Hypoxia-inducible factor-1 alpha contributes to hypoxia-induced chemoresistance in gastric cancer

Hypoxia-inducible factor 1alpha determines gastric cancer chemosensitivity via modulation of p53 and NF-kappaB

BACKGROUND

Reduced chemosensitivity of solid cancer cells represents a pivotal obstacle in clinical oncology. Hence, the molecular characterization of pathways regulating chemosensitivity is a central prerequisite to improve cancer therapy. The hypoxia-inducible factor HIF-1alpha has been linked to chemosensitivity while the underlying molecular mechanisms remain largely elusive. Therefore, we comprehensively analysed HIF-1alpha's role in determining chemosensitivity focussing on responsible molecular pathways.

METHODOLOGY AND PRINCIPAL FINDINGS

RNA interference was applied to inactivate HIF-1alpha or p53 in the human gastric cancer cell lines AGS and MKN28. The chemotherapeutic agents 5-fluorouracil and cisplatin were used and chemosensitivity was assessed by cell proliferation assays as well as determination of cell cycle distribution and apoptosis. Expression of p53 and p53 target proteins was analyzed by western blot. NF-kappaB activity was characterized by means of electrophoretic mobility shift assay. Inactivation of HIF-1alpha in gastric cancer cells resulted in robust elevation of chemosensitivity. Accordingly, HIF-1alpha-competent cells displayed a significant reduction of chemotherapy-induced senescence and apoptosis. Remarkably, this phenotype was completely absent in p53 mutant cells while inactivation of p53 per se did not affect chemosensitivity. HIF-1alpha markedly suppressed chemotherapy-induced activation of p53 and p21 as well as the retinoblastoma protein, eventually resulting in cell cycle arrest. Reduced formation of reactive oxygen species in HIF-1alpha-competent cells was identified as the molecular mechanism of HIF-1alpha-mediated inhibition of p53. Furthermore, loss of HIF-1alpha abrogated, in a p53-dependent manner, chemotherapy-induced DNA-binding of NF-kappaB and expression of anti-apoptotic NF-kappaB target genes. Accordingly, reconstitution of the NF-kappaB subunit p65 reversed the increased chemosensitivity of HIF-1alpha-deficient cells.

CONCLUSION AND SIGNIFICANCE

In summary, we identified HIF-1alpha as a potent regulator of p53 and NF-kappaB activity under conditions of genotoxic stress. We conclude that p53 mutations in human tumors hold the potential to confound the efficacy of HIF-1-inhibitors in cancer therapy.

Anti-apoptotic role of HIF-1 and AP-1 in paclitaxel exposed breast cancer cells under hypoxia

Background

Hypoxia is a hallmark of solid tumors and is associated with metastases, therapeutic resistance and poor patient survival.

Results

In this study, we showed that hypoxia protected MDA-MB-231 breast cancer cells against paclitaxel- but not epirubicin-induced apoptosis. The possible implication of HIF-1 and AP-1 in the hypoxia-induced anti-apoptotic pathway was investigated by the use of specific siRNA. Specific inhibition of the expression of these two transcription factors was shown to increase apoptosis induced by chemotherapeutic agents under hypoxia indicating an involvement of HIF-1 and AP-1 in the anti-apoptotic effect of hypoxia. After HIF-1 specific inhibition and using TaqMan Human Apoptosis Array, 8 potential HIF-1 target genes were identified which could take part in this protection. Furthermore, Mcl-1 was shown to be a potential AP-1 target gene which could also participate to the hypoxia-induced chemoresistance.

Conclusions

Altogether, these data highlight two mechanisms by which hypoxia could mediate its protective role via the activation of two transcription factors and, consecutively, changes in gene expression encoding different anti- and pro-apoptotic proteins.

