Tae Gyun Kim

H‐ras, but not N‐ras, induces an invasive phenotype in human breast epithelial cells: A role for MMP‐2 in the h‐ras‐induced invasive phenotype

Elevated p21ras expression is associated with tumor aggressiveness in breast cancer including the extent of invasion into fat tissues, infiltration into lymphatic vessels and tumor recurrence. In the present study, we have examined the roles of H‐ras and N‐ras, members of the human ras gene family, in the pathogenesis of breast cancer. We show that H‐ras, but not N‐ras, induces an invasive phenotype in human breast epithelial cells (MCF10A) as determined by the Matrigel invasion assay, whereas both H‐ras and N‐ras induce anchorage‐independent growth, as shown by soft agar assay. We examined the effects of H‐ras and N‐ras activation on the expression of MMP‐2 and MMP‐9, which can degrade type IV collagen, the major structural collagen of the basement membrane. We show that MMP‐2 is efficiently induced by H‐ras, whereas MMP‐9 induction is more prominent in N‐ras‐activated MCF10A cells. We also show that H‐ras‐mediated invasiveness is significantly inhibited when the expression of MMP‐2 is down‐regulated, using an oligodeoxyribonucleotide complementary to the MMP‐2 mRNA, or when MMP‐2 activity is blocked by its inhibitor TIMP‐2 (tissue inhibitors of matrix metalloproteinase‐2). Our results show that the H‐ras‐induced invasive phenotype is associated more closely with the expression of MMP‐2 in human breast epithelial cells, rather than the induction of MMP‐9 expression, as shown previously for rat embryonic fibroblasts. Int. J. Cancer 85:176–181, 2000. ©2000 Wiley‐Liss, Inc.

Inhibition of HIV-1 reverse transcriptase and HIV-1 integrase and antiviral activity of Korean seaweed extracts

Forty-seven species of marine macroalgae from the coast of Korea havebeen screened for the presence of inhibitory compounds against humanimmunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) and HIV-1integrase (IN). One of 4 Chlorophyta, 8 of 17 Phaeophyta and 6 of 26 Rhodophytashowed inhibitory activity against HIV-1 reverse transcriptase. Five species(Ecklonia cava, Ishige okamurae,Sargassum confusum, Sargassumhemiphyllum, Sargassum ringgoldianum) belongingto Phaeophyta showed to inhibit the 3′-processing activity of HIV-1integrase. In cell-based assays, the methanol extracts ofBossiella sp. and Chondriacrassicaulis inhibited cytopathogenecity of HIV-1 at a concentrationbelow that cytotoxic for MT4 cells.

Differential regulation of thyroid hormone receptor-mediated function by endocrine disruptors

It is well known that endocrine disruptors (EDs) act as anti-estrogenic agents and affect the function of reproductive organ. EDs are also thought to affect thyroid hormone (TH) system which is important for biological functions such as growth, development and metabolism. However, it is still not clear how EDs are able to regulate TH receptor (TR)-mediated functions. In this study, therefore, the modulatory effects of representative EDs such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorinated biphenyl (Aroclor 1254) and bisphenol A (BPA) were examined using TR-expressing GH3 cells (a rat pituitary gland epithelial tumor cell line) activated by triiodothyronine (T3). EDs tested significantly blocked T3 binding to TR in a dose-dependent manner. Biochemical characterization by Scatchard and Lineweaver-Burk plot analyses indicated that TCDD and aroclor 1254 bound to TH receptors in a competitive inhibitory manner, whereas BPA bound to TH receptors in a non-competitive pattern. The different inhibitory mode of action by EDs was also found in regulating TR-mediated production of prolactin (PRL). Aroclor 1254 exposure for 48 h enhanced T3-mediated PRL production, but BPA down-regulated. These results suggest that the EDs (TCDD, Aroclor 1254 and BPA) could differentially bind to TR and distinctly regulate the action of TR function, even though EDs are structurally similar.

Modulation of chemical carcinogen-induced unscheduled DNA synthesis by dehydroepiandrosterone (DHEA) in the primary rat hepatocytes

Modulation of unscheduled DNA synthesis by dehydroepiandrosterone (DHEA) after exposure to various chemical carcinogens was investigated in the primary rat hepatocytes. Unscheduled DNA synthesis was induced by treatment of such direct acting carcinogens as methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) or procarcinogens including benzo(a)pyrene (BaP) and 7,12-dimethylbenz(a)anthracene (DMBA). Unscheduled DNA synthesis was determined by measuring [methyl-3H]thymidine radioactivity incorporated into nuclear DNA of hepatocytes treated with carcinogens in the presence or absence of DHEA. Hydroxyurea (5×10−3 M) was added to growth medium to selectively suppress normal replication. DHEA at concentrations ranging from 1×10−6 M to 5×10−4 M did not significantly inhibit unscheduled DNA synthesis induced by either MMS (1×10−4 M) or EMS (1×10−2 M). In contrast, DHEA significantly inhibited unscheduled DNA synthesis induced by BaP (6.5×10−5 M) and DMBA (2×10−5 M). DHEA-induced hepatotoxicity in rats was examined using lactate dehydrogenase (LDH) release as an indicator of cytotoxicity. DHEA exhibit no significant increase in LDH release compared with the solvent control at 18 h. These data suggest that nontoxic concentration of DHEA does not affect the DNA excision repair process, but it probably influence the enzymatic system responsible for the metabolic activation of procarcinogens and thereby decreases the amount of the effective DNA adducts formed by the ultimate reactive carcinogenic species.