Overexpression of G1-S cyclins and cyclin-dependent kinases during multistage human pancreatic duct cell carcinogenesis

Immunohistochemical analysis of a panel of cancer stem cell markers and potential therapeutic markers in pancreatic ductal adenocarcinoma

PURPOSE

Pancreatic Ductal Adenocarcinoma (PDAC) is the most common type of pancreatic malignancies. It is known for its aggressive nature and high mortality rate. This calls for an urgent need of new prognostic and therapeutic markers that can be targeted for personalized treatment of the patient.

METHODS

Among 142 patients diagnosed with pancreatic cancers at Aga Khan University Hospital, a total of 62 patients were selected based on their confirmed diagnosis of PDAC. Immunohistochemistry was performed on Formalin-Fixed Paraffin-Embedded (FFPE) sections using selected antibodies (CD44, CD133, L1CAM, HER2, PD-L1, EGFR, COX2 and cyclin D1). All the slides were scored independently by two pathologists as per the set criteria.

RESULTS

Expression of all cancer stem cell markers was found to be significantly associated with one or more potential therapeutic markers. CD44 expression was significantly associated with HER2 (p = 0.032), COX2 (p = 0.005) and EGFR expression (p = 0.008). CD133 expression also showed significant association with HER2 (p = 0.036), COX2 (p = 0.004) and EGFR expression (p = 0.018). L1CAM expression was found to be associated with expression of COX2 (p = 0.017). None of the proteins markers showed association with overall survival of the patient. On the other hand, among the clinicopathological characteristics, histological differentiation (p = 0.047), lymphovascular invasion (p = 0.021) and perineural invasion (p = 0.014) were found to be significantly associated with patient's overall survival.

CONCLUSION

Internationally, this is the first report that assesses the selected panel of cancer stem cell markers and potential therapeutic targets in a single study and evaluates its combined expression. The study clearly demonstrates association between expression of cancer stem cell markers and therapeutic targets hence paves a way for precision medicine for pancreatic cancer patients.

The NF-κB/miR-488/ERBB2 axis modulates pancreatic cancer cell malignancy and tumor growth through cell cycle signaling

Pancreatic cancer is one of the malignancies having the poorest prognosis due to late diagnoses and lack of efficient treatment regimens. The identification of potential miRNA-targeted gene axes could act as targets for developing novel treatment strategies. Herein, it was assessed that miR-488 expression was markedly downregulated within pancreatic carcinoma. Higher expression of miR-488 was shown to be linked to better prognosis rates of pancreatic carcinoma as per online data. Within two pancreatic tumor cells, MIA PaCa-2 and PANC-1, miR-488 overexpression significantly suppressed malignant cytological behavior by inhibiting cell viability, enhancing cell apoptosis, and inducing cell cycle G2/M-phase arrest. Moreover, miR-488 overexpression also decreased the protein levels of cell cycle regulators, including cyclin A, cyclin B, CDK1, and CDK2. miR-488 directly targets ERBB2 (receptor tyrosine-protein kinase2) to suppress the expression of ERBB2 by targeting its 3'UTR. ERBB2 knockdown in MIA PaCa-2 and PANC-1 cell lines suppressed, but miR-488 inhibition enhanced the cancer cell biological malignant behavior; the effects of miR-488 inhibition on pancreatic cancer cells were significantly reversed by ERBB2 knockdown. NF-κB suppressed the expression of miR-488 transcriptionally via targeting its promoter region, consequentially repressing the tumor-suppressive effects of miR-488 upon pancreatic tumor cells. Thus, an NF-κB/miR-488/ERBB2 axis modulating pancreatic cancer cell malignancy and tumor growth through cell cycle signaling was conclusively demonstrated.

Playing on the Dark Side: SMYD3 Acts as a Cancer Genome Keeper in Gastrointestinal Malignancies

Simple Summary

The activity of SMYD3 in promoting carcinogenesis is currently under debate. Growing evidence seems to confirm that SMYD3 overexpression correlates with poor prognosis, cancer growth and invasion, especially in gastrointestinal tumors. In this review, we dissect the emerging role played by SMYD3 in the regulation of cell cycle and DNA damage response by promoting homologous recombination (HR) repair and hence cancer cell genomic stability. Considering the crucial role of PARP1 in other DNA repair mechanisms, we also discuss a recently evaluated synthetic lethality approach based on the combined use of SMYD3 and PARP inhibitors. Interestingly, a significant proportion of HR-proficient gastrointestinal tumors expressing high levels of SMYD3 from the PanCanAtlas dataset seem to be eligible for this innovative strategy. This promising approach could be taken advantage of for therapeutic applications of SMYD3 inhibitors in cancer treatment.

Abstract

The SMYD3 methyltransferase has been found overexpressed in several types of cancers of the gastrointestinal (GI) tract. While high levels of SMYD3 have been positively correlated with cancer progression in cellular and advanced mice models, suggesting it as a potential risk and prognosis factor, its activity seems dispensable for autonomous in vitro cancer cell proliferation. Here, we present an in-depth analysis of SMYD3 functional role in the regulation of GI cancer progression. We first describe the oncogenic activity of SMYD3 as a transcriptional activator of genes involved in tumorigenesis, cancer development and transformation and as a co-regulator of key cancer-related pathways. Then, we dissect its role in orchestrating cell cycle regulation and DNA damage response (DDR) to genotoxic stress by promoting homologous recombination (HR) repair, thereby sustaining cancer cell genomic stability and tumor progression. Based on this evidence and on the involvement of PARP1 in other DDR mechanisms, we also outline a synthetic lethality approach consisting of the combined use of SMYD3 and PARP inhibitors, which recently showed promising therapeutic potential in HR-proficient GI tumors expressing high levels of SMYD3. Overall, these findings identify SMYD3 as a promising target for drug discovery.

