Restoration of Smad4 in BxPC3 pancreatic cancer cells attenuates proliferation without altering angiogenesis

New insight into the role of SMAD4 mutation/deficiency in the prognosis and therapeutic resistance of pancreatic ductal adenocarcinomas

Pancreatic ductal adenocarcinoma (PDAC) patients have an unfavorable prognosis and disappointing treatment outcomes because of late diagnosis, high chemotherapy resistance, ineffective adjuvant chemotherapy, unavailable molecular targeted therapy, and profound immunosuppressive effects in the tumor microenvironment (TME). There are a variety of critical driver proteins, such as KRAS, TP53, PTEN and SMAD4, putatively involved in PDAC etiology. Current knowledge of their molecular mechanisms is still limited. SMAD4 gene alterations in ∼55 % of patients emphasize its key role in PDAC progression, metastasis, resistance and immunity. Despite extensive studies on the TGF-β/SMAD pathway, the impact of SMAD4 mutation/deficiency on PDAC prognosis and treatment, especially its mechanism in drug resistance, has not yet been elucidated. This review summarizes the latest advances in the effect of SMAD4 deficiency on the prognosis and therapeutic resistance of PDAC patients. It might be a predictive and prognostic biomarker or therapeutic target to achieve the desired clinical benefits. Moreover, we discuss potential strategies to implement targeted therapies in terms of SMAD4 genetic status.

Genome-wide CRISPR Screen Reveals RAB10 as a Synthetic Lethal Gene in Colorectal and Pancreatic Cancers Carrying SMAD4 Loss

The TGFβ signaling mediator SMAD4 is frequently mutated or deleted in colorectal and pancreatic cancers. SMAD4 acts as a tumor suppressor and its loss is associated with poorer patient outcomes. The purpose of this study was to find synthetic lethal interactions with SMAD4 deficiency to find novel therapeutic strategies for the treatment of patients with SMAD4-deficient colorectal or pancreatic cancers. Using pooled lentiviral single-guide RNA libraries, we conducted genome-wide loss-of-function screens in Cas9-expressing colorectal and pancreatic cancer cells harboring altered or wild-type SMAD4. The small GTPase protein RAB10 was identified and validated as a susceptibility gene in SMAD4-altered colorectal and pancreatic cancer cells. Rescue assays showed that RAB10 reintroduction reversed the antiproliferative effects of RAB10 knockout in SMAD4-negative cell lines. Further investigation is necessary to shed light on the mechanism by which RAB10 inhibition decreases cell proliferation of SMAD4-negative cells.

Significance

This study identified and validated RAB10 as new synthetic lethal gene with SMAD4. This was achieved by conducting a whole-genome CRISPR screens in different colorectal and pancreatic cell lines. A future RAB10 inhibitors could correspond to a new therapeutic solution for patients with cancer with SMAD4 deletion.

SMAD2/3 mediate oncogenic effects of TGF-β in the absence of SMAD4

TGF-β signaling is involved in pancreatic ductal adenocarcinoma (PDAC) tumorigenesis, representing one of the four major pathways genetically altered in 100% of PDAC cases. TGF-β exerts complex and pleiotropic effects in cancers, notably via the activation of SMAD pathways, predominantly SMAD2/3/4. Though SMAD2 and 3 are rarely mutated in cancers, SMAD4 is lost in about 50% of PDAC, and the role of SMAD2/3 in a SMAD4-null context remains understudied. We herein provide evidence of a SMAD2/3 oncogenic effect in response to TGF-β1 in SMAD4-null human PDAC cancer cells. We report that inactivation of SMAD2/3 in SMAD4-negative PDAC cells compromises TGF-β-driven collective migration mediated by FAK and Rho/Rac signaling. Moreover, RNA-sequencing analyses highlight a TGF-β gene signature related to aggressiveness mediated by SMAD2/3 in the absence of SMAD4. Using a PDAC patient cohort, we reveal that SMAD4-negative tumors with high levels of phospho-SMAD2 are more aggressive and have a poorer prognosis. Thus, loss of SMAD4 tumor suppressive activity in PDAC leads to an oncogenic gain-of-function of SMAD2/3, and to the onset of associated deleterious effects.

In pancreatic ductal adenocarcinoma cells and patient tissue, SMAD2/3 is shown to mediate oncogenic effects of TGF-β in the absence of SMAD4.

