Porcupine (PORCN), an endoplasmic reticulum (ER)-resident membrane-bound O-acyltransferase (MBOAT) [1], regulates the Wnt signaling pathway by catalyzing the attachment of palmitoleic acid (C16:1) to serine (Ser) residues on Wnt ligands [2]. This modification occurs specifically at the Hairpin2 domain of Wnt proteins and is indispensable for their binding to Frizzled receptors (FZD) and subsequent pathway activation [2]. Immature Wnt proteins require PORCN-mediated lipid modification prior to being transported extracellularly by the Wnt transporter Wntless (WLS), enabling their interaction with cell surface receptors FZD and co-receptors LRP5/6 to initiate signaling. As the exclusive catalytic enzyme for all 19 human Wnt ligands, PORCN inhibition ablates Wnt signaling [3,4]. Given the pivotal role of Wnt signaling in embryonic development, stemness maintenance, and tumorigenesis, PORCN represents a prime therapeutic target for Wnt-driven pathologies.

The catalytic mechanism of PORCN involves aligning the thiohydroxyl bond of palmitoleoyl-CoA with the Ser hydroxyl group at the Wnt modification site near the active center. His336 in the catalytic center of PORCN activates the Ser209 of Wnt through deprotonation, enabling its nucleophilic attack on the thioester bond of palmitoleoyl-CoA to catalyze fatty acyl transfer [5]. The unique structure of palmitoleoyl-CoA—featuring a 90° bend at the C9 unsaturated double bond, causing tight folding of the fatty acyl chain—is stabilized by PORCN's Trp300 residue, ensuring strict substrate specificity for chain length and double bond positioning [5]. Localized to the ER membrane in a funnel-shaped conformation with multiple transmembrane helices (N-terminus lumenal, C-terminus cytoplasmic) [2], PORCN contains evolutionarily conserved Wnt-binding pockets (e.g., in Homo sapiens, Drosophila melanogaster) that enable a single enzyme to modify all 19 Wnt family members [6]. This structural architecture directly underlies its broad catalytic capability.

Dysregulation of PORCN-mediated Wnt signaling contributes to oncogenesis in colorectal, breast, pancreatic, hepatic, gastric, and lung cancers, as well as non-cancerous conditions including neurodegenerative disorders, pulmonary hypertension, and osteoporosis [7]. As the rate-limiting step in Wnt activation, palmitoylation drives therapeutic interest in PORCN [5]. Small molecule inhibitors (e.g., LGK974, ETC-159, CGX1321) in phase I trials show promise for treating Wnt-dependent malignancies by blocking Wnt ligand acylation [8]. In summary, PORCN governs cellular growth, development, and metabolic balance through lipid modification of Wnt proteins. Its structural features, substrate specificity, and evolutionary conservation underscore its centrality in physiology and disease, validating it as a therapeutic target for Wnt-related disorders.