Role of hypoxia-inducible transcription factor 1alpha for progression and chemosensitivity of murine hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a hypervascularized tumor entity with association of arterial vessel density with poor prognosis. The hypoxia-inducible transcription factor HIF-1alpha represents a pivotal regulator of angiogenesis and is thought to determine the angiogenic nature of HCC. However, the precise role of HIF-1alpha during the pathogenesis of HCC remains elusive. We established a functional inactivation of HIF-1alpha in vitro and in vivo via RNAi and Cre/loxP-mediated recombination, respectively, to determine HIF-1alpha's role for tumor growth and chemosensitivity in transgenic and orthotopic murine HCC models. HIF-1alpha-deficient HCC cells displayed significantly reduced anchorage-independent growth and enhanced sensitivity toward etoposide, while basic cellular proliferation was unaffected. Analysis of gross tumor growth failed to detect reduced growth of HIF-1alpha-deficient tumors in the orthotopic and the transgenic HCC model, respectively. In line with the in vitro data, treatment of HIF-1alpha-deficient tumors with etoposide resulted in greater antiproliferative efficacy when compared to wild-type mice. Taken together, our study does not support a pivotal role of HIF-1alpha for tumor growth and angiogenesis in two murine HCC models. However, our data point toward a significant function of HIF-1alpha in determining chemosensitivity of HCC and therefore warrant validation of HIF-1alpha-inhibitors as adjuvant therapeutic agents in clinical studies of human HCC.

Expression and significance of hypoxia-inducible factor-1 alpha and MDR1/P-glycoprotein in human colon carcinoma tissue and cells

PURPOSE

Hypoxia in tumors is generally associated with chemoresistance and radioresistance. However, the correlation between the heterodimeric hypoxia-inducible factor-1 (HIF-1) and the multidrug resistance (MDR1) gene/transporter P-glycoprotein (P-gp) has not been clearly investigated. This study aims at examining the expression levels of HIF-1α and MDR1/P-gp in human colon carcinoma tissues and cell lines (HCT-116, HT-29, LoVo, and SW480) and ascertaining whether HIF-1α plays an important role in tumor multidrug resistance with MDR1/P-gp.

METHODS

The expression and distribution of HIF-1α and P-gp proteins were detected in human colon carcinoma tissues and cell lines by immunohistochemistry and immunocytochemistry using streptavidin/peroxidase (SP) and double-label immunofluorescence methods. HIF-1α and MDR1 mRNA expression levels in cell lines were analyzed using RT-PCR under normoxic and hypoxic conditions, respectively.

RESULTS

The immunohistochemical method shows that HIF-1α and P-gp expression were not correlated with gender, age, location, and differentiation degree (P > 0.05). However, the expression of HIF-1α and P-gp at different Dukes' stages and whether involved in lymphatic invasion shows a significant difference (P < 0.05). Correlation analysis displays that HIF-1α protein expression was correlated significantly with P-gp expression (P < 0.01). Double-label immunofluorescence demonstrates that coexpression of HIF-1α and P-gp does exist in human colon carcinoma tissues. The mRNA expression of HIF-1α and MDR1 was detected in the four human colon carcinoma cell lines under both normoxia and hypoxia. Optical density values representing mRNA expression levels of HIF-1α and MDR1 were found to be significantly higher in the same type cells under hypoxic conditions than that under normoxic conditions, respectively (P < 0.01). However, no significant differences of HIF-1α or MDR1 mRNA expression were found among these cell lines, which exposed under the same PaO(2) cultural conditions (P > 0.05). And the immunocytochemistry results were corresponding with the analysis of mRNA expression.

CONCLUSIONS

These results suggest that hypoxia induce the expression of HIF-1α and MDR1/P-gp in colon carcinoma and HIF-1α expression may be associated with the gene MDR1 (P-gp) and interactively involved in the occurrence of tumor multidrug resistance.

Se-methylselenocysteine sensitizes hypoxic tumor cells to irinotecan by targeting hypoxia-inducible factor 1alpha

PURPOSE

Hypoxic tumor cells overexpressing hypoxia-inducible factor 1alpha (HIF-1alpha) are generally resistant to chemo/radiotherapy. We have reported that Se-methylselenocysteine (MSC) therapeutically enhances the efficacy and selectivity of irinotecan against human tumor xenografts. The aim of this study was to delineate the mechanism responsible for the observed efficacy targeting on HIF-1alpha and its transcriptionally regulated genes VEGF and CAIX.

METHODS

We investigated the mechanism of HIF-1alpha inhibition by MSC and its critical role in the therapeutic outcome by generating HIF-1alpha stable knockdown (KD) human head and neck squamous cell carcinoma, FaDu by transfecting HIF-1alpha short hairpin RNA.

