Protein kinase C and adenylate cyclase as targets for growth inhibition of human gastric cancer cells

Therapeutic opportunities in colon cancer: Focus on phosphodiesterase inhibitors

Despite novel technologies, colon cancer remains undiagnosed and 25% of patients are diagnosed with metastatic colon cancer. Resistant to chemotherapeutic agents is one of the major problems associated with treating colon cancer which creates the need to develop novel agents targeting towards newer targets. A phosphodiesterase is a group of isoenzyme, which, hydrolyze cyclic nucleotides and thereby lowers intracellular levels of cAMP and cGMP leading to tumorigenic effects. Many in vitro and in vivo studies have confirmed increased PDE expression in different types of cancers including colon cancer. cAMP-specific PDE inhibitors increase intracellular cAMP that leads to activation of effector molecules-cAMP-dependent protein kinase A, exchange protein activated by cAMP and cAMP gated ion channels. These molecules regulate cellular responses and exert its anticancer role through different mechanisms including apoptosis, inhibition of angiogenesis, upregulating tumor suppressor genes and suppressing oncogenes. On the other hand, cGMP specific PDE inhibitors exhibit anticancer effects through cGMP dependent protein kinase and cGMP dependent cation channels. Elevation in cGMP works through activation of caspases, suppression of Wnt/b-catenin pathway and TCF transcription leading to inhibition of CDK and survivin. These studies point out towards the fact that PDE inhibition is associated with anti-proliferative, anti-apoptotic and anti-angiogenic pathways involved in its anticancer effects in colon cancer. Thus, inhibition of PDE enzymes can be used as a novel approach to treat colon cancer. This review will focus on cAMP and cGMP signaling pathways leading to tumorigenesis and the use of PDE inhibitors in colon cancer.

Forskolin exerts anticancer roles in non-Hodgkin's lymphomas via regulating Axin/β-catenin signaling pathway

Background

Non-Hodgkin’s lymphomas (NHLs) account for 85% of lymphomas, which are characterized by high-degree malignancy, rapid progress, and even invasion into central nervous system in pediatric patients. Although the cure rate of pediatric NHL has improved, some patients have still underwent recurrence or death. This study focuses on the effects and mechanism of forskolin on the progression of NHL, aiming to find efficient therapy methods for pediatric NHL.

Methods

MTT, flow cytometry and mice tumor bearing experiments were used to evaluate the effects of forskolin on NHL cell proliferation, apoptosis and tumorigenesis. Western blotting and RT-PCR assays were used to detect protein and mRNA expression. Immunohistochemistry technology was recruited to analyze Ki-67 expression in tumor tissues.

Results

Forskolin significantly increased the expression of cleaved caspase-3/9 in both NHL Toledo and NK-92 cell lines, and inhibited cell growth. Besides, forskolin obviously reduced the expression of β-catenin protein, promoted its ubiquitination, enhanced its transportation from nuclear to cytoplasm, as well as decreased the expression of its downstream oncogenes c-myc and cyclin D1 through upregulating Axin expression and stability and inhibiting Axin ubiquitination. Moreover, forskolin enhanced the effects of SP600125, an inhibitor of c-Jun N-terminal kinase signaling on cell apoptosis promotion and tumorigenesis inhibition via Axin-induced β-catenin signaling repression.

Conclusion

The current study clarifies that forskolin can inhibit the progression of NHL through Axin-mediated inhibition of β-catenin signaling. Moreover, forskolin improves the effects of SP600125 on cell apoptosis enhancement and tumorigenesis inhibition of NHL cells. These findings provide theoretical foundation of serving forskolin as a new effective therapeutic drug for pediatric NHL.

The Natural cAMP Elevating Compound Forskolin in Cancer Therapy: Is It Time?

Cancer is a major public health problem and the second leading cause of mortality around the world. Although continuous advances in the science of oncology and cancer research are now leading to improved outcomes for many cancer patients, novel cancer treatment options are strongly demanded. Naturally occurring compounds from a variety of vegetables, fruits, and medicinal plants have been shown to exhibit various anticancer properties in a number of in vitro and in vivo studies and represent an attractive research area for the development of new therapeutic strategies to fight cancer. Forskolin is a diterpene produced by the roots of the Indian plant Coleus forskohlii. The natural compound forskolin has been used for centuries in traditional medicine and its safety has also been documented in conventional modern medicine. Forskolin directly activates the adenylate cyclase enzyme, that generates cAMP from ATP, thus, raising intracellular cAMP levels. Notably, cAMP signaling, through the PKA-dependent and/or -independent pathways, is very relevant to cancer and its targeting has shown a number of antitumor effects, including the induction of mesenchymal-to-epithelial transition, inhibition of cell growth and migration and enhancement of sensitivity to conventional antitumor drugs in cancer cells. Here, we describe some features of cAMP signaling that are relevant to cancer biology and address the state of the art concerning the natural cAMP elevating compound forskolin and its perspectives as an effective anticancer agent. J. Cell. Physiol. 232: 922-927, 2017. © 2016 Wiley Periodicals, Inc.

