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Biomedical subjects

Z Dong

Publications and source records attributed to Z Dong.

At least 37 records · Page 2Linked to original sources
PubMed2001

Inhibitory mechanisms of tea polyphenols on the ultraviolet B-activated phosphatidylinositol 3-kinase-dependent pathway.

In this study, we investigated the effect of tea polyphenols, (-)-epigallocatechin-3-gallate or theaflavins, on UVB-induced phosphatidylinositol 3-kinase (PI3K) activation in mouse epidermal JB6 Cl 41 cells. Pretreatment of cells with these polyphenols inhibited UVB-induced PI3K activation. Furthermore, UVB-induced activation of Akt and ribosomal p70 S6 kinase (p70 S6-K), PI3K downstream effectors, were also attenuated by the polyphenols. In addition to LY294002, a PI3K inhibitor, pretreatment with a specific mitogen-activated protein/extracellular signal-regulated protein kinases (Erks) kinase 1 inhibitor, U0126, or a specific p38 kinase inhibitor, SB202190, blocked UVB-induced activation of both Akt and p70 S6-K. Pretreatment with LY294002 restrained UVB-induced phosphorylation of Erks, suggesting that in UVB signaling, the Erk pathway is mediated by PI3K. Moreover, pretreatment with rapamycin, an inhibitor of p70 S6-K, inhibited UVB-induced activation of p70 S6-K, but UVB-induced activation of Akt did not change. Interestingly, UVB-induced p70 S6-K activation was directly blocked by the addition of (-)-epigallocatechin-3-gallate or theaflavins, whereas these polyphenols showed only a weak inhibition on UVB-induced Akt activation. Because PI3K is an important factor in carcinogenesis, the inhibitory effect of these polyphenols on activation of PI3K and its downstream effects may further explain the anti-tumor promotion action of these tea constituents.

Animals↗
PubMed2001

MSK1 and JNKs mediate phosphorylation of STAT3 in UVA-irradiated mouse epidermal JB6 cells.

Phosphorylation of Tyr(705) and Ser(727) of signal transducer and activator of transcription 3 (STAT3) are known to be required for maximal activation by diverse stimuli. Tyr(705) phosphorylation is generally accepted to be mediated by the Janus kinase family. But the mechanism for STAT3 (Ser(727)) phosphorylation is not well understood. Here, we provide evidence that UVA-induced phosphorylation of STAT3 at Ser(727) is inhibited by pretreatment of JB6 cells with PD98059 or SB202190. Phosphorylation of STAT3 (Ser(727)) is also markedly prevented by a dominant negative mutant of ERK2, c-Jun N-terminal kinase 1 (JNK1), or p38 kinase and in knockout Jnk1(-/-) or Jnk2(-/-) cells. Furthermore, STAT3 (Ser(727)) phosphorylation is suppressed by C- or N-terminal "kinase-dead" mutants of mitogen- and stress-activated protein kinase 1 (MSK1), a downstream kinase of ERKs and p38 kinase, and H89, a potential MSK1 inhibitor. In vitro experiments showed that active MSK1 and JNKs, but not ERKs or p38 kinase, phosphorylate STAT3 (Ser(727)). Additionally, the role of MAPKs in mediating UVA-stimulated DNA binding activity of STAT3 was investigated. Overall, these results suggest that UVA-induced Ser(727) phosphorylation of STAT3 may occur through MSK1 and JNKs.

Animals↗
PubMed2001

Vascular endothelial growth factor: acting as an autocrine growth factor for human gastric adenocarcinoma cell MGC803.

