Geou Yarh Liou

Reactive oxygen species in cancer

Abstract Elevated rates of reactive oxygen species (ROS) have been detected in almost all cancers, where they promote many aspects of tumour development and progression. However, tumour cells also express increased levels of antioxidant proteins to detoxify from ROS, suggesting that a delicate balance of intracellular ROS levels is required for cancer cell function. Further, the radical generated, the location of its generation, as well as the local concentration is important for the cellular functions of ROS in cancer. A challenge for novel therapeutic strategies will be the fine tuning of intracellular ROS signalling to effectively deprive cells from ROS-induced tumour promoting events, towards tipping the balance to ROS-induced apoptotic signalling. Alternatively, therapeutic antioxidants may prevent early events in tumour development, where ROS are important. However, to effectively target cancer cells specific ROS-sensing signalling pathways that mediate the diverse stress-regulated cellular functions need to be identified. This review discusses the generation of ROS within tumour cells, their detoxification, their cellular effects, as well as the major signalling cascades they utilize, but also provides an outlook on their modulation in therapeutics.

Macrophage-secreted cytokines drive pancreatic acinar-to-ductal metaplasia through NF-κB and MMPs

Macrophages infiltrating the pancreas in response to inflammation induce cellular transdifferentiation by secreting cytokines that activate NF-κB signaling and matrix metalloproteinase expression.

Mutant KRAS-induced expression of ICAM-1 in pancreatic acinar cells causes attraction of macrophages to expedite the formation of precancerous lesions.

UNLABELLED Desmoplasia and an inflammatory environment are defining features of pancreatic cancer. Unclear is how pancreatic cells that undergo oncogenic transformation can cross-talk with immune cells and how this contributes to the development of pancreatic lesions. Here, we demonstrate that pancreatic acinar cells expressing mutant KRAS can expedite their transformation to a duct-like phenotype by inducing local inflammation. Specifically, we show that KRAS(G12D) induces the expression of intercellular adhesion molecule-1 (ICAM-1), which serves as chemoattractant for macrophages. Infiltrating macrophages amplify the formation of KRAS(G12D)-caused abnormal pancreatic structures by remodeling the extracellular matrix and providing cytokines such as TNF. Depletion of macrophages or treatment with a neutralizing antibody for ICAM-1 in mice expressing oncogenic Kras under an acinar cell-specific promoter resulted in both a decreased formation of abnormal structures and decreased progression of acinar-to-ductal metaplasia to pancreatic intraepithelial neoplastic lesions. SIGNIFICANCE We here show that oncogenic KRAS in pancreatic acinar cells upregulates the expression of ICAM-1 to attract macrophages. Hence, our results reveal a direct cooperative mechanism between oncogenic Kras mutations and the inflammatory environment to drive the initiation of pancreatic cancer.

Mutant KRas-Induced Mitochondrial Oxidative Stress in Acinar Cells Upregulates EGFR Signaling to Drive Formation of Pancreatic Precancerous Lesions

The development of pancreatic cancer requires the acquisition of oncogenic KRas mutations and upregulation of growth factor signaling, but the relationship between these is not well established. Here, we show that mutant KRas alters mitochondrial metabolism in pancreatic acinar cells, resulting in increased generation of mitochondrial reactive oxygen species (mROS). Mitochondrial ROS then drives the dedifferentiation of acinar cells to a duct-like progenitor phenotype and progression to PanIN. This is mediated via the ROS-receptive kinase protein kinase D1 and the transcription factors NF-κB1 and NF-κB2, which upregulate expression of the epidermal growth factor, its ligands, and their sheddase ADAM17. In vivo, interception of KRas-mediated generation of mROS reduced the formation of pre-neoplastic lesions. Hence, our data provide insight into how oncogenic KRas interacts with growth factor signaling to induce the formation of pancreatic cancer.

Protein kinase D1 drives pancreatic acinar cell reprogramming and progression to intraepithelial neoplasia

The transdifferentiation of pancreatic acinar cells to a ductal phenotype (acinar-to-ductal metaplasia, ADM) occurs after injury or inflammation of the pancreas and is a reversible process. However, in the presence of activating Kras mutations or persistent epidermal growth factor receptor (EGF-R) signaling, cells that underwent ADM can progress to pancreatic intraepithelial lesions (PanINs) and eventually pancreatic cancer. In transgenic animal models, ADM and PanINs are initiated by high-affinity ligands for EGF-R or activating Kras mutations, but the underlying signaling mechanisms are not well understood. Here, using a conditional knockout approach, we show that Protein Kinase D1 (PKD1) is sufficient to drive the reprogramming process to a ductal phenotype and progression to PanINs. Moreover, using 3D explant culture of primary pancreatic acinar cells, we show that PKD1 acts downstream of TGFα and Kras to mediate formation of ductal structures through activation of the Notch pathway.

