transcription in a mouse thyrotropic tumor propagated subcutaneously in mice in vivo. The observations suggest that LH beta and TSH beta subunit genes are regulated much more acutely than is the alpha subunit gene. This discoordinate regulation of the two subunit genes raises the possibility that cis-trans mechanisms may be involved in the regulation of the subunit genes; we propose that the beta subunit genes are regulated in cis, whereas the alpha gene expression may be regulated by either a trans mechanism dictated by the expression of the beta genes or by cis mechanisms. We plan to use the cloned recombinant alpha and beta gene sequences to construct a series of expression vectors which will be introduced into cell-lines under conditions in which the endogenous gene promoters can be regulated. In addition, we plan to study the tissue-specific utilization of different cis-acting promoters in the alpha subunit gene. To further extend these studies, we also plan to structurally characterize the gene encoding the FSH beta subunit, to examine alpha gene expression by in situ cytohybridizaton, and possibly to pursue studies of a possible linkage to the LH gene of a somatostatin fusion.
Showing the most recent 10 out of 36 publications