PRR11 unveiled as a top candidate biomarker within the RBM3-regulated transcriptome in pancreatic cancer

The outlook for patients with pancreatic cancer remains dismal. Treatment options are limited and chemotherapy remains standard of care, leading to only modest survival benefits. Hence, there is a great need to further explore the mechanistic basis for the intrinsic therapeutic resistance of this disease, and to identify novel predictive biomarkers. RNA‐binding motif protein 3 (RBM3) has emerged as a promising biomarker of disease severity and chemotherapy response in several types of cancer, including pancreatic cancer. The aim of this study was to unearth RBM3‐regulated genes and proteins in pancreatic cancer cells in vitro, and to examine their expression and prognostic significance in human tumours. Next‐generation RNA sequencing was applied to compare transcriptomes of MIAPaCa‐2 cells with and without RBM3 knockdown. The prognostic value of differentially expressed genes (DEGs) was examined in The Cancer Genome Atlas (TCGA). Top deregulated genes were selected for further studies in vitro and for immunohistochemical analysis of corresponding protein expression in tumours from a clinically well‐annotated consecutive cohort of 46 patients with resected pancreatic cancer. In total, 19 DEGs (p < 0.01) were revealed, among which some with functions in cell cycle and cell division stood out; PDS5A (PDS cohesin associated factor A) as the top downregulated gene, CCND3 (cyclin D3) as the top upregulated gene, and PRR11 (proline rich 11) as being highly prognostic in TCGA. Silencing of RBM3 in MiaPaCa‐2 cells led to congruent alterations of PDS5A, cyclin D3, and PRR11 levels. High protein expression of PRR11 was associated with adverse clinicopathological features and shorter overall survival. Neither PDS5A nor cyclin D3 protein expression was prognostic. This study unveils several RBM3‐regulated genes with potential clinical relevance in pancreatic cancer, among which PRR11 shows the most consistent association with disease severity, at both transcriptome and protein levels.

Abemaciclib Is Effective Against Pancreatic Cancer Cells and Synergizes with HuR and YAP1 Inhibition

Mutation or promoter hypermethylation of CDKN2A is found in over 90% of pancreatic ductal adenocarcinomas (PDAC) and leads to loss of function of cell-cycle inhibitors p16 (INK4A) and p14 (ARF) resulting in unchecked proliferation. The CDK4/6 inhibitor, abemaciclib, has nanomolar IC₅₀s in PDAC cell lines and decreases growth through inhibition of phospho-Rb (pRb), G₁ cell-cycle arrest, apoptosis, and the senescent phenotype detected with β-galactosidase staining and relevant mRNA elevations. Daily abemaciclib treatments in mouse PDAC xenograft studies were safe and demonstrated a 3.2-fold decrease in tumor volume compared with no treatment (P < 0.0001) accompanying a decrease in both pRb and Ki67. We determined that inhibitors of HuR (ELAVL1), a prosurvival mRNA stability factor that regulates cyclin D1, and an inhibitor of Yes-Associated Protein 1 (YAP1), a pro-oncogenic, transcriptional coactivator important for CDK6 and cyclin D1, were both synergistic with abemaciclib. Accordingly, siRNA oligonucleotides targeted against HuR, YAP1, and their common target cyclin D1, validated the synergy studies. In addition, we have seen increased sensitivity to abemaciclib in a PDAC cell line that harbors a loss of the ELAVL1 gene via CRISP-Cas9 technology. As an in vitro model for resistance, we investigated the effects of long-term abemaciclib exposure. PDAC cells chronically cultured with abemaciclib displayed a reduction in cellular growth rates (GR) and coresistance to gemcitabine and 5-fluorouracil (5-FU), but not to HuR or YAP1 inhibitors as compared with no treatment controls. We believe that our data provide compelling preclinical evidence for an abemaciclib combination-based clinical trial in patients with PDAC. IMPLICATIONS: Our data suggest that abemaciclib may be therapeutically relevant for the treatment in PDAC, especially as part of a combination regimen inhibiting YAP1 or HuR.

Expression of chosen cell cycle and proliferation markers in pancreatic intraepithelial neoplasia

Introduction

Pancreatic ductal adenocarcinoma is one of the most aggressive tumours that develops from precursor lesions, most frequently including pancreatic intraepithelial neoplasia (PanIN). Deregulation of the cell cycle, responsible for uncontrolled cell proliferation, is an important phenomenon in the development of this cancer.

Aim

To evaluate the cell cycle and the expression of proliferation markers, namely Ki67, PCNA, and cyclin D1 in pancreatic intraepithelial neoplasia at its different stages of progression.

Material and methods

The study group consisted of 70 patients with different pancreatic diseases (pancreatic ductal adenocarcinoma, pancreatitis, and pancreatic cysts), who also had pancreatic intraepithelial neoplasia. Expression of Ki67, PCNA, and Cyclin D1 was analysed immunohistochemically using appropriate antibodies.

