cGMP-independent anti-tumour actions of the inhibitor of soluble guanylyl cyclase, ODQ, in prostate cancer cell lines

Background and purpose:

Soluble guanylyl cyclase (sGC) is a receptor for nitric oxide that generates cGMP. This second messenger molecule has established roles in cellular physiology; however, less is known about its effects in tumour cells.

Experimental approach:

The effects of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS2028), both selective sGC inhibitors on proliferation, death and migration were determined in prostate cancer cell lines.

Key results:

Western blot analysis confirmed the presence of α1 and β1 subunits of sGC in LNCaP and PC-3 cells. Sodium nitroprusside (SNP) increased cGMP accumulation in LNCaP and PC-3, but not DU-145 cells. SNP-stimulated cGMP production in LNCaP cells was dose-dependently reduced by ODQ, with more than 90% inhibition being observed at 0.1 μM. ODQ activated caspase-3 in all three cell lines, but not in normal prostate epithelial cells, at concentrations over 10 μM. High concentrations of ODQ also promoted DNA fragmentation and nucleosome accumulation in the cytosol of LNCaP cells. Interestingly, the chemically related inhibitor, NS2028 was without effect on caspase-3. In addition, ODQ inhibited LNCaP, Du145 and PC-3 cell growth. Finally, although fibroblast growth factor-2 did not enhance cGMP levels in LNCaP cells, its ability to stimulate LNCaP motility was abolished by ODQ.

Conclusions and implications:

These observations taken together suggest that the action of ODQ in LNCaP cells did not reflect sGC inhibition. We conclude that ODQ promotes cell death and inhibits growth and migration of prostate cancer cells and that these actions are independent of its effects on GMP levels.     

A pharmacological model reveals biased dependency on PI3K isoforms for tumor cell growth

Aim:

To identify the contribution of individual isoform (α, β, γ, δ) of class I PI3Ks to tumor cell growth for proper use of PI3K inhibitors in cancer therapy.

Methods:

A panel of human rhabdomyosarcoma Rh30 cells stably expressing myristoylation (Myr)-tagged one of class I PI3K p110 subunits was established. PI3K activity was analyzed by measuring phosphorylated Akt with Western blotting, and isoform-specific PI3K activities were validated with PI3K isoform-selective inhibitors. The growth of prostate cancer PC-3 cells and B cell type leukemia Raji cells was determined using SRB assay and CCK-8 assay, respectively.

Results:

The phosphorylation of Akt in Rh30-Myr-p110α, β, γ, δ cells was preferentially inhibited by PI3K isoform-selective inhibitors A66 (PI3Kα), TGX221 (PI3Kβ), AS604850 (PI3Kγ) and CAL-101 (PI3Kδ), respectively. A newly obtained PI3K inhibitor WJD008 (10 μmol/L) completely abrogated Akt phosphorylation by all the isoforms of class I PI3Ks, thus acted as a pan-PI3K inhibitor. In prostate cancer PC-3 cells, the PI3K isoform-selective inhibitors were much less potent than WJD008 in suppression of the proliferation. In B cell type leukemia Raji cells, inhibition of PI3Kδ alone or all the isoforms of class I PI3Ks displayed similar potency against the cell proliferation, whereas selective inhibition of individual PI3Kα/β/γ isoforms resulted in negligible activity.

Conclusion:

Rh30-Myr-p110α, β, γ, δ cells are a useful cell model to identify the selectivity of PI3K inhibitors. Pan-PI3K inhibitors are suitable for treating PC-3 cells, whereas selective PI3Kδ inhibitor is sufficient to block Raji cell growth. The biased dependency on PI3K isoforms for tumor cell growth rationalizes the use of PI3K inhibitors with different selectivity for cancer therapy.     

Characterization of a novel curcumin analog P1 as potent inhibitor of the NF-κB signaling pathway with distinct mechanisms

Aim:

Curcumin has shown promising anticancer activity, which relies on its inhibition on NF-κB pathway. In this study, we characterized the pharmacological profile of a novel curcumin analog P1 and elucidate the related mechanisms.