TGFβ Signaling in the Pancreatic Tumor Microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is associated with poor clinical outcomes, largely attributed to incomplete responses to standard therapeutic approaches. Recently, selective inhibitors of the Transforming Growth Factor β (TGFβ) signaling pathway have shown early promise in the treatment of PDAC, particularly as a means of augmenting responses to chemo- and immunotherapies. However, TGFβ is a potent and pleiotropic cytokine with several seemingly paradoxical roles within the pancreatic tumor microenvironment (TME). Although TGFβ signaling can have potent tumor-suppressive effects in epithelial cells, TGFβ signaling also accelerates pancreatic tumorigenesis by enhancing epithelial-to-mesenchymal transition (EMT), fibrosis, and the evasion of the cytotoxic immune surveillance program. Here, we discuss the known roles of TGFβ signaling in pancreatic carcinogenesis, the biologic consequences of the genetic inactivation of select components of the TGFβ pathway, as well as past and present attempts to advance TGFβ inhibitors in the treatment of PDAC patients.

Anti-Tumor Effects of MAPK-Dependent Tumor-Selective Oncolytic Vaccinia Virus Armed with CD/UPRT against Pancreatic Ductal Adenocarcinoma in Mice

Engineered vaccinia virus serves as an oncolytic virus for cancer virotherapy. We evaluated the oncolytic characteristics of VGF- and O1-deleted recombinant mitogen-activated protein kinase (MAPK)-dependent vaccinia virus (MDRVV). We found that compared with viruses with the deletion of either gene alone, MDRVV is more attenuated in normal cells and can replicate in cancer cells that exhibit constitutive ERK1/2 activation in the MAPK pathway. We armed MDRVV with a bifunctional fusion gene encoding cytosine deaminase and uracil phosphoribosyltransferase (CD/UPRT), which converts 5-fluorocytosine (5-FC) into chemotherapeutic agents, and evaluated its oncolytic activity alone or in combination with 5-FC in human pancreatic cancer cell lines, tumor mouse models of peritoneal dissemination and liver metastasis, and ex vivo-infected live pancreatic cancer patient-derived tissues. CD/UPRT-armed MDRVV alone could efficiently eliminate pancreatic cancers, and its antitumor effects were partially enhanced in combination with 5-FC in vitro and in vivo. Moreover, the replication of MDRVV was detected in tumor cells of patient-derived, surgically resected tissues, which showed enlarged nuclei and high expression of pERK1/2 and Ki-67, and not in stromal cells. Our findings suggest that systemic injections of CD/UPRT-armed MDRVV alone or in combination with 5-FC are promising therapeutic strategies for pancreatic ductal adenocarcinoma.

Novel Non-integrating DNA Nano-S/MAR Vectors Restore Gene Function in Isogenic Patient-Derived Pancreatic Tumor Models

We describe herein non-integrating minimally sized nano-S/MAR DNA vectors, which can be used to genetically modify dividing cells in place of integrating vectors. They represent a unique genetic tool, which avoids vector-mediated damage. Previous work has shown that DNA vectors comprising a mammalian S/MAR element can provide persistent mitotic stability over hundreds of cell divisions, resisting epigenetic silencing and thereby allowing sustained transgene expression. The composition of the original S/MAR vectors does present some inherent limitations that can provoke cellular toxicity. Herein, we present a new system, the nano-S/MAR, which drives higher transgene expression and has improved efficiency of establishment, due to the minimal impact on cellular processes and perturbation of the endogenous transcriptome. We show that these features enable the hitherto challenging genetic modification of patient-derived cells to stably restore the tumor suppressor gene SMAD4 to a patient-derived SMAD4 knockout pancreatic cancer line. Nano-S/MAR modification does not alter the molecular or phenotypic integrity of the patient-derived cells in cell culture and xenograft mouse models. In conclusion, we show that these DNA vectors can be used to persistently modify a range of cells, providing sustained transgene expression while avoiding the risks of insertional mutagenesis and other vector-mediated toxicity.

Roles of Smads Family and Alternative Splicing Variants of Smad4 in Different Cancers

Transforming Growth Factor β (TGF-β) is one of the most common secretory proteins which are recognized by membrane receptors joined to transcription regulatory factor. TGF-β signals are transduced by the Smads family that regulate differentiation, proliferation, early growth, apoptosis, homeostasis, and tumor development. Functional study of TGF-β signaling pathway and Smads role is vital for certain diseases such as cancer. Alternative splicing produces a diverse range of protein isoforms with unique function and the ability to react differently with various pharmaceutical products. This review organizes to describe the general study of Smads family, the process of alternative splicing, the general aspect of alternative splicing of Smad4 in cancer and the possible use of spliceoforms for the diagnosis and therapeutic purpose. The main aim and objective of this article are to highlight some particular mechanisms involving in alternatives splicing of cancer and also to demonstrate new evidence about alternative splicing in different steps given cancer initiation and progression.