Results

Statistically significant differences were demonstrated in Ki67, PCNA, and Cyclin D1 expression between normal pancreatic ducts and various stages of PanIN (p < 0.001). Expression of these proteins increased from normal pancreas to PanIN 1, 2, and 3. Expression of these proteins was higher in stages PanIN 1, 2, and 3 compared to normal pancreas. The expression of Ki67, PCNA, and cyclin D1 was associated with age (p < 0.001), Ki67 and PCNA with sex (p < 0.001), and PCNA with the type of primary disease (p = 0.031). Simultaneously, a directly proportional relationship was established between the expression of all proteins examined (p < 0.001).

Conclusions

An increase in the expression of Ki67, PCNA, and cyclin D1 suggests that these proteins may enhance epithelial cell proliferation and may influence the development of pancreatic intraepithelial neoplasia. Moreover, immunohistochemical assessment of Ki67, PCNA, and cyclin D1 expression may be helpful in the differential diagnosis of PanIN.

Cyclin-dependent kinase inhibitors and the treatment of gastrointestinal cancers

The cell cycle is a highly conserved and tightly regulated biological system that controls cellular proliferation and differentiation. The cell cycle regulatory proteins, which include the cyclins, the cyclin-dependent kinases (CDKs), and the CDK inhibitors, are critical for the proper temporal and spatial regulation of cellular proliferation. Conversely, alterations in cell cycle regulatory proteins, leading to the loss of normal cell-cycle control, are a hallmark of many cancers, including gastrointestinal cancers. Accordingly, overexpression of CDKs and cyclins and by contrast loss of CDK inhibitors, are all linked to gastrointestinal cancers and are often associated with less favorable prognoses and outcomes. Because of the importance that the cell cycle regulatory proteins play in tumorigenesis, currently there is a broad spectrum of cell-cycle inhibitors under development that, as a group, hold promise as effective cancer treatments. In support of this approach to cancer treatment, the growing availability of molecular diagnostics techniques may help in identifying patients who have driving abnormalities in the cell-cycle machinery and are thus more likely to respond to cell-cycle inhibitors. In this review, we discuss the prevalence of cell-cycle abnormalities in patients with gastrointestinal cancers and provide a preclinical and clinical overview of new agents that target cell-cycle abnormalities with a special emphasis on gastrointestinal cancers.

Cyclin-dependent kinase 4 overexpression is mostly independent of gene amplification and constitutes an independent prognosticator for nasopharyngeal carcinoma

Data mining in the public domain demonstrates that cyclin-dependent kinase 4 (CDK4) is highly expressed in nasopharyngeal carcinomas (NPC). Associated with cyclin-D, CDK4 phosphorylates and inactivates retinoblastoma (Rb) protein family members and mediates progression through the G1- to the S-phase of the cell cycle. Amplification and overexpression of CDK4 has been identified in various human malignancies. However, its expression and amplification has never been systemically evaluated in NPC. This study aimed to evaluate the amplification and expression status, correlation with clinicopathological features, and prognostic implications of CDK4 based on public domain dataset and in our well-defined cohort of NPC patients. The association between CDK4 transcript level and gene dosage was explored by analysis of an independent public domain dataset. We retrospectively assessed CDK4 immunoexpression in biopsies of 124 consecutive NPC patients devoid of initial distant metastasis and treated according to consistent guidelines. The results were correlated with clinicopathological features, local recurrence-free survival (LRFS), distant metastasis-free survival (DMeFS), and disease-specific survival (DSS). High levels of CDK4 protein were positively correlated with the T 3, 4 status (p = 0.024); N 2, 3 status (p < 0.001); and the American Joint Committee on Cancer stage 3, 4 (p < 0.001). Multivariate analysis suggested high CDK4 expression was an independent prognostic indicator of worse DMeFS (p = 0.001, hazard ratio (HR) = 3.226) and DSS (p = 0.037, HR = 1.838). Although CDK4 is frequently upregulated, its gene locus is very uncommonly amplified in NPC. CDK4 overexpression is mostly independent with gene amplification and represents a potential prognostic biomarker in NPC and may indicate tumor aggressiveness through cell cycle dysregulation.

Inflammation-induced NFATc1-STAT3 transcription complex promotes pancreatic cancer initiation by KrasG12D

Cancer-associated inflammation is a molecular key feature in pancreatic ductal adenocarcinoma. Oncogenic KRAS in conjunction with persistent inflammation is known to accelerate carcinogenesis, although the underlying mechanisms remain poorly understood. Here, we outline a novel pathway whereby the transcription factors NFATc1 and STAT3 cooperate in pancreatic epithelial cells to promote Kras(G12D)-driven carcinogenesis. NFATc1 activation is induced by inflammation and itself accelerates inflammation-induced carcinogenesis in Kras(G12D) mice, whereas genetic or pharmacologic ablation of NFATc1 attenuates this effect. Mechanistically, NFATc1 complexes with STAT3 for enhancer-promoter communications at jointly regulated genes involved in oncogenesis, for example, Cyclin, EGFR and WNT family members. The NFATc1-STAT3 cooperativity is operative in pancreatitis-mediated carcinogenesis as well as in established human pancreatic cancer. Together, these studies unravel new mechanisms of inflammatory-driven pancreatic carcinogenesis and suggest beneficial effects of chemopreventive strategies using drugs that are currently available for targeting these factors in clinical trials.

SIGNIFICANCE

Our study points to the existence of an oncogenic NFATc1-STAT3 cooperativity that mechanistically links inflammation with pancreatic cancer initiation and progression. Because NFATc1-STAT3 nucleoprotein complexes control the expression of gene networks at the intersection of inflammation and cancer, our study has significant relevance for potentially managing pancreatic cancer and other inflammatory-driven malignancies.

