Peroxisome proliferator-activated receptor gamma induces pancreatic cancer cell apoptosis

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) decreases the growth of certain cancer cells. In the present study, we found that six different human pancreatic cancer cell lines (AsPC-1, BxPC-3, Capan-2, HPAF-II, MIA PaCa-2, and PANC-1) expressed PPAR-gamma m-RNA and synthesized the protein. The endogenous and exogenous PPAR-gamma ligands 15-deoxy-d12,14-prostaglandin J(2) (15-PGJ(2)) and ciglitazone decreased cell number, cell viability, and increased floating/attached ratio, in a time- and dose-dependent fashion. 15-PGJ(2) increased intracellular nucleosome concentration after 6 h, but did not increase caspase-3 activity even after 96 h. Combined treatment with both 15-PGJ(2) and the caspase-3 inhibitor DEVD-CHO had no effect on cell viability, but the general caspase inhibitor ZVAD-FMK reduced 15-PGJ(2)-induced apoptosis. We concluded that the six human pancreatic cancer cells tested all expressed PPAR-gamma receptor, and treatment with PPAR-gamma agonists decreased cell viability and growth in a time- and dose-dependent manner. These effects were partially mediated by induction of caspase-3 independent apoptosis.     

Neurotensin Stimulates Inositol Phospholipid Metabolism and Calcium Mobilization in Murine Neuroblastoma Clone N1E-115

Murine neuroblastoma cells (clone N1E-115) possess neurotensin receptors that mediate cyclic GMP synthesis. Because of the hypothesized relationship between phospholipid metabolism, intracellular Ca2+, and cyclic GMP synthesis, we determined with these cells the effects of neurotensin on 32P labeling of phospholipids, release of inositol phosphates, and intracellular Ca2+ (as determined with the use of Quin-2, a fluorescent probe sensitive to free Ca2+ levels). Neurotensin stimulated incorporation of 32P into phospholipids, especially phosphatidylinositol and phosphatidate. Neurotensin also stimulated the release of [3H]inositol phosphates with an EC50 of about 1 nM. Mean basal Ca2+ concentration in these cells was 134 nM and this level was increased in a rapid and dose-dependent manner by neurotensin, with an EC50 of 4 nM. Since the EC50 for neurotensin in stimulating cyclic GMP synthesis is 1.5 nM and the KD for binding of [3H]neurotensin at 0 degrees C is 11 nM, all these different effects appear to be shared proximal consequences of neurotensin receptor activation.     

Flt3 mutation activates p21WAF1/CIP1 gene expression through the action of STAT5

Metastin, a post-translationally modified variant of KiSS1, was recently identified as an endogenous peptide agonist for a novel G-protein coupled receptor, hOT7T175 (AXOR12, GPR54). In this study, we analyzed the role of KiSS1 and hOT7T175 in both pancreatic cancer tissues and pancreatic cancer cell lines. Furthermore, we synthesized novel short variant forms of metastin and tested the inhibitory effect of those variants on in vitro cell functions that are relevant to metastasis. Pancreatic cancer tissues showed significantly lower expression of KiSS1 mRNA than normal tissues (p=0.018), while cancer tissues showed significantly higher expression of hOT7T175 mRNA than normal pancreatic tissues (p=0.027). In human pancreatic cancer cell lines, KiSS1 mRNA was highly expressed in 2 out of 6 pancreatic cancer cell lines, while hOT7T175 mRNA was expressed in all cell lines at various degrees. PANC-1 cells showed the highest expression of hOT7T175. Exogenous metastin did not suppress cell proliferation but significantly reduced the in vitro migration of PANC-1 cells (p<0.01). Metastin induced activation of ERK1 in PANC-1 and AsPC-1 cells. Finally, we synthesized 3 novel short variant forms of metastin, FM053a2TFA, FM059a2TFA, and FM052a4TFA. These metastin variants significantly suppressed the migration of PANC-1 cells and activated ERK1. These data suggest that the metastin receptor, hOT7T175, is one of the promising targets for suppression of metastasis, and that small metastin variants could be an anti-metastatic agent to pancreatic cancer.     