Methods:

HEK293/NF-κB cells, stably transfected with an NF-κB-responsive luciferase reporter plasmid, were generated for high-throughput screen (HTS). Eight cancer cell lines, including PC3, COLO 205, HeLa cells etc. were tested. Cell viability was assessed using the sulforhodamine B (SRB) assays. Cell apoptosis was evaluated using FACS, immunocytochemistry, and Western blotting. H₂-DCFDA and MitoSOX Red were used to detect cellular and mitochondrial reactive oxygen species (ROS). The mitochondrial function was evaluated using mitochondrial oxygen consumption assay.

Results:

P1, a tropinone curcumin, was found in HTS targeting the NF-κB pathway. Its IC₅₀ value in inhibition of TNF-α-induced NF-κB activation was 0.8 μmol/L, whereas its IC₅₀ values in inhibiting the growth of A549 and HeLa cells were 1.24 and 0.69 μmol/L, respectively, which was 20- to 30-fold more potent than curcumin. The inhibition of P1 on the NF-κB pathway was further addressed in HeLa cells. The compound up to 10 μmol/L did not affect the binding of NF-κB to DNA, but markedly inhibited NF-κB nuclear translocation, IκB degradation and IκB kinase phosphorylation. The compound (1 and 3 μmol/L) concentration-dependently induced ROS generation, whereas curcumin up to 20 μmol/L had no effect. P1-induced ROS generation was mainly localized in mitochondria, and reversed by NAC. Moreover, the compound significantly enhanced TNF-α-induced apoptosis.

Conclusion:

P1 is a novel curcumin analog with potent anticancer activities, which exerts a distinct inhibition on the NF-κB pathway.     

Cyclic bisbibenzyls induce growth arrest and apoptosis of human prostate cancer PC3 cells

Aim:

To investigate the cytotoxic effects of four cyclic bisbibenzyls, Riccardin C (Ric), Pakyonol (Pak), Marchantin M (Mar), and Plagiochin E (Pla) against chemoresistant prostate cancer PC3 cells.

Methods:

Cell growth was assayed by MTT method, and apoptotic related protein Bcl-2 and Bax, poly(ADP-ribose) polymerase (PARP) were examined by Western blotting. Cell cycle and apoptosis of PC3 cells were evaluated with flow cytometry and morphologic examinations.

Results:

The four compounds inhibited proliferation and elicited cell death in a dose- and time-dependent manner with IC₅₀ values of 3.22 μmol/L for Ric, 7.98 μmol/L for Pak, 5.45 μmol/L for Mar, and 5.99 μmol/L for Pla, respectively. Furthermore, exposed to these chemicals caused a decrease in the antiapoptotic protein Bcl-2 and an increase in proapoptotic Bax expression. PARP cleavage and caspase-3 activity were also observed.

Conclusion:

The results suggest that cyclic bisbibenzyls could be used for the development of novel therapeutic chemicals against prostate cancer.     

β-Asarone protects PC12 cells against OGD/R-induced injury via attenuating Beclin-1-dependent autophagy

Aim:

To explore the effects of β-asarone from Acorus Tatarinowii Schott on autophagy in an ischemic stroke model of PC12 cells.

Methods:

The ischemic stroke model of PC12 cells was made by OGD/R (2 h oxygen-glucose deprivation followed by 24 h reperfusion). Drug administration was started 1 h before OGD and last for 3 h. Then the cells were incubated in the drug-free and full culture medium under normoxic conditions for 24 h. After the treatments, Beclin-1, intracellular free calcium concentration ([Ca²⁺]_i) and mitochondrial membrane potential (MMP) were analyzed using flow cytometry. Cell viability was measured using MTT assay. Cell morphology was studied under inverted phase contrast microscope, and autophagosomes were observed under transmission electron microscope.

Results:

Pretreatment with β-asarone (20, 30, or 45 μg/mL) or the calcium channel antagonist nimodipine (10 μmol/L) significantly increased the cell viability and MMP, and decreased Beclin-1 expression and [Ca²⁺]_i in OGD/R-treated PC12 cells. Under inverted phase contrast microscope, pretreatment with β-asarone or nimodipine dramatically increase the number of cells and improved the cellular morphology. Autophagosomes were found in OGD/R-treated PC12 cells as well as in drug plus OGD/R-treated PC12 cells.

Conclusion:

β-Asarone protects PC12 cells against OGD/R-induced injury partly due to attenuating Beclin-1-dependent autophagy caused by decreasing [Ca²⁺]_i and increasing MMP.     