Immunoassay-based proteome profiling of 24 pancreatic cancer cell lines

Pancreatic ductal adenocarcinoma is one of the most deadly forms of cancers, with a mortality that is almost identical to incidence. The inability to predict, detect or diagnose the disease early and its resistance to all current treatment modalities but surgery are the prime challenges to changing the devastating prognosis. Also, relatively little is known about pancreatic carcinogenesis. In order to better understand relevant aspects of pathophysiology, differentiation, and transformation, we analysed the cellular proteomes of 24 pancreatic cancer cell lines and two controls using an antibody microarray that targets 741 cancer-related proteins. In this analysis, 72 distinct disease marker proteins were identified that had not been described before. Additionally, categorizing cancer cells in accordance to their original location (primary tumour, liver metastases, or ascites) was made possible. A comparison of the cells' degree of differentiation (well, moderately, or poorly differentiated) resulted in unique marker sets of high relevance. Last, 187 proteins were differentially expressed in primary versus metastatic cancer cells, of which the majority is functionally related to cellular movement.

The cyclins: a family of widely expressed tumor antigens?

Continuous cell division is a hallmark of cancer and cell-cycle regulators therefore represent relevant target molecules for tumor therapy. Among these targets the cyclins are of particular interest as they are overexpressed in various tumor entities with little expression in normal tissue. Here we review evidence that these molecules are recognized by the immune system, summarize why cyclins A, B and D in particular appear to be interesting targets for active and passive immunotherapy, and discuss whether the entire family could be an interesting novel class of tumor antigens for cancer treatment and prevention.

Expression of p53, p16 and Ki67 proteins in ductal adenocarcinoma of the pancreatic head and their relation with survival and cell differentiation

OBJECTIVE

To determine the expression of p53, p16 and Ki-67 and its relevance in survival and cell differentiation.

METHODS

Fifteen duodenopancreatectomized patients were included. Immunohistochemical expression of p53, p16 and Ki-67 was determined in paraffin embedded tumor blocks. The relation of these expressions with different variables was studied.

RESULTS

Ninety-three per cent of tumors showed expression of p53 and p16. Ki-67 was expressed in 86.66% of tumors (labeling index - LI 11.91 ± 9.47). The presence of combined alterations was not related to significant differences in tumor type, stage or survival; similar results were obtained analyzing isolated expressions. When groups of p16 and Ki-67 expressions where created, the median survival was not significant. However, there was a slightly better survival in patients with focal expression of p16 (median survival 20.75 versus 14.34), when compared to patients with diffuse expression.

CONCLUSION

The overexpression of p53, p16 and Ki-67 was not related to survival or tumor grade, when comparing isolated or combined expressions.

Methoxychalcone induces cell-cycle arrest and apoptosis in human hormone-resistant prostate cancer cells through PI 3-kinase-independent inhibition of mTOR pathways

BACKGROUND

Chalcones are contained in fruits and vegetables, and have been suggested to display anticancer activities. In this study, the anticancer mechanism of WJ9708011 (a methoxychalcone derivative) was delineated in human prostate cancer cells.

METHOD

Cell proliferation was examined by sulforhodamine B and clonogenic assays. Cell-cycle progression and mitochondrial membrane potential (DeltaPsi(m)) were detected by flow cytometric analysis. Expressions of protein and mRNA were detected by Western blot and RT-PCR technique, respectively. The protein synthesis was examined by [(3)H]leucine incorporation assay. The overexpression or knockdown techniques for specific target protein were also used in this study.

RESULTS

WJ9708011 induced time- and concentration-dependent G1 arrest of the cell cycle and subsequent apoptosis in human prostate cancer cells. The G1-arrest effect was confirmed by down-regulated expressions of several G1-phase regulators, including cyclin D1, cyclin E, cyclin-dependent kinase (Cdk)-4, Cdk2, phospho-RB, E2F-1, and Cdc25A. The mRNA expressions of cyclin D1 and cyclin E were also inhibited through the suppression of NF-kappaB. WJ9708011 blocked the protein synthesis and inhibited mammalian target of rapamycin (mTOR) signaling pathways. The suppression of mTOR pathways were irrespective of Akt- and AMPK-activated protein kinase (AMPK), but were attributed to mitochondrial stress, in which the down-regulation of survivin protein level may play a crucial role.

CONCLUSIONS

The data suggest that WJ9708011 induces transcriptional and translational suppression of cell-cycle regulators that might be through Akt- and AMPK-independent loss of DeltaPsi(m) and inhibition of mTOR signaling pathway, leading to G1 arrest of the cell cycle and subsequent apoptotic cell death.

Bmi-1 is related to proliferation, survival and poor prognosis in pancreatic cancer

B-cell-specific Moloney murine leukemia virus insertion site 1 (BMI1) is a member of the polycomb group of transcriptional repressors. Until now, its expression and functional significance in pancreatic carcinogenesis was unknown. In the present study, we demonstrated that expression of BMI1 was markedly up-regulated in pancreatic cancer cell lines and surgically resected cancer specimens. In addition, BMI1 expression levels correlated positively with the presence of lymph node metastases and negatively with patient survival rates, suggesting a role for BMI1 in the progression of pancreatic cancer. Furthermore, stable down-regulation of BMI1 suppressed cell growth, delayed the G1/S transition, and enhanced the susceptibility of different pancreatic cell lines to apoptosis following expression of a lentiviral-mediated shRNA targeted for BMI1. Expression of the short-hairpin RNA also correlated with the up-regulation of p21 and Bax and the down-regulation of cyclin D1, cyclin-dependent kinase (CDK)-2 and -4, Bcl-2, and phospho-Akt. Finally, growth suppression following BMI1 depletion was confirmed in a nude mouse model. In conclusion, our findings indicate that BMI1 plays an important role in the late progression of pancreatic cancer and may represent a novel therapeutic target for the treatment of pancreatic cancer.