Inhibition of Cell Proliferation and Growth of Pancreatic Cancer by Silencing of Carbohydrate Sulfotransferase 15 In Vitro and in a Xenograft Model

Chondroitin sulfate E (CS-E), a highly sulfated glycosaminoglycan, is known to promote tumor invasion and metastasis. Because the presence of CS-E is detected in both tumor and stromal cells in pancreatic ductal adenocarcinoma (PDAC), multistage involvement of CS-E in the development of PDAC has been considered. However, its involvement in the early stage of PDAC progression is still not fully understood. In this study, to clarify the direct role of CS-E in tumor, but not stromal, cells of PDAC, we focused on carbohydrate sulfotransferase 15 (CHST15), a specific enzyme that biosynthesizes CS-E, and investigated the effects of the CHST15 siRNA on tumor cell proliferation in vitro and growth in vivo. CHST15 mRNA is highly expressed in the human pancreatic cancer cell lines PANC-1, MIA PaCa-2, Capan-1 and Capan-2. CHST15 siRNA significantly inhibited the expression of CHST15 mRNA in these four cells in vitro. Silencing of the CHST15 gene in the cells was associated with significant reduction of proliferation and up-regulation of the cell cycle inhibitor-related gene p21^CIP1/WAF1. In a subcutaneous xenograft tumor model of PANC-1 in nude mice, a single intratumoral injection of CHST15 siRNA almost completely suppressed tumor growth. Reduced CHST15 protein signals associated with tumor necrosis were observed with the treatment with CHST15 siRNA. These results provide evidence of the direct action of CHST15 on the proliferation of pancreatic tumor cells partly through the p21^CIP1/WAF1 pathway. Thus, CHST15-CS-E axis-mediated tumor cell proliferation could be a novel therapeutic target in the early stage of PDAC progression.     

(N-stearyl, norleucine17) VIP hybrid inhibits the growth of pancreatic cancer cell lines

The effects vasoactive intestinal peptide (VIP) antagonists were investigated on pancreatic cancer cell lines. (N-Stearyl, Norleucine17) VIP hybrid ((SN)VIPhyb) inhibited 125I-VIP binding to human Capan-2 cells with an IC50 value of 0.01 microM whereas VIP hybrid had an IC50 value of 0.2 microM. By RT-PCR and Northern blot, VPAC1 receptor mRNA was detected in CAPAN-2 cells. One microM (SN)VIPhyb and 10 microM VIPhyb inhibited the ability of 30 nM VIP to elevate cyclic AMP and increase c-fos mRNA. (SN)VIPhyb, 1 microM inhibited the clonal growth of CAPAN-2 cells in vitro. In vivo, (SN)VIPhyb (10 microg/day s.c.) inhibited CAPAN-2 xenograft growth in nude mice. These results indicate that (SN)VIPhyb is a pancreatic cancer VPAC receptor antagonist.     

Effects of cholecystokinin on cytosolic calcium in human pancreatic cancer cells.

Cholecystokinin (CCK) has been shown to increase cytosolic calcium and stimulate enzyme release from pancreatic acinar cells and a rat acinar cell line, AR42J. CCK is also trophic to normal pancreas and pancreatic cancer; however, the cellular mechanisms which regulate CCK-stimulated growth are unknown. The effect of CCK on intracellular calcium was evaluated in four human pancreatic cancer cell lines known to grow in response to CCK but not secrete enzymes (SW-1990, MIA PaCa-2, BXPC-3 and PANC-1) and a rat acinar cell line (AR42J) shown to secrete enzymes but not grow with CCK. By using single cell fluorescence microscopy in fura-2 loaded cells, intracellular calcium [Ca2+]i was measured. After obtaining baseline fluorescent cell images, synthetic CCK-octapeptide (CCK8) was added to the cells and images of cell fluorescence captured. [Ca2+]i of the rat acinar cells increased (603%) over the baseline within the first minute after the addition of CCK (4.10(-13) M to 4.10(-10) M) in 77% of cells tested. In contrast [Ca2+]i failed to significantly change in the human cancer cells treated with CCK. To further localize the defect in hormone signal transduction in cancer cells, cells were suspended in low calcium media and the plasma membranes were selectively permeabilized with digitonin. Media free calcium concentration was continuously monitored by fura-2 fluorescence. Addition of inositol 1,4,5-trisphosphate (IP3) resulted in a marked increase in medium calcium concentration indicating IP3 was capable of releasing calcium from intracellular stores in both the AR42J rat acinar cell line and in the human pancreas cancer cell lines. In conclusion, CCK does not increase cytosolic calcium in human pancreatic cancer cells in contrast to rat acinar cells although all contain IP3-sensitive intracellular Ca2+ pools. Our results suggest that growth promoting and secretory effects of CCK on pancreatic cells may occur via two independent signalling pathways.     

