G-protein-coupled receptor kinase-2 (GRK2) belongs to the GRK family of serine/threonine protein kinases critical in the regulation of G-protein-coupled receptors. Apart from this canonical role, GRK2 is also involved in several signaling pathways via distinct intracellular interactomes. In the present study, we examined the role of GRK2 in TNFα signaling in colon epithelial cell–biological processes including wound healing, proliferation, apoptosis, and gene expression. Knockdown of GRK2 in the SW480 human colonic cells significantly enhanced TNFα-induced epithelial cell wound healing without any effect on apoptosis/proliferation. Consistent with wound-healing effects, GRK2 knockdown augmented TNFα-induced matrix metalloproteinases (MMPs) 7 and 9, as well as urokinase plasminogen activator (uPA; factors involved in cell migration and wound healing). To assess the mechanism by which GRK2 affects these physiological processes, we examined the role of GRK2 in TNFα-induced MAPK and NF-κB pathways. Our results demonstrate that while GRK2 knockdown inhibited TNFα-induced IκBα phosphorylation, activation of ERK was significantly enhanced in GRK2 knockdown cells. Our results further demonstrate that GRK2 inhibits TNFα-induced ERK activation by inhibiting generation of reactive oxygen species (ROS). Together, these data suggest that GRK2 plays a critical role in TNFα-induced wound healing by modulating MMP7 and 9 and uPA levels via the ROS–ERK pathway. Consistent with in vitro findings, GRK2 heterozygous mice exhibited enhanced intestinal wound healing. Together, our results identify a novel role for GRK2 in TNFα signaling in intestinal epithelial cells.
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The polyamine biosynthetic enzyme arginine decarboxylase has emerged multiple times from different proteins folds by convergent evolution, and has also emerged independently, at different times, from the same protein fold by pseudoconvergent evolution. In some cases, the enzyme cofactor is an internally produced pyruvoyl group, in others it is pyridoxal 5'-phosphate. The origin of this enzyme from such diverse structural classes and with different catalytic mechanisms indicates that the emergence of polyamine biosynthesis on Earth was, and is, inevitable. For more information, please see review article, “Evolution of Biosynthetic Diversity” by Anthony J. Michael, pages 2277–2299.
G-protein-coupled receptor kinase-2 is a critical regulator of TNFα signaling in colon epithelial cells
Michael D. Steury, Peter C. Lucas, Laura R. McCabe, Narayanan Parameswaran; G-protein-coupled receptor kinase-2 is a critical regulator of TNFα signaling in colon epithelial cells. Biochem J 15 July 2017; 474 (14): 2301–2313. doi: https://doi.org/10.1042/BCJ20170093
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