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A major question regarding the sensitivity of solid tumors to targeted kinase inhibitors is why some tumors respond and others do not. The observation that many tumors express EGF receptor (EGFR), yet only a small subset with EGFR-activating mutations respond clinically to EGFR inhibitors (EGFRIs), suggests that responsive tumors uniquely depend on EGFR signaling for their survival. The nature of this dependence is not understood. Here, we investigate dependence on EGFR signaling by comparing non-small-cell lung cancer cell lines driven by EGFR-activating mutations and genomic amplifications using a global proteomic analysis of phospho-tyrosine signaling. We identify an extensive receptor tyrosine kinase signaling network established in cells expressing mutated and activated EGFR or expressing amplified c-Met. We show that in drug sensitive cells the targeted tyrosine kinase drives other RTKs and an extensive network of downstream signaling that collapse with drug treatment. Comparison of the signaling networks in EGFR and c-Met-dependent cells identify a 'core network' of [approximately equal to 50] proteins that participate in pathways mediating drug response. EGF receptor | c-Met | oncogene dependence | proteomics | stable isotope labeling with amino acids in cell culture

Protein tyrosine phosphatase (PTP) receptor T (PTPRT) is the most frequently mutated PTP in human cancers. However, the cell signaling pathways regulated by PTPRT have not yet been elucidated. Here, we report identification of signal transducer and activator of transcription 3 (STAT3) as a substrate of PTPRT. Phosphorylation of a tyrosine at amino acid Y705 is essential for the function of STAT3, and PTPRT specifically dephosphorylated STAT3 at this position. Accordingly, overexpression of normal PTPRT in colorectal cancer cells reduced the expression of STAT3 target genes. These studies illuminate a mechanism regulating the STAT3 pathway and suggest that this signaling pathway plays an important role in colorectal tumorigenesis. colorectal cancer | tyrosine phosphorylation | signaling

An abstract of the article "The protein kinase Akt1 regulates the interferon response through phosphorylation of the transcriptional repressor EMSY," by Scott A. Ezell and colleagues is presented.

Disparities in cancer patient responses have prompted widespread searches to identify differences in sensitive vs. nonsensitive populations and form the basis of personalized medicine. This customized approach is dependent upon the development of pathway-specific therapeutics in conjunction with biomarkers that predict patient responses. Here, we show that Cdk5 drives growth in subgroups of patients with multiple types of neuroendocrine neoplasms. Phosphoproteomics and high throughput screening identified phosphorylation sites downstream of Cdk5. These phosphorylation events serve as biomarkers and effectively pinpoint Cdk5-driven tumors. Toward achieving targeted therapy, we demonstrate that mouse models of neuroendocrine cancer are responsive to selective Cdk5 inhibitors and biomimetic nanoparticles are effective vehicles for enhanced tumor targeting and reduction of drug toxicity. Finally, we show that biomarkers of Cdk5-dependent tumors effectively predict response to anti-Cdk5 therapy in patient-derived xenografts. Thus, a phosphoprotein-based diagnostic assay combined with Cdk5-targeted therapy is a rational treatment approach for neuroendocrine malignancies., Competing Interests: The authors declare no competing interest.