Vascular endothelial growth factor (VEGF) is known to be a highly specific mitogen for endothelial cells through two high-affinity tyrosine kinase receptors, VEGFR-1 and VEGFR-2, which are almost specifically expressed in endothelial cells. However, recent findings showed that VEGF receptors may also expressed by nonendothelial cells, especially by tumor cells. To further understand the functional expression of VEGF receptors by nonendothelial cells, our preliminary screening detected the expression of VEGFR-2 in 115 different paraffin-embedded cancer specimens including 35 cases of bladder tumor, 30 cases of breast cancer, 25 cases of intestinal cancer, and 25 cases of lung cancer with immunohistochemistry. The results showed that VEGFR-2 was widely expressed in different tumor tissues. By reverse transcription PCR, NCI-H23, NCI-H460, MGC803, MDA-MB-231, 293, and MCF7 cells were evaluated for the mRNA expression of both VEGF and VEGFR-2. The data indicated that all these tumor cell lines expressed detectable amounts of VEGF mRNA, but only 293, MCF7, and MGC803 cells coexpressed VEGFR-2. Immunoblot analysis also demonstrated the expression of VEGFR-2 at protein level. We further demonstrate that exogenous rhVEGF(165) could stimulate cell growth in MGC803, a tumor cell line derived from gastric adenocarcinoma, in a dose- and time-dependent manner. Furthermore, the antibodies against rhVEGF(165) and VEGFR-2 could block rhVEGF(165)-mediated proliferation of MGC803 cells. These unexpected results provided direct evidence that VEGF may act as an autocrine growth factor to induce the proliferation of gastric adenocarcinoma cells as well as tumor angiogenic cells, thus suggesting a promising tumor therapeutic application based upon the VEGF system.

Adenocarcinoma↗
PubMed2001

Differential regulation of matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 expression in co-cultures of prostate cancer and stromal cells.

Tumor-stromal interactions have been suggested to be a critical factor in both tumor invasion and tumor metastasis. Here, we examined the role of tumor-stromal interactions using co-cultures of prostate cancer (PC) cells derived from primary and metastatic tumors with primary or immortalized stromal (fibroblast and smooth muscle) cells and their effect on matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) expression. Co-cultures of PC and stromal cells showed enhanced levels of pro-MMP-9 and reduced levels of TIMP-1 and TIMP-2. Whereas enhanced expression of pro-MMP-9 occurred in PC cells, the TIMPs were down-regulated in stromal cells. Induction of pro-MMP-9 and reduction of TIMP expression did not require cell-cell contact and were mediated by a soluble factor(s) present in the conditioned medium of the effector cell. Collagen I is a potent inducer of pro-MMP-9 in PC cells. Consistently, preliminary characterization of the soluble factor in the fibroblast conditioned medium revealed m.w. of approximately 100 to 250 kDa, and its effect on pro-MMP-9 expression was partly inhibited by an anti-alpha2 integrin antibody, a major collagen I receptor. Expression of pro-MMP-9 protein and mRNA was also induced in metastatic PC-3 cells grown in human fetal bone implants in SCID mice. Together, these findings demonstrate the importance of tumor-stromal interactions in the regulation of MMP and TIMP expression and their potential role in PC progression.

Animals↗
PubMed2001

Two novel glycosides from the fruits of Morinda citrifolia (noni) inhibit AP-1 transactivation and cell transformation in the mouse epidermal JB6 cell line.

The fruit juice of Morinda citrifolia (noni), a plant originally grown in the Hawaiian and Tahitian islands, has long been used by islanders to treat diseases, including cancer. Two novel glycosides, 6-O-(beta-D-glucopyranosyl)-1-O-octanoyl-beta-D-glucopyranose and asperulosidic acid, extracted from the juice of noni fruits, were used to examine their effects on 12-O-tedtradecanoylphorbol-13-acetate (TPA)- and epidermal growth factor (EGF)-induced AP-1 transactivation and cell transformation in mouse epidermal JB6 cells. The results indicated that both compounds were effective in suppressing TPA- or EGF-induced cell transformation and associated AP-1 activity. TPA- or EGF-induced phosphorylation of c-Jun, but not extracellular signal-regulated kinases or p38 kinases, was also blocked by the compounds, indicating that c-Jun N-terminal kinases were critical in mediating TPA- or EGF-induced AP-1 activity and subsequent cell transformation in JB6 cells.

