TY - JOUR
T1 - Differential expression of the thyrostimulin subunits, glycoprotein α2 and β5 in the rat pituitary
AU - Nagasaki, Hiroshi
AU - Wang, Zhiwei
AU - Jackson, Valerie R.
AU - Lin, Steven
AU - Nothacker, Hans Peter
AU - Civelli, Olivier
PY - 2006/8
Y1 - 2006/8
N2 - Two glycoprotein hormone subunits, (glycoprotein hormone α2-subunit GPA2)and (glycoprotein hormone β5-subunit GPB5) have been recently discovered which, when expressed in vitro, heterodimerize to form a new hormone called thyrostimulin. Thyrostimulin activates the thyroid-stimulating hormone receptor (TSHR) and has thyrotropic activity. Immunological studies have indicated that both subunits co-localize in pituitary cells. To explore the function of thyrostimulin in the rat, we have cloned rat GIPA2 and GPB5, reconstituted the heterodimers in vitro, and confirmed that rat thyrostimulin activates TSHR with an affinity similar to that of TSH. In situ hybridization of the pituitary showed that while GPA2 is expressed in the anterior lobe, GPB5 is not detected in any of the lobes. A quantitative analysis showed that the co-localization of GPA2 and GPB5 is restricted in the rat to the eye and the testis. We found that GPB5 can be detected in the pituitary by quantitative-PCR, but at extremely low levels, 2000-fold lower than TSH P-subunit (GPBtsh). Furthermore, the levels of GPB5 remain constant during the estrus cycle, while those of GPA2 vary. Finally, we found that none of the thyrostimulin subunits was induced by TRH in pituitary cell culture. These data point at the thyrostimulin system as being functionally different to the TSH system.
AB - Two glycoprotein hormone subunits, (glycoprotein hormone α2-subunit GPA2)and (glycoprotein hormone β5-subunit GPB5) have been recently discovered which, when expressed in vitro, heterodimerize to form a new hormone called thyrostimulin. Thyrostimulin activates the thyroid-stimulating hormone receptor (TSHR) and has thyrotropic activity. Immunological studies have indicated that both subunits co-localize in pituitary cells. To explore the function of thyrostimulin in the rat, we have cloned rat GIPA2 and GPB5, reconstituted the heterodimers in vitro, and confirmed that rat thyrostimulin activates TSHR with an affinity similar to that of TSH. In situ hybridization of the pituitary showed that while GPA2 is expressed in the anterior lobe, GPB5 is not detected in any of the lobes. A quantitative analysis showed that the co-localization of GPA2 and GPB5 is restricted in the rat to the eye and the testis. We found that GPB5 can be detected in the pituitary by quantitative-PCR, but at extremely low levels, 2000-fold lower than TSH P-subunit (GPBtsh). Furthermore, the levels of GPB5 remain constant during the estrus cycle, while those of GPA2 vary. Finally, we found that none of the thyrostimulin subunits was induced by TRH in pituitary cell culture. These data point at the thyrostimulin system as being functionally different to the TSH system.
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U2 - 10.1677/jme.1.01932
DO - 10.1677/jme.1.01932
M3 - Article
C2 - 16901922
AN - SCOPUS:33747879288
SN - 0952-5041
VL - 37
SP - 39
EP - 50
JO - Journal of Molecular Endocrinology
JF - Journal of Molecular Endocrinology
IS - 1
ER -