Genomic profiling of gastric carcinoma in situ and adenomas by array-based comparative genomic hybridization

Although genomic copy number aberrations (CNAs) of gastric carcinoma at the advanced stage have already been extensively characterized by array comparative genomic hybridization (array CGH) analysis, those of gastric carcinoma in situ (CIS) are still poorly understood. Furthermore, no reports have demonstrated correlations between CNAs and histopathological features of gastric adenoma. In this study, we investigated CNAs of 20 gastric CISs (Vienna category 4.2) and 20 adenomas including seven low-grade adenomas (LGA; Vienna category 3) and 13 high-grade adenomas (HGA; Vienna category 4.1), using oligonucleotide-based array CGH. The most frequent aberrations in CIS were gains at 8q (85%) and 20q (50%), and losses at 5q (50%) and 17p (50%), suggesting that these CNAs are involved in the development of CIS. We found that the pattern of CNAs in HGA was quite different from that in LGA. The most frequent CNAs in HGA were gains at 8q (62%) and 7pq (54%), whereas those in LGA were gain at 7q21.3-q22.1 (57%) and loss at 5q (43%). Interestingly, gains at 8q and 7pq, both of which occurred most frequently in HGA, were not detected in any cases of LGA. Of note, 8q gain was detected most frequently in both HGA and CIS but was undetected in LGA. Since HGA is believed to have a higher risk of progression to invasive carcinoma than LGA, these data suggest that 8q gain is important for the malignant transformation of gastric adenoma.

Differential roles of cyclin D1 and D3 in pancreatic ductal adenocarcinoma

Background

The cyclin D1 (CCND1) and cyclin D3 (CCND3) are frequently co-overexpressed in pancreatic ductal adenocarcinoma (PDAC). Here we examine their differential roles in PDAC.

Results

CCND1 and CCND3 expression were selectively suppressed by shRNA in PDAC cell lines with expression levels of equal CCND1 and CCND3 (BxPC3), enhanced CCND1 (HPAC) or enhanced CCND3 (PANC1). Suppression of cell proliferation was greater with CCND3 than CCND1 downregulation. CCND3 suppression led to a reduced level of phosphorylated retinoblastoma protein (^Ser795p-Rb/p110) and resulted in decreased levels of cyclin A mRNA and protein. A global gene expression analysis identified deregulated genes in D1- or D3-cyclin siRNA-treated PANC1 cells. The downregulated gene targets in CCND3 suppressed cells were significantly enriched in cell cycle associated processes (p < 0.005). In contrast, focal adhesion/actin cytoskeleton, MAPK and NF B signaling appeared to characterize the target genes and their interacting proteins in CCND1 suppressed PANC1 cells.

Conclusions

Our results suggest that CCND3 is the primary driver of the cell cycle, in cooperation with CCND1 that integrates extracellular mitogenic signaling. We also present evidence that CCND1 plays a role in tumor cell migration. The results provide novel insights for common and differential targets of CCND1 and CCND3 overexpression during pancreatic duct cell carcinogenesis.

Insulin-like growth factor binding protein-5 influences pancreatic cancer cell growth

AIM: To investigate the functional significance of insulin-like growth factor binding protein-5 (IGFBP-5) overexpression in pancreatic cancer (PaC).

METHODS: The effects of IGFBP-5 on cell growth were assessed by stable transfection of BxPC-3 and PANC-1 cell lines and measuring cell number and DNA synthesis. Alterations in the cell cycle were assessed by flow cytometry and immunoblot analyses. Changes in cell survival and signal transduction were evaluated after mitogen activated protein kinase and phosphatidylinositol 3-kinase (PI3K) inhibitor treatment.

RESULTS: After serum deprivation, IGFBP-5 expression increased both cell number and DNA synthesis in BxPC-3 cells, but reduced cell number in PANC-1 cells. Consistent with this observation, cell cycle analysis of IGFBP-5-expressing cells revealed accelerated cell cycle progression in BxPC-3 and G2/M arrest of PANC-1 cells. Signal transduction analysis revealed that Akt activation was increased in BxPC-3, but reduced in PANC-1 cells that express IGFBP-5. Inhibition of PI3K with LY294002 suppressed extracellular signal-regulated kinase-1 and -2 (ERK1/2) activation in BxPC-3, but enhanced ERK1/2 activation in PANC-1 cells that express IGFBP-5. When MEK1/2 was blocked, Akt activation remained elevated in IGFBP-5 expressing PaC cells; however, inhibition of PI3K or MEK1/2 abrogated IGFBP-5-mediated cell survival.

CONCLUSION: These results indicate that IGFBP-5 expression affects the cell cycle and survival signal pathways and thus it may be an important mediator of PaC cell growth.

