Tiki proteins are glycosylphosphatidylinositol‐anchored proteases

Abstract

Wnt signalling pathways play pivotal roles in development, homeostasis and human diseases, and are tightly regulated. We previously identified Tiki as a novel family of Wnt inhibitory proteases. Tiki proteins were predicted as type I transmembrane proteins and can act in both Wnt‐producing and Wnt‐responsive cells. Here, we characterize Tiki proteins as glycosylphosphatidylinositol (GPI)‐anchored proteases. TIKI1/2 proteins are enriched on the detergent‐resistant membrane microdomains and can be released from the plasma membrane by GPI‐specific glycerophosphodiesterases GDE3 and GDE6, but not by GDE2. The GPI anchor determines the cellular localization of Tiki proteins and their regulation by GDEs, but not their inhibitory activity on Wnt signalling. Our study uncovered novel characteristics and potential regulations of the Tiki family proteases.

Tiki proteins are substrates of membrane‐type matrix metalloproteinases

“…Matrix metalloproteinases are a family of zinc‐dependent endopeptidases and belong to the metzincin superfamily [24]. However, unlike GDE3, a GPI‐specific lipase that can shed and release TIKI2 protein from the cell surface to conditioned media (CM) [12], we could not detect TIKI2 signal in CM when coexpressed with MMP15 (data not shown). We speculate that there may be multiple MMP15 cleavage sites on TIKI2, which may dilute the signals of TIKI2 in CM.…”

“…Tiki proteins are glycosylphosphatidylinositol‐anchored proteases and can be potentially regulated by GPI‐specific lipases GDE3 and GDE6 [7,10,12]. This study uncovers a novel regulation of TIKI2 proteins on the cell surface by MT‐MMPs MMP14, MMP15 and MMP16.…”

“…HA‐TIKI1, HA‐TIKI2 and TIKI2N‐FLAG‐His were described previously [12]. HA‐TIKI2N was constructed by fusing the extracellular domain of TIKI2 with an amino‐terminal HA tag.…”

“…Tiki proteins contain a large extracellular TIKI/GumN domain that functions as a catalytic core [7,10]. Tiki proteins were recently reported to be glycosylphosphatidylinositol-anchored proteins (GPI-APs) that are enriched on detergent-resistant membrane microdomains on the plasma membrane [12]. Mechanistically, Tiki proteins hydrolyse the amino terminus of Wnt3a and induce Wnt3a to form oxidized oligomers, which lose the receptor binding ability [7].…”

“…Mechanistically, Tiki proteins hydrolyse the amino terminus of Wnt3a and induce Wnt3a to form oxidized oligomers, which lose the receptor binding ability [7]. Furthermore, Tiki proteins antagonize Wnt signalling in both Wnt-producing and Wnt-responsive cells in both Xenopus embryos and mammalian cells [7,12]. However, the regulation of Tiki proteins is still unknown.…”