Biphasic regulation by bile acids of dermal fibroblast proliferation through regulation of cAMP production and COX-2 expression level

We have previously reported that the bile acids chenodeoxycholate (CDCA) and ursodeoxycholate (UDCA) decreased PGE1-induced cAMP production in a time- and dose-dependent manner not only in hepatocytes but also in nonhepatic cells, including dermal fibroblasts. In the present study, we investigated the physiological relevance of this cAMP modulatory action of bile acids. PGE1 induced cAMP production in a time- and dose-dependent manner. Moreover, PGE1 (1 microM), forskolin (1-10 microM), and the membrane-permeable cAMP analog CPT-cAMP (0.1-10 microM) decreased dermal fibroblast proliferation in a dose-dependent manner with a maximum inhibition of approximately 80%. CDCA alone had no significant effect on cell proliferation at a concentration up to 25 microM. However, CDCA significantly reduced PGE1-induced cAMP production by 80-90% with an EC(50) of approximately 20 microM. Furthermore, at concentrations < or =25 microM, CDCA significantly attenuated the PGE-1-induced decreased cell proliferation. However, at concentrations of 50 microM and above, while still able to almost completely inhibit PGE-1-induced cAMP production, CDCA, at least in part through an increased cyclooxygenase-2 (COX-2) expression level and PGE2 synthesis, produced a direct and significant decrease in cell proliferation. Indeed, the CDCA effect was partially blocked by approximately 50-70% by both indomethacin and dexamethasone. In addition, overexpression of COX-2 cDNA wild type resulted in an increased efficacy of CDCA to block cell proliferation. The effects of CDCA on both cAMP production and cell proliferation were similar to those of UDCA and under the same conditions cholate had no effect. Results of the present study underline pathophysiological consequences of cholestatic hepatobiliary disorders, in which cells outside of the enterohepatic circulation can be exposed to elevated bile acid concentrations. Under these conditions, low bile acid concentrations can attenuate the negative hormonal control on cell proliferation, resulting in the stimulation of cell growth, while at high concentrations these bile acids provide for a profound and prolonged inhibition of cell proliferation.

The cross talk between protein kinase A- and RhoA-mediated signaling in cancer cells

The cross talk between cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) and RhoA-mediated signal transductions and the effect of this cross talk on biologic features of human prostate and gastric cancer cells were investigated. In the human gastric cancer cell line, SGC-7901, lysophosphatidic acid (LPA) increased RhoA activity in a dose-dependent manner. The cellular permeable cAMP analog, 8-chlorophenylthio-cAMP (CPT-cAMP), inhibited the LPA-induced RhoA activation and caused phosphorylation of RhoA at serine(188). Immunofluorescence microscopy, Western blotting, and green fluorescent protein (GFP)-tagged RhoA location assay in live cells revealed that RhoA was distributed in both the cytoplasm and nucleus of SGC-7901 cells. Treatment with LPA and/or CPT-cAMP did not induce obvious translocation of RhoA in the cells. The LPA treatment caused formation of F-actin in SGC-7901 cells, and CPT-cAMP inhibited the formation. In a modified Boyden chamber assay, LPA stimulated the migration of SGC-7901 cells, and CPT-cAMP dose-dependently inhibited the stimulating effect of LPA. In soft agar assay, LPA stimulated early proliferation of SGC-7901 cells, and CPT-cAMP significantly inhibited the growth of LPA-stimulated cells. In the prostate cancer cell line, PC-3, LPA caused morphologic changes from polygonal to round, and transfection with plasmid DNA encoding constitutively active RhoA(63L) caused a similar change. Treatment with CPT-cAMP inhibited the changes in both cases. However, in PC-3 cells transfected with a plasmid encoding mutant RhoA188A, LPA induced rounding, but CPT-cAMP could not prevent the change. Results of this experiment indicated that cAMP/PKA inhibited RhoA activation, and serine188 phosphorylation on RhoA was necessary for PKA to exert its inhibitory effect on RhoA activation. The cross talk between cAMP/PKA and RhoA-mediated signal transductions had significant affect on biologic features of gastric and prostate cancer cells, such as morphologic and cytoskeletal change, migration, and anchorage-independent growth. The results may be helpful in implementing novel therapeutic strategies for invasive and metastatic prostate and gastric cancers.

Involvement of PKC betaII in anti-proliferating action of a new antitumor compound gnidimacrin

Daphnane-type diterpene gnidimacrin (NSC 252940) shows significant antitumor activity against murine tumors and human tumor cell lines. This compound binds to and directly activates protein kinase C (PKC), arresting the cell cycle at the G(1) phase through inhibition of cdk2 activity in human K562 leukemia cells. In our study, we examined whether cellular PKC is involved in the antiproliferating effect of gnidimacrin. In a 24-hr exposure of K562 cells to high concentrations of bryostatin 1 (0.11-3.3 microM), both expression of PKC alpha and PKC betaII was downregulated, and thereafter these cells became resistant to gnidimacrin in response to the degree of PKC downregulation. In addition, PKC alpha and PKC betaII genes were transfected to gnidimacrin-resistant human hepatoma HLE cells that demonstrated positive expression of PKC alpha and negative expression of PKC betaII. PKC betaII gene-transfected cells became sensitive to gnidimacrin in relation to the degree of PKC betaII expression. The most sensitive clone to show 0.001 microg/mL (1.2 nM) as IC(50) in a continuous 4-day exposure was obtained. While PKC alpha gene-transfected cells exhibited an increase in PKC alpha expression and became sensitive to gnidimacrin, sensitivity was one-hundredth of that in PKC betaIotaIota gene-transfected cells. These results suggest that PKC, in particular PKC betaIotaIota, is necessary in the antitumor effect of gnidimacrin.

Mechanism of antitumor action of PKC activator, gnidimacrin

Daphnane-type diterpene gnidimacrin isolated from the Chinese plant Stellera chamaejasme L. is an antitumor agent that activates protein kinase C (PKC). The mechanism of antitumor action of gnidimacrin and the possible involvement of PKC were examined using sensitive K562 and refractory HLE cells. Gnidimacrin did bind to K562 cells 3 times more than to HLE cells. Immunoblot analyses revealed pronounced PKC betaII expression in gnidimacrin sensitive cell lines including K562 cells, while refractory HLE cells strongly expressed PKC alpha, but not PKC betaII. In a 24-hr exposure of K562 cells to gnidimacrin, G1 phase arrest and inhibition of cdk2 kinase activity was found at growth-inhibitory concentration (0.0005 microg/ml). Complete inhibition of cdk2 activity and maximum G1 phase arrest were observed at 0.005 microg/ml, however, these biological effects were reduced at 0.05 microg/ml (260 times the 50% inhibitory concentration). Cellular PKC after a 24-hr exposure was examined by immunoblot analysis and specific binding of [3H]phorbol-12,13-dibutyrate as a ligand of PKC. Expression and the amount of functional PKC of K562 cells were not changed at 0.002 microg/ml, but down-regulated to less than 1/10th of the control at 0.05 microg/ml. The reduction of biological effects at 0.05 microg/ml is most likely due to PKC down-regulation. Our results suggest that PKC (particularly betaII) is one of the major determinants of the ability of cells to respond to gnidimacrin and that the antitumor action might be associated with cell-cycle regulation through suppression of cdk2 activity.

Radiological retrospective study of gastric cancer in humans: two patterns of development in elevated type gastric cancer

A better understanding of the process of gastric cancer development would undoubtedly be helpful in diagnosis and treatment. However, there is little literature available concerning the natural history of elevated type gastric cancer in humans and this disease had not been systematically investigated. In this study the natural history of elevated type human gastric cancer was retrospectively investigated in 12 radiologically followed-up patients. The cases were divided into two groups according the whether obvious abnormal findings were absent (group A, n = 5) or present (group B, n = 7) at initial examination. Clinico-pathological features, including outcomes and DNA content of the tumours in both groups, were investigated and compared. Although the mean period between the initial and final examinations was significantly shorter in group A (19.6 +/- 11.7 months) than in group B (43.4 +/- 17.3 months), tumour size was significantly larger in group A (5.5 +/- 2.5 cm) than in group B (2.4 +/- 2.5 cm). Furthermore, group A showed deeper neoplastic cell invasion and worse outcomes. The DNA content of two cases in group A and four cases in group B was examined. One case in group A showed and aneuploid pattern, while all of those in group B showed a diploid pattern. These results indicate that the tumours in group A grew much faster than those in group B, which suggests the presence of two different patterns of development in elevated type gastric cancer.

Antitumor activity of daphnane-type diterpene gnidimacrin isolated from Stellera chamaejasme L

The daphnane-type diterpene gnidimacrin, isolated from the root of the Chinese plant, Stellera chamaejasme L., was found to strongly inhibit cell growth of human leukemias, stomach cancers and non-small cell lung cancers in vitro at concentrations of 10(-9) to 10(-10) M. On the other hand, even at 10(-6) to 10(-5) M, the small cell lung cancer cell line H69 and the hepatoma cell line HLE were refractory to gnidimacrin. The agent showed significant antitumor activity against murine leukemias and solid tumors in an in vivo system. In K562, a sensitive human leukemia cell line, gnidimacrin induced blebbing of the cell surface, which was completely inhibited by staurosporine at concentrations above 10(-8) M, and arrested the cell cycle transiently to G2 and finally the G1 phase at growth-inhibitory concentrations. It inhibited phorbol-12,13-dibutyrate(PDBu) binding to K562 cells and directly stimulated protein kinase C (PKC) activity in the cells in a dose-dependent manner (3-100 nM). Although activation of PKC isolated from refractory H69 cells was observed only with 100 nM gnidimacrin, the degree of activation was lower than that produced by 3 nM in K562 cells. Our results suggest that gnidimacrin acts as a PKC activator for tumor cells and that this mechanism may be responsible for its antitumor activity.