Precise Regulation of Porcupine Activity Is Required for Physiological Wnt Signaling

By K. Proffitt, D. Virshup. 2012

124 citations recorded by the source corpus.

Background: Wnts control development and differentiation; their secretion may be regulated. Results: All Wnt activity absolutely requires post-translational modification by the O-acyltransferase PORCN, whose abundance or activity modulates signaling tightly and over a large dynamic range. Conclusion: Subtle changes in PORCN activity have major consequences and cause the human disease focal dermal hypoplasia. Significance: PORCN is a key regulator of all Wnt signaling. Gradients of diverse Wnt proteins regulate development, renewal, and differentiation. Porcupine (PORCN) is a membrane-bound O-acyltransferase that is required for post-translational modification of all Wnts to enable their transport, secretion, and activity. Mutations in PORCN are associated with focal dermal hypoplasia (FDH), whereas gene deletion causes embryonic lethality in mice. To study the protein in more detail, zinc finger nucleases were used to edit the PORCN genomic locus, establishing two HT1080 fibrosarcoma clones null for PORCN activity that facilitate the study of PORCN structure and function. We establish that PORCN is a key non-redundant node for the regulation of global Wnt signaling because PORCN null cells are completely incapable of autocrine Wnt signaling. The strength of Wnt signaling is exquisitely sensitive to PORCN expression, with a dynamic range of at least 3 orders of magnitude, suggesting that PORCN activity is a key modulator of all Wnt ligand activity. Consistent with this, we find that multiple FDH-associated mutants have only subtle alterations in enzyme activity yet are associated with a severe FDH phenotype. These studies support an essential regulatory role of PORCN in shaping Wnt signaling gradients.

Subfields: Cellular and Molecular Neuroscience, Molecular Biology, Social Psychology

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Citations in the corpus

Wnt signaling in development and tissue homeostasis (2018, background): “This is an essential step in Wnt protein secretion (Herr and Basler, 2012) and introduces a modification that is required for Wnt activity (Janda et al., 2012; Proffitt and Virshup, 2012; Willert et al., 2003).”
Notum is required for neural and head induction via Wnt deacylation, oxidation and inactivation (2015, unknown): “…palmitoleoylated serine, is not secreted, nor are any of the Wnt proteins that are expressed in cells/embryos deficient for Porcupine (Barrott et al., 2011; Bie- 4 Developmental Cell 32, 1–12, March 23, 2015 ª2015 Elsevier Inc. chele et al., 2011; Proffitt and Virshup, 2012; Takada et al., 2006).”
Stearoyl CoA desaturase is required to produce active, lipid-modified Wnt proteins (2013, background): “Wnt signaling is tightly linked to and fine tuned by Porcn expression (Proffitt and Virshup, 2012), placing Porcn as an attractive target for the development of drugs that modulate Wnt pathway activity in Wnt-driven diseases (Chen et al.”
In vitro reconstitution of Wnt acylation reveals structural determinants of substrate recognition by the acyltransferase human Porcupine (2018, background): “In contrast, N301A and H336A mutants of hPORCN, which are thought to be catalytically deficient mutants (4, 22, 24), showed significantly decreased enzymatic activities (Fig.”
Structural model of PORCN illuminates disease-associated variants and drug binding sites (2021, methodology): “However, mutation of Asn306 has no effect on the catalytic activity of PORCN in cell-based assays (Proffitt and Virshup, 2012; Rios-Esteves et al., 2014) but markedly decreased activity in a purified system where only PAM-CoA was available as a”