Thapsigargin induces rapid, transient growth inhibition and c-fos expression followed by sustained growth stimulation in mouse keratinocyte cultures

Functional Module Connectivity Map (FMCM): a framework for searching repurposed drug compounds for systems treatment of cancer and an application to colorectal adenocarcinoma

Drug repurposing has become an increasingly attractive approach to drug development owing to the ever-growing cost of new drug discovery and frequent withdrawal of successful drugs caused by side effect issues. Here, we devised Functional Module Connectivity Map (FMCM) for the discovery of repurposed drug compounds for systems treatment of complex diseases, and applied it to colorectal adenocarcinoma. FMCM used multiple functional gene modules to query the Connectivity Map (CMap). The functional modules were built around hub genes identified, through a gene selection by trend-of-disease-progression (GSToP) procedure, from condition-specific gene-gene interaction networks constructed from sets of cohort gene expression microarrays. The candidate drug compounds were restricted to drugs exhibiting predicted minimal intracellular harmful side effects. We tested FMCM against the common practice of selecting drugs using a genomic signature represented by a single set of individual genes to query CMap (IGCM), and found FMCM to have higher robustness, accuracy, specificity, and reproducibility in identifying known anti-cancer agents. Among the 46 drug candidates selected by FMCM for colorectal adenocarcinoma treatment, 65% had literature support for association with anti-cancer activities, and 60% of the drugs predicted to have harmful effects on cancer had been reported to be associated with carcinogens/immune suppressors. Compounds were formed from the selected drug candidates where in each compound the component drugs collectively were beneficial to all the functional modules while no single component drug was harmful to any of the modules. In cell viability tests, we identified four candidate drugs: GW-8510, etacrynic acid, ginkgolide A, and 6-azathymine, as having high inhibitory activities against cancer cells. Through microarray experiments we confirmed the novel functional links predicted for three candidate drugs: phenoxybenzamine (broad effects), GW-8510 (cell cycle), and imipenem (immune system). We believe FMCM can be usefully applied to repurposed drug discovery for systems treatment of other types of cancer and other complex diseases.

A PKC-Sp1 signaling pathway induces early differentiation of human keratinocytes through upregulation of TSG101

The TSG101 protein has been implicated in multiple biological functions including regulation of gene transcription, vesicular trafficking, cellular growth and differentiation. However, the cellular signals that control TSG101 functions are unclear. Here, we demonstrate that TSG101 is upregulated during keratinocyte differentiation in both human foreskin tissue and reconstructed organotypic skin cultures. In addition, we found that TSG101 siRNA inhibits calcium-induced early differentiation of human foreskin keratinocytes, indicating an essential and downstream role for TSG101 in this process. Furthermore, the PKC agonist TPA promotes expression of TSG101 and keratin 10 in keratinocytes under low calcium conditions, while co-treatment with the PKC inhibitor GF 109203X blocks TPA-induced TSG101 and keratin 10 upregulation. Previous work has established that the TSG101 gene is controlled by a TATA-less promoter that harbors a Sp1-binding site. Here we show that both calcium and TPA activate PKC, stimulate phosphorylation of Sp1, and augment the activity of the TSG101 promoter in a manner dependent on its Sp1-binding site. Release of calcium from intracellular stores with thapsigargin, an endoplasmic reticulum Ca2+-ATPase inhibitor that elevates intracellular free Ca2+ without activating PKC, does not affect Sp1 phosphorylation and TSG101 promoter activity. Taken together, these data suggest that an intracellular calcium store independent PKC-Sp1 signaling pathway induces early keratinocyte differentiation through upregulation of TSG101.

Haploinsufficiency of Atp2a2, Encoding the Sarco(endo)plasmic Reticulum Ca2+-ATPase Isoform 2 Ca2+ Pump, Predisposes Mice to Squamous Cell Tumors via a Novel Mode of Cancer Susceptibility

A null mutation in one copy of the Atp2a2 or ATP2A2 gene, encoding sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2), leads to squamous cell tumors in mice and to Darier disease in humans, a skin disorder that also involves keratinocytes. Here, we examined the time course and genetic mechanisms of tumor development in the mutant animals. Atp2a2+/- mice overexpressed keratins associated with keratinocyte hyperactivation in normal forestomachs as early as 2 months of age. By the age of 5 to 7 months, 22% of mutants had developed papillomas of the forestomach, and 89% of mutants older than 14 months had developed squamous cell papillomas and/or carcinomas, with a preponderance of the latter. Tumors occurred in regions that had keratinized epithelium and were subjected to repeated mechanical irritation. The genetic mechanism of tumorigenesis did not involve loss of heterozygosity, as tumor cells analyzed by laser capture microdissection contained the wild-type Atp2a2 allele. Furthermore, immunoblot and immunohistochemical analysis showed that tumor keratinocytes expressed the SERCA2 protein. Mutations were not observed in the ras proto-oncogenes; however, expression of wild-type ras was up-regulated, with particularly high levels of K-ras. Loss of the p53 tumor suppressor gene occurred in a single massive tumor, whereas other tumors had increased levels of p53 protein but no mutations in the p53 gene. These findings show that SERCA2 haploinsufficiency predisposes mice to tumor development via a novel mode of cancer susceptibility involving a global change in the tumorigenic potential of keratinized epithelium in Atp2a2+/- mice.

Intracellular calcium pool emptying induces DNA synthesis in HaCaT keratinocytes

Calcium signaling provides a central control mechanism for growth, differentiation and apoptosis of epidermal keratinocytes. Moreover, calcium signaling is important for carcinogenesis in view of the observations suggesting that emptying of intracellular stores in keratinocytes [e.g. by a selective blocker of calcium pump in the endoplasmic reticulum (ER), thapsigargin] facilitates skin cancer development. In this work, we analyzed whether calcium content in the intracellular stores is linked to HaCaT keratinocyte growth and apoptosis control. Treatment with thapsigargin caused calcium release from the intracellular pool and permanent pool depletion (up to 24 h) could be achieved using a high dose (1 micro M) of this inhibitor. HaCaT cells cultured in these conditions exhibited an increased rate of DNA synthesis, assessed by the BrdU incorporation assay. Moreover, a weak stimulation of involucrin (terminal differentiation marker) was observed. Studies where intracellular free calcium (Cai2+) was chelated with BAPTA [1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid] revealed that abrogation of thapsigargin-induced Cai2+elevation did not counteract its effects on DNA synthesis, but blocked thapsigargin-induced involucrin expression. Apoptosis was readily achieved by extracellular calcium chelation using EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid], but was not observed after thapsigargin or BAPTA alone or in combination. In conclusion, depletion of intracellular calcium stores causes stimulation of keratinocyte proliferation independently of the elevation of Cai2+.

Sequential activation of store-operated currents in human gingival keratinocytes

Calcium ion store-activated currents in undifferentiated human gingival keratinocytes were measured with the whole cell patch clamp and fura techniques. Thapsigargin or intracellular inositol 1,4,5-trisphosphate and BAPTA rapidly induced an early transient current with I(CRAC) (calcium release activated calcium ion current) characteristics, and several later, larger sustained currents that depended on the mode of store depletion. Thapsigargin activated two currents within minutes of I(CRAC) activation. The first was a nonspecific cation current, I(NSC). A second conducted Na+ and Cs+, and was partially inhibited by thapsigargin (INa1). Dialysis with inositol 1,4,5-trisphosphate and BAPTA induced a later current that also conducted Na+ and Cs+, but was inhibited by extracellular calcium ion (INa2), with properties consistent with an epithelial Na+ channel current in some cells, and a calcium ion-insensitive Na+ current (INa3). Comparison of thapsigargin-evoked current changes with fura-2/AM results from separate cells indicated that both the I(CRAC) and the later, larger calcium ion conducting currents contributed to changes in intracellular calcium ion concentration, and likely play important parts in calcium ion signaling in undifferentiated keratinocytes.

Thapsigargin-induced grp78 expression is mediated by the increase of cytosolic free calcium in 9L rat brain tumor cells

Exposure of 9L rat brain tumor cells to 300 nM thapsigargin (TG), a sarcoendoplasmic Ca(2+)-ATPases inhibitor, leads to an immediate suppression of general protein synthesis followed by an enhanced synthesis of the 78-kDa glucose-regulated protein, GRP78. Synthesis of GRP78 increases significantly and continues to rise after 4 h of treatment, and this process coincides with the accumulation of grp78 mRNA. TG-induced grp78 expression can be suppressed by the cytosolic free calcium ([Ca(2+)](c)) chelator dibromo-1, 2-bis(aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA) in a concentration-dependent manner. Induction of grp78 is completely abolished in the presence of 20 microM BAPTA under which the TG-induced increase of [Ca(2+)](c) is also completely prevented. By adding ethyleneglycol bis(beta-aminoethyl)ether-N,N,N',N' tetraacetic acid in the foregoing experiments, in a condition such that endoplasmic reticulum calcium ([Ca(2+)](ER)) is depleted and calcium influx from outside is prevented, TG-induced grp78 expression is also abolished. These data lead us to conclude that increase in [Ca(2+)](c), together with the depletion of [Ca(2+)](ER), are the major causes of TG-induced grp78 expression in 9L rat brain tumor cells. By using electrophoretic mobility shift assays (EMSA), we found that the nuclear extracts prepared from TG-treated cells exhibit an increase in binding activity toward the extended grp78 promoter as well as the individual cis-acting regulatory elements, CRE and CORE. Moreover, this increase in binding activity is also reduced by BAPTA. By competitory assays using the cis-acting regulatory elements as the competitors as well as the EMSA probes, we further show that all of the tested cis elements-CRE, CORE, and C1-are involved in the basal as well as in the TG-induced expression of grp78 and that the protein factor(s) that binds to the C1 region plays an important role in the formation and maintenance of the transcription complex.

Ca2+ mobilization and capacitative Ca2+ entry regulate DNA synthesis in cultured chick retinal neuroepithelial cells

Release of Ca2+ from intracellular Ca2+ stores (Ca2+ mobilization) and capacitative Ca2+ entry have been shown to be inducible in neuroepithelial cells of the early embryonic chick retina. Both types of Ca2+ responses decline parallel with retinal progenitor cell proliferation. To investigate their potential role in the regulation of neuroepithelial cell proliferation, we studied the effects of 2,5-di-tert-butylhydroquinone (DBHQ), an inhibitor of the Ca2+ pump of intracellular Ca2+ stores, and of SK&F 96365, an inhibitor of capacitative Ca2+ entry, on DNA synthesis in retinal organ cultures from embryonic day 3 (E3) chicks and in dissociated cultures from E7 and E9 chick retinae. We demonstrate that both antagonists inhibit [3H]-thymidine incorporation in a dose-dependent manner without affecting cell viability or morphology. The inhibition of [3H]-thymidine incorporation by SK&F 96365 occurred in the same concentration range (IC50: approximately 4 microM) as the blockade of capacitative Ca2+ entry in the E3 retinal organ culture. At a concentration of 5 microM SK&F 96365. DNA synthesis was reduced by 71, 40 and 32% in the E3, E7 and E9 cultures, respectively. Application of DBHQ at concentrations which led to depletion of intracellular Ca2+ stores also inhibited [3H]-thymidine incorporation with IC50 values of 20-30 microM in the different cultures. Our results suggest the involvement of Ca2+ mobilization and capacitative Ca2+ entry in the regulation of DNA synthesis in the developing neural retina.

Phytol is a novel tumor promoter on ICR mouse skin

Phytol is a branched, long-chain aliphatic alcohol which has various biological effects. In this study, we examined phytol as a tumor promoter in a mouse skin initiation-promotion model, and compared its promotion activity with that of 12-O-tetradecanoyl phorbol-13-acetate (TPA). Female ICR mice, 7 weeks of age, were initiated with 100 microg of 7,12-dimethylbenz(a)anthracene, and were then topically promoted twice a week for 16 weeks with 100 mg of phytol or with 2.5 microg of TPA. In this model 95% of animals treated with phytol developed skin tumors within 16 weeks. The average number of lesions per mouse treated with phytol was significantly lower than that in mice treated with TPA, and this significant difference continued up to 16 weeks after the end of promotion treatment. Characterization of hyperplasia 48 h after topical application of agents showed that epidermal thickness and vertical thickness following topical application of phytol were significantly increased compared with vehicle controls, but were significantly smaller than in animals treated with TPA. Ornithine decarboxylase (ODC) activity following topical application of phytol was increased in a dose-dependent manner and showed a weak, delayed induction (which was maximal 11-12 h after treatment) as compared with the case of TPA. The specific binding of [3H]phorbol-12,13-dibutyrate (PDBU) by JB6 cells was not inhibited by phytol at concentrations up to 1 mM. These results indicate that phytol has a weak tumor promoter activity compared to TPA and is a non-TPA-type tumor promoter in this model of mouse skin carcinogenesis.

Alterations in calcium metabolism in murine macrophages by the benzene metabolite 1,4-benzoquinone

Exposure of murine peritoneal macrophages to very low concentrations of 1,4-benzoquinone (BQ) induced immediate increases in intracellular Ca2+ concentrations ([Ca2+]i). Increases in [Ca2+]i were induced by concentrations as low as 5 nM and the response was dose dependent and linear up to 1 microM. The sources of Ca2+ were from both internal inositol triphosphate (IP3)-sensitive and -insensitive sites and from the external medium. BQ did not induce IP3 formation and did not affect binding to its receptors. 1, 4-Hydroquinone had no effect on [Ca2+]i. Catechol did elicit some increases in [Ca2+]i, but did so only at much higher concentrations (5 microM). The action of BQ was almost identical to that of the established Ca2+-ATPase inhibitor thapsigargin except that there were some intracellular stores of Ca2+ released by thapsigargin that were not released by BQ. BQ also was mitogenic for macrophages in conjunction with phorbol myristate acetate. These data suggest that BQ raises [Ca2+]i by inhibition of Ca2+-ATPases, is a comitogen, and does so at concentrations that could be achieved in vivo in the general urban population.