Crosstalk between insulin receptor and G protein-coupled receptor signaling systems leads to Ca oscillations in pancreatic cancer PANC-1 cells

We examined crosstalk between the insulin receptor and G protein-coupled receptor (GPCR) signaling pathways in individual human pancreatic cancer PANC-1 cells. Treatment of cells with insulin (10 ng/ml) for 5 min markedly enhanced the proportion of cells that display an increase in intracellular [Ca²⁺] induced by picomolar concentrations of the GPCR agonist neurotensin. Interestingly, insulin increased the proportion of a subpopulation of cells that exhibit intracellular [Ca²⁺] oscillations in response to neurotensin at concentrations as low as 50-200 pM. Insulin enhanced GPCR-induced Ca²⁺ signaling in a time- and dose-dependent manner; a marked potentiation was obtained after an exposure to a concentration of 10 ng/ml for 5 min. Treatment with the mTORC1 inhibitor rapamycin abrogated the increase in GPCR-induced [Ca²⁺]_i oscillations produced by insulin. Our results identify a novel aspect in the crosstalk between insulin receptor and GPCR signaling systems in pancreatic cancer cells, namely that insulin increases the number of [Ca²⁺]_i oscillating cells induced by physiological concentrations of GPCR agonists through an mTORC1-dependent pathway.     

Neurotensin and EGF induce synergistic stimulation of DNA synthesis by increasing the duration of ERK signaling in ductal pancreatic cancer cells

Neurotensin (NT) and epidermal growth factor (EGF) induced rapid extracellular-regulated protein kinase (ERK) activation through different signaling pathways in the K-Ras mutated human pancreatic carcinoma cell lines PANC-1 and MIA PaCa-2. NT stimulated ERK activation via a protein kinase C (PKC)-dependent (but EGF receptor-independent) pathway in PANC-1 and MIA PaCa-2 cells, whereas EGF promoted ERK activation through a PKC-independent pathway in these cells. Concomitant stimulation of these cells with NT and EGF induced a striking increase in the duration of ERK pathway activation as compared with that obtained in cells treated with each agonist alone. Stimulation with NT + EGF promoted synergistic stimulation of DNA synthesis and anchorage-independent growth. Addition of the MEK inhibitor U0126, either prior to stimulation with NT + EGF or 2 h after stimulation with NT + EGF prevented the synergistic increase in DNA synthesis and suppressed the sustained phase of ERK activation. Furthermore, treatment with the selective PKC inhibitor GF-1 converted the sustained ERK activation in response to NT and EGF into a transient signal and also abrogated the synergistic increase in DNA synthesis. Collectively, our results suggest that the sustained phase of ERK signaling mediates the synergistic effects of NT and EGF on DNA synthesis in pancreatic cancer cells.     

Identification of glycation at the N-terminus of albumin by gas chromatography-mass spectrometry.