Animals↗
PubMed2001

Mechanisms of inhibition of the Ras-MAP kinase signaling pathway in 30.7b Ras 12 cells by tea polyphenols (-)-epigallocatechin-3-gallate and theaflavin-3,3'-digallate.

Our previous study showed that tea polyphenols inhibited MAP kinase and AP-1 activities in mouse epidermal JB6 cells and the corresponding H-ras-transformed cell line 30.7b Ras 12. The present study investigated the mechanisms of this inhibition. The cells were incubated with (-)-epigallocatechin-3-gallate (EGCG) or theaflavin-3,3'-digallate (TFdiG) (20 mM) for different times, and the cell lysate was analyzed by immunoblotting. EGCG treatment decreased the levels of phospho-Erk1/2 and -MEK1/2 time-dependently (by 60% at 60 min). TFdiG lowered their levels by 38%-50% at 15 min. TFdiG effectively decreased total Raf-1 protein levels, most likely through lysosomal degradation. EGCG did not affect protein levels or the activity of Raf-1 significantly but decreased its association with MEK1 as determined by co-immunoprecipitation. In addition, EGCG and TFdiG (10 mM) inhibited the phosphorylation of Elk-1 by isolated phospho-Erk1/2 in vitro. This inhibition of Erk1/2 activity is Elk-1 concentration-dependent and ATP concentration-independent, which suggests that EGCG and TFdiG interfere with the binding of the protein substrate to the kinase. The presently demonstrated specific mechanisms of inhibition of MAP kinases by EGCG and TFdiG may help us to understand the effects of tea consumption on cancer, inflammatory diseases, and cardiovascular diseases.

Adenosine Triphosphate↗
PubMed2001

Ultraviolet B-induced phosphorylation of histone H3 at serine 28 is mediated by MSK1.

N-terminal tail phosphorylation of histone H3 plays an important role in gene expression, chromatin remodeling, and chromosome condensation. Phosphorylation of histone H3 at serine 10 was shown to be mediated by RSK2, mitogen- and stress-activated protein kinase-1 (MSK1), and mitogen-activated protein kinases depending on the specific stimulation or stress. Our previous study showed that mitogen-activated protein kinases MAP kinases are involved in ultraviolet B-induced phosphorylation of histone H3 at serine 28 (Zhong, S., Zhong, Z., Jansen, J., Goto, H., Inagaki, M., and Dong, Z., J. Biol. Chem. 276, 12932-12937). However, downstream effectors of MAP kinases remain to be identified. Here, we report that H89, a selective inhibitor of the nucleosomal response, totally inhibits ultraviolet B-induced phosphorylation of histone H3 at serine 28. H89 blocks MSK1 activity but does not inhibit ultraviolet B-induced activation of MAP kinases p70/85(S6K), p90(RSK), Akt, and protein kinase A. Furthermore, MSK1 markedly phosphorylated serine 28 of histone H3 and chromatin in vitro. Transfection experiments showed that an N-terminal mutant MSK1 or a C-terminal mutant MSK1 markedly blocked MSK1 activity. Compared with wild-type MSK1, cells transfected with N-terminal or C-terminal mutant MSK1 strongly blocked ultraviolet B-induced phosphorylation of histone H3 at serine 28 in vivo. These data illustrate that MSK1 mediates ultraviolet B-induced phosphorylation of histone H3 at serine 28.

Animals↗
PubMed2001

Omega 3 but not omega 6 fatty acids inhibit AP-1 activity and cell transformation in JB6 cells.