Clinicopathological significance of SMAD4 loss in pancreatic ductal adenocarcinomas: a systematic review and meta-analysis

Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer mortality. Although advances have been made in understanding the pathogenesis of PDAC, the outcome still remains poor. The aim of this study is to conduct a meta-analysis to evaluate the precise association between SMAD4 loss and clinicopathological significance in PDAC. A literature search was made in PubMed, Web of Science, Google scholar, and EMBASE for related publications. The data were extracted and assessed by two reviewers independently. Analysis of pooled data was performed, Odds Ratio or Hazard Ratio with corresponding confidence intervals was calculated and summarized. 12 relevant articles were included for full review in detail and meta-analysis. The frequency of SMAD4 protein loss was significantly increased in PDAC than in nonmalignant pancreatic tissue, Odd Ratio was 0.05 with 95% confidence interval 0.01-0.23, p<0.0001. SMAD4 loss was significantly associated with poor overall survival in patients with PDAC, Hazard Ratio was 0.61 with 95% confidence interval 0.38-0.99, p=0.05. SMAD4 loss was not correlated with the size, grades, and lymph node metastasis of PDAC. In conclusion, SMAD4 is a biomarker for the diagnosis of PDAC. SMAD4 loss is significantly related to poor prognosis in patients with PDAC.

TGFβ engages MEK/ERK to differentially regulate benign and malignant pancreas cell function

While TGFβ signals are anti-proliferative in benign and well-differentiated pancreatic cells, TGFβ appears to promote the progression of advanced cancers. To better understand dysregulation of the TGFβ pathway, we first generated mouse models of neoplastic disease with TGFβ receptor deficiencies. These models displayed reduced levels of pERK irrespective of KRAS mutation. Furthermore, exogenous TGFβ led to rapid and sustained TGFBR1-dependent ERK phosphorylation in benign pancreatic duct cells. Similar to results that our group has published in colon cancer cells, inhibition of ERK phosphorylation in duct cells mitigated TGFβ-induced upregulation of growth suppressive pSMAD2 and p21, prevented downregulation of the pro-growth signal CDK2 and ablated TGFβ-induced EMT. These observations suggest that ERK is a key factor in growth suppressive TGFβ signals, yet may also contribute to detrimental TGFβ signaling such as EMT. In neoplastic PanIN cells, pERK was not necessary for either TGFβ-induced pSMAD2 phosphorylation or CDK2 repression, but was required for upregulation of p21 and EMT indicating a partial divergence between TGFβ and MEK/ERK in early carcinogenesis. In cancer cells, pERK had no effect on TGFβ-induced upregulation of pSMAD2 and p21, suggesting the two pathways have completely diverged with respect to the cell cycle. Furthermore, inhibition of pERK both reduced levels of CDK2 and prevented EMT independent of exogenous TGFβ, consistent with most observations identifying pERK as a tumor promoter. Combined, these data suggest that during carcinogenesis pERK initially facilitates and later antagonizes TGFβ-mediated cell cycle arrest, yet remains critical for the pathological, EMT-inducing arm of TGFβ signaling.

Angiogenic gene signature in human pancreatic cancer correlates with TGF-beta and inflammatory transcriptomes

Pancreatic ductal adenocarcinomas (PDACs) are hypovascular, but overexpress pro-angiogenic factors and exhibit regions of microvasculature. Using RNA-seq data from The Cancer Genome Atlas (TCGA), we previously reported that ∼12% of PDACs have an angiogenesis gene signature with increased expression of multiple pro-angiogenic genes. By analyzing the recently expanded TCGA dataset, we now report that this signature is present in ∼35% of PDACs but that it is mostly distinct from an angiogenesis signature present in pancreatic neuroendocrine tumors (PNETs). These PDACs exhibit a transcriptome that reflects active TGF-β signaling, and up-regulation of several pro-inflammatory genes, and many members of JAK signaling pathways. Moreover, expression of SMAD4 and HDAC9 correlates with endothelial cell abundance in PDAC tissues. Concomitantly targeting the TGF-β type I receptor (TβRI) kinase with SB505124 and JAK1-2 with ruxolitinib suppresses JAK1 phosphorylation and blocks proliferative cross-talk between human pancreatic cancer cells (PCCs) and human endothelial cells (ECs), and these anti-proliferative effects were mimicked by JAK1 silencing in ECs. By contrast, either inhibitor alone does not suppress their enhanced proliferation in 3D co-cultures. These findings suggest that targeting both TGF-β and JAK1 signaling could be explored therapeutically in the 35% of PDAC patients whose cancers exhibit an angiogenesis gene signature.