RESULTS

While cytotoxic efficacy in combination with methylselenic acid (MSA) with SN-38 (active metabolites of MSC and irinotecan) could not be confirmed in vitro against normoxic tumor cells, the hypoxic tumor cells were more sensitive to the combination. Reduction in HIF-1alpha either by MSA or shRNA knockdown resulted in significant increase in cytotoxicity of SN38 in vitro against hypoxic, but not the normoxic tumor cells. Similarly, in vivo, either MSC in combination with irinotecan treatment of parental xenografts or HIF-1alpha KD tumors treated with irinotecan alone resulted in comparable therapeutic response and increase in the long-term survival of mice bearing FaDu xenografts.

CONCLUSIONS

Our results show that HIF-1alpha is a critical target for MSC and its inhibition was associated with enhanced antitumor activity of irinotecan. Inhibition of HIF-1alpha appeared to be mediated through stabilization of PHD2, 3 and downregulation of ROS by MSC. Thus, our findings support the development of MSC as a HIF-1alpha inhibitor in combination chemotherapy.

Pim-1 plays a pivotal role in hypoxia-induced chemoresistance

Hypoxia changes the responses of cancer cells to many chemotherapy agents, resulting in chemoresistance. The underlying molecular mechanism of hypoxia-induced drug resistance remains unclear. Pim-1 is a survival kinase, which phosphorylates Bad at serine 112 to antagonize drug-induced apoptosis. Here we show that hypoxia increases Pim-1 in a hypoxia-inducible factor-1alpha-independent manner. Inhibition of Pim-1 function by dominant-negative Pim-1 dramatically restores the drug sensitivity to apoptosis induced by chemotherapy under hypoxic conditions in both in vitro and in vivo tumor models. Introduction of siRNAs for Pim-1 also resensitizes cancer cells to chemotherapy drugs under hypoxic conditions, whereas forced overexpression of Pim-1 endows solid tumor cells with resistance to cisplatin, even under normoxia. Dominant-negative Pim-1 prevents a decrease in mitochondrial transmembrane potential in solid tumor cells, which is normally induced by cisplatin (CDDP), followed by the reduced activity of Caspase-3 and Caspase-9, indicating that Pim-1 participates in hypoxia-induced drug resistance through the stabilization of mitochondrial transmembrane potential. Our results demonstrate that Pim-1 is a pivotal regulator involved in hypoxia-induced chemoresistance. Targeting Pim-1 may improve the chemotherapeutic strategy for solid tumors.

Inhibition of HIF-1alpha activity by homeodomain-interacting protein kinase-2 correlates with sensitization of chemoresistant cells to undergo apoptosis

BACKGROUND

Homeodomain-interacting protein kinase-2 (HIPK2), a transcriptional co-repressor with apoptotic function, can affect hypoxia-inducible factor 1 (HIF-1) transcriptional activity, through downmodulation of its HIF-1alpha subunit, in normoxic condition. Under hypoxia, a condition often found in solid tumors, HIF-1alpha is activated to induce target genes involved in chemoresistance, inhibition of apoptosis and tumor progression. Here, we investigated whether the HIPK2 overexpression could downregulate HIF-1alpha expression and activity in tumor cells treated with hypoxia-mimicking condition, and evaluated whether HIPK2-dependent downregulation of HIF-1alpha could sensitize chemoresistant tumor cells to adriamycin (ADR)-induced apoptosis.

METHODS

Tumor cell lines carrying wild-type p53, siRNA p53, or mutant p53 were overexpressed with HIPK2 (full length or catalytic inactive mutant) and treated with cobalt chloride (CoCl2) to mimic hypoxia, in the presence or absence of ADR treatment. HIF-1alpha expression was measured by semiquantitative reverse-transcriptase (RT)-PCR and Western immunoblotting and HIF-1 activity was evaluated by luciferase assay using reporter plasmid containing hypoxia response elements (HREs) upstream of luciferase gene. HIF-1 target genes, including multidrug resistance 1 (MDR1) and the antiapoptotic Bcl2 were determined by RT-PCR. Cell survival and apoptosis were measured by colony assay and cleavage of the caspase-3 substrate PARP, respectively.

RESULTS

Overexpression of HIPK2 resulted in downmodulation of cobalt-stabilized HIF-1alpha protein and HIF-1alpