Mediated intracellular signaling signal transducers

As noted earlier, signal-transducing systems undergo desensitization when the signal persists. Desensitization of the /3-adrenergic receptor is mediated by a protein kinase that phosphorylates the receptor on the intracellular domain that normally interacts with Gs (Fig. 12-17). When the receptor is occupied by epinephrine,... 

As observed with the other D2-like receptors, the D4 receptors mediate additional signaling events that are independent of the changes in cAMP levels. Some of these intracellular signals can be transduced by the Gpy complex. This is probably the case in HEK 293 transfected with a Gpy-sensitive adenylyl cyclase (ACII), in which activation of D4 receptor paradoxically produced a stimulation of cAMP production (Watts and Neve,... 

TSH (also called thyrotropin), which is secreted by the pituitary, plays a central role in the regulation of growth and function of the thyroid gland. TSH receptors are functionally coupled to G-proteins thus, the extracellular stimulus by TSH is transduced into intracellular signals mediated by a number of G-proteins. Activation of Gs-protein results in the stimulation of the adenylate cyclase-cAMP-protein phosphorylation cascade. Other G-proteins coupled to TSH-receptor activation include Gg-protein, which mediates the phospholipase C-phosphatidylinositol 4,5-bisphosphate-Ca + signaling pathway (see Chapter 30 for a detailed discussion). 

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