Hyun-Soon Jong

Class I Histone Deacetylase-Selective Novel Synthetic Inhibitors Potently Inhibit Human Tumor Proliferation

We have developed previously a class of synthetic hybrid histone deacetylase (HDAC) inhibitors, which were built from hydroxamic acid of trichostatin A and pyridyl ring of MS-275. In this study we evaluated the antitumor effects of these novel hybrid synthetic HDAC inhibitors, SK-7041 and SK-7068, on human cancer cells. Both SK-7041 and SK-7068 effectively inhibited cellular HDAC activity at nanomolar concentrations and induced the time-dependent hyperacetylation of histones H3 and H4. These HDAC inhibitors preferentially inhibited the enzymatic activities of HDAC1 and HDAC2, as compared with the other HDAC isotypes, indicating that class I HDAC is the major target of SK-7041 and SK-7068. We found that these compounds exhibited potent antiproliferative activity against various human cancer cells in vitro. Growth inhibition effect of SK-7041 and SK-7068 was related with the induction of aberrant mitosis and apoptosis in human gastric cancer cells. Both compounds induced the accumulation of cells at mitosis after 6 h of treatment, which was demonstrated by accumulation of tetraploid cells, lack of G2 cyclin/cyclin-dependent kinase inactivation, and higher mitotic index. After 12 h of treatment, apoptotic cells were increased through mitochondrial and caspase-mediated pathway. Finally, in vivo experiment showed that SK-7041 or SK-7068 was found to reduce the growth of implanted human tumors in nude mice. Therefore, based on isotype specificity and antitumor activity, SK-7041 and SK-7068 HDAC inhibitors are expected to be promising anticancer therapeutic agents and need additional clinical development.

Transcriptional silencing of the DLC-1 tumor suppressor gene by epigenetic mechanism in gastric cancer cells

DLC-1 (deleted in liver cancer) gene is frequently deleted in hepatocellular carcinoma. However, little is known about the genetic status and the expression of this gene in gastric cancer. In this study, Northern and Southern analysis showed that seven of nine human gastric cancer cell lines did not express DLC-1 mRNA, but contained the DLC-1 gene. To identify the mechanism of the loss of DLC-1 mRNA expression in these cell lines, we investigated the methylation status of DLC-1 gene by using methylation-specific PCR (MSP) and Southern blot, and found that five of seven DLC-1 nonexpressing gastric cancer cell lines were methylated in the DLC-1 CpG island. Treatment with 5-aza-2′-deoxycytidine (5-Aza-dC) induced DLC-1 mRNA expression in the gastric cancer cell lines that have the methylated alleles. Studies using SNU-601 cell line with methylated DLC-1 alleles revealed that nearly all CpG sites within DLC-1 CpG island were methylated, and that the in vitro methylation of the DLC-1 promoter region is enough to repress DLC-1 mRNA expression, regardless of the presence of transcription factors capable of inducing this gene. In all, 29 of 97 (30%) primary gastric cancers were also shown to be methylated, demonstrating that methylation of the DLC-1 CpG island is not uncommon in gastric cancer. In addition, we demonstrated that DLC-1 mRNA expression was induced, and an increase in the level of acetylated H3 and H4 was detected by the treatment with trichostatin A (TSA) in two DLC-1 nonexpressing cell lines that have the unmethylated alleles. Taken together, the results of our study suggest that the transcriptional silencing of DLC-1, by epigenetic mechanism, may be involved in gastric carcinogenesis.

AKAP12/Gravin is inactivated by epigenetic mechanism in human gastric carcinoma and shows growth suppressor activity.

AKAP12/Gravin, one of the A-kinase anchoring proteins (AKAPs), functions as a kinase scaffold protein and as a dynamic regulator of the β2-adrenergic receptor complex. However, the biological role of AKAP12 in cancer development is not well understood. The AKAP12 gene encodes two major isoforms of 305 and 287 kDa (designated AKAP12A and AKAP12B, respectively, in this report). We found that these two isoforms are independently expressed and that they are probably under the control of two different promoters. Moreover, both isoforms were absent from the majority of human gastric cancer cells. The results from methylation-specific PCR (MSP) and bisulfite sequencing revealed that the 5′ CpG islands of both AKAP12A and AKAP12B are frequently hypermethylated in gastric cancer cells. Treatment with DNA methyltransferase inhibitor and/or histone deacetylase inhibitor efficiently restored the expression of AKAP12 isoforms, confirming that DNA methylation is directly involved in the transcriptional silencing of AKAP12 in gastric cancer cells. Hypermethylation of AKAP12A CpG island was also detected in 56% (10 of 18) of primary gastric tumors. The restoration of AKAP12A in AKAP12-nonexpressing cells reduced colony formation and induced apoptotic cell death. In conclusion, our results suggest that AKAP12A may function as an important negative regulator of the survival pathway in human gastric cancer.

Cyclooxygenase-2 Inhibits Novel Ginseng Metabolite-Mediated Apoptosis

Recently, a novel intestinal bacterial metabolite of ginseng protopanaxadiol saponins, i.e., 20-O-(beta-D-glucopyranosyl)-20(S)-protopanaxadiol (IH-901), has been reported to induce apoptosis in a variety of cancer cells. Here we show a differential effect of IH-901 on several cell types. Exposure to IH-901 for 48 hours at a supposedly subapoptotic concentration of 40 mumol/L led to both apoptotic cell death and G1 arrest in Hep3B cells, but only resulted in G1 arrest in MDA-MB-231, Hs578T, and MKN28 cells. Additionally, the treatment of MDA-MB-231, but not of Hep3B, with IH-901 up-regulated cyclooxygenase-2 (COX-2) mRNA (2 hours) and protein (6 hours), and enhanced the production of prostaglandin E2. In MDA-MB-231 cells, IH-901 induced the sustained activation of extracellular signal-regulated kinase (ERK), whereas inhibition of mitogen-activated protein/ERK kinase blocked IH-901-mediated COX-2 induction and resulted in apoptosis, suggesting the involvement of an ERK-COX-2 pathway. Combined treatment with IH-901 and nonsteroidal anti-inflammatory drugs inhibited COX-2 enzyme and induced apoptosis in MDA-MB-231 and Hs578T cells. Adenovirus-mediated COX-2 small interfering RNAs also effectively inhibited COX-2 protein expression and enhanced IH-901-mediated apoptosis without inhibiting ERK 1/2 phosphorylation, thus providing direct evidence that COX-2 is an antiapoptotic molecule. Moreover, IH-901-mediated G1 arrest resulted from an increase in p27Kip1 mRNA and protein expression followed by a decrease in CDK2 kinase activity that was concurrent with the hypophosphorylation of Rb and p130. In conclusion, IH-901 induced both G1 arrest and apoptosis, and this apoptosis could be inhibited by COX-2 induction.

Histone deacetylase inhibitor enhances 5-fluorouracil cytotoxicity by down-regulating thymidylate synthase in human cancer cells

Thymidylate synthase (TS) overexpression is a key determinant of 5-fluorouracil (5-FU) resistance in human cancer cells. TS is also acutely up-regulated with 5-FU treatment, and, thus, novel strategies targeting TS down-regulation seem to be promising in terms of modulating 5-FU resistance. Here, we report that histone deacetylase inhibitors can reverse 5-FU resistance by down-regulating TS. By using cDNA microarrays and validation experiments, we found that trichostatin A reduced the expression of both TS mRNA and TS protein. Cotreatment with trichostatin A and cycloheximide restored TS mRNA expression, suggesting that TS mRNA is repressed through new protein synthesis. On the other hand, TS protein expression was significantly reduced by lower doses of trichostatin A (50 nmol/L). Mechanistically, TS protein was found to interact with heat shock protein (Hsp) complex, and trichostatin A treatment induced chaperonic Hsp90 acetylation and subsequently enhanced Hsp70 binding to TS, which led to the proteasomal degradation of TS protein. Of note, combined treatment with low-dose trichostatin A and 5-FU enhanced 5-FU–mediated cytotoxicity in 5-FU–resistant cancer cells in accordance with TS protein down-regulation. We conclude that a combinatorial approach using histone deacetylase inhibitors may be useful at overcoming 5-FU resistance. [Mol Cancer Ther 2006;5(12):3085–95]

Up-regulation of human telomerase catalytic subunit during gastric carcinogenesis

Telomerase activation is thought to be essential for the stabilization of telomere length, through which immortalization and oncogenesis are achieved, but little is known about the regulation of telomerase in human gastric carcinoma cells.

Genetic integrity of transforming growth factor β (TGF‐β) receptors in cervical carcinoma cell lines: loss of growth sensitivity but conserved transcriptional response to TGF‐β

Transforming growth factor β (TGF‐β) exerts an inhibitory effect on the growth of most epithelial cell types, and the loss of responsiveness to this growth inhibition has been implicated in the development of a variety of human cancers. The genetic alteration of TGF‐β receptors is known to play a critical role in this escape from growth regulation. We asked whether there is a correlation between TGF‐β sensitivity and the genetic status of TGF‐β type I and type II receptors (RI and RII, respectively) in human cervical carcinoma cell lines. Among 8 cell lines examined, 3 (ME‐180, C‐33A and HeLaS3) showed resistance to TGF‐β and 3 (SiHa, CaSki and HeLa229) showed minimal response to the growth inhibitory effect of TGF‐β; the other cell lines (HeLa and HT‐3) were sensitive. Northern blot analysis revealed that the RII mRNA was not expressed in 2 TGF‐β‐resistant cell lines (ME‐180 and C‐33A) but was expressed in the other cell lines. Southern blot analysis of RI and RII revealed a homozygous deletion of the entire TGF‐β RII gene in the cell line ME‐180. We then asked whether the other TGF‐β‐resistant or refractory cell lines had microsatellite instability and/or poly‐adenine tract mutations of RII. We also checked for point mutations in the individual exons of the entire RII using polymerase chain reaction‐single‐strand conformational polymorphism (PCR‐SSCP). Although C‐33A exhibited poly‐adenine microsatellite instability, its RII gene showed no signs of mutation. The molecular integrity of the TGF‐β receptors in all cell lines, except ME‐180 and C‐33A, could be confirmed by examining the distinct transcriptional induction of plasminogen activator inhibitor‐1 (PAI‐1), p21WAF1/CIP1 and, in some cases, the accompanying downregulation of c‐myc in response to TGF‐β. Our observations, taken together, indicate that inactivation of the RII contributes to the resistance to TGF‐β of some cervical carcinoma cell lines. Loss of or attenuated sensitivity to TGF‐β growth inhibition in other cells may be attributed to the disruption of distal components in the TGF‐β signal pathway, but not to the receptor system. Int. J. Cancer 77:620–625, 1998.

Inhibitors of histone deacetylases induce tumor-selective cytotoxicity through modulating Aurora-A kinase

The molecular basis of the antitumor selectivity of histone deacetylase inhibitors (HDIs) remains unclear. Centrosomal Aurora-A kinase regulates chromosomal segregation during mitosis. The overexpression or amplification of Aurora-A leads to genetic instability, and its inhibition has shown significant antitumor effects. In this paper, we report that structurally related hydroxamate LAQ824 and SK-7068 induce tumor-selective mitotic defects by depleting Aurora-A. We found that HDI-treated cancer cells, unlike nontransformed cells, exhibit defective mitotic spindles. After HDI, Aurora-A was selectively downregulated in cancer cells, whereas Aurora-B remained unchanged in both cancer and nontransformed cells. LAQ824 or SK-7068 treatment inhibited histone deacetylase (HDAC) 6 present in Aurora-A/heat shock protein (Hsp) 90 complex. Inhibition of HDAC6 acetylated Hsp90 and resulted in dissociation of acetylated Hsp90 from Aurora-A. As a result, Hsp70 binding to Aurora-A was enhanced in cancer cells, leading to proteasomal degradation of Aurora-A. Overall, these provide a novel molecular basis of tumor selectivity of HDI. LAQ824 and SK-7068 might be more effective HDIs in cancer cells with Aurora-A overexpression.

The signaling network of transforming growth factor beta1, protein kinase Cdelta, and integrin underlies the spreading and invasiveness of gastric carcinoma cells

ABSTRACT Integrin-mediated cell adhesion and spreading enables cells to respond to extracellular stimuli for cellular functions. Using a gastric carcinoma cell line that is usually round in adhesion, we explored the mechanisms underlying the cell spreading process, separate from adhesion, and the biological consequences of the process. The cells exhibited spreading behavior through the collaboration of integrin-extracellular matrix interaction with a Smad-mediated transforming growth factor β1 (TGFβ1) pathway that is mediated by protein kinase Cδ (PKCδ). TGFβ1 treatment of the cells replated on extracellular matrix caused the expression and phosphorylation of PKCδ, which is required for expression and activation of integrins. Increased expression of integrins α2 and α3 correlated with the spreading, functioning in activation of focal adhesion molecules. Smad3, but not Smad2, overexpression enhanced the TGFβ1 effects. Furthermore, TGFβ1 treatment and PKCδ activity were required for increased motility on fibronectin and invasion through matrigel, indicating their correlation with the spreading behavior. Altogether, this study clearly evidenced that the signaling network, involving the Smad-dependent TGFβ pathway, PKCδ expression and phosphorylation, and integrin expression and activation, regulates cell spreading, motility, and invasion of the SNU16mAd gastric carcinoma cell variant.

Aberrant methylation of integrin alpha4 gene in human gastric cancer cells.

Integrins are adhesion receptors that mediate both cell–extracellular matrix and cell–cell interactions. It has also been reported that the loss of integrin α4 expression might be associated with metastasis in several cancers. However, the molecular mechanism for loss of their expression in cancers has not been explored. In the present study, we found that the integrin α4 expression is lost in human gastric cancer cell lines and that this is recovered by treatment with DNA methyltransferase inhibitor, implying transcriptional silencing by DNA methylation. Methylation-specific PCR (MSP) and bisulfite genomic DNA sequencing demonstrated the CpG methylation-dependent silencing of integrin α4 expression in eight of nine (88.8%) gastric cancer cell lines and in 84.7% of 46 primary tumors. We also investigated whether the restoration of integrin α4 in integrin α4-inactivated cells affects their ability to invade extracellular matrix, using matrigel assays. Interestingly, integrin α4-stable transfectants had markedly less invasive ability than the parental cells. Taken together, these results suggest that the transcriptional repression of the integrin α4 gene is caused by aberrant DNA methylation, and that this may play an important role in human gastric carcinogenesis.