Receptor serine/threonine protein kinase

The TGF- Ss exert their biological actions by binding to specific receptors, of which there are three types (I, II and III). All are transmembrane glycoproteins. All three TGF-)Ss bind to all three receptor types, although they bind with higher affinity to types I and II receptors (53 kDa and 65 kDa, respectively). The intracellular domains of the type I and II receptors display endogenous serine/threonine protein kinase activity. 

Gj, G0, Gq). As a result, the inner leaflet of the plasma membrane is the source of a variety of chemical mediators that are released as a consequence of receptor activation. These mediators include inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DAG), which are both products of Pi-specific phospholipase C (Fig. 6-23) and arachidonic acid, which is an unsaturated fatty acid product of phospholipase A2 and phosphatidate (a product of phospholipase D). IP3 induces the release of Ca2+ ions from intracellular endoplasmic reticulum stores. DAG is a known activator of a lipid-dependent serine/threonine protein kinase (protein kinase C). 

Butein is a simple chalcone formed by the union of a phloroglucinol ring with a catechol one through a propenone chain. It has been characterised as a PTK specific inhibitor, because it reduced the extent of the EGF-induced phosphorylation of the EGF receptor localised in human hepatocellular carcinoma cells, and the activity of the soluble EGF receptor and of p60 ". In contrast with other flavonoids, butein was ineffective against serine/threonine protein kinases [55]. 

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