Panoply™ Human CSNK1E Over-expressing Stable Cell Line

Casein kinase 1ε (CK1ε or CSNK1E) and Axin1 are key components of the β-catenin degradation complex in the canonical Wnt signaling pathway. Studies have shown that CK1ε can interact with AXIN1, but its physiological function and role in tumorigenesis remain unclear. Here, researchers found that CK1δ/ε inhibitors significantly increased AXIN1 protein levels in colorectal cancer (CRC) cells by targeting CK1ε. Mechanistic studies revealed that CK1ε promotes the interaction between the E3 ubiquitin ligase SIAH1 and AXIN1, thereby promoting AXIN1 degradation via the ubiquitin-proteasome pathway. Genetic or pharmacological inhibition of CK1ε, as well as knockdown of SIAH1, downregulated the expression of downstream genes in the Wnt/β-catenin pathway, inhibited CRC cell viability, and suppressed CRC development and progression in vitro and in vivo. In summary, these findings indicate that CK1ε plays an oncogenic role in the development and progression of CRC by regulating AXIN1 stability. These findings reveal a novel mechanism by which CK1ε regulates the Wnt/β-catenin signaling pathway and highlight the potential value of targeting the CK1ε/SIAH1 axis in CRC treatment.

To evaluate the regulatory effect of CK1ε on AXIN1 stability, researchers treated HEK293T cells with the protein synthesis inhibitor cycloheximide (CHX). CHX treatment reduced AXIN1 protein levels, and the half-life of AXIN1 protein was further shortened in CK1ε-overexpressing cells (Figure 1A). As expected, treatment with Wnt3a-conditioned medium (Wnt3a-CM) reduced endogenous AXIN1 levels, and this process was blocked by the proteasome inhibitor MG132, but not by the lysosomal inhibitors CQ and Baf-A1, indicating that Wnt-induced AXIN1 degradation is mediated by the proteasome (Figure 1B). Similarly, MG132 also blocked the degradation of exogenous AXIN1 regulated by CK1ε (Figure 1C). Furthermore, AXIN1 ubiquitination was enhanced in CK1ε-overexpressing cells (Figure 1D). Conversely, CSNK1E deficiency or treatment with the CK1δ/ε inhibitor SR3029 significantly reduced AXIN1 ubiquitination levels in CRC cells (Figure 1E). To investigate the formation of ubiquitin chains associated with AXIN1, researchers used a specific ubiquitin K48 antibody to detect AXIN1 ubiquitination, and the results showed that knockout of CSNK1E significantly attenuated K48-linked ubiquitination of AXIN1 (Figure 1F). These results indicate that CK1ε promotes AXIN1 degradation through the K48-mediated ubiquitin-proteasome pathway.

Figure 1. CK1ε regulates AXIN1 stability via the ubiquitin-proteasome pathway. (Yan M, et al., 2024)