Biomedical subjects

Heetae Kim

Publications and source records attributed to Heetae Kim.

10 recordsLinked to original sources

PubMed2006

Mitogen-activated protein kinase kinase-4 promotes cell survival by decreasing PTEN expression through an NF kappa B-dependent pathway.

Mitogen-activated protein kinase kinase-4 (MKK4/SEK1) cooperates with phosphatidylinositol 3-kinase to maintain the survival of non-small cell lung cancer (NSCLC) cells, but the biochemical basis of this phenomenon has not been elucidated. Here we used genetic approaches to modulate MKK4 expression in mouse embryo fibroblasts (MEF cells) and NSCLC cells to identify prosurvival signals downstream of MKK4. Relative to wild-type MEF cells, MKK4-null MEF cells were highly susceptible to apoptosis by LY294002, paclitaxel, or serum starvation. MKK4 promoted the survival of MEF cells by decreasing the expression of phosphatase and tensin homologue deleted from chromosome 10 (PTEN). MKK4 inhibited PTEN transcription by activating NFkappaB, a transcriptional suppressor of PTEN. MKK4 was required for nuclear translocation of RelA/p65 and processing of the NFkappaB2 precursor (p100) into the mature form (p52). Studies on a panel of NSCLC cell lines revealed a subset with high MKK4/high NFkappaB/low PTEN that was relatively resistant to apoptosis. Thus, MKK4 promotes cell survival by activating phosphatidylinositol 3-kinase through an NFkappaB/PTEN-dependent pathway.

Animals↗

PubMed2006

Inducible overexpression of c-Jun in MCF7 cells causes resistance to vinblastine via inhibition of drug-induced apoptosis and senescence at a step subsequent to mitotic arrest.

c-Jun is a major component of the AP-1 transcription factor and plays a key role in regulation of diverse biological processes including proliferation and apoptosis. Treatment of a wide variety of cells with the microtubule inhibitor vinblastine leads to a robust increase in c-Jun expression, JNK-mediated c-Jun phosphorylation, and activation of AP-1-dependent transcription. However, the role of c-Jun induction in the response of cells to vinblastine remains obscure. In this study we used MCF7 breast cancer cell lines that express the dominant-negative form of c-Jun, TAM-67, as well as cells that overexpress c-Jun, under the control of an inducible promoter. Vinblastine induced c-Jun protein expression, c-Jun phosphorylation, and AP-1 activation in MCF7 cells, and these parameters were strongly inhibited by inducible TAM-67 expression and strongly enhanced by inducible c-Jun expression. Vinblastine-induced cell death was not affected by TAM-67 expression whereas cells were protected by c-Jun overexpression. Further investigation revealed that apoptotic and senescent cells were observed after vinblastine treatment and that both outcomes were strongly inhibited by c-Jun overexpression. Although c-Jun expression inhibited cell death, it did not affect the ability of vinblastine to induce mitotic arrest. These results indicate that c-Jun expression plays a protective role in the cellular response to vinblastine and operates post-mitotic block to inhibit drug-induced apoptosis and senescence.

Antineoplastic Agents, Phytogenic↗

PubMed2006

The combination of the rexinoid, LG100268, and a selective estrogen receptor modulator, either arzoxifene or acolbifene, synergizes in the prevention and treatment of mammary tumors in an estrogen receptor-negative model of breast cancer.