Epidemiological and animal-based investigations have indicated that the development of skin cancer is in part associated with poor dietary practices. Lipid content and subsequently the derived fatty acid composition of the diet are believed to play a major role in the development of tumorigenesis. Omega 3 (omega3) fatty acids, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), can effectively reduce the risk of skin cancer whereas omega 6 (omega6) fatty acids such as arachidonic acid (AA) reportedly promote risk. To investigate the effects of fatty acids on tumorigenesis, we performed experiments to examine the effects of the omega3 fatty acids EPA and DHA and of the omega6 fatty acid AA on phorbol 12-tetradecanoate 13-acetate (TPA)-induced or epidermal growth factor (EGF)-induced transcription activator protein 1 (AP-1) transactivation and on the subsequent cellular transformation in a mouse epidermal JB6 cell model. DHA treatment resulted in marked inhibition of TPA- and EGF-induced cell transformation by inhibiting AP-1 transactivation. EPA treatment also inhibited TPA-induced AP-1 transactivation and cell transformation but had no effect on EGF-induced transformation. AA treatment had no effect on either TPA- or EGF-induced AP-1 transactivation or transformation, but did abrogate the inhibitory effects of DHA on TPA- or EGF-induced AP-1 transactivation and cell transformation in a dose-dependent manner. The results of this study demonstrate that the inhibitory effects of omega3 fatty acids on tumorigenesis are more significant for DHA than for EPA and are related to an inhibition of AP-1. Similarly, because AA abrogates the beneficial effects of DHA, the dietary ratio of omega6 to omega3 fatty acids may be a significant factor in mediating tumor development.

Animals↗
PubMed2001

Study on the abundance of CFCs varying with the latitude at the bottom of the troposphere in the southern hemisphere.

As the main ozone depleting compounds, the abundance of CFCs in the troposphere and stratosphere has been focused on all the while. However, there are few reports concerning on the CFCs' latitudinal dependence. Relying on the longterm monitoring that has been performed in Shanghai from 1997 and Cooperating with the Chinese Third Antarctic Inland Ice-sheet Traversal Party, we did intensive sampling in the southern hemisphere from the beginning of November to the end of December in 1998 and then got the corresponding concentrations of CFC-12, CFC-11, and CFC-113 according to the latitude. The data were studied inductively in accordance with the geographical location and meteorological condition of every sampling point. In summary, the average concentrations of CFCs (refer to CFC-11, CFC-12, and CFC-113) in equatorial area are the highest in the southern hemisphere; however, the concentrations in prevailing west-wind belt and polar east-wind belt are much lower and at the same levels, which should be a perfect implication of the mean background in the southern hemisphere. Being related to the special polar circumfluence, the concentrations of CFCs on the glacier reveal a special rise. Compared with the mean background of the southern hemisphere that is represented by the data of the prevailing west-wind belt and Polar east-wind belt, the concentrations in Shanghai bear the same level.

Air Movements↗
PubMed2001

Suppression of skin tumorigenesis in c-Jun NH(2)-terminal kinase-2-deficient mice.

Previous studies have shown that c-Jun NH(2)-terminal kinase (JNK) belongs to the mitogen-activated protein kinase (MAPK) family of signal transduction components that are rapidly initiated and activated by many extracellular stimuli. However, the potential role of JNK in mediating tumor promotion and carcinogenesis is unclear. We show here that in JNK2-deficient (Jnk2(-/-)) mice, the multiplicity of papillomas induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) was lower than that in wild-type mice. Papillomas on wild-type mice grew rapidly and were well vascularized compared with Jnk2(-/-) mice. After the 12th week of TPA treatment, the mean number of tumors per mouse was 4.13-4.86 in wild-type mice but only 1.13-2.5 in Jnk2(-/-) mice. TPA induced phosphorylation of extracellular signal-regulated kinases and activator protein-1 DNA binding activity in wild-type mice, but the phosphorylation of extracellular signal-regulated kinases and activator protein-1 DNA binding were inhibited in Jnk2(-/-) mice. These data suggest that JNK2 is critical in the tumor promotion process.

Animals↗
PubMed2001

Organ-specific activation of activator protein-1 in transgenic mice by 12-o-tetradecanoylphorbol-13-acetate with different administration methods.

