Editors' ChoiceCell Biology

Specifying Substrate Specificity

Sci. Signal.  18 Jun 2013:
Vol. 6, Issue 280, pp. ec140
DOI: 10.1126/scisignal.2004423

Various ligands, including those in the epidermal growth factor (EGF) and transforming growth factor (TGF) families, are initially produced as transmembrane precursors that are cleaved by ADAMs (A disintegrin and metalloproteinases) to produce the active soluble form. Dang et al. performed an shRNA screen and found that in HEK cells, knockdown of protein kinase C α (PKCα) or protein phosphatase 1 inhibitor 14D (PPP1R14D), which is activated by PKC phosphorylation, reduced ADAM17-mediated cleavage of TGF-α, but not that of the EGF ligand neuregulin, in response to the phorbol ester TPA. Knockdown of PKCδ attenuated phosphorylation of Ser286 in neuregulin, an intracellular phosphorylation event that occurs before cleavage, in response to angiotensin II (AngII) or TPA, and a nonphosphorylatable form of neuregulin prevented TPA-induced cleavage. Phosphorylation of Ser58 in PPP1R14D enables it to bind and inhibit a PP1 complex, and PPP1R14D coimmunoprecipitated to a greater extent with PP1α from TPA-treated Jurkat cells (a T cell line) and from TPA- or AngII-treated HEK cells than from untreated control cells. In addition, PPP1R14D immunoprecipitated from TPA- or AngII-treated cells inhibited recombinant PP1α to a greater extent than that immunoprecipitated from untreated control cells. Neither TPA treatment nor knockdown of PKCα or PPP1R14D appreciably decreased the protease activity of ADAM17 in cells. ADAM inhibitors generate unwanted side effects because of nonspecific inhibition of substrate cleavage, and these results suggest that the cleavage specificity of ADAM17 can be determined by distinct signaling pathways acting on its substrates, which could be targeted clinically to achieve greater specificity.

M. Dang, N. Armbruster, M. A. Miller, E. Cermeno, M. Hartmann, G. W. Bell, D. E. Root, D. A. Lauffenburger, H. F. Lodish, A. Herrlich, Regulated ADAM17-dependent EGF family ligand release by substrate-selecting signaling pathways. Proc. Natl. Acad. Sci. U.S.A. 110, 9776–9781 (2013). [Abstract] [Full Text]