PURPOSE: We tested whether a selective estrogen receptor modulator (SERM) and a rexinoid are active for prevention and treatment in the mouse mammary tumor virus-neu mouse model of estrogen receptor-negative breast cancer. EXPERIMENTAL DESIGN: For prevention, mice were fed a powdered control diet, the SERM arzoxifene (Arz, 20 mg/kg diet), the rexinoid LG100268 (268, 30 mg/kg diet), or the combination for 60 weeks. In a second prevention study, mice were fed Arz (6 mg/kg diet), 268 (30 mg/kg diet), the combination of Arz and 268, the SERM acolbifene (Acol, 3 mg/kg diet), or the combination of Acol and 268 for 52 weeks. For the treatment studies, mice with tumors were fed combinations of a SERM and 268 for 4 weeks. RESULTS: The rexinoid 268 and the SERMs Arz and Acol, as individual drugs, delayed the development of estrogen receptor-negative tumors. Moreover, the combination of a SERM and 268 was strikingly synergistic, as no tumors developed in any mouse fed the combination of 268 and a SERM. Moreover, this drug combination also induced significant tumor regression when used therapeutically. These drugs did not inhibit transgene expression in vitro or in vivo, and the combination of Arz and 268 inhibited proliferation and induced apoptosis in the tumors. CONCLUSION: The combination of a rexinoid and SERM should be considered for future clinical trials.

Animals↗

PubMed2006

Epidermal growth factor induces insulin receptor substrate-2 in breast cancer cells via c-Jun NH(2)-terminal kinase/activator protein-1 signaling to regulate cell migration.

The epidermal growth factor (EGF) and insulin-like growth factor (IGF) signaling pathways are critically involved in cancer development and progression. However, how these two signals cross-talk with each other to regulate cancer cell growth is not clearly understood. In this study, we found that EGF remarkably induced expression of major IGF signaling components, insulin receptor substrate (IRS)-1 and IRS-2, an effect that could be blocked by EGF receptor (EGFR) tyrosine kinase inhibitors. Although both extracellular signal-regulated kinase and c-Jun NH(2)-terminal kinase (JNK) signaling pathways were involved in the EGF up-regulation of IRS-1, the IRS-2 induction by EGF was specifically mediated by JNK signaling. Consistent with this, EGF increased IRS-2 promoter activity, which was associated with recruitment of activator protein-1 (AP-1) transcription factors and was inhibited by blocking AP-1 activity. Moreover, EGF treatment enhanced IGF-I and integrin engagement-elicited tyrosine phosphorylation of IRS and their downstream signaling, such as binding to phosphatidylinositol 3'-kinase regulatory subunit p85. Finally, repressing the induction of IRS-2 levels abolished the EGF enhancement of cell motility, suggesting that increased IRS-2 is essential for the EGF regulation of breast cancer cell migration. Taken together, our results reveal a novel mechanism of cross-talk between the EGF and IGF signaling pathways, which could have implications in therapeutic applications of targeting EGFR in tumors. Because AP-1 activity is involved in breast cancer progression, our work may also suggest IRS-2 as a useful marker for aggressive breast cancer.

Breast Neoplasms↗

PubMed2006

Akt phosphorylates and suppresses the transactivation of retinoic acid receptor alpha.

The transactivation of nuclear receptors is regulated by both ligand binding and phosphorylation. We previously showed that RARalpha (retinoic acid receptor alpha) phosphorylation by c-Jun N-terminal kinase contributes to retinoid resistance in a subset of NSCLC cells (non-small cell lung cancer cells), but the aetiology of this resistance in the remainder has not been fully elucidated [Srinivas, Juroske, Kalyankrishna, Cody, Price, Xu, Narayanan, Weigel and Kurie (2005) Mol. Cell. Biol. 25, 1054-1069]. In the present study, we report that Akt, which is constitutively activated in NSCLC cells, phosphorylates RARalpha and inhibits its transactivation. Biochemical and functional analyses showed that Akt interacts with RARalpha and phosphorylates the Ser96 residue of its DNA-binding domain. Mutation of Ser96 to alanine abrogated the suppressive effect of Akt. Overexpression of a dominant-negative form of Akt in an NSCLC cell line decreased RAR phosphorylation, increased RAR transactivation and enhanced the growth-inhibitory effects of an RAR ligand. The findings presented here show that Akt inhibits RAR transactivation and contributes to retinoid resistance in a subset of NSCLC cells.

Animals↗

PubMed2005

Receptor-selective retinoids inhibit the growth of normal and malignant breast cells by inducing G1 cell cycle blockade.

