Julie Nardone

Global Survey of Phosphotyrosine Signaling Identifies Oncogenic Kinases in Lung Cancer

Despite the success of tyrosine kinase-based cancer therapeutics, for most solid tumors the tyrosine kinases that drive disease remain unknown, limiting our ability to identify drug targets and predict response. Here we present the first large-scale survey of tyrosine kinase activity in lung cancer. Using a phosphoproteomic approach, we characterize tyrosine kinase signaling across 41 non-small cell lung cancer (NSCLC) cell lines and over 150 NSCLC tumors. Profiles of phosphotyrosine signaling are generated and analyzed to identify known oncogenic kinases such as EGFR and c-Met as well as novel ALK and ROS fusion proteins. Other activated tyrosine kinases such as PDGFRalpha and DDR1 not previously implicated in the genesis of NSCLC are also identified. By focusing on activated cell circuitry, the approach outlined here provides insight into cancer biology not available at the chromosomal and transcriptional levels and can be applied broadly across all human cancers.

Signaling networks assembled by oncogenic EGFR and c-Met.

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 ≈50 proteins that participate in pathways mediating drug response.

Foxp1 is an essential transcriptional regulator of B cell development

Forkhead transcription factors are key participants in development and immune regulation. Here we demonstrate that absence of the gene encoding the forkhead transcription factor Foxp1 resulted in a profound defect in early B cell development. Foxp1 deficiency was associated with decreased expression of all B lineage genes in B220+ fetal liver cells as well as with a block in the transition from pro–B cell to pre–B cell involving diminished expression of recombination-activating genes 1 and 2. Foxp1 bound to the Erag enhancer and was involved in controlling variable-(diversity)-joining recombination of the gene encoding immunoglobulin heavy chain in a B cell lineage–specific way. Our results identify Foxp1 as an essential participant in the transcriptional regulatory network of B lymphopoiesis.

Profiling of UV-induced ATM/ATR signaling pathways

To ensure survival in the face of genomic insult, cells have evolved complex mechanisms to respond to DNA damage, termed the DNA damage checkpoint. The serine/threonine kinases ataxia telangiectasia-mutated (ATM) and ATM and Rad3-related (ATR) activate checkpoint signaling by phosphorylating substrate proteins at SQ/TQ motifs. Although some ATM/ATR substrates (Chk1, p53) have been identified, the lack of a more complete list of substrates limits current understanding of checkpoint pathways. Here, we use immunoaffinity phosphopeptide isolation coupled with mass spectrometry to identify 570 sites phosphorylated in UV-damaged cells, 498 of which are previously undescribed. Semiquantitative analysis yielded 24 known and 192 previously uncharacterized sites differentially phosphorylated upon UV damage, some of which were confirmed by SILAC, Western blotting, and immunoprecipitation/Western blotting. ATR-specific phosphorylation was investigated by using a Seckel syndrome (ATR mutant) cell line. Together, these results provide a rich resource for further deciphering ATM/ATR signaling and the pathways mediating the DNA damage response.

Survey of Tyrosine Kinase Signaling Reveals ROS Kinase Fusions in Human Cholangiocarcinoma

Cholangiocarcinoma, also known as bile duct cancer, is the second most common primary hepatic carcinoma with a median survival of less than 2 years. The molecular mechanisms underlying the development of this disease are not clear. To survey activated tyrosine kinases signaling in cholangiocarcinoma, we employed immunoaffinity profiling coupled to mass spectrometry and identified DDR1, EPHA2, EGFR, and ROS tyrosine kinases, along with over 1,000 tyrosine phosphorylation sites from about 750 different proteins in primary cholangiocarcinoma patients. Furthermore, we confirmed the presence of ROS kinase fusions in 8.7% (2 out of 23) of cholangiocarcinoma patients. Expression of the ROS fusions in 3T3 cells confers transforming ability both in vitro and in vivo, and is responsive to its kinase inhibitor. Our data demonstrate that ROS kinase is a promising candidate for a therapeutic target and for a diagnostic molecular marker in cholangiocarcinoma. The identification of ROS tyrosine kinase fusions in cholangiocarcinoma, along with the presence of other ROS kinase fusions in lung cancer and glioblastoma, suggests that a more broadly based screen for activated ROS kinase in cancer is warranted.

The enzymatic activity of 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase is enhanced by NPM-ALK: new insights in ALK-mediated pathogenesis and the treatment of ALCL

Anaplastic large cell lymphoma represents a subset of neoplasms caused by translocations that juxtapose the anaplastic lymphoma kinase (ALK) to dimerization partners. The constitutive activation of ALK fusion proteins leads to cellular transformation through a complex signaling network. To elucidate the ALK pathways sustaining lymphomagenesis and tumor maintenance, we analyzed the tyrosine-kinase protein profiles of ALK-positive cell lines using 2 complementary proteomic-based approaches, taking advantage of a specific ALK RNA interference (RNAi) or cell-permeable inhibitors. A well-defined set of ALK-associated tyrosine phosphopeptides, including metabolic enzymes, kinases, ribosomal and cytoskeletal proteins, was identified. Validation studies confirmed that vasodilator-stimulated phosphoprotein and 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate cyclohydrolase (ATIC) associated with nucleophosmin (NPM)-ALK, and their phosphorylation required ALK activity. ATIC phosphorylation was documented in cell lines and primary tumors carrying ALK proteins and other tyrosine kinases, including TPR-Met and wild type c-Met. Functional analyses revealed that ALK-mediated ATIC phosphorylation enhanced its enzymatic activity, dampening the methotrexate-mediated transformylase activity inhibition. These findings demonstrate that proteomic approaches in well-controlled experimental settings allow the definition of informative proteomic profiles and the discovery of novel ALK downstream players that contribute to the maintenance of the neoplastic phenotype. Prediction of tumor responses to methotrexate may justify specific molecular-based chemotherapy.

Survey of Activated FLT3 Signaling in Leukemia

Activating mutations of FMS-like tyrosine kinase-3 (FLT3) are found in approximately 30% of patients with acute myeloid leukemia (AML). FLT3 is therefore an attractive drug target. However, the molecular mechanisms by which FLT3 mutations lead to cell transformation in AML remain unclear. To develop a better understanding of FLT3 signaling as well as its downstream effectors, we performed detailed phosphoproteomic analysis of FLT3 signaling in human leukemia cells. We identified over 1000 tyrosine phosphorylation sites from about 750 proteins in both AML (wild type and mutant FLT3) and B cell acute lymphoblastic leukemia (normal and amplification of FLT3) cell lines. Furthermore, using stable isotope labeling by amino acids in cell culture (SILAC), we were able to quantified over 400 phosphorylation sites (pTyr, pSer, and pThr) that were responsive to FLT3 inhibition in FLT3 driven human leukemia cell lines. We also extended this phosphoproteomic analysis on bone marrow from primary AML patient samples, and identify over 200 tyrosine and 800 serine/threonine phosphorylation sites in vivo. This study showed that oncogenic FLT3 regulates proteins involving diverse cellular processes and affects multiple signaling pathways in human leukemia that we previously appreciated, such as Fc epsilon RI-mediated signaling, BCR, and CD40 signaling pathways. It provides a valuable resource for investigation of oncogenic FLT3 signaling in human leukemia.

Phosphoproteomic analysis identifies the M0-91 cell line as a cellular model for the study of TEL-TRKC fusion-associated leukemia.

Phosphoproteomic analysis identifies the M0-91 cell line as a cellular model for the study of TEL-TRKC fusion-associated leukemia