SMAD4 loss enables EGF, TGFβ1 and S100A8/A9 induced activation of critical pathways to invasion in human pancreatic adenocarcinoma cells

Epidermal Growth Factor (EGF) receptor overexpression, KRAS, TP53, CDKN2A and SMAD4 mutations characterize pancreatic ductal adenocarcinoma. This mutational landscape might influence cancer cells response to EGF, Transforming Growth Factor β1 (TGFβ1) and stromal inflammatory calcium binding proteins S100A8/A9. We investigated whether chronic exposure to EGF modifies in a SMAD4-dependent manner pancreatic cancer cell signalling, proliferation and invasion in response to EGF, TGFβ1 and S100A8/A9. BxPC3, homozigously deleted (HD) for SMAD4, and BxPC3-SMAD4+ cells were or not stimulated with EGF (100 ng/mL) for three days. EGF pre-treated and non pretreated cells were stimulated with a single dose of EGF (100 ng/mL), TGFβ1 (0,02 ng/mL), S100A8/A9 (10 nM). Signalling pathways (Reverse Phase Protein Array and western blot), cell migration (Matrigel) and cell proliferation (XTT) were evaluated. SMAD4 HD constitutively activated ERK and Wnt/β-catenin, while inhibiting PI3K/AKT pathways. These effects were antagonized by chronic EGF, which increased p-BAD (anti-apoptotic) in response to combined TGFβ1 and S100A8/A9 stimulation. SMAD4 HD underlied the inhibition of NF-κB and PI3K/AKT in response to TGFβ1 and S100A8/A9, which also induced cell migration. Chronic EGF exposure enhanced cell migration of both BxPC3 and BxPC3-SMAD4+, rendering the cells less sensitive to the other inflammatory stimuli. In conclusion, SMAD4 HD is associated with the constitutive activation of the ERK and Wnt/β-catenin signalling pathways, and favors the EGF-induced activation of multiple signalling pathways critical to cancer proliferation and invasion. TGFβ1 and S100A8/A9 mainly inhibit NF-κB and PI3K/AKT pathways and, when combined, sinergize with EGF in enhancing anti-apoptotic p-BAD in a SMAD4-dependent manner.

Angiogenesis in pancreatic ductal adenocarcinoma: A controversial issue

Pancreatic ductal adenocarcinoma (PDAC) occurs in the majority of cases with early loco-regional spread and distant metastases at diagnosis, leading to dismal prognosis with a 5-year overall survival rate moderately over than 5%. This malignancy is largely resistant to chemotherapy and radiation, but the reasons of the refractoriness to the therapies is still unknown. Evidence is accumulating to indicate that the PDAC microenvironment and vascularity strongly contribute to the clinical features of this disease. In particular, PDAC is characterized by excessive dense extracellular matrix deposition associated to vasculature collapse and hypoxia with low drug delivery, explaining at least partly the low efficacy of antiangiogenic drugs in this cancer. Strategies aimed to modulate tumor stroma favoring vasculature perfusion and chemotherapeutics delivery are under investigation.

Insights Into SMAD4 Loss in Pancreatic Cancer From Inducible Restoration of TGF-β Signaling

