CK1

Casein kinase 1 (CK1) is a conserved family of serine/threonine protein kinases that includes the α, β, γ1-3, δ, and ε isoforms, which share highly conserved catalytic domains but differ in regulatory regions that influence substrate selection and cellular functions^[1]. CK1 isoforms participate in multiple signaling networks and regulate protein phosphorylation events involved in cell survival, proliferation, differentiation, and intracellular signaling^[1]. Mechanistically, CK1 has a central role in Wnt/β-catenin signaling, where distinct isoforms phosphorylate pathway components and control β-catenin stability and transcriptional activity^[2]. In particular, CK1α functions as a negative regulator of canonical Wnt signaling by initiating phosphorylation events that promote β-catenin degradation and suppress pathway activation^[2][3]. Dysregulation of CK1-dependent signaling has been linked to tumorigenesis and other disease processes, making CK1 an important experimental target in cancer biology and signal transduction research^[1][2]. Compared with related isoforms, CK1α shows a prominent role in restraining Wnt signaling, whereas CK1δ and CK1ε are strongly associated with circadian clock regulation through phosphorylation-dependent control of PERIOD protein stability and localization^[1][4][5]. In disease and physiological models, alterations in CK1δ or CK1ε activity have been associated with circadian rhythm disorders, while aberrant CK1 signaling has also been implicated in neurodegenerative pathology^[4][5]. For experimental applications, small-molecule CK1 modulators, including isoform-targeting inhibitors such as IC261, have been used to investigate CK1-dependent signaling mechanisms and disease-relevant pathways^[1].