Additionally, recent reports revealed that upregulated myc expression sensitizes cells for therapeutics targeting CK1e. In our studies, IC261 induced a transient full G2/M arrest at a cell type dependent concentration. We have also shown that at half of this concentration ) the subG1 population increases. This increase of apoptotic cells cannot be due to G2/ M arrest, because at IC50 the population of 4N cells is not significantly increased. It was shown, that CK1 phosphorylates Bid and thereby prevents cleavage by caspase 8. Therefore an inhibition of CK1 at low concentrations of IC261 could lead to activation of pro-apoptotic protein Bid and thereby to increased apoptosis indicated by increased subG1 population. However, it remains unclear why at higher concentrations of IC261 the cell cycle arrest at G2/M is dominant over the pro-apoptotic effect. In summary this study provides data that extends the 
knowledge of IC261 induced effects in cells. We demonstrate that the CK1 kinase inhibitor IC261 mediates off-CK1-target effects by depolymerizing MTs in a dose-dependent and reversible manner. Therefore, results of previous studies using IC261 as a CK1 inhibitor should be interpreted carefully. Here, we also present evidence that CK1 is neither localized at the TGN nor at the GA, but co-localizes with the COPI protein b-COP. Opportunistic pathogens secrete multiple virulence factors to modulate interactions with the host, to acquire nutrients from the environment and to facilitate adhesion and colonization to a variety of substrates. Pseudomonas aeruginosa secretes a series of proteases that target host proteins to modulate the immune response and to facilitate colonization in infected tissues. Bacterial adherence and colonization may be facilitated by the degradation of host immune and signaling proteins that would otherwise initiate or potentiate the host response. Alternatively, remodeling the local environment of a bacterium may promote its adherence or growth. While the pathophysiological mechanisms in patients have not been fully elucidated, AP has been shown to cleave bacterial flagellin, host signaling molecules and the epithelial ARRY-142886 sodium channel. Cleavage of flagellin and cytokines would putatively alter the host response to the pathogen, while ENaC cleavage would be predicted to remodel the airway surface hydration state, reduce muco-cilliary clearance, and facilitate bacterial adherence and colonization. The combined effects of blunting the host immune response and altering ion channel activity would putatively contribute to an increase in bacterial load within the airway and the apparent virulence of the pathogen. To evaluate the potential use of the aprI inhibitor as a modulator of AP activity in airway epithelial cells, AP and AP Inh were purified. Tight association and protease inhibition were CUDC-907 HDAC inhibitor measured in vitro and demonstrated that near stoichiometric addition of the inhibitor completely bound the protease and inhibited its activity. This inhibition was blocked with N-terminal fusions to the inhibitor, consistent with the known structures of the proteaseinhibitor complexes. ENaC-mediated sodium transport in a model cell line and primary airway cultures confirmed that AP addition to the apical bathing surface activated ENaC and that near stoichiometric addition of AP Inh blocked the observed ENaC activation. Similarly, ENaC activation was observed in response to apical addition of serralysin from S. marcescens. This activation was blocked by the addition of the purified AP Inh protein. These data show that multiple M10/serralysin family members can activate ENaC and more broadly implicate the M10 protease family as modulators of ENaC activity.