Pancreatic ductal adenocarcinoma (PDAC) is the fourth-leading cause of cancer death in the United States. The TGF-β signaling protein SMAD family member 4 is lost in 60% of PDAC, and this has been associated with poorer prognosis. However, the mechanisms by which SMAD4 loss promotes PDAC development are not fully understood. We expressed SMAD4 in human PDAC cell lines BxPC3 and CFPAC1 by selection of stable clones containing an inducible SMAD4 tetracycline inducible expression system construct. After 24 hours of SMAD4 expression, TGF-β signaling-dependent G1 arrest was observed in BxPC3 cells with an increase in the G1 phase fraction from 48.9% to 71.5%. Inhibition of cyclin-dependent kinase inhibitor 1A by small interfering RNA eliminated the antiproliferative effect, indicating that up-regulation of cyclin-dependent kinase inhibitor 1A/p21 by TGF-β signaling is necessary for the phenotype. SMAD4 expression had no impact on invasion in BxPC3 cells, but reduced migration. Microarray analysis of gene expression at 8, 24, and 48 hours after SMAD4 expression characterized the regulatory impact of SMAD4 expression in a SMAD4-null PDAC cell line and identified novel targets of TGF-β signaling. Among the novel TGF-β targets identified are anthrax toxin receptor 2 (3.58× at 8 h), tubulin, β-3 class III (7.35× at 8 h), cell migration inducing protein, hyaluronan binding (8.07× at 8 h), IL-1 receptor-like 1 (0.403× at 8 h), regulator of G protein signaling 4 (0.293× at 8 h), and THAP domain containing 11 (0.262× at 8 h). The gene expression changes we observed upon restoration of TGF-β signaling provide numerous new targets for future investigations into PDAC biology and progression.

SMAD4 and its role in pancreatic cancer

Transforming growth factor-β (TGF-β) regulates cell functions and has key roles in pancreatic cancer development. SMAD4, as one of the Smads family of signal transducer from TGF-β, mediates pancreatic cell proliferation and apoptosis and is specifically inactivated in half of advanced pancreatic cancers. In recent years, many advances concerning SMAD4 had tried to unravel the complex signaling mechanisms of TGF-β and its dual role of tumor-suppressive and tumor-promoting efforts in pancreatic cancer initiation and progression through SMAD4-dependent TGF-β signaling and SMAD4-independent TGF-β signaling pathways. Meanwhile, its potential prognostic value based on immunohistochemical expression in surgical sample was variably reported by several studies and short of a systematic analysis. This review aimed to discuss the structure, functions, and regulation of this principal protein and its effects in determining the progression and prognosis of pancreatic cancer.

Loss of canonical Smad4 signaling promotes KRAS driven malignant transformation of human pancreatic duct epithelial cells and metastasis

Pancreatic ductal adenocarcinoma (PDAC) is the fourth most common cause of cancer death in North America. Activating KRAS mutations and Smad4 loss occur in approximately 90% and 55% of PDAC, respectively. While their roles in the early stages of PDAC development have been confirmed in genetically modified mouse models, their roles in the multistep malignant transformation of human pancreatic duct cells have not been directly demonstrated. Here, we report that Smad4 represents a barrier in KRAS-mediated malignant transformation of the near normal immortalized human pancreatic duct epithelial (HPDE) cell line model. Marked Smad4 downregulation by shRNA in KRAS^G12V expressing HPDE cells failed to cause tumorigenic transformation. However, KRAS-mediated malignant transformation occurred in a new HPDE-TGF-β resistant (TβR) cell line that completely lacks Smad4 protein expression and is resistant to the mito-inhibitory activity of TGF-β. This transformation resulted in tumor formation and development of metastatic phenotype when the cells were implanted orthotopically into the mouse pancreas. Smad4 restoration re-established TGF-β sensitivity, markedly increased tumor latency by promoting apoptosis, and decreased metastatic potential. These results directly establish the critical combination of the KRAS oncogene and complete Smad4 inactivation in the multi-stage malignant transformation and metastatic progression of normal human HPDE cells.

JDP2 inhibits the epithelial-to-mesenchymal transition in pancreatic cancer BxPC3 cells

Pancreatic carcinoma is one of the most malignant and aggressive cancers. Increased motility and invasiveness of pancreatic cancer cells are believed to be associated with epithelial-to-mesenchymal transition (EMT). However, the molecular basis of EMT in pancreatic cancer cells is poorly understood. In this study, we examined the relationship between Jun dimerization protein 2 (JDP2), which is an AP-1 inhibitor, and EMT in human pancreatic carcinoma cells. We demonstrated that transforming growth factor-β1 (TGF-β1) promoted epidermal growth factor (EGF)-induced EMT in co-treated human pancreatic BxPC3 cells and that JDP2 overexpression reversed the EMT that was induced by co-treatment with TGF-β1 and EGF. These results suggest that EGF plays a principal role in EMT through its association with TGF-β1 in human pancreatic BxPC3 cells and that JDP2 may be a molecular target for pancreatic carcinoma intervention.

