Beschreibung:
<jats:sec><jats:label /><jats:p>Signaling scaffolds guide the flow of information and the spatial organization of the enzymes within the ERK1/2 signaling pathway. However, mechanisms that control assembly and dynamics within scaffolding complexes as well as mechanisms regulating the cellular distribution of these complexes remain largely unknown. Our studies unravel a novel, multi‐level paradigm in which allosteric modifications alter the ability of the scaffold protein Shoc2 to actively accelerate transmission of ERK1/2 signals. Shoc2 accelerates ERK1/2 signaling by tethering to close proximity essential proteins of the pathway, Ras and RAF‐1. Germ‐line mutations in Shoc2 affect spatial distribution of Shoc2 or its ability to assemble the signaling complex and cause Noonan‐like syndrome, a congenital disorder that presents with a wide spectrum of developmental abnormalities.</jats:p><jats:p>Our lab studies mechanisms that fine‐tune ERK1/2 signals transmitted through the Shoc2 complex. We found that Shoc2 assembles an elegant multi‐protein complex that incorporates a number of proteins of the ubiquitin system. To fine‐tune amplitude of ERK1/2 signal transmitted via the complex, Shoc2 tethers the E3 ligase HUWE1, the (AAA+) ATPases, PSMC5 and VCP/p97 as well as the deubiquitinating enzyme, USP7. All of these enzymes are integral to the intricate feedback mechanism by which ubiquitination controls amplitude of the Shoc2‐ERK1/2 signals.</jats:p><jats:p>Our studies show that HUWE1 ubiquitinates Shoc2 and RAF‐1, while ATPases modulate ubiquitination of Shoc2 and RAF‐1 through remodeling of the complex. We used fluorescence microscopy and biochemical analysis to demonstrate that PSMC5 and VCP/p97 are involved in recruitment of the Shoc2 scaffolding complexes to endosomes for complex remodeling. Importantly, we found that in the context of the Shoc2 complex, USP7 functions as a “molecular switch” that uses its enzymatic activity to trigger the “turn‐off” of the ERK1/2 signals transmitted via the scaffolding complex. We found that congenital Shoc2 mutations affect mechanisms controlling Shoc2 ubiquitination leading to aberrant signal transmission.</jats:p><jats:p>In summary, our studies are the first to demonstrate that the Shoc2 scaffold employs multi‐protein enzymatic machinery to govern the amplitude of Shoc2‐ERK1/2 signals. We also show that mislocalization of the Shoc2 complexes affects remodeling of the scaffolding module and may lead to the developmental pathology. Overall, these studies significantly advance our understanding of the mechanisms by which non‐enzymatic scaffolds regulate specificity and dynamics of the ERK1/2 signaling networks.</jats:p></jats:sec><jats:sec><jats:title>Support or Funding Information</jats:title><jats:p>National Cancer Institute (R00CA126161 to EG), National Institute of General Medical Sciences (GM113087 to EG), American Cancer Society (RSG‐14‐172‐01‐CSM to EG)</jats:p></jats:sec>