It has previously been shown that neurotensin binds to high-affinity receptors in the adenocarcinoma HT29 cell line, and that receptor occupancy leads to inositol phosphate formation. The present study was designed to investigate further the effects of neurotensin on calcium mobilization and protein kinase C (PKC) activation in HT29 cells, and to assess the role of GTP-binding proteins (G-proteins) in the neurotensin response. Direct measurements of cytosolic Ca2+ variations using the fluorescent indicator quin 2 showed that neurotensin (0.1-1 microM) elicited Ca2+ transients in HT29 cells. These transients occurred after the neurotensin-stimulated formation of Ins(1,4,5)P3, as measured by means of a specific radioreceptor assay. In addition, the peptide induced a decrease in the 45Ca2+ content of cells previously equilibrated with this isotope. The peptide effect was rapid, long-lasting and concentration-dependent, with an EC50 of 2 nM. Phorbol 12-myristate 13-acetate (PMA) inhibited by 50% the neurotensin effects on both intracellular Ca2+ and inositol phosphate levels. The inhibition by PMA was abolished in PKC-depleted cells. Pertussis toxin had no effect on either the Ca2+ or inositol phosphate responses to neurotensin. Epidermal growth factor (EGF) receptors which are present in HT29 cells have been shown to be down-regulated through phosphorylation by PKC in a variety of systems. Here, PMA markedly (70-80%) inhibited EGF binding to HT29 cells. Scatchard analysis revealed that PMA abolished the high-affinity component of EGF binding, an effect that was totally reversed in PKC-depleted cells. In contrast, neurotensin slightly (10-20%) inhibited EGF binding to HT29 cells, and its effect was only partly reversed by PKC depletion. Neurotensin had no detectable effect on sn-1,2-diacylglycerol levels in HT29 cells, as measured by a specific and sensitive enzymic assay. In membranes prepared from HT29 cells, monoiodo[125I-Tyr3]neurotensin bound to a single population of receptors with a dissociation constant of 0.27 nM. Sodium and GTP inhibited neurotensin binding in a concentration-dependent manner. Maximal inhibition reached 80% with Na+ and 35% with GTP.IC50 values were 20 mM and 0.2 microM for Na+ and GTP respectively. Li+ and K+ were less effective than Na+ and the effects of GTP were shared by GDP and guanosine-5'-[beta gamma- imido]triphosphate but not by ATP. Scatchard analysis of binding data indicated that Na+ and GTP converted the high-affinity neurotensin-binding sites into lower affinity binding sites. The properties of the effects of Na+ and GTP on neurotensin-receptor interactions are characteristic of those receptors which interact with G-proteins.(ABSTRACT TRUNCATED AT 400 WORDS)     

An intermediate-conductance Ca2+-activated K+ channel is important for secretion in pancreatic duct cells

Potassium channels play a vital role in maintaining the membrane potential and the driving force for anion secretion in epithelia. In pancreatic ducts, which secrete bicarbonate-rich fluid, the identity of K(+) channels has not been extensively investigated. In this study, we investigated the molecular basis of functional K(+) channels in rodent and human pancreatic ducts (Capan-1, PANC-1, and CFPAC-1) using molecular and electrophysiological techniques. RT-PCR analysis revealed mRNAs for KCNQ1, KCNH2, KCNH5, KCNT1, and KCNT2, as well as KCNN4 coding for the following channels: KVLQT1; HERG; EAG2; Slack; Slick; and an intermediate-conductance Ca(2+)-activated K(+) (IK) channel (K(Ca)3.1). The following functional studies were focused on the IK channel. 5,6-Dichloro-1-ethyl-1,3-dihydro-2H-benzimidazole-2-one (DC-EBIO), an activator of IK channel, increased equivalent short-circuit current (I(sc)) in Capan-1 monolayer, consistent with a secretory response. Clotrimazole, a blocker of IK channel, inhibited I(sc). IK channel blockers depolarized the membrane potential of cells in microperfused ducts dissected from rodent pancreas. Cell-attached patch-clamp single-channel recordings revealed IK channels with an average conductance of 80 pS in freshly isolated rodent duct cells. These results indicated that the IK channels may, at least in part, be involved in setting the resting membrane potential. Furthermore, the IK channels are involved in anion and potassium transport in stimulated pancreatic ducts.     

Plasminogen-induced aggregation of PANC-1 cells requires conversion to plasmin and is inhibited by endogenous plasminogen activator inhibitor-1