SMAD4-dependent polysome RNA recruitment in human pancreatic cancer cells

Pancreatic cancer is the fourth leading cause of cancer death in the United States because most patients are diagnosed too late in the course of the disease to be treated effectively. Thus, there is a pressing need to more clearly understand how gene expression is regulated in cancer cells and to identify new biomarkers and therapeutic targets. Translational regulation is thought to occur primarily through non-SMAD directed signaling pathways. We tested the hypothesis that SMAD4-dependent signaling does play a role in the regulation of mRNA entry into polysomes and that novel candidate genes in pancreatic cancer could be identified using polysome RNA from the human pancreatic cancer cell line BxPC3 with or without a functional SMAD4 gene. We found that (i) differentially expressed whole cell and cytoplasm RNA levels are both poor predictors of polysome RNA levels; (ii) for a majority of RNAs, differential RNA levels are regulated independently in the nucleus, cytoplasm, and polysomes; (iii) for most of the remaining polysome RNA, levels are regulated via a "tagging" of the RNAs in the nucleus for rapid entry into the polysomes; (iv) a SMAD4-dependent pathway appears to indeed play a role in regulating mRNA entry into polysomes; and (v) a gene list derived from differentially expressed polysome RNA in BxPC3 cells generated new candidate genes and cell pathways potentially related to pancreatic cancer.

Differential regulation of polysome mRNA levels in mouse Hepa-1C1C7 cells exposed to dioxin

The environmental agent 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin) causes a multitude of human illnesses. In order to more fully understand the underlying biology of TCDD toxicity, we tested the hypothesis that new candidate genes could be identified using polysome RNA from TCDD-treated mouse Hepa-1c1c7 cells. We found that (i) differentially expressed whole cell and cytoplasm RNA levels are both poor predictors of polysome RNA levels; (ii) for a majority of RNAs, differential RNA levels are regulated independently in the nucleus, cytoplasm, and polysomes; (iii) for the remaining polysome RNAs, levels are regulated via several different mechanisms, including a "tagging" of mRNAs in the nucleus for immediate polysome entry; and (iv) most importantly, a gene list derived from differentially expressed polysome RNA generated new genes and cell pathways potentially related to TCDD biology.

PKCalpha-induced drug resistance in pancreatic cancer cells is associated with transforming growth factor-beta1

Background

Drug resistance remains a great challenge in the treatment of pancreatic cancer. The goal of this study was to determine whether TGF-β1 is associated with drug resistance in pancreatic cancer.

Methods

Pancreatic cancer BxPC3 cells were stably transfected with TGF-β1 cDNA. Cellular morphology and cell cycle were determined and the suppressive subtracted hybridization (SSH) assay was performed to identify differentially expressed genes induced by TGF-β1. Western blotting and immunohistochemistry were used to detect expression of TGF-β1-related genes in the cells and tissue samples. After that, the cells were further treated with an anti-cancer drug (e.g., cisplatin) after pre-incubated with the recombinant TGF-β1 plus PKCα inhibitor Gö6976. TGF-β1 type II receptor, TβRII was also knocked down using TβRII siRNA to assess the effects of these drugs in the cells. Cell viability was assessed by MTT assay.

Results

Overexpression of TGF-β1 leads to a markedly increased invasion potential but a reduced growth rate in BxPC3 cells. Recombinant TGF-β1 protein increases expression of PKCα in BxPC3 cells, a result that we confirmed by SSH. Moreover, TGF-β1 reduced the sensitivity of BxPC3 cells to cisplatin treatment, and this was mediated by upregulation of PKCα. However, blockage of PKCα with Gö6976 and TβRII with siRNA reversed the resistance of BxPC3 cells to gemcitabine, even in the presence of TGF-β1. Immunohistochemical data show that pancreatic cancers overexpress TGF-β1 and P-gp relative to normal tissues. In addition, TGF-β1 expression is associated with P-gp and membranous PKCα expression in pancreatic cancer.

Conclusions

TGF-β1-induced drug resistance in pancreatic cancer cells was associated with PKCα expression. The PKCα inhibitor Gö6976 could be a promising agent to sensitize pancreatic cancer cells to chemotherapy.