AKT1 mediates bypass of the G1/S checkpoint after genotoxic stress in normal human cells

Certain forms of hexavalent chromium [Cr(VI)] are human carcinogens. Our recent work has shown that a broad range protein tyrosine phosphatase (PTP) inhibitor, sodium orthovanadate (SOV), abrogated both Cr(VI)-induced growth arrest and clonogenic lethality. Notably, SOV enhanced Cr(VI) mutation frequency, ostensibly through forced survival of genetically damaged cells. In the present study, co-treatment with this PTP inhibitor bypassed the Cr(VI)-induced G(1)/S checkpoint arrest in diploid human lung fibroblasts (HLF). Moreover, the PTP inhibitor abrogated the Cr(VI)-induced decrease in the expression of key effectors of the G(1)/S checkpoint [Cyclin D1, phospho Ser 807/811 Rb (pRB), p27]. Cr(VI)-induced G(1) arrest was associated with the cytoplasmic appearance of pRb and the nuclear localization of p27, both of which were reversed by the PTP inhibitor. The PTP inhibitor's reversal of G(1)/S checkpoint effector localization after Cr exposure was found to be Akt1-dependent, as this was abrogated by transfection with either akt1 siRNA or an Akt1-kinase dead plasmid. Furthermore, Akt1 activation alone was sufficient to induce G(1)/S checkpoint bypass and to prevent Cr(VI)-induced changes in pRb and p27 localization. In conclusion, this work establishes Akt1 activation to be both sufficient to bypass the Cr(VI)-induced G(1)/S checkpoint, as well as necessary for the observed PTP inhibitor effects on key mediators of the G(1)/S transition. The potential for Akt to bypass G(1)/S checkpoint arrest in the face of genotoxic damage could increase genomic instability, which is a hallmark of neoplastic progression.

Mirk/Dyrk1B maintains the viability of quiescent pancreatic cancer cells by reducing levels of reactive oxygen species

The kinase Mirk/dyrk1B mediated the clonogenic growth of pancreatic cancer cells in earlier studies. It is now shown that Mirk levels increased 7-fold in SU86.86 pancreatic cancer cells when over a third of the cells were accumulated in a quiescent G(0) state, defined by Hoechst/Pyronin Y staining. Depletion of Mirk by a doxycycline-inducible short hairpin RNA increased the G(0) fraction to approximately 50%, suggesting that Mirk provided some function in G(0). Mirk reduced the levels of reactive oxygen species (ROS) in quiescent cultures of SU86.86 cells and of Panc1 cells by increasing transcription of the antioxidant genes ferroxidase, superoxide dismutase (SOD)2, and SOD3. These genes were functional antioxidant genes in pancreatic cancer cells because ectopic expression of SOD2 and ferroxidase in Mirk-depleted cells lowered ROS levels. Quiescent pancreatic cancer cells quickly lost viability when depleted of Mirk because of elevated ROS levels, exhibiting up to 4-fold less colony-forming activity and 4-fold less capability for dye exclusion. As a result, reduction of ROS by N-acetyl cysteine led to more viable cells. Mirk also destabilizated cyclin D1 and D3 in quiescent cells. Thus, quiescent pancreatic cancer cells depleted of Mirk became less viable because they were damaged by ROS, and had increased levels of G(1) cyclins to prime cells to escape quiescence.

PDX-1 acts as a potential molecular target for treatment of human pancreatic cancer

OBJECTIVES

The purpose of this study was to investigate whether pancreatic and duodenal homeobox factor 1 (PDX-1) could serve as a potential molecular target for the treatment of pancreatic cancer.

METHODS

Cell proliferation, invasion capacity, and protein levels of cell cycle mediators were determined in human pancreatic cancer cells transfected with mouse PDX-1 (mPDX-1) alone or with mPDX-1 short hairpin RNA (shRNA) and/or human PDX-1 shRNA (huPDX-1 shRNA). Tumor cell growth and apoptosis were also evaluated in vivo in PANC-1 tumor-bearing severe combined immunodeficient mice receiving multiple treatments of intravenous liposomal huPDX-1 shRNA.

RESULTS

mPDX-1 overexpression resulted in the significant increase of cell proliferation and invasion in MIA PaCa2, but not PANC-1 cells. This effect was blocked by knocking down mPDX-1 expression with mPDX-1 shRNA. Silencing of huPDX-1 expression in PANC-1 cells inhibited cell proliferation in vitro and suppressed tumor growth in vivo which was associated with increased tumor cell apoptosis. PDX-1 overexpression resulted in dysregulation of the cell cycle with up-regulation of cyclin D, cyclin E, and Cdk2 and down-regulation of p27.

CONCLUSIONS

PDX-1 regulates cell proliferation and invasion in human pancreatic cancer cells. Down-regulation of PDX-1 expression inhibits pancreatic cancer cell growth in vitro and in vivo, implying its use as a potential therapeutic target for the treatment of pancreatic cancer.

Inhibition of CDK4 impairs proliferation of pancreatic cancer cells and sensitizes towards TRAIL-induced apoptosis via downregulation of survivin

Pancreatic ductal adenocarcinoma is one of the most common causes of cancer death in Western countries with an average survival after diagnosis of 3-6 months and a five-year survival rate under 5%. Because of the lack of effective therapies, there is the need to characterize new molecular treatment strategies. Abnormal regulation of the cell cycle is a hallmark of neoplasia. Cyclin-dependent kinase 4 (CDK4), a key regulator of G1-phase of the cell cycle, has been shown to be overexpressed in pancreatic cancer. Until now, the contribution of CDK4 to tumor maintenance of pancreatic cancer has not been investigated. In this study, we used the chemical CDK4 inhibitor 2-bromo-12,13-dihydro-5H-indolo[2,3-a]pyrrolo[3,4-c]carbazole-5,7(6H)-dione, as well as RNA interference, to investigate the function of CDK4 in pancreatic cancer cells. Both approaches led to a reduction of pancreatic cancer cell proliferation due to G1-phase cell cycle arrest and Rb activation. Furthermore, we observed increased sensitivity of G1-arrested pancreatic cancer cells towards TRAIL-induced apoptosis. Sensitization towards TRAIL was due to the transcriptional downregulation of survivin. These findings show that a combined sensitizer/inducer strategy may be a potential therapeutic strategy for pancreatic ductal adenocarcinoma.

