Analysis of intercellular signal transduction in the tumor microenvironment

Gong BMC Systems Biology 2013, 7(Suppl 3):S5 http://www.biomedcentral.com/1752-0509/7/S3/S5 RESEARCH Open Access Analysis of intercellular signal transduction in the tumor microenvironment Haijun Gong From Asia Pacific Bioinformatics Network (APBioNet) Twelfth International Conference on Bioinformatics (InCoB2013) Taicang China. 20-22 September 2013 Abstract Background: Recent cancer studies revealed, the interaction between pancreatic cancer cells and pancreatic stellate cells is of importance in the cancer progression. The activation of stellate cells is mediated by some growth factors and cytokines secreted by the cancer cells. In turn, the activated stellate cells will synthesize and secrete multiple growth factors to continuously stimulate the growth of surrounding cancer cells through paracrine pathways. The mechanism behind the evolution of stellate cells from quiescent state to a cancer-associated phenotype is still not well understood. Results: To systematically investigate the interaction between cancer cells and stellate cells, we constructed a multicellular discrete value model, which is composed of several intracellular and intercellular signaling pathways that are frequently mutated in the pancreatic cancer, to study the cell cycle progression and angiogenesis. We, then, introduced and applied a formal verification technique, Symbolic Model Checking, to automatically analyze the cells’ proliferation, angiogenesis and apoptosis in the proposed signal transduction model of tumor microenvironment. Conclusions: Our studies predicted some important temporal logic properties and dynamic behaviors in the pancreatic cancer cells and stellate cells. The verification technique identified several signaling components, including the RAS, RAGE, AKT, IKK, DVL, RB and PTEN, whose mutation or loss of function can promote cell growth and inhibit apoptosis, some of which have been confirmed by existing experiments. Our formal studies demonstrated that, the bidirectional interaction between cancer cells and stellate cells could significantly increase cell proliferation, inhibit apoptosis, induce tumor angiogenesis, and promote cancer metastasis. Tumor microenvironment signaling pathway, discrete value model, model checking, formal verification Background Pancreatic ductal adenocarcinoma (PDAC) is a form of cancer in the pancreatic duct, which is the fourth leading cause of cancer death in the United States, and it has an extremely poor prognosis. The pathological study of PDAC has revealed a number of genetic mutations [1], including the KRAS, CDKN2A, and TP53 genes. A recent global genomic analysis [2] has identified around ten cellular signaling pathways that are frequently altered in pancreatic cancers, including the pathways of Correspondence: Department of Mathematics and Computer Science, Saint Louis University, St. Louis, MO, 63103 USA Hedgehog, Wnt, Notch, KRAS, apoptosis, TGF-b, cJUN, and G1/S phase transition. In addition, a number of growth factors and cytokines, for example, the Insulinlike growth factor (IGF), Insulin, Hedgehog (Hh), transforming growth factor (TGF-b), and the Advanced Glycation End products (AGEs) are overexpressed in the microenvironment of pancreatic cancer cells, leading to uncontrolled cancer cell proliferation, unorganized angiogenesis and evasion of apoptosis. Recent experimental studies in pancreatic cancer [3-5] revealed, the interaction between pancreatic cancer cells (PCCs) and pancreatic stellate cells (PSCs, stromal cells of the pancreas) can stimulate cancer progression and © 2013 Gong; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Gong BMC Systems Biology 2013, 7(Suppl 3):S5 http://www.biomedcentral.com/1752-0509/7/S3/S5 tumor angiogenesis (formation of new blood vessels). Pancreatic cancer cells can recruit and activate PSCs to produce and maintain a growth-permissive environment for cancer progression and drug resistance. The activation of PSCs is mediated by several growth factors and cytokines, and many of which are secreted by the pancreatic cancer cells. In turn, the activated PSCs will synthesize and secrete multiple cytokines and growth factors, including Hedgehog and Wnt, through the paracrine and autocrine feedback loops to continuously stimulate cancer cells’ growth. These bidirectional interactions [4] will promote cancer progression and unorganized angiogenesis. Besides, PSCs can also secrete a large amount of extracellular matrix (ECM) proteins, which are important components of the fibrous tissue along with stromal cells. Thus, the tumor microenvironment of pancreatic cancer cells and the bidirectional interaction with stellate cells can significantly increase cell proliferation, inhibit apoptosis, induce tumor angiogenesis, and promote cancer metastasis. The mechanism behind the evolution of PSCs from quiescent state to a cancer-associated myofibroblast-like phenotype is still not very clear. Several findings [4,5] have indicated that the pro-angiogenic factor VEGF is of considerable importance in the stellate cell’s activation and angiogenesis. To systematically understand the tumor microenvironment and the bidirectional interaction between cancer cells and stellate cells, it is imperative to investigate the intracellular and intercellular signaling pathways that regulate the cell cycle progression and angiogenesis. Our previous work [6-9] developed Statistical Model Checking and Symbolic Model Checking techniques to study the intracellular signaling pathways in a single cell. Since the pathways implicated in the tumor microenvironment are highly interconnected, to the best of the author’s knowledge, no computational multicellular model has been developed to study the interaction between pancreatic cancer cells and stellate cells due to the complexity of networks. In this work, we construct a novel in silico discrete value model of multicellular signaling pathways, which are frequently mutated [2] in pancreatic cancers, to study the interaction between PSCs and PCCs. Our 3-cell model is composed of two types of cells: two pancreatic cancer cells (PCCs) and one stellate cell (PSC), which are regulated by the Hedgehog, Wnt, AGE, Rb-E2F, P53, RAS, PI3K, VEGF and IGF signaling pathways. Since the mechanism behind the interaction between PCCs and PSCs is not well understood, our model and analysis will provide some insights into the study of tumor microenvironment and the evolution of stellate cell from a quiescent state to an active state. Page 2 of 12 In order to formally and automatically analyze the complex network, we introduce a powerful verification technique, called Model Checking [10], which determines whether or not a model (state-transition s (...truncated)