PANC-1 cells express proteinase-activated receptors (PARs)-1, -2, and respond to their activation by transient elevation of cytosolic [Ca(2+)] and accelerated aggregation (Wei et al., 2006, J Cell Physiol 206:322-328). We studied the effect of plasminogen (PGN), an inactive precursor of the PAR-1-activating protease, plasmin (PN) on aggregation of pancreatic adenocarcinoma (PDAC) cells. A single dose of PGN time- and dose-dependently promoted PANC-1 cells aggregation in serum-free medium, while PN did not. PANC-1 cells express urokinase plasminogen activator (uPA), which continuously converted PGN to PN. This activity and PGN-induced aggregation were inhibited by the uPA inhibitor amiloride. PGN-induced aggregation was also inhibited by alpha-antiplasmin and by the PN inhibitor epsilon-aminocaproic acid (EACA). Direct assay of uPA activity revealed very low rate, markedly enhanced in the presence of PGN. Moreover, in PGN activator inhibitor 1-deficient PANC-1 cells, uPA activity and PGN-induced aggregation were markedly potentiated. Two additional human PDAC cell lines, MiaPaCa and Colo347, were assayed for PGN-induced aggregation. Both cell lines responded by aggregation and exhibited PGN-enhanced uPA activity. We hypothesized that the continuous conversion of PGN to PN by endogenous uPA is limited by PN's degradation and negatively controlled by endogenously produced PAI-1. Indeed, we found that PANC-1 cells inactivate PN with t1/2 of approximately 7 h, while the continuous addition of PN promoted aggregation. Our data suggest that PANC-1 cells possess intrinsic, PAI-1-sensitive mechanism for promotion of aggregation and differentiation by prolonged exposure to PGN and, possibly, additional precursors of PARs agonists.     

Berberine diminishes side population and down-regulates stem cell-associated genes in the pancreatic cancer cell lines PANC-1 and MIA PaCa-2

Cancer stem cells play an important role in metastasis and the relapse of drug resistant cancers. Side-population (SP) cells are capable of effluxing Hoechst 33342 dye and are referred to as cancer stem cells. We investigated the effect of berberine on pancreatic cancer stem cells of PANC-1 and MIA PaCa-2. For both cell lines, the proportions of SP cells in the presence of berberine were investigated and compared to the proportions in the presence of gemcitabine, a standard pancreatic anti-cancer drug. The proportions of SP cells in the PANC-1 and MIA PaCa-2 cell lines were about 9 and <0.1 %, respectively. After berberine and gemcitabine treatments, the SP cell proportion of PANC-1 decreased to 5.7 ± 2.0 and 6.8 ± 0.8 %, respectively, which compares to the control proportion of (9.7 ± 1.7). After berberine and gemcitabine treatment of PANC-1, of the four stem cell-associated genes (SOX2, POU5F1, NANOG, and NOTCH1), all but NOTCH1 were down-regulated. Unfortunately, the effect of berberine and gemcitabine treatments on MIA PaCa-2 SP cells could not be clearly observed because SP cells represented only a very small proportion of MIA PaCa-2 cells. However, SOX2, POU5F1, and NANOG genes were shown to be effectively down-regulated in the MIA PaCa-2 cell line as a whole. Taken together, these results indicate that berberine is as effective at targeting pancreatic cancer cell lines as gemcitabine. Therefore, we believe that POU5F1, SOX2, and NANOG can serve as potential markers, and berberine may be an effective anti-cancer agent when targeting human pancreatic cancer cells and/or their cancer stem cells.     

Melanin has a role in Ca2+ homeostasis in human melanocytes

We have examined whether melanin affects Ca2+ homeostasis in cultured normal human melanocytes. Intracellular Ca2+ concentrations ([Ca2+]i), were measured in four Caucasian and in three Negroid melanocyte cultures. Under resting conditions [Ca2+]i was around 100 nM in all cultures, but differences between cells within cultures were observed. All cultures responded to endothelin-1 (ET-1) with increases in [Ca2+]i and there were no differences between Caucasian and Negroid cultures. However, large differences in responses between cells within cultures were observed, indicating that melanocyte cultures are very heterogeneous. The addition of 2.5 mM CaCl2 to melanocytes kept in Ca2+-free medium resulted in rapid and transient increases in [Ca2+]i of up to 1500 nM. These increases were on average more than two times smaller in melanocyte cultures established from Negroid donors compared with Caucasian cultures. In addition, well melanized Caucasian melanocytes, cultured in the presence of 400 microM tyrosine and 10 mM NH4Cl, showed a reduced increase in cytoplasmic Ca2+ concentration upon the addition of extracellular Ca2+. The difference in maintaining Ca2+ homeostasis between poorly and well melanized melanocytes may be the result of the clearance of cytoplasmic Ca2+ into melanosomes and the greater capacity for this in the more pigmented melanocytes.     