Sonic hedgehog signaling pathway in pancreatic cystic neoplasms and ductal adenocarcinoma

OBJECTIVES

Hedgehog (Hh) signaling is an important mediator of tumorigenesis of pancreatic ductal adenocarcinoma (PA). It is intriguing to explore whether Hh signaling is also involved in pancreatic cystic neoplasms, which are phenotypically different from PA.

METHODS

Patients with solid and pseudopapillary tumor (SPT; n = 12), mucinous cystic neoplasm (MCN; n = 18), intraductal papillary mucinous neoplasm (IPMN; n = 18), and PA (n = 20) were studied. Expression of Hh signaling molecules including sonic Hh (sHh), smoothened (Smo), patched 1 (Ptc1), and Gli were determined using immunohistochemistry and/or Western blotting. Cell cycle-regulator genes, including cyclin A, B, C, and D1 messenger RNA, were determined using ribonuclease protection assay.

RESULTS

Six of 12 SPT, 8 of 18 MCN, 17 of 18 IPMN, and 20 of 20 PA displayed Hh signaling using immunohistochemistry. Sonic Hh was predominantly expressed in stromal cells neighboring to the neoplastic cells of SPT and IPMN; in contrast, sHh was expressed in both stromal cells and neoplastic epithelial cells of MCN and PA. The quantitative expression of sHh signaling detected by Western blotting showed that expression of Ptc1 and Gli, but not Smo, corresponded to the magnitude of sonic hedgehog ligand. The expression of cyclin D1 messenger RNA was highest in PA, followed by MCN, IPMN, and SPT, which matches with Ptc1 and Gli.

CONCLUSIONS

Hedgehog signaling pathway might play a role during tumorigenesis of SPT, MCN, IPMN, and PA. Mucinous cystic neoplasm and PA exhibit an autocrine regulation of sHh, whereas SPT and IPMN do not. Overexpression of Ptc1 and Gli, reflected by cyclin D1, might represent proliferative potential of various pancreatic neoplasms.

Clinical significance of p16INK4a and p53 overexpression in endocrine tumors of the gastrointestinal tract

This study was designed to determine the expression of p16, p53, and CD117 in gastrointestinal tract endocrine tumors. Immunohistochemical studies of p16, p53, and CD117 were performed in 57 gastrointestinal tract endocrine tumors, including 22 poorly differentiated endocrine carcinomas (PDECs) and 35 well-differentiated endocrine tumors (WDETs). Overexpression of p16 and p53 was observed in 16 (73%) and 10 (45%) of the PDECs, respectively, whereas only 1 WDET showed overexpression of p53 and none showed overexpression of p16. A total of 18 (82%) of the PDECs showed overexpression of p16 or p53 proteins. This is closely associated with PDEC (P < .0001). By using overexpression of p16 or p53 as the criteria for PDEC, the sensitivity and specificity are 81.8% and 97.1%, respectively, with positive and negative predictive values of 94.7% and 89.5%, respectively. CD117 was not detected in any of the 57 gastrointestinal endocrine tumors by immunohistochemical analysis.

A small molecule based on the pRb2/p130 spacer domain leads to inhibition of cdk2 activity, cell cycle arrest and tumor growth reduction in vivo

One strategy in the development of anticancer therapeutics has been to arrest malignant proliferation through inhibition of the enzymatic activity of cyclin-dependent kinases (cdks), which are key regulatory molecules of the cell cycle. Over the past few years, numerous compounds with remarkable cdk inhibitory activity have been studied in cancer therapy, although it is very difficult to point out the best cdk to target. An excellent candidate appears to be cdk2, whose alteration is a pathogenic hallmark of tumorigenesis. The small molecule described in our study showed an inhibitory effect on the kinase activity of cdk2, a significant growth arrest observed in a colony formation assay and a reduction in the size of the tumor in nude mice, thus suggesting its potential role as a promising new type of mechanism-based antitumor drug, also for the treatment of hyperproliferative disorders.

Cyclin E Expression and Outcome in Pancreatic Ductal Adenocarcinoma

The association of high cyclin E expression with poor outcome in some cancers, in particular breast cancer, suggests that it may play an important role in tumor biology. Because the influence of cyclin E expression on outcome is yet to be examined in pancreatic cancer, we assessed the relationship between the expression of cyclin E, p27(Kip1), and survival in a large cohort of pancreatic cancer patients with long-term follow-up. Expression of cyclin E and p27(Kip1) was assessed by immunohistochemistry using tissue microarrays of tumor samples from 118 patients with pancreatic ductal adenocarcinoma (75 resections and 43 biopsies). High cyclin E expression (>10% positive nuclei) was identified in 39 of 118 (33%) patients. This was associated with poor prognosis on univariate analysis in the whole cohort (P = 0.005), as well as in the subgroup of 75 patients who underwent operative resection (P = 0.04). On multivariate analysis, high cyclin E expression was an independent predictor of poor survival in both the entire cohort (P = 0.005) and the resected subgroup (P = 0.03), and was superior to all tested clinicopathologic factors (tumor size, lymph node metastases, differentiation, margin involvement, and perineural invasion) as a marker of survival. Low p27(Kip1) expression (<5% positive nuclei) was present in 41 of 111 (37%) patients, but was not associated with survival, and coexpression of p27(Kip1) did not influence the association of high cyclin E expression with poor survival. High cyclin E expression is a strong independent predictor of poor outcome in patients with pancreatic cancer. Thus, if these data are confirmed in independent cohorts, measurement of cyclin E may add significant prognostic information to the currently used clinicopathologic variables and hence have potential clinical utility in the management of this disease.