Despite advances in treatment, breast cancer continues to be the second leading cause of cancer mortality in women. Statistics suggest that while focus on treatment should continue, chemopreventive approaches should also be pursued. Previous studies have demonstrated that naturally occurring retinoids such as 9-cis retinoic acid (9cRA) can prevent breast cancer in animal models. However, these studies have also shown that these compounds are too toxic for general use. Work from our laboratory showed that an RXR-selective retinoid LGD1069 prevented tumor development in animal models of cancer with reduced toxicity as compared to an RAR-selective retinoid TTNPB. In the present study, we investigated the mechanisms by which receptor-selective retinoids inhibit the growth of normal and malignant breast cells. Our results demonstrate that the synthetic retinoids tested are as effective as 9cRA in suppressing the growth of normal human mammary epithelial cells (HMECs) and estrogen receptor-positive (ER-positive) breast cancer cells. Although the receptor-selective retinoids induce minimal amounts of apoptosis in T47D breast cancer cells, the predominant factor that leads to growth arrest is G1 cell cycle blockade. Our data indicate that this blockade results from the downregulation of Cyclin D1 and Cyclin D3, which in turn causes Rb hypophosphorylation. Non-toxic retinoids that are potent inducers of cell cycle arrest may be particularly useful for the prevention of breast cancer.

Antineoplastic Agents↗

PubMed2005

cFos is critical for MCF-7 breast cancer cell growth.

The activating protein-1 (AP-1) transcription factor is a converging point of multiple signal transduction pathways in many cells. We have previously demonstrated that overexpressing Tam67, a dominant-negative (DN) form of cJun, blocks AP-1 activity and inhibits breast cancer cell growth. We hypothesized that Tam67 forms dimers with other AP-1 proteins to suppress the growth of breast cancer cells. In the present study, we used immunoprecipitation-Western blotting to demonstrate that Tam67 binds all Jun and Fos proteins in breast cancer cells. In addition, we used two variants of the Tam67 mutant to investigate whether Jun or Fos protein was required for breast cancer cell growth. We created a Tam/Fos mutant in which the cJun dimerization domain was replaced by the cFos dimerization domain, and a Tam/Squelcher mutant in which the cJun dimerization domain was deleted. We then isolated MCF-7 cell lines that stably expressed these cJun-DN mutants under the control of an inducible promoter. Using AP-1-dependent reporter assays, we observed that Tam67 and Tam/Fos mutants inhibited AP-1 transcriptional activity, while the Tam/Squelcher mutant did not. We then determined whether Tam/Fos or Tam/Squelcher inhibited breast cell growth as well as Tam67. We found that while Tam67 repressed cell growth, neither Tam/Fos nor Tam/Squelcher mutant affected cell growth. These results indicate that Tam67 likely inactivates Fos family member proteins to suppress breast cancer cell growth. Finally, we performed antisense experiments to knock down the expression of individual family members (cJun or cFos). Our results demonstrated that antisense cFos inhibited breast cancer cell proliferation and colony formation, while antisense cJun did not. These results suggest that Tam67 suppresses breast cancer cell growth by interacting with Fos family members, specifically with cFos, to produce an inactive AP-1 complex.

Breast Neoplasms↗

PubMed2004

AP-1 blockade in breast cancer cells causes cell cycle arrest by suppressing G1 cyclin expression and reducing cyclin-dependent kinase activity.

