The segment polarity gene porcupine encodes a putative multitransmembrane protein involved in Wingless processing.

Abstract

The Wnt protein Wingless (Wg) functions as a signal in patterning of both the Drosophila embryo and imaginal discs. Lack of porcupine ~7orc) activity is associated with mutant phenotypes similar to those of wg mutations. In porc mutant embryos, Wg protein is confined to the cells that produce it, suggesting that Porc plays a role in processing or secretion of Wg. porc encodes a novel transmembrane protein that appears to be concentrated at the endoplasmic reticulum. We present both genetic and in vitro evidence demonstrating that porc is involved specifically in the processing of Wg. We identified a human sequence related to Porc suggesting the existence of a family of proteins involved in processing of Wnts.[Key Words: Drosophila; transmembrane protein; Wingless; porcupine]Received October 1, 1996; revised version accepted October 30, 1996.Like its murine homolog, the proto-oncogene Wnt-1, Drosophila wingless {wgl encodes a secreted protein that has potent effects on the differentiation of responsive cells (for review see, Klingensmith and Nusse 1994; Siegfried and Perrimon 1994}. Wg has been implicated in a number of developmental processes that include embryonic segmentation, gut formation, and imaginal discs patteming. To identify components involved in Wg signaling, a genetic approach has been undertaken. To date, four segment polarity genes, dishevelled {dsh), armadillo (arm), zeste-white3 (zw3), and porcupine (porc) have been implicated in Wg signaling. The current model (for review, see Bhanot et al. 1996;Perrimon 1996) is that Wg, which requires Pore activity to be secreted, interacts with the seven-transmembrane DFz2 receptor to activate a signal transduction pathway that is mediated by Dsh, Zw3, and Arm. This pathway operates in a number of developmental processes and, depending on the cell type, regulates different sets of transcription factors. For example, Wg signaling regulates engrafted (en) in the embryonic epidermis and genes of the achaete scute complex at the wing margin.The function of Pore in Wg signaling is not elucidated. Embryos that are missing both the maternal and zygotic pore gene product have a cuticular phenotype identical to wg mutant embryos {Perrimon et al. 19891. Interestingly, Wg has an altered, less diffuse distribution in pore mutant embryos. In wild-type animals, expression studies have shown that Wg protein is found outside its RNA expression domain. In the embryonic epidermis, Wg protein antibody staining appears punctate because of the accumulation of Wg in intracellular vesicles. These vesicles are detected both in wg-expressing and neighboring wg nonexpressing cells, and the distribution of these vesicles appears graded on either side of the wg-expressing cells {van den Heuvel et al. 1989;Gonzalez et al. 1991;Couso et al. 1994}. In pore mutant animals, Wg appears to be confined to the expressing cells, and is very stable {van den Heuvel et al. 1993; Siegfried et al. 19941, sug-gesting that pore encodes a product required for secretion, processing or normal diffusion of...

ERAD‐dependent control of the Wnt secretory factor Evi

“…Wnt proteins are palmitoylated at a conserved serine residue by the ER‐resident O‐acyltransferase Porcn (Kadowaki et al , 1996; Willert et al , 2003; Takada et al , 2006), which is required for the Wnt proteins to interact with Evi (Herr & Basler, 2012) (Fig 2A). To determine whether Wnt palmitoylation and consequently Evi‐Wnt interactions are required for the Wnt‐mediated increase in Evi protein, we treated wild‐type, Wnt3, or Wnt5B stable transfected HEK293T cells with the Porcn inhibitor LGK974 to block Wnt palmitoylation.…”

Controlled levels of canonical Wnt signaling are required for neural crest migration

“…The most prominent modifications are glycosylation and acylation (Komekado et al, 2007;Kurayoshi et al, 2007;Janda et al, 2012;Takada et al, 2006). Although the mechanism by which the lipid residues are attached to the Wntpolypepide backbone is still not fully understood several comperative and loss-offunction studies suggest the involvement of the Porcupine (Porcn), an ER resident protein in this process (van den Heuvel et al, 1993;Kadowaki et al, 1996;Hofmann, 2000;Barrott et al, 2011;Biechele et al, 2011). Beginning with Wnt secretion, Wntdependent signal transduction requires binding of the Wnt ligand to the extracellular cysteine-rich domain of the seven-transmembrane-span receptor Frizzled (Fz) (Vinson et al, 1989;Adler et al, 1990;Park et al, 1994;Wang et al, 1996) and activation of the cytoplasmic phosphoprotein Disheveled (Dsh) (Wallingford and Habas, 2005), which regulates and branches all of the Wnt pathways Komiya and Habas, 2008) (Fig.1.3).…”

Wnts as ligands: processing, secretion and reception

“…In addition, palmitoylation of Wnt proteins has been shown to be necessary for their N-linked glycosylation, the lipid moiety perhaps serving to anchor the proteins to the endoplasmic reticulum (ER) membrane in close proximity to the oligosaccharyl transferase complex. (Kadowaki et al, 1996;Tanaka et al, 2002;Willert et al, 2003;Zhai et al, 2004). This proposed role for palmitoylation during N-linked glycosylation might also aid in Wnt transport between cells as glycosylation might increase Wnt interactions with heparin sulfate proteoglycans (HSPGs) present on the surface of Wnt responding cells (see below).…”

“…Upon overexpression in tissue culture cells, several different N-linked glycosylated intermediate Wnt protein products are observed in cell lysates Reichsman et al, 1996;Tanaka et al, 2002). By contrast, fewer forms of Wnt are found secreted into media (Kadowaki et al, 1996). These data, coupled with the fact that when overexpressed, a large proportion of newly synthesized Wnt protein is found associated with chaperone proteins , suggest that Wnt protein processing and secretion are highly regulated processes.…”