Substrate specificity analysis of protein kinase complex Dbf2-Mob1 by peptide library and proteome array screening

BACKGROUND: The mitotic exit network (MEN) is a group of proteins that form a signaling cascade that is essential for cells to exit mitosis in Saccharomyces cerevisiae. The MEN has also been implicated in playing a role in cytokinesis. Two components of this signaling pathway are the protein kinase Dbf2 and its binding partner essential for its kinase activity, Mob1. The components of MEN that act upstream of Dbf2-Mob1 have been characterized, but physiological substrates for Dbf2-Mob1 have yet to be identified. RESULTS: Using a combination of peptide library selection, phosphorylation of opitmal peptide variants, and screening of a phosphosite array, we found that Dbf2-Mob1 preferentially phosphorylated serine over threonine and required an arginine three residues upstream of the phosphorylated serine in its substrate. This requirement for arginine in peptide substrates could not be substituted with the similarly charged lysine. This specificity determined for peptide substrates was also evident in many of the proteins phosphorylated by Dbf2-Mob1 in a proteome chip analysis. CONCLUSION: We have determined by peptide library selection and phosphosite array screening that the protein kinase Dbf2-Mob1 preferentially phosphorylated substrates that contain an RXXS motif. A subsequent proteome microarray screen revealed proteins that can be phosphorylated by Dbf2-Mob1 in vitro. These proteins are enriched for RXXS motifs, and may include substrates that mediate the function of Dbf2-Mob1 in mitotic exit and cytokinesis. The relatively low degree of sequence restriction at the site of phosphorylation suggests that Dbf2 achieves specificity by docking its substrates at a site that is distinct from the phosphorylation sit

Effects of dose modifications on the safety and efficacy of dacomitinib for EGFR mutation-positive non-small-cell lung cancer

Aim: We evaluated reasons for dacomitinib dose reduction (DR) and examined adverse event (AE) incidence, key efficacy end points (progression-free survival [PFS]/overall survival [OS]), and pharmacokinetics in dose-reducing patients in the ARCHER 1050 trial. Patients & methods: Newly diagnosed patients with EGFR mutation-positive, advanced non-small-cell lung cancer received oral dacomitinib (45 mg once-daily [QD]), with stepwise toxicity-managing DR (30 and 15 mg QD) permitted. Results: Skin toxicities (62.7%) were the most common DR-leading AEs. The AE incidence and severity decreased following DRs. Initial plasma dacomitinib exposure (45 mg QD) was generally lower in patients remaining at 45 mg QD compared with dose-reducing patients. Median PFS and OS were similar in all dacomitinib-treated patients and dose-reducing patients. Conclusion: Tolerability-guided dose modifications enabled patients to continue with dacomitinib and benefit from PFS/OS improvement

Initiation of the TORC1-regulated G0 program requires Igo1/2, which license specific mRNAs to evade degradation via the 5'-3' mRNA decay pathway

Eukaryotic cell proliferation is controlled by growth factors and essential nutrients, in the absence of which cells may enter into a quiescent (G0) state. In yeast, nitrogen and/or carbon limitation causes downregulation of the conserved TORC1 and PKA signaling pathways and, consequently, activation of the PAS kinase Rim15, which orchestrates G0 program initiation and ensures proper life span by controlling distal readouts, including the expression of specific genes. Here, we report that Rim15 coordinates transcription with posttranscriptional mRNA protection by phosphorylating the paralogous Igo1 and Igo2 proteins. This event, which stimulates Igo proteins to associate with the mRNA decapping activator Dhh1, shelters newly expressed mRNAs from degradation via the 5′-3′ mRNA decay pathway, thereby enabling their proper translation during initiation of the G0 program. These results delineate a likely conserved mechanism by which nutrient limitation leads to stabilization of specific mRNAs that are critical for cell differentiation and life span

Effects of dose modifications on the safety and efficacy of dacomitinib for EGFR mutation-positive non-small-cell lung cancer

Aim: We evaluated reasons for dacomitinib dose reduction (DR) and examined adverse event (AE) incidence, key efficacy end points (progression-free survival [PFS]/overall survival [OS]), and pharmacokinetics in dose-reducing patients in the ARCHER 1050 trial. Patients & methods: Newly diagnosed patients with EGFR mutation-positive, advanced non-small-cell lung cancer received oral dacomitinib (45 mg once-daily [QD]), with stepwise toxicity-managing DR (30 and 15 mg QD) permitted. Results: Skin toxicities (62.7%) were the most common DR-leading AEs. The AE incidence and severity decreased following DRs. Initial plasma dacomitinib exposure (45 mg QD) was generally lower in patients remaining at 45 mg QD compared with dose-reducing patients. Median PFS and OS were similar in all dacomitinib-treated patients and dose-reducing patients. Conclusion: Tolerability-guided dose modifications enabled patients to continue with dacomitinib and benefit from PFS/OS improvement