The metabolic enhancer piracetam ameliorates the impairment of mitochondrial function and neurite outgrowth induced by ?-amyloid peptide

Background and purpose:

β-Amyloid peptide (Aβ) is implicated in the pathogenesis of Alzheimer''s disease by initiating a cascade of events from mitochondrial dysfunction to neuronal death. The metabolic enhancer piracetam has been shown to improve mitochondrial dysfunction following brain aging and experimentally induced oxidative stress.

Experimental approach:

We used cell lines (PC12 and HEK cells) and murine dissociated brain cells. The protective effects of piracetam in vitro and ex vivo on Aβ-induced impairment of mitochondrial function (as mitochondrial membrane potential and ATP production), on secretion of soluble Aβ and on neurite outgrowth in PC12 cells were investigated.

Key results:

Piracetam improves mitochondrial function of PC12 cells and acutely dissociated brain cells from young NMRI mice following exposure to extracellular Aβ_1-42. Similar protective effects against Aβ_1-42 were observed in dissociated brain cells from aged NMRI mice, or mice transgenic for mutant human amyloid precursor protein (APP) treated with piracetam for 14 days. Soluble Aβ load was markedly diminished in the brain of those animals after treatment with piracetam. Aβ production by HEK cells stably transfected with mutant human APP was elevated by oxidative stress and this was reduced by piracetam. Impairment of neuritogenesis is an important consequence of Aβ-induced mitochondrial dysfunction and Aβ-induced reduction of neurite growth in PC12 cells was substantially improved by piracetam.

Conclusion and implications:

Our findings strongly support the concept of improving mitochondrial function as an approach to ameliorate the detrimental effects of Aβ on brain function.This article is commented on by Moncada, pp. 217–219 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2010.00706.x and to view related papers by Pravdic et al. and Puerta et al. visit http://dx.doi.org/10.1111/j.1476-5381.2010.00698.x and http://dx.doi.org/10.1111/j.1476-5381.2010.00663.x     

Icariin potentiates the antitumor activity of gemcitabine in gallbladder cancer by suppressing NF-κB

Aim:

Gemcitabine has been increasingly prescribed for the treatment of gallbladder cancer. However, the response rate is low. The aim of this study is to determine whether icariin, a flavonoid isolated from Epimedi herba, could potentiate the antitumor activity of gemcitabine in gallbladder cancer.

Methods:

Human gallbladder carcinoma cell lines GBC-SD and SGC-996 were tested. Cell proliferation and apoptosis were analyzed using MTT assay and flow cytometry, respectively. The expression of apoptosis- and proliferation-related molecules was detected with Western blotting. Caspase-3 activity was analyzed using colorimetric assay, and NF-κB activity was measured with ELISA. A gallbladder cancer xenograft model was established in female BALB/c (nu/nu) mice. The mice were intraperitoneally administered gemcitabine (125 mg/kg) in combination with icariin (40 mg/kg) for 2 weeks.

Results:

Icariin (40–160 μg/mL) dose-dependently suppressed cell proliferation and induced apoptosis in both GBC-SD and SGC-996 cells, with SGC-996 cells being less sensitive to the drug. Icariin (40 μg/mL) significantly enhanced the antitumor activity of gemcitabine (0.5 μmol/L) in both GBC-SD and SGC-996 cells. The mice bearing gallbladder cancer xenograft treated with gemcitabine in combination with icariin exhibited significantly smaller tumor size than the mice treated with either drug alone. In GBC-SD cells, icariin significantly inhibited both the constitutive and gemcitabine-induced NF-κB activity, enhanced caspase-3 activity, induced G₀-G₁ phase arrest, and suppressed the expression of Bcl-2, Bcl-xL and surviving proteins.

Conclusion:

Icariin, by suppressing NF-κB activity, exerts antitumor activity, and potentiates the antitumor activity of gemcitabine in gallbladder cancer. Combined administration of gemcitabine and icariin may offer a better therapeutic option for the patients with gallbladder cancer.     

Pharmacology of α7 nicotinic acetylcholine receptor mediated extracellular signal-regulated kinase signalling in PC12 cells

Background and purpose:

Neuronal nicotinic acetylcholine receptors (nAChR) can modulate cell survival and memory processing. The involvement of specific nAChR subtypes in downstream signalling events has been ill defined thus far, because of a lack of subtype-selective ligands. In this study, we investigated activation and modulation of α7 nAChR-mediated phosphorylation of extracellular signal-regulated kinases (ERK1/2) in PC12 cells, using selective agonists and positive allosteric modulators.

Experimental approach:

We used undifferentiated PC12 cells endogenously expressing α7 nAChR for both biochemical and functional studies. ERK phosphorylation changes were measured by using a novel In-Cell Western procedure. α7 nAChR-mediated Ca²⁺ signalling was determined by using the fluorometric imaging plate reader assay.

Key results:

Robust induction of ERK phosphorylation followed exposure of PC12 cells to the selective agonist PNU-282987 in the presence of the α7 nAChR modulator PNU-120596. ERK phosphorylation was transient and was attenuated by the selective antagonist methyllycaconitine. Consistent with allosteric modulation of α7 nAChRs, PNU-120596 enhanced both the agonist potency and efficacy in activating ERK. Moreover, α7 nAChR agonists could be quantitatively differentiated based on their potency in activating ERK signalling. The rank order of potencies correlated fairly well with the corresponding binding K_i values of these α7 nAChR agonists.

Conclusions and implications:

The present work extends previous observations demonstrating the involvement of α7 nAChRs in ERK1/2 phosphorylation in PC12 cells. The In-Cell Western procedure allowed a detailed investigation of α7 nAChR function and downstream ERK signalling in response to agonist and allosteric modulators.     

Involvement of microRNA-21 in mediating chemoresistance to docetaxel in androgen-independent prostate cancer PC3 cells

Aim:

To investigate whether microRNA-21 was involved in mediating the chemoresistance of prostate cancer cells to docetaxel.

Methods:

A microarray technique was used to determine the miRNA profile in docetaxel-resistant PC3 cells. Real-time PCR was used to confirm the array results. miR-21 mimics and inhibitors were synthesized and introduced to cells using Lipofectamine 2000. Cell proliferation was examined with the CCK-8 assay. Luciferase reporter containing PDCD 3′UTR was constructed and the activity was detected by a dual luciferase assay. PDCD4 protein expression was evaluated using Western blot.

Results:

A docetaxel-resistant prostate cancer PC3 cell line (PC3R) was established . Using microarrays, miR-21 was found to be up-regulated in PC3R cells. Ectopic expression of miR-21 increased the resistance to docetaxel in PC3 wild type cells. In contrast, silencing of miR-21 in PC3R cells sensitized the cells to docetaxel. The IC₅₀ values for miR-21-silencing cells and control cells were 28.31 and 35.89 nmol/L, respectively. PDCD4, a direct target gene of miR-21, could mediate chemoresistance to docetaxel in PC3 cells.

Conclusion:

Our findings suggest that miR-21 contributed to the resistance of PC3 cells to docetaxel, and that targeting miR-21 may offer a promising therapeutic approach in sensitizing prostate cancer to docetaxel treatment.     

α-Mangostin suppresses human gastric adenocarcinoma cells in vitro via blockade of Stat3 signaling pathway

Aim:

To investigate the anti-tumor effects of α-mangostin, a major xanthone identified in the pericarp of mangosteen (Garcinia mangostana Linn), against human gastric adenocarcinoma cells in vitro, and the mechanisms of the effects.

Methods:

Human gastric adenocarcinoma cell lines BGC-823 and SGC-7901 were treated with α-mangostin. The cell viability was measured with MTT assay, and cell apoptosis was examined using flow cytometry and TUNEL assay. The expression of the relevant proteins was detected using Western blot.

Results:

Treatment with α-mangostin (3–10 μg/mL) inhibited the viability of both BGC-823 and SGC-7901 cells in dose- and time-manners. Furthermore, α-mangostin (7 μg/mL) time-dependently increased the apoptosis index of the cancer cells, reduced the mitochondrial membrane potential of the cancer cells, and significantly increased the release of cytochrome c and AIF into cytoplasm. Moreover, the α-mangostin treatment markedly suppressed the constitutive Stat3 protein activation, and Stat3-regulated Bcl-xL and Mcl-1 protein levels in the cancer cells.

Conclusion:

The anti-tumor effects of α-mangostin against human gastric adenocarcinoma cells in vitro can be partly attributed to blockade of Stat3 signaling pathway.     