12-O-Tetradecanoylphorbol-13-acetate (TPA) is widely used as a tumor promoter with organotropy in skin and esophagus. TPA-induced, organ-specific tumor promotion is not correlated with the distribution of its receptor, protein kinase C (PKC). Using five administration methods (painting, drinking, gavage feeding, i.p. injection, and i.v. injection), we analyzed TPA-stimulated activator protein-1 (AP-1) activity in various organs (liver, kidney, brain, lung, spleen, heart, stomach, colon, esophagus, and skin) from transgenic mice expressing the AP-1 luciferase reporter gene. Topical application of TPA by painting the skin on the back of mice raised AP-1 activity 122.6-fold, and the highest peak of AP-1 activity was at 12 h after administration of TPA. Drinking water containing TPA caused a 25.8-fold induction of AP-1 activity in the skin, whereas gavage feeding with TPA caused a 34.2-fold induction of AP-1 in the skin. Intraperitoneal or i.v. injection of TPA induced a 49.56-fold or 20.4-fold increase in AP-1 activity in the skin, respectively. The highest peaks of AP-1 activity in the skin were at 12 h after drinking, feeding, or injection of TPA. More interesting, in the esophagus, i.p. injection of TPA raised AP-1 activity 13.9-fold, drinking TPA raised AP-1 activity 8.4-fold, and painting with TPA caused a 2.4-fold induction of AP-1 activity. In the colon, i.p. injection of TPA raised AP-1 activity 3.9-fold, drinking TPA induced a 1.2-fold increase in AP-1 activity, but painting with TPA had no effect. AP-1 activity in other organs was not detectable after administration of TPA by painting, drinking, or injection. Phosphorylation of extracellular signal-regulated kinases in the skin increased at 12 h after painting, drinking, or i.p. injection of TPA. In addition, phosphorylation of p38 kinase was raised slightly after TPA administration, but phosphorylation of c-Jun NH(2)-terminal kinases was not detected at any time point after TPA administration. Similar changes in MAP kinases were also seen in the esophagus after TPA administration. These results indicate that the skin is the most sensitive organ to TPA induction of AP-1 activity. The data suggest that the organ-specific, tumor-promoting effect of TPA may be through AP-1 activation and phosphorylation of ERKs and p38 kinase.

Animals↗
PubMed2001

Mitogen- and stress-activated protein kinase 1 mediates activation of Akt by ultraviolet B irradiation.

In this study, we investigated the mechanism by which UVB irradiation activates Akt (also known as protein kinase B (PKB)) in mouse epidermal JB6 cells. Treatment with a phosphatidylinositol 3-kinase inhibitor, LY 294002, or expression of a dominant negative mutant of p85 (regulatory component of phosphatidylinositol 3-kinase) inhibited UVB-induced Akt activation. Interestingly, Akt activation by UVB was attenuated by treatment with PD 98059, a specific mitogen-activated protein kinase/extracellular signal-regulated protein kinase (Erk) kinase 1 inhibitor, or SB 202190, a specific p38 kinase inhibitor. Furthermore, the expression of a dominant negative mutant of Erk2 or p38 kinase, but not that of c-Jun N-terminal kinase 1 (JNK1), blocked UVB-induced Akt activation. The expression of a dominant negative mutant of p85 or treatment with LY 294002 also inhibited UVB-induced Erk phosphorylation. The UVB-activated mitogen-activated protein kinase members, which were immunoprecipitated from cells exposed to UVB, did not phosphorylate Akt. Instead, Akt was phosphorylated at both threonine 308 and serine 473 and activated by UVB-activated mitogen- and stress-activated protein kinase 1 (Msk1). The expression of a Msk1 C-terminal kinase-dead mutant inhibited UVB-induced phosphorylation and activation of Akt. These data thus suggested that UVB-induced Akt activation was mediated through Msk1, which is a downstream kinase of the Erk and p38 kinase signaling pathways.

Animals↗
PubMed2001

Proteinase inhibitors I and II from potatoes block UVB-induced AP-1 activity by regulating the AP-1 protein compositional patterns in JB6 cells.

