Microtubules Depolymerization Caused by the CK1 Inhibitor IC261 May Be Not Mediated by CK1 Blockage

Abstract

The ubiquitously expressed serine/threonine specific casein kinase 1 (CK1) family plays important roles in the regulation of various physiological processes. Small-molecule inhibitors, such as the CK1δ/ε selectively inhibitor IC261, have been used to antagonize CK1 phosphorylation events in cells in many studies. Here we present data to show that, similarly to the microtubule destabilizing agent nocodazole, IC261 depolymerizes microtubules in interphase cells. IC261 treatment of interphase cells affects the morphology of the TGN and Golgi apparatus as well as the localization of CK1δ, which co-localizes with COPI positive membranes. IC261-induced depolymerization of microtubules is rapid, reversible and can be antagonized by pre-treatment of cells with taxol. At lower concentrations of IC261, mitotic spindle microtubule dynamics are affected; this leads to cell cycle arrest and, depending on the cellular background, to apoptosis in a dose-dependent manner. In addition, FACS analysis revealed that IC261 could induce apoptosis independent of cell cycle arrest. In summary this study provides additional and valuable information about various IC261-induced effects that could be caused by microtubule depolymerization rather than by inhibition of CK1. Data from studies that have used IC261 as an inhibitor of CK1 should be interpreted in light of these observations.

Effects of altered expression and activity levels of CK1δ and ɛ on tumor growth and survival of colorectal cancer patients

“…These observations and our own data are in line with previous findings that the effects of CK1‐specific inhibitors are dependent on the cellular background and can lead to G2/M arrest or apoptosis . In addition, it has to be considered that IC261 may also affect cell division through direct binding to the microtubule apparatus . Therefore, IC261 inhibition data should always be interpreted with caution.…”

“…6,26,27,29 In addition, it has to be considered that IC261 may also affect cell division through direct binding to the microtubule apparatus. 21,30 Therefore, IC261 inhibition data should always be interpreted with caution. In contrast, off-target effects have so far not been described for compounds 1 and 2.…”

CK1δ in lymphoma: gene expression and mutation analyses and validation of CK1δ kinase activity for therapeutic application

“…The observed effects are dependent on inhibitor concentration, cell line, and duration of inhibitor exposure. Cell cycle arrest, as observed for some cell lines being treated with IC261 and compound 1, can be explained by CK1 effects on microtubule dynamics and chromosome segregation (Behrend et al, 2000 ; Stoter et al, 2014 ). However, Cheong and colleagues meanwhile demonstrated, that IC261 could have a similar effect on cellular microtubule dynamics as the spindle poison colchicine (Cheong et al, 2011 ).…”

A competitive cell-permeable peptide impairs Nme-1 (NDPK-A) and Prune-1 interaction: therapeutic applications in cancer

“…Furthermore, and most importantly, this occurred with greater specificity in relation to serine inhibition of phosphorylation. Nonetheless, doubts were raised about the IC261 specificity of action against CKIδ/ε inhibition, as IC261 was also demonstrated to alter microtubule depolymerization [56]. Then the CPP was developed that mimicked the region of Nme-1 that is involved in the interaction with Prune-1, including Ser120, Ser122, and Ser125.…”

“…Of interest, Nme-1 has also been reported to interact with microtubules [76] and its biochemical nucleotide diphospho kinase (NDPK) activity within centrosomes during cell division has also been described [77,78]. Of note, IC261 inhibition of CKI δ/ε, which are responsible for Nme-1 phosphorylation, is also known to impair microtuble depolymerization [56]. Altogether, these data suggest an additional role for the Nme-1-Prune-1 complex during cell division and mitosis, and so anomalies due to incorrect formation of the Nme-1-Prune-1 complex in affected children might result in neural developmental defects in the central nervous system (e.g., in brain, cerebellum, and optic nerve).…”