Microarray analysis of cytoplasmic versus whole cell RNA reveals a considerable number of missed and false positive mRNAs

With no known exceptions, every published microarray study to determine differential mRNA levels in eukaryotes used RNA extracted from whole cells. It is assumed that the use of whole cell RNA in microarray gene expression analysis provides a legitimate profile of steady-state mRNA. Standard labeling methods and the prevailing dogma that mRNA resides almost exclusively in the cytoplasm has led to the long-standing belief that the nuclear RNA contribution is negligible. We report that unadulterated cytoplasmic RNA uncovers differentially expressed mRNAs that otherwise would not have been detected when using whole cell RNA and that the inclusion of nuclear RNA has a large impact on whole cell gene expression microarray results by distorting the mRNA profile to the extent that a substantial number of false positives are generated. We conclude that to produce a valid profile of the steady-state mRNA population, the nuclear component must be excluded, and to arrive at a more realistic view of a cell's gene expression profile, the nuclear and cytoplasmic RNA fractions should be analyzed separately.

14-3-3sigma Modulates pancreatic cancer cell survival and invasiveness

PURPOSE

The purpose of the present study was to investigate the potential role of 14-3-3sigma in pancreatic ductal adenocarcinoma (PDAC).

EXPERIMENTAL DESIGN

14-3-3 isoform expression was determined by real-time quantitative PCR in laser capture normal pancreatic ductal cells and pancreatic cancer cells and in 5 pancreatic cancer cell lines. PANC-1 cells, with low levels of 14-3-3sigma, were stably transfected with a human 14-3-3sigma cDNA. Conversely, high endogenous 14-3-3sigma levels in T3M4 cells were suppressed by specific short hairpin RNA. Apoptosis, motility, and invasiveness were studied.

RESULTS

The cancer cells in 7 PDAC samples expressed high levels of 14-3-3sigma mRNA by quantitative PCR when compared with normal pancreatic duct cells. 14-3-3sigma protein levels were high in BxPC3, COLO-357, and T3M4 cells, intermediate in ASPC-1 cells, and low in PANC-1 cells. Most cell lines released detectable amount of 14-3-3sigma into conditioned medium. Overexpression of 14-3-3sigma in PANC-1 cells led to resistance to cisplatinum-induced apoptosis, increased basal migration, and increased invasion in response to epidermal growth factor and insulin-like growth factor-I. By contrast, short hairpin RNA-mediated knockdown of endogenous 14-3-3sigma in T3M4 cells did not alter migration but led to enhanced cisplatinum sensitivity, increased invasiveness in response to epidermal growth factor, and decreased invasiveness in response to insulin-like growth factor-I.

CONCLUSIONS

14-3-3sigma contributes to the chemoresistance of pancreatic cancer cells and exerts cell type-dependent effects on cell migration and invasion. Therefore, strategies aimed at suppressing 14-3-3sigma expression and function may have a therapeutic benefit in subgroups of patients with PDAC.

Hepatocyte growth factor-mediated cell invasion in pancreatic cancer cells is dependent on neuropilin-1

Neuropilin-1 (Np-1), a receptor for semaphorin 3A and vascular endothelial growth factor, is expressed at high levels in pancreatic ductal adenocarcinoma (PDAC). To assess the potential role of Np-1 in PDAC, COLO-357 pancreatic cancer cells, which express relatively low levels of Np-1, were stably transfected with the Np-1 cDNA. Np-1 overexpression was associated with enhanced cell invasiveness in response to hepatocyte growth factor (HGF), and this effect was abolished by small interfering RNA-mediated down-regulation of c-Met. Conversely, in PANC-1 pancreatic cancer cells, which express relatively high levels of Np-1, suppression of endogenous Np-1 completely abolished HGF-mediated cell invasion. To determine which pathways are involved in Np-1-mediated facilitation of c-Met-dependent cell invasiveness, the effects of HGF on signaling were examined next in sham-transfected and Np-1-overexpressing COLO-357 cells. HGF actions on c-Met tyrosine phosphorylation and p38 mitogen-activated protein kinase (MAPK) activation were increased in Np-1-overexpressing COLO-357 cells by comparison with HGF effects in sham-transfected cells. SB203580, an inhibitor of p38 MAPK, suppressed HGF-induced invasion in Np-1-overexpressing cells, whereas U0126, a MAP/extracellular signal-regulated kinase kinase inhibitor, was without effect. PP2, a Src inhibitor, and LY294002, a phosphatidylinositol 3-kinase inhibitor, also suppressed HGF-induced invasion in these cells. Immunoprecipitation studies revealed that Np-1 associated with c-Met, but not with epidermal growth factor receptor, family members. Confocal microscopy indicated that this association occurred on the plasma membrane and that HGF promoted the internalization of Np-1-c-Met complex, leading to its perinuclear localization. These findings indicate that Np-1 is required for efficient activation of c-Met-dependent pathways that promote cell invasiveness.