Downregulation of TRAF2 Mediates NIK-Induced Pancreatic Cancer Cell Proliferation and Tumorigenicity

Background Increased levels of NF-κB are hallmarks of pancreatic ductal adenocarcinoma (PDAC) and both classical and alternative NF-κB activation pathways have been implicated. Methodology/Principal Findings Here we show that activation of the alternative pathway is a source for the high basal NF-κB activity in PDAC cell lines. Increased activity of the p52/RelB NF-κB complex is mediated through stabilization and activation of NF-κB-inducing kinase (NIK). We identify proteasomal downregulation of TNF receptor-associated factor 2 (TRAF2) as a mechanism by which levels of active NIK are increased in PDAC cell lines. Such upregulation of NIK expression and activity levels relays to increased proliferation and anchorage-independent growth, but not migration or survival of PDAC cells. Conclusions/Significance Rapid growth is one characteristic of pancreatic cancer. Our data indicates that the TRAF2/NIK/NF-κB2 pathway regulates PDAC cell tumorigenicity and could be a valuable target for therapy of this cancer.

The Presence of Interleukin-13 at Pancreatic ADM/PanIN Lesions Alters Macrophage Populations and Mediates Pancreatic Tumorigenesis

The contributions of the innate immune system to the development of pancreatic cancer are still ill defined. Inflammatory macrophages can initiate metaplasia of pancreatic acinar cells to a duct-like phenotype (acinar-to-ductal metaplasia [ADM]), which then gives rise to pancreatic intraepithelial neoplasia (PanIN) when oncogenic KRas is present. However, it remains unclear when and how this inflammatory macrophage population is replaced by tumor-promoting macrophages. Here, we demonstrate the presence of interleukin-13 (IL-13), which can convert inflammatory into Ym1+ alternatively activated macrophages, at ADM/PanIN lesions. We further show that Ym1+ macrophages release factors, such as IL-1ra and CCL2, to drive pancreatic fibrogenesis and tumorigenesis. Treatment of mice expressing oncogenic KRas under an acinar cell-specific promoter with a neutralizing antibody for IL-13 significantly decreased the accumulation of alternatively activated macrophages at these lesions, resulting in decreased fibrosis and lesion growth.

Detecting Reactive Oxygen Species by Immunohistochemistry

In cultured cells, an increase in cellular levels of reactive oxygen species (ROS) can be detected using multiple techniques including colorimetric assays, immunoblotting, and immunofluorescence. These methods can also be applied for ROS measurement in tissue samples, but often require tissue homogenization, and therefore do not distinguish between the different cell types within a tissue. Here, we describe a detailed protocol for determination of altered oxidative stress levels in different cell types in tissues, by detecting ROS-caused alteration of macromolecules using immunohistochemistry (IHC). This method is demonstrated by using 4HNE as a marker for lipid peroxidation in mouse pancreas tissue that contains precancerous lesions high in cellular oxidative stress.

NFATc4 Regulates Sox9 Gene Expression in Acinar Cell Plasticity and Pancreatic Cancer Initiation

Acinar transdifferentiation toward a duct-like phenotype constitutes the defining response of acinar cells to external stress signals and is considered to be the initial step in pancreatic carcinogenesis. Despite the requirement for oncogenic Kras in pancreatic cancer (PDAC) development, oncogenic Kras is not sufficient to drive pancreatic carcinogenesis beyond the level of premalignancy. Instead, secondary events, such as inflammation-induced signaling activation of the epidermal growth factor (EGFR) or induction of Sox9 expression, are required for tumor formation. Herein, we aimed to dissect the mechanism that links EGFR signaling to Sox9 gene expression during acinar-to-ductal metaplasia in pancreatic tissue adaptation and PDAC initiation. We show that the inflammatory transcription factor NFATc4 is highly induced and localizes in the nucleus in response to inflammation-induced EGFR signaling. Moreover, we demonstrate that NFATc4 drives acinar-to-ductal conversion and PDAC initiation through direct transcriptional induction of Sox9. Therefore, strategies designed to disrupt NFATc4 induction might be beneficial in the prevention or therapy of PDAC.

Protein kinase D enzymes: novel kinase targets in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by advanced stage desmoplastic tumors with a high prevalence of genetic abnormalities. Occurrence of PDA is linked to activating Kras mutations and aberrant epidermal growth factor receptor signaling, leading to additional activation of wild-type Kras. As Kras is difficult to target, there is a constant need to identify novel targets acting downstream of this molecule in driving the formation or progression of PDA. Recently, it was shown that protein kinase D enzymes not only are increasingly expressed in PDA but also causatively linked to the development and progression of this cancer. They act downstream of both mutant Kras and growth factors and therefore may represent ideal novel targets.