Signaling: Regulated Proteolysis PDF

Signaling: Regulated Proteolysis Copyright and Disclosure All materials found on GCSoM’s course and project sites may be subject to copyright protection and are restricted from further dissemination, retention, or copying. I have no financial relationship with a commercial entity producing health c...

Signaling: Regulated Proteolysis Copyright and Disclosure All materials found on GCSoM’s course and project sites may be subject to copyright protection and are restricted from further dissemination, retention, or copying. I have no financial relationship with a commercial entity producing health care-related products and/or services.  Learning Objectives explain the concept of regulated proteolysis enlist signaling pathways that govern in development describe the pathway mediated by the receptor Notch explain the pathway activated by secreted Wnt proteins describe the pathway activated by secreted Hedgehog proteins elaborate on the pathway that depends on the activation of the latent gene regulatory protein NF-κB  Notch Signaling in development, the pathway controls cell fate by amplifying molecular differences between adjacent cells lateral inhibition is a process via which isolated single cells in a population of precursor/identical cells commit to a fate; these “specialized” cells inhibit their neighbors from acquiring the fate lateral inhibition is achieved by the binding of ligand Delta (or other Delta- like ligands) to Notch receptor on neighboring cells to inhibit differentiation Mol Biol Cell. Alberts B, et al. NY: Garland Science in some tissues, Notch signaling works in the opposite way, causing neighboring cells to behave similarly Notch Signaling Notch and Delta are single-pass transmembrane proteins activated by Delta on an adjacent cell, an intracellular protease cleaves the cytoplasmic domain of Notch; the released domain moves to the nucleus to activate gene transcription in the nucleus, the intracellular Notch domain binds CSL converting it from a transcriptional repressor to an activator after its synthesis, Notch is cleaved into two domains that re-assemble to a heterodimer (the mature receptor); the binding of Delta to Notch induces the second cleavage in the extracellular domain, and a third cleavage releases the intracellular Notch domain (see above)  Notch Signaling Notch signaling acts to control differentiation Notch signaling is essential in intestinal cell differentiation in the transit amplifying (TA) compartment of the intestinal crypt Notch is also important in neuronal differentiation and in other tissues 5 in absence of Wnt in presence of Wnt Wnt Signaling the controlled proteolysis of beta-catenin is essential for the control of canonical Wnt signaling Wnt signaling is essential for stem cell maintenance in the intestine and controls cell fate Wnt signaling deregulated in most cases of colorectal cancer By JWSchmidt at the English language Wikipedia, CC BY-SA 3.0, 6 https://commons.wikimedia.org/w/index.php?curid=37704912  Wnt Signaling  Wnt proteins: secreted local mediators; Frizzled: Wnt receptors  the pathway controls the localization of beta-catenin; usually located at adherens junctions; the “free” cytosolic beta-catenin is maintained at low levels through degradation  glycogen synthase kinase-3b phosphorylates cytosolic beta-catenin, targeting it for degradation; adenomatous polyposis coli (APC) promotes the degradation by mediating the association of the degradation complex with beta-catenin binding of Wnts to Frizzled and a co-receptor (LRP) inhibits beta-catenin degradation through Dishevelled and a serine/threonine kinase casein kinase 1; beta- catenin accumulates in the cytoplasm and nucleus in the nucleus, beta-catenin binds DNA-binding proteins LEF-1/TCF and induces genes that support cell growth and proliferation Molecular Biology of the Cell. Alberts B, Johnson A, Lewis J, et al. New York: Garland Science  Hedgehog Signaling Hedgehog ligands: secreted local mediators active Hedgehog proteins are covalently coupled to cholesterol, which restricts their diffusion Patched and Smoothened are the transmembrane receptors; in the absence of a Hedgehog signal, Patched inhibits the activity of Smoothened binding of Hedgehog to Patched allows Smoothened to relay the signal into the cell in the absence of Hedgehog, a gene regulatory protein Ci is processed to a smaller protein that accumulates in the nucleus, where it acts as a transcriptional repressor the proteolytic processing of the Ci protein depends on a complex when Hedgehog binds to Patched, unprocessed Ci protein is released from its complex and enters the nucleus, where it activates the transcription of Molecular Biology of the Cell. Alberts B, Johnson A, Lewis Hedgehog target genes J, et al. New York: Garland Science  NF-κB Signaling NF-κB proteins (homo- or heterodimers of RelA, RelB, c-Rel, NF-κB1, NF-κB2) are latent gene regulatory proteins, usually inactive in the cytoplasm in response to inflammation, active NF-κB turns on gene transcription IκB binds NF-κB proteins to inactive these in cytoplasmic complexes cytokines (TNF-α, IL-1) bind their receptors, trigger the phosphorylation/degradation of IκB IκB is phosphorylated by the serine/threonine kinase IκB kinase (IKK) the degradation of IkB exposes a nuclear localization signal on the NF-kB proteins allowing for nuclear localization some proteins recruited to the TNF-a receptor contribute to the MAP-kinase cascade or lead to apoptosis Molecular Biology of the Cell. Alberts B, Johnson A, Lewis J, et al. New York: Garland Science  New Perspectives The ability to transduce a signal across a membrane … remains only poorly understood. Recently, a new mechanism of transduction across a membrane has been described. In this model proteases embedded within the membrane are triggered to catalyze the proteolytic release of membrane-anchored transcription factors. These novel proteases are polytopic membrane proteins with catalytic sites embedded in the lipid bilayer. http://grantome.com/grant/NIH/R01-GM073831-02 10  Putting It Together Notch receptors are activated by cleavage when bound by a ligand on the neighboring cell; the intracellular Notch domain enters the nucleus to stimulate gene transcription in Wnt signaling, the proteolysis of beta-catenin is inhibited when Wnt ligands bind to their receptors; beta-catenin enters the nucleus and activates gene transcription In Hedgehog signaling, in the absence of ligands, cytoplasmic gene regulatory protein Ci is cleaved to form a transcriptional repressor; in the presence of ligands, the larger form of Ci activates gene transcription NF-κB is inactivated by inhibitory protein IκB in a complex in the cytoplasm; proinflammatory cytokines trigger a phosphorylation cascade that ultimately phosphorylates IκB, marking it for degradation; this enables the freed NF-κB to enter the nucleus and activate gene transcription  Resources The University of Tokyo, http://csls-text.c.u-tokyo.ac.jp/active/09_02.html Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. New York: Garland Science