tailieunhanh - Báo cáo khoa học: Role of cleavage and shedding in human thyrotropin receptor function and trafficking

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 , part of the a-subunit of the receptor is shed from thyroid and transfected L 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 | Eur. J. Biochem. 270 3486-3497 2003 FEBS 2003 doi Role of cleavage and shedding in human thyrotropin receptor function and trafficking Mylene Quellari1 Agnes Desroches1 Isabelle Beau1 Emmanuelle Beaudeux1 and Micheline Misrahi1 2 1INSERM E120 Recepteurs Signalisations et Physiopathologie Thyroidienne et de la Reproduction and 2Laboratoire d Hormonologie et Biologie Moleculaire Hopital Bicetre IFR Bicetre Le Kremlin Bicetre France The thyrotropin receptor TSHR undergoes a cleavage at the cell membrane leading to a heterodimer comprising an a extracellular and a P-transmembrane and intracellular subunits held together by disulfide bonds. Moreover part of the a-subunit of the receptor is shed from thyroid and transfected L cells. To undestland the role of ck rv ag e 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 p1 or p2-subunits without further modification of receptor structure. Fumciionrll Undies performed in COS-7 cells showed that both mutants display an increased basal activation of the cAMP pathway when compared with the wild-type receptor. By contrast deMon of almost the eniíre extracellular domain of the receptor TM409 mutant totally impairs receptor function thus confirming a role of the juxtamembrane extracellular region in receptor function. The p1 mutant receptor exhibited an increased internalization when compared with the hormone-activated holoreceptor. Furthermore no recyciing was observed in the cuse of the P1 mutant receptor. These observatíons strongly argue for a different conformation between the receptor activated by cleavage and shedding on the one hand and the receptor activated by the ligand on the other hand. Cleavabe nnd shedding of a receptor already activated by a transmembrane activating mutation M453T further increase its activity showing that the extracellular domain still exerts a .