Hyperoside induces both autophagy and apoptosis in non-small cell lung cancer cells in vitro

Aim:

Hyperoside (quercetin-3-O-β-D-galactopyranoside) is a flavonol glycoside found in plants of the genera Hypericum and Crataegus, which exhibits anticancer, anti-oxidant, and anti-inflammatory activities. In this study we investigated whether autophagy was involved in the anticancer mechanisms of hyperoside in human non-small cell lung cancer cells in vitro.

Methods:

Human non-small cell lung cancer cell line A549 was tested, and human bronchial epithelial cell line BEAS-2B was used for comparison. The expression of LC3-II, apoptotic and signaling proteins was measured using Western blotting. Autophagosomes were observed with MDC staining, LC3 immunocytochemistry, and GFP-LC3 fusion protein techniques. Cell viability was assessed using MTT assay.

Results:

Hyperoside (0.5, 1, 2 mmol/L) dose-dependently increased the expression of LC3-II and autophagosome numbers in A549 cells, but had no such effects in BEAS-2B cells. Moreover, hyperoside dose-dependently inhibited the phosphorylation of Akt, mTOR, p70S6K and 4E-BP1, but increased the phosphorylation of ERK1/2 in A549 cells. Insulin (200 nmol/L) markedly enhanced the phosphorylation of Akt and decreased LC3-II expression in A549 cells, which were reversed by pretreatment with hyperoside, whereas the MEK1/2 inhibitor U0126 (20 μmol/L) did not blocked hyperoside-induced LC3-II expression. Finally, hyperoside dose-dependently suppressed the cell viability and induced apoptosis in A549 cells, which were significantly attenuated by pretreatment with the autophagy inhibitor 3-methyladenine (2.5 mmol/L).

Conclusion:

Hyperoside induces both autophagy and apoptosis in human non-small cell lung cancer cells in vitro. The autophagy is induced through inhibiting the Akt/mTOR/p70S6K signal pathways, which contributes to anticancer actions of hyperoside.     

An integrated pathway interaction network for the combination of four effective compounds from ShengMai preparations in the treatment of cardio-cerebral ischemic diseases

Aim:

SMXZF (a combination of ginsenoside Rb1, ginsenoside Rg1, schizandrin and DT-13) derived from Chinese traditional medicine formula ShengMai preparations) is capable of alleviating cerebral ischemia-reperfusion injury in mice. In this study we used network pharmacology approach to explore the mechanisms of SMXZF in the treatment of cardio-cerebral ischemic diseases.

Methods:

Based upon the chemical predictors, such as chemical structure, pharmacological information and systems biology functional data analysis, a target-pathway interaction network was constructed to identify potential pathways and targets of SMXZF in the treatment of cardio-cerebral ischemia. Furthermore, the most related pathways were verified in TNF-α-treated human vascular endothelial EA.hy926 cells and H2O2-treated rat PC12 cells.

Results:

Three signaling pathways including the NF-κB pathway, oxidative stress pathway and cytokine network pathway were demonstrated to be the main signaling pathways. The results from the gene ontology analysis were in accordance with these signaling pathways. The target proteins were found to be associated with other diseases such as vision, renal and metabolic diseases, although they exerted therapeutic actions on cardio-cerebral ischemic diseases. Furthermore, SMXZF not only dose-dependently inhibited the phosphorylation of NF-κB, p50, p65 and IKKα/β in TNF-α-treated EA.hy926 cells, but also regulated the Nrf2/HO-1 pathway in H2O2-treated PC12 cells.

Conclusion:

NF-κB signaling pathway, oxidative stress pathway and cytokine network pathway are mainly responsible for the therapeutic actions of SMXZF against cardio-cerebral ischemic diseases.     

Development of β-amino-carbonyl compounds as androgen receptor antagonists

Aim： Androgen receptor （AR） antagonists have proven to be useful in the early control of prostate cancer. The aim of this study was to identify and characterize a novel β-amino-carbonyl-based androgen receptor antagonist. Methods Different isomers of the β-amino-carbonyl compounds were obtained by chiral separation. The bioactivities of the isomers were evaluated by AR nuclear translocation, mammalian two-hybrid, competitive receptor binding and cell proliferation assays. The expression of genes downstream of AR was analyzed with real-time PCR. The therapeutic effects on tumor growth in vivo were observed in male SClD mice bearing LNCaP xenografts. Results： Compound 21 was previously identified as an AR modulator by the high-throughput screening of a diverse compound library. In the present study, the two isomers of compound 21, termed compounds 21-1 and 2.1.-2, were characterized as partial AR agonists in terms of androgen-induced AR nuclear translocation, prostate-specific antigen expression and cell proliferation. Further structural modifications led to the discovery of a androgen receptor antagonist （compound 6012）, which blocked androgen receptor nuclear translocation, androgen-responsive gene expression and androgen-dependent LNCaP cell proliferation. Four stereoisomers of compound 6012 were isolated, and their bioactivities were assessed. The pharmacological effects of 6012, including AR binding, androgen-induced AR translocation, NH2- and COOH-terminal interaction, growth inhibition of LNCaP cells in vitro and LNCaP xenograft growth in nude mice, were mainly restricted to isomer 6012-4 （1R, 3S）. Conclusion： Compound 6012-4 was determined to be a novel androgen receptor antagonist with prostate cancer inhibitory activities comparable to bicalutamide both in vitro and in vivo.     

Salvianolic acid B inhibits autophagy and protects starving cardiac myocytes

Aim:

To investigate the protective or lethal role of autophagy and the effects of Salvianolic acid B (Sal B) on autophagy in starving myocytes.

Methods:

Cardiac myocytes were incubated under starvation conditions (GD) for 0, 1, 2, 3, and 6 h. Autophagic flux in starving cells was measured via chloroquine (3 μmol/L). After myocytes were treated with Sal B (50 μmol/L) in the presence or absence of chloroquine (3 μmol/L) under GD 3 h, the amount of LC3-II, the abundance of LC3-positive fluorescent dots in cells, cell viability and cellular ATP levels were determined using immunoblotting, immunofluorescence microscopy, MTT assay and luminometer, respectively. Moreover, electron microscopy (EM) and immunofluorescent duel labeling of LC3 and Caspase-8 were used to examine the characteristics of autophagy and apoptosis.

Results:

Immunoblot analysis showed that the amount of LC3-II in starving cells increased in a time-dependent manner accompanied by increased LC3-positive fluorescence and decreased cell viability and ATP content. Sal B (50 μmol/L) inhibited the increase in LC3-II, reduced the abundance of LC3 immunofluorescence and intensity of Caspase-8 fluorescence, and enhanced cellular viability and ATP levels in myocytes under GD 3 h, regardless of whether chloroquine was present.

Conclusion:

Autophagy induced by starvation for 3 h led to cell injury. Sal B protected starving cells by blocking the early stage of autophagic flux and inhibiting apoptosis that occurred during autophagy.     

Anti-apoptotic effects of protein kinase C-δ and c-fos in cisplatin-treated thyroid cells

Background and purpose:

We showed previously that cisplatin inititates a signalling pathway mediated by PKC-δ/extracellular signal-regulated kinase (ERK), important for maintaining viability in PC Cl3 thyroid cells. The studies described herein examined whether c-fos was associated with cisplatin resistance and the signalling link between c-fos and PKC-δ/ERK.

Experimental approach:

Cells were treated with various pharmacological inhibitors of PKCs and ERK, or were depleted of c-fos, PKC-δ, PKC-ε and caspase-3 by small interfering RNA (siRNA), then incubated with cisplatin and cytotoxicity assessed.

Key results:

Cisplatin provokes the induction of c-fos and the activation of conventional PKC-β, and novel PKC-δ and -ε. The cisplatin-provoked c-fos induction was decreased by Gö6976, a PKC-β inhibitor; by siRNA for PKC-δ- but not that for PKC-ε or by PD98059, a mitogen-activated protein kinase/ERK kinase inhibitor. Expression of c-fos was abolished by GF109203X, an inhibitor of all PKC isoforms, or by PD98059 plus Gö6976 or by PKC-δ-siRNA plus Gö6976. When c-fos expression was blocked by siRNA, cisplatin cytotoxicity was strongly enhanced with increased caspase-3 activation. In PKC-δ-depleted cells treated with cisplatin, caspase-3 activation was increased and cell viability decreased. In these PKC-δ-depleted cells, PD98059 did not affect caspase-3 activation.

Conclusions and implications:

In PC Cl3 cells, in the cell signalling pathways that lead to cisplatin resistance, PKC-δ controls ERK activity and, together with PKC-β, also the induction of c-fos. Hence, the protective role of c-fos in thyroid cells has the potential to provide new opportunities for therapeutic intervention.