DNA-PKcs is important for Akt activation and gemcitabine resistance in PANC-1 pancreatic cancer cells

Pancreatic cancer is one of the most aggressive human malignancies with extremely poor prognosis. The moderate activity of the current standard gemcitabine and gemcitabine-based regimens was due to pre-existing or acquired chemo-resistance of pancreatic cancer cells. In this study, we explored the potential role of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) in gemcitabine resistance, and studied the underlying mechanisms. We found that NU-7026 and NU-7441, two DNA-PKcs inhibitors, enhanced gemcitabine-induced cytotoxicity and apoptosis in PANC-1 pancreatic cancer cells. Meanwhile, PANC-1 cells with siRNA-knockdown of DNA-PKcs were more sensitive to gemcitabine than control PANC-1 cells. Through the co-immunoprecipitation (Co-IP) assay, we found that DNA-PKcs formed a complex with SIN1, the latter is an indispensable component of mammalian target of rapamycin (mTOR) complex 2 (mTORC2). DNA-PKcs–SIN1 complexation was required for Akt activation in PANC-1 cells, while inhibition of this complex by siRNA knockdown of DNA-PKcs/SIN1, or by DNA-PKcs inhibitors, prevented Akt phosphorylation in PANC-1 cells. Further, SIN1 siRNA-knockdown also facilitated gemcitabine-induced apoptosis in PANC-1 cells. Finally, DNA-PKcs and p-Akt expression was significantly higher in human pancreatic cancer tissues than surrounding normal tissues. Together, these results show that DNA-PKcs is important for Akt activation and gemcitabine resistance in PANC-1 pancreatic cancer cells.     

Enhancement in alpha-tocopherol succinate-induced apoptosis by all-trans-retinoic acid in primary leukemic cells: role of antioxidant defense, Bax and c-myc

GPR56 is an atypical G protein-coupled receptor (GPCR) with an unusually large N-terminal extracellular region, which contains a long Ser/Thr-rich region forming a mucin-like stalk and due to this feature, GPR56 is thought to be an adhesion GPCR. Recent studies demonstrate that GPR56 plays a role in brain development and tumorigenesis. Here, we report that human GPR56 undergoes GPS (GPCR proteolytic site)-mediated protein cleavage to generate its extracellular domain as an N-terminal fragment (GPR56-N). We also show that GPR56-N is highly glycosylated with N-linked carbohydrate chains. Mouse Gpr56 is ubiquitously expressed in various tissues, with high levels in kidney and pancreas. GPR56 mRNA is detected in diverse human cancer cells including pancreatic cancer cells PANC-1, Capan-1, and MiaCaPa-2. Interestingly, GPR56 protein is either negligible or undetectable in these pancreatic cancer cells, despite the fact that high levels of GPR56 mRNA are observed. Moreover, we have found that protein levels of GPR56 in pancreatic cancer cells were not affected when cells were treated with a proteasome inhibitor MG132. Taken together, these results define the biochemical properties of GPR56 protein, and suggest that the expression of GPR56 protein is suppressed in human pancreatic cancer cells. Yue Huang and Jun Fan contributed equally to this work.     

HLA-A0201 positive pancreatic cell lines: new findings and discrepancies

Pancreatic cancer is being pursued as an immunotherapy target using antigen-specific vaccine approaches activating CD8(+) CTL and CD4(+) T-helper cells. CD8(+) CTL exert their anti-tumor effects in an HLA-restricted manner and only tumor cells carrying a matched HLA class I sub-type are targets for antigen-specific CTL. In the process of characterizing CD8(+) T cell responses against pancreatic cancer, we screened a number of human pancreatic tumor cell lines for HLA-A0201 positive (HLA-A2(+)) cell lines to be used in the evaluation of CTL function. This analysis revealed some new findings and discrepancies in the literature on the HLA sub-type of some commonly used pancreatic cell lines. We found that Capan-1 cells, originally reported to be HLA-A0201(+), actually only express HLA-A010101 and HLA-A300101 and were targets for HLA-A0201-restricted CTL only after transduction with an HLA-A0201-expressing lentivirus. Panc-1 cells were found to be HLA-A0201 positive, in agreement with published reports, while CF-Pac-1 cells were found to express both HLA-A020101 and HLA-A030101. We also found a normal human pancreatic ductal epithelial cell line, HPDE, to be HLA-A0201 positive. Our findings were verified with two different sequence-based typing methods, antibody staining followed by flow cytometry analysis, and functional analysis using an HLA-A0201-restricted peptide-specific T cell response.