The AP-1 transcription factor is a central component of signal transduction pathways in many cells, although the exact role of AP-1 in controlling cell growth and malignant transformation is unknown. We have previously shown that AP-1 complexes are activated by peptide and steroid growth factors in both normal and malignant breast cells, and that blocking AP-1 by overexpressing a dominant-negative form of cJun (cJun-DN, TAM67) inhibits breast cancer cell growth both in vivo and in vitro. We hypothesized that TAM67 inhibits cell growth by altering the expression of cell cycle regulatory proteins, thus causing a cell cycle block. In the present study, we used clones of MCF7 breast cancer cells that express TAM67 under the control of an inducible promoter. First, we determined the effect of AP-1 blockade on cell growth, then we performed 3H-thymidine incorporation and flow cytometry assays to investigate whether TAM67 inhibits the cell cycle. We observed that in the presence of serum TAM67 inhibited cell growth and caused a block in the G1 phase of the cell cycle. Next, we performed Western-blotting and CDK kinase assays to determine the effects of TAM67 on retinoblastoma (Rb) phosphorylation, the expression of cell cycle regulatory proteins, and CDK activity. We discovered that TAM67 inhibited Rb phosphorylation and reduced E2F activity. We also found that TAM67 decreased the expression of D and E cyclins, reduced CDK2 and CDK4 activity, and increased the CDK inhibitor p27. The studies of gene expression at the RNA level showed that TAM67 decreased cyclin Ds mRNA expression. Our study suggests that in the presence of serum, TAM67 inhibits breast cancer growth predominantly by inducing inhibitors of cyclin-dependent kinases (such as p27) and by reducing the expression of the cyclins involved in transitioning from G1 into S phase of the cell cycle. These studies lay the foundation for future attempt to develop new agents for the treatment and prevention of breast cancer.

Blood↗

PubMed2004

Dynamics of normal and superfluid fogs using diffusing-wave spectroscopy.

The dynamics of normal and superfluid fogs are studied using the technique of diffusing-wave spectroscopy. For a water fog generated with a 1.75 MHz piezoelectric driver below the liquid surface, the 7 microm diameter droplets are found to have diffusive dynamics for correlation times long compared to the viscous time. For a fog of 10 microm diameter superfluid helium droplets in helium vapor at 1.5 K the motion appears to be ballistic for correlation times short compared to the viscous time. The velocity correlations between the helium droplets are found to depend on the initial velocity with which the droplets are injected from the helium surface into the fog.

Journal Article↗

PubMed2003

Effect of epidermal growth factor receptor inhibitor on development of estrogen receptor-negative mammary tumors.

BACKGROUND: Although antiestrogens have been effective in preventing estrogen receptor (ER)-positive breast cancer, chemopreventive agents are still needed to prevent ER-negative breast cancer. Tyrosine kinase inhibitors are promising agents for the treatment and prevention of human cancers. ZD1839 (gefitinib or Iressa) is an orally active epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor that blocks signal transduction pathways in epithelial cells. We examined whether ZD1839 blocks signal transduction and prevents the development of ER-negative breast cancer. METHODS: The ability of ZD1839 to block signal transduction in normal, immortalized, and malignant breast cells was assessed by western blotting with specific antibodies to detect phosphorylation of cytoplasmic signaling molecules. The effect of ZD1839 on growth of these breast cells was assessed with anchorage-dependent and anchorage-independent growth assays. Its effect on ER-negative mammary tumorigenesis was assessed in MMTV-erbB2 transgenic mice. All statistical tests were two-sided. RESULTS: ZD1839 suppressed the phosphorylation of EGFR and mitogen-activated protein kinase in normal and malignant breast cells. ZD1839 treatment statistically significantly suppressed mammary tumorigenesis in MMTV-erbB2 transgenic mice; median time to tumor development was approximately 230 days in vehicle-treated mice and more than 310 days in mice treated with ZD1839 at 100 mg/kg (P<.001). ZD1839 reduced proliferation of normal breast cells by 20.3% (95% confidence interval [CI] = -13.7% to 44.2%) and of tumor cells by 42.0% (95% CI = 20.2% to 58.2%). ZD1839 also increased expression of the cell cycle regulator p27 in normal mammary tissue by 48.7% (95% CI = 27.0% to 74.2%) and in tumor tissue by 50.3% (95% CI = 35.8% to 66.7%). CONCLUSION: This study appears to provide the preclinical rationale for the development of these EGFR tyrosine kinase inhibitors for the prevention of human breast cancer.

Animals↗