Comprehensive analysis of 19q12 amplicon in human gastric cancers

Amplification at 19q12 has been observed in multiple tumor types, while cyclin E1 (CCNE1) has been considered to be the key oncogene within this amplicon. We have previously applied cDNA microarray analysis to systematically characterize gene expression patterns of gastric tumor and nontumor samples. We identified a cluster of five tightly coregulated genes all located at chromosome 19q12, including CCNE1. We found that the 19q12 gene cluster is highly expressed in gastric tumors compared to nontumor gastric samples. Array based comparative genomic hybridization and real-time PCR was used to define the boundary of the 19q12 amplicon to a region of approximately 200 kb. Interestingly, we found that in some cases amplification at 19q12 was not associated with DNA copy number gain at CCNE1, suggesting that some other genes within the 19q12 amplicon may also have important function during gastric tumorigenesis. We found high expression of the 19q12 gene cluster to be statistically correlated with the cell proliferation gene signature. Using the SAM software, we identified a set of 577 genes whose expression levels positively correlated with the 19q12 gene cluster. GO term analysis revealed that this genelist is enriched with genes involved in cell cycle regulation and cell proliferation. In conclusion, expression array analysis combined with array comparative genomic hybridization and real-time PCR provides a new and powerful tool to identify clusters of genes which may be regulated by genomic DNA aberrations. In addition, our study indicates that amplification at 19q12 is associated with cell proliferation in vivo.

Mouse models of cell cycle regulators: new paradigms

In yeast, a single cyclin-dependent kinase (Cdk) is able to regulate diverse cell cycle transitions (S and M phases) by associating with multiple stage-specific cyclins. The evolution of multicellular organisms brought additional layers of cell cycle regulation in the form of numerous Cdks, cyclins and Cdk inhibitors to reflect the higher levels of organismal complexity. Our current knowledge about the mammalian cell cycle emerged from early experiments using human and rodent cell lines, from which we built the current textbook model of cell cycle regulation. In this model, the functions of different cyclin/Cdk complexes were thought to be specific for each cell cycle phase. In the last decade, studies using genetically engineered mice in which cell cycle regulators were targeted revealed many surprises. We discovered the in vivo functions of cell cycle proteins within the context of a living animal and whether they are essential for animal development. In this review, we discuss first the textbook model of cell cycle regulation, followed by a global overview of data obtained from different mouse models. We describe the similarities and differences between the phenotypes of different mouse models including embryonic lethality, sterility, hematopoietic, pancreatic, and placental defects. We also describe the role of key cell cycle regulators in the development of tumors in mice, and the implications of these data for human cancer. Furthermore, animal models in which two or more genes are ablated revealed which cell cycle regulators interact genetically and functionally complement each other. We discuss for example the interaction of cyclin D1 and p27 and the compensation of Cdk2 by Cdc2. We also focus on new functions discovered for certain cell cycle regulators such as the regulation of S phase by Cdc2 and the role of p27 in regulating cell migration. Finally, we conclude the chapter by discussing the limitations of animal models and to what extent can the recent findings be reconciled with the past work to come up with a new model for cell cycle regulation with high levels of redundancy among the molecular players.

Cyclin D3 expression in primary Ta/T1 bladder cancer

Cyclin D3 deregulation has recently been reported in bladder cancer but its prognostic significance remains uncertain. A cohort of 159 patients with stage Ta or T1 primary bladder tumours was investigated to determine the significance of cyclin D3 expression in association with other G1-S phase regulators of the cell cycle (p53, p21Waf1, p27kip1, cyclin D1), including tumour proliferation (ki67-MIB1); its association with conventional clinicopathological parameters; and the relationship between cyclin D3 and loss of heterozygosity (LOH) at the 9p21 (p16INK4a locus) chromosome region. The end point of the study was progression-free survival. Cyclin D3, other G1-S phase regulators, and tumour proliferation were investigated by immunohistochemistry and measured by the grid-counting method. To validate the immunohistochemical expression, cyclin D3 was additionally assessed by western blotting in selected cases. LOH at the 9p21 chromosome region (marker D9S171) was assessed in 125 cases using an AB Prism 310 genetic analyser and a set of microsatellite fluorescence-labelled primers. Cyclin D3 overexpression was related to larger tumour size (>5 cm; p < 0.0001) and high tumour proliferation (>10%; p = 0.025). Mean cyclin D3 expression increased with 2004 WHO grading categories in stage Ta (p = 0.035, ANOVA) and stage T1 (p = 0.047, t test) tumours. Cyclin D3 was not related to other clinicopathological parameters, G1-S phase modulators, or 9p21 LOH. Cox's multivariate analysis selected cyclin D3 as an independent predictor of progression-free survival (p = 0.0012, relative risk (RR) = 5.2366) together with tumour size (p = 0.0115, RR = 4.4442) and cyclin D1 (p = 0.0065, RR = 3.3023). Cyclin D3 expression had the highest risk ratio. Our results suggest that expression of cyclin D3 is relevant to the progression-free survival of patients with Ta/T1 bladder carcinomas.