The CK1? Activator Pyrvinium Enhances the Catalytic Efficiency (kcat/Km) of CK1?.

ABSTRACT: The serine/threonine protein kinase casein kinase 1? (CK1?) functions as a negative regulator of Wnt signaling, phosphorylating ?-catenin at serine 45 (P-S45) to initiate its eventual ubiquitin-mediated degradation. We previously showed that the repurposed, FDA-approved anthelminthic drug pyrvinium potently inhibits Wnt signaling in vitro and in vivo. Moreover, we proposed that pyrvinium's Wnt inhibitory activity was the result of its function as an activator of CK1?. An understanding of the mechanism by which pyrvinium activates CK1? is important because pyrvinium was given an orphan drug designation by the FDA to treat familial adenomatous polyposis, a precancerous condition driven by constitutive Wnt signaling. In the current study, we show that pyrvinium stimulates the phosphorylation of S45 ?-catenin, a known CK1? substrate, in a cell-based assay, and does so in a dose- and time-dependent manner. Alternative splicing of CK1? results in four forms of the protein with distinct biological properties. We evaluated these splice products and identified the CK1? splice variant, CK1?S, as the form that exhibits the most robust response to pyrvinium in cells. Kinetic studies indicate that pyrvinium also stimulates the kinase activity of purified, recombinant CK1?S in vitro, increasing its catalytic efficiency (kcat/Km) toward substrates. These studies provide strong and clear mechanistic evidence that pyrvinium enhances CK1? kinase activity.

SUBMITTER: Shen C 

PROVIDER: S-EPMC6942998 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature