Leptin, a secreted protein of the ob gene by white adipose tissue, plays an important role in the regulation of food intake and energy consumption in the brain and acts as a potential growth stimulator in normal and neoplastic breast cancer cells. However, a potential role of leptin as an endocrine regulator is unknown in ovarian cancer. In the present study, we investigated the expression of leptin receptors in immortalized ovarian surface epithelium (IOSE) and ovarian cancer cell lines, and potential effect of leptin on the cell growth and activation of mitogen-activated protein kinases (MAPKs) in the BG-1 ovarian cancer cell line. Both short and long isoforms of leptin receptors are expressed in IOSE-80PC (a post-crisis line), BG-1, OVCAR-3, and SKOV-3 cells. In addition, treatment with leptin resulted in the growth stimulation of BG-1 cells, an activation of ERK1/2 and inhibition of constitutive phosphorylation of p38 MAPK. These results suggest that further studies are necessary to validate whether leptin may be a potential regulator for ovarian cancer.

BackgroundCompound K [20-O-β-(D-glucopyranosyl)-20(S)-protopanaxadiol], a metabolite of the protopanaxadiol-type saponins of Panax ginseng C.A. Meyer, has been reported to possess anti-tumor properties to inhibit angiogenesis and to induce tumor apoptosis. In the present study, we investigated the effect of Compound K on apoptosis and explored the underlying mechanisms involved in HL-60 human leukemia cells.MethodsWe examined the effect of Compound K on the viabilities of various cancer cell lines using MTT assays. DAPI assay, Annexin V and PI double staining, Western blot assay and immunoprecipitation were used to determine the effect of Compound K on the induction of apoptosis.ResultsCompound K was found to inhibit the viability of HL-60 cells in a dose- and time-dependent manner with an IC50 of 14 μM. Moreover, this cell death had typical features of apoptosis, that is, DNA fragmentation, DNA ladder formation, and the externalization of Annexin V targeted phosphatidylserine residues in HL-60 cells. In addition, compound-K induced a series of intracellular events associated with both the mitochondrial- and death receptor-dependent apoptotic pathways, namely, (1) the activation of caspases-3, -8, and -9; (2) the loss of mitochondrial membrane potential; (3) the release of cytochrome c and Smac/DIABLO to the cytosol; (4) the translocation of Bid and Bax to mitochondria; and (5) the downregulations of Bcl-2 and Bcl-xL. Furthermore, a caspase-8 inhibitor completely abolished caspase-3 activation, Bid cleavage, and subsequent DNA fragmentation by Compound K. Interestingly, the activation of caspase-3 and -8 and DNA fragmentation were significantly prevented in the presence of cycloheximide, suggesting that Compound K-induced apoptosis is dependent on de novo protein synthesis.ConclusionsThe results indicate that caspase-8 plays a key role in Compound K-stimulated apoptosis via the activation of caspase-3 directly or indirectly through Bid cleavage, cytochrome c release, and caspase-9 activation.

We have previously demonstrated that costunolide, a biologically active compound that was isolated from the stem bark of Magnolia sieboldii, induced apoptosis in human cancer cells. In the present study, we investigated the underlying mechanisms and suggest that costunolide induces apoptosis in human promonocytic leukemia U937 cells by depleting the intracellular thiols. Costunolide treatment rapidly depleted the intracellular reduced glutathione (GSH) and protein thiols, and this preceded the occurrence of apoptosis. Pretreatment with sulfhydryl compounds such as GSH, N-acetyl-L-cysteine, dithiothreitol and 2-mercaptoethanol almost completely blocked the costunolide-induced apoptosis, highlighting the significance of the intracellular thiol level in the process. Furthermore, overexpression of Bcl-2 also significantly attenuated the effects of costunolide. The apoptosis-inducing activity of costunolide is likely to depend on the exomethylene moiety because derivatives in which this group was reduced, such as dihydrocostunolide and saussurea lactone, did not deplete the cellular thiols and showed no apoptotic activity. Taken together, the present study demonstrates that the costunolide-induced apoptosis depends on intracellular thiols contents, which are modulated by Bcl-2.

It has been previously demonstrated that human ovarian cancer cells express FSH receptor (FSHR). However, whether FSHR plays a role in ovarian cancer development is still ambiguous. To investigate the role of FSHR in tumor progression, we overexpressed the receptor in SV40 Tag immortalized ovarian surface epithelium (OSE) cell lines (IOSE-80PC, a postcrisis line, and IOSE-398), which are preneoplastic and nontumorigenic. We compared the expression levels of several selected oncogenes in nontransfected (80PC), vector-transfected (80PCV), FSHR-transfected IOSE (80PCF) cells, and established ovarian cancer cell lines (OVCAR-3 and SKOV-3). Significantly increased protein levels of epithelial growth factor receptor, HER-2/neu, and c-Myc, but not K-Ras, were observed in FSHR-overexpressing 80PCF cells when compared with 80PCV cells. Constitutive phosphorylation of ERK1/2 was augmented in 80PCF cells, whereas phosphorylation of the other MAPK including p38 and Jun N-terminal kinase was unchanged. Considerable constitutive phosphorylation of ERK1/2 was also observed in OVCAR-3 and SKOV-3 cell lines when compared with 80PCV. More importantly, 80PCF cells grew more rapidly than 80PC and 80PCV cells. In conclusion, we have demonstrated that FSHR was highly expressed in OVCAR-3 and 80PCF cells transfected with FSHR overexpression vector. The 80PCF cell line showed increased levels of epithelial growth factor receptor, HER-2/neu, and c-myc and constitutive activation of ERK1/2. The rate of proliferation of the 80PCF cells was increased, compared with control cell lines. These results suggest that the overexpression of FSHR may be associated with enhanced levels of potential oncogenic pathways and increased proliferation in preneoplastic ovarian surface epithelial cells.

Despite evidence that gonadotropins may facilitate peritoneal metastasis of ovarian cancer by increasing cell adhesion, the action and molecular mechanism of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in ovarian cancer invasion is not well characterized. In the present study, we investigated the effects of FSH and LH on the invasive activity and the expression of metastasis-related proteinases in human epithelial ovarian cancer by Western blot, zymography, reverse transcription-PCR (RT-PCR), ELISA, and Boyden chamber assay. Treatment with FSH or LH (10, 100, or 1,000 ng/mL) significantly increased the invasion of ovarian cancer cell lines, including BG-1, CaOV-3, and SKOV-3 cells but not OVCAR-3 cells. In addition, treatment of SKOV-3 cells with FSH or LH (100 or 1,000 ng/mL) enhanced the expression and activation of matrix metalloproteinases (MMP-2 and MMP-9) as shown by RT-PCR, gelatin zymography, and ELISA. Pretreatment with [(2R)-2-(hydroxamido-carbonylmethyl)-4-methylpentanoyl]-Ltryptophan methylamide (10 Mmol/L), a total MMP inhibitor, and 3-(4-phenoxyphenylsulfonyl)-propylthiirane (20 Mmol/L), a specific gelatinase inhibitor, neutralized the proinvasive effect of gonadotropins in SKOV-3 cells. In addition, the secretion of tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) and plasminogen activator inhibitor-1 was significantly decreased by FSH and LH (100 or 1,000 ng/mL). We further showed that gonadotropins induced an increase in SKOV-3 invasiveness via the activation of protein kinase A (PKA) and phosphatidylinositol 3-kinase (PI3K) signaling pathways. Taken together, these results suggest that gonadotropins may contribute to ovarian cancer metastasis via activation of proteolysis and increase in invasion through the PKA and PI3K pathways.