Previous biochemical studies have indicated that the membrane-bound thyrotropin-releasing hormone (TRH)-degrading enzyme (TRH-DE) from brain and liver and the serum TRH-DE are derived from the same gene. These studies also suggested that the serum enzyme is of liver origin. The present study was undertaken to verify these hypotheses. In different species, a close relationship between the activities of the serum enzyme and the particulate liver enzyme was noticed.

Thyrotropin-releasing hormone receptor (TRHR) has already been cloned in mammals where thyrotropin-releas-inghormone (TRH) isknowntoactasapowerful stimulator of thyroid-stimulating hormone (TSH) secretion. The TRH receptor of amphibians has not yet been characterized, although TRH is specifically important in the adaptation of skin color to environmental changes via the secretion of a-melanocyte-stimulating hormone (a-MSH).

The thyrotropin receptor (TSHR) is a member of the G protein-coupled receptor superfamily. It has by now been clearly established that the maturation of the glycopro-teins synthesized in the endoplasmic reticulum involves interactions with molecular chaperones, which promote the folding and assembly of the glycoproteins. In this study, we investigated whether calnexin (CNX), calreti-culin (CRT) and BiP, three of the main molecular chap-erones present in the endoplasmic reticulum, interact with the TSHR and what effects these interactions might have on the folding of the receptor....

The thyrotropin receptor (TSHR) undergoes a cleavage at the cell membrane, leading to a heterodimer, comprising an aextracellular and a b-transmembrane and intracellular subunits, held togetherbydisulfidebonds.Moreover, part of the a-subunit of the receptor is shed from thyroid and transfected L cells.To understand the role of cleavage and shedding, we constructed deletion mutants starting, respectively, at the most N-terminal (S314), and C-terminal (L378) cleavage sites previously mapped, corresponding to free b1orb2-subunits without further modification of receptor structure....

Protein kinase Ce (PKCe) is activated by thyrotropin-releasing hormone (TRH), a regulator of pituitary function in rat pituitary GH4C1 cells. We analyzed the downstream mechanism after PKCe activation. Exposure of GH4C1 cells to TRH or a phorbol ester increased the phosphorylation of three p52 proteins (p52a, p52b and p52c) and decreased the phosphoryla-tion of destrin and cofilin.