Inhibition of transforming growth factor beta signaling reduces pancreatic adenocarcinoma growth and invasiveness

Transforming growth factor beta (TGFbeta) is a pleiotropic factor that regulates cell proliferation, angiogenesis, metastasis, and immune suppression. Dysregulation of the TGFbeta pathway in tumor cells often leads to resistance to the antiproliferative effects of TGFbeta while supporting other cellular processes that promote tumor invasiveness and growth. In the present study, SD-208, a 2,4-disubstituted pteridine, ATP-competitive inhibitor of the TGFbeta receptor I kinase (TGFbetaRI), was used to inhibit cellular activities and tumor progression of PANC-1, a human pancreatic tumor line. SD-208 blocked TGFbeta-dependent Smad2 phosphorylation and expression of TGFbeta-inducible proteins in cell culture. cDNA microarray analysis and functional gene clustering identified groups of TGFbeta-regulated genes involved in metastasis, angiogenesis, cell proliferation, survival, and apoptosis. These gene responses were inhibited by SD-208. Using a Boyden chamber motility assay, we demonstrated that SD-208 inhibited TGFbeta-stimulated invasion in vitro. An orthotopic xenograft mouse model revealed that SD-208 reduced primary tumor growth and decreased the incidence of metastasis in vivo. Our findings suggest mechanisms through which TGFbeta signaling may promote tumor progression in pancreatic adenocarcinoma. Moreover, they suggest that inhibition of TGFbetaRI with a small-molecule inhibitor may be effective as a therapeutic approach to treat human pancreatic cancer.

Targeting signal transduction in pancreatic cancer treatment

Pancreatic cancer is a lethal disease with a 5-year survival rate of 4%. The only opportunity for improved survival continues to be complete surgical resection for those with localized disease. Although chemotherapeutic options are limited for the few patients with resectable disease, this problem is even more magnified in the majority (85%) of patients with unresectable or metastastic disease. Therefore, there is an urgent need for improved therapeutic options. The recent success of inhibitors of signal transduction for the treatment of other cancers supports the need to identify and validate aberrant signaling pathways important for pancreatic tumor growth. This review focuses on the validation of specific signaling networks and the present status of inhibitors of these pathways as therapeutic approaches for pancreatic cancer treatment.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid induces growth inhibition and enhances gemcitabine-induced cell death in pancreatic cancer

PURPOSE

Pancreatic cancer is an aggressive human malignancy that is generally refractory to chemotherapy. Histone deacetylase inhibitors are novel agents that modulate cell growth and survival. In this study, we sought to determine whether a relatively new histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), inhibits pancreatic cancer cell growth.

EXPERIMENTAL DESIGN

The effects of SAHA on the growth of three pancreatic cancer cell lines (BxPC3, COLO-357, and PANC-1) were examined with respect to cell cycle progression, p21 induction and localization, and interactions with the nucleoside analogue gemcitabine.

RESULTS

SAHA induced a G(1) cell cycle arrest in BxPC-3 cells and COLO-357 cells but not in PANC-1 cells. This arrest was dependent, in part, on induction of p21 by SAHA, as p21 was not induced in PANC-1 cells, and knockdown of p21 using small interfering RNA oligonucleotides nearly completely suppressed the effects of SAHA on cell cycle arrest in COLO-357 and partly attenuated the effects of SAHA in BxPC-3. COLO-357 and BxPC-3 cells, but not PANC-1 cells, were also sensitive to gemcitabine. In the gemcitabine-resistant PANC-1 cells, a 48-h cotreatment with SAHA rendered the cells sensitive to the inhibitory and proapoptotic effects of gemcitabine. An additive effect on growth inhibition by SAHA and gemcitabine was observed in COLO-357 and BxPC-3 cells. Moreover, analysis of p21 distribution in COLO-357 cells revealed that SAHA induced the cytoplasmic localization of both p21 and phospho-p21.

CONCLUSIONS

These data indicate that SAHA exerts proapoptotic effects in pancreatic cancer cells, in part, by up-regulating p21 and sequestering it in the cytoplasm, raising the possibility that SAHA may have therapeutic potential in the treatment of pancreatic cancer.