Proteinase inhibitor I (Inh I) and proteinase inhibitor II (Inh II) from potato tubers are effective proteinase inhibitors of chymotrypsin and trypsin. Inh I and Inh II were shown to suppress irradiation-induced transformation in mouse embryo fibroblasts suggesting that they possess anticarcinogenic characteristics. We have previously demonstrated that Inh I and Inh II could effectively block UV irradiation-induced activation of transcription activator protein 1 (AP-1) in mouse JB6 epidermal cells, which mechanistically may explain their anticarcinogenic actions. In the present study, we investigated the effects of Inh I and Inh II on the expression and composition pattern of the AP-1 complex following stimulation by UV B (UVB) irradiation in the JB6 model. We found that Inh I and Inh II specifically inhibited UVB-induced AP-1, but not NFkappaB, activity in JB6 cells. Both Inh I and Inh II up-regulated AP-1 constituent proteins, JunD and Fra-2, and suppressed c-Jun and c-Fos expression and composition in bound AP-1 in response to UVB stimulation. This regulation of the AP-1 protein compositional pattern in response to Inh I or Inh II may be critical for the inhibition of UVB-induced AP-1 activity by these agents found in potatoes.

Base Sequence↗
PubMed2001

Signal transduction pathways involved in phosphorylation and activation of p70S6K following exposure to UVA irradiation.

Ultraviolet light A (UVA) plays an important role in the etiology of human skin cancer, and UVA-induced signal transduction has a critical role in UVA-induced skin carcinogenesis. The upstream signaling pathways leading to p70(S6K) phosphorylation and activation are not well understood. Here, we observed that UVA induces phosphorylation and activation of p70(S6K). Further, UVA-stimulated p70(S6K) activity and phosphorylation at Thr(389) were blocked by wortmannin, rapamycin, PD98059, SB202190, and dominant negative mutants of phosphatidylinositol (PI) 3-kinase p85 subunit (DNM-Deltap85), ERK2 (DNM-ERK2), p38 kinase (DNM-p38), and JNK1 (DNM-JNK1) and were absent in Jnk1-/- or Jnk2-/- knockout cells. The p70(S6K) phosphorylation at Ser(411) and Thr(421)/Ser(424) was inhibited by rapamycin, PD98059, or DNM-ERK2 but not by wortmannin, SB202190, DNM-Deltap85, or DNM-p38. However, Ser(411), but not Thr(421)/Ser(424) phosphorylation, was suppressed in DNM-JNK1 and abrogated in Jnk1-/- or Jnk2-/- cells. In vitro assays indicated that Ser(411) on immunoprecipitated p70(S6K) proteins is phosphorylated by active JNKs and ERKs, but not p38 kinase, and Thr(421)/Ser(424) is phosphorylated by ERK1, but not ERK2, JNKs, or p38 kinase. Moreover, p70(S6K) co-immunoprecipitated with PI 3-kinase and possibly PDK1. The complex possibly possessed a partial basal level of phosphorylation, but not at MAPK sites, which was available for its activation by MAPKs in vitro. Thus, these results suggest that activation of MAPKs, like PI 3-kinase/mTOR, may be involved in UVA-induced phosphorylation and activation of p70(S6K).

Androstadienes↗
PubMed2001

Lymphoproliferative disorders in renal transplant patients in Japan.

Post-transplantation lymphoproliferative disorders (PT-LPD) are characterized by a clinically and morphologically heterogeneous group of lymphoid proliferation occurring after organ or bone marrow transplantation. The immunodeficient state provides a basis for lymphomagenesis probably through activation of oncogenic viruses. Twenty-four patients in whom PT-LPD developed after renal transplantation in Japan were analyzed. They received hemodialysis for 4 to 226 (median 13) months before transplantation. In situ hybridization was performed to detect Epstein-Barr virus (EBV). Polymerase chain reaction and Southern hybridization with primers in the tax and pol regions of human T-cell leukemia virus type I (HTLV-1) were performed on DNA extracted from paraffin-embedded specimens. Immunohistochemical analysis revealed that 12 cases were B-cell type, 10 cases (42%) T-cell type and 2 NK-cell type. Five of the T-cell cases were classified as adult T-cell lymphoma with proven HTLV-1 genome in the tumor and seropositivity for the virus. These cases were classified as adult T-cell lymphoma (ALT). More than 80% of B-cell, 30% of T-cell and both NK/T-cell lymphomas were EBV-positive. Co-infection of EBV and HTLV-1 was found in 2 cases with ATL. These findings showed that ATL is common among Japanese renal transplant patients, which might be due to transmission of HTLV-1 via blood transfusion during hemodialysis.

Adolescent↗
PubMed2001

Up-regulation of apoptosis inhibitory protein IAP-2 by hypoxia. Hif-1-independent mechanisms.

Hypoxia is a key determinant of tissue pathology during tumor development and organ ischemia. However, little is known regarding hypoxic regulation of genes that are directly involved in cell death or death resistance. Here we report the striking induction by severe hypoxia of the anti-apoptotic protein IAP-2. Hypoxic cells with IAP-2 up-regulation became resistant to apoptosis. IAP-2 was induced by hypoxia per se rather than by the secondary effects of hypoxia, including ATP depletion and cell injury. The inductive response did not relate to alterations of cellular redox status or arrest of mitochondrial respiration. On the other hand, IAP-2 induction was attenuated by actinomycin D, suggesting a role for gene transcription. In vitro nuclear run-on assays demonstrated specific increases in IAP-2 transcriptional activity after hypoxia exposure. HIF-1, the primary transcription factor that is responsible for multiple gene activation under hypoxia, does not have a role in IAP-2 expression. HIF-1 and IAP-2 were induced by different degrees of hypoxia; severe hypoxia or anoxia was required for IAP-2 induction. Moreover, cobalt chloride and desferrioxamine activated HIF-1 but not IAP-2. Finally, IAP-2 was induced by severe hypoxia in mouse embryonic stem cells that were deficient of HIF-1. Thus, this study not only provides the first demonstration of hypoxic regulation of an anti-apoptotic gene but also suggests the participation of novel hypoxia-responsive transcription mechanisms.

3T3 Cells↗
PubMed2001

Bcl-2 prevents Bax oligomerization in the mitochondrial outer membrane.

ATP depletion results in Bax translocation from cytosol to mitochondria and release of cytochrome c from mitochondria into cytosol in cultured kidney cells. Overexpression of Bcl-2 prevents cytochrome c release, without ameliorating ATP depletion or Bax translocation, with little or no association between Bcl-2 and Bax as demonstrated by immunoprecipitation (Saikumar, P., Dong, Z., Patel, Y., Hall, K., Hopfer, U., Weinberg, J. M., and Venkatachalam, M. A. (1998) Oncogene 17, 3401-3415). Now we show that translocated Bax forms homo-oligomeric structures, stabilized as chemical adducts by bifunctional cross-linkers in ATP-depleted wild type cells, but remains monomeric in Bcl-2-overexpressing cells. The protective effects of Bcl-2 did not require Bcl-2/Bax association, at least to a degree of proximity or affinity that was stable to conditions of immunoprecipitation or adduct formation by eight cross-linkers of diverse spacer lengths and chemical reactivities. On the other hand, nonionic detergents readily induced homodimers and heterodimers of Bax and Bcl-2. Moreover, associations between translocated Bax and the voltage-dependent anion channel protein or the adenine nucleotide translocator protein could not be demonstrated by immunoprecipitation of Bax, or by using bifunctional cross-linkers. Our data suggest that the in vivo actions of Bax are at least in part dependent on the formation of homo-oligomers without requiring associations with other molecules and that Bcl-2 cytoprotection involves mechanisms that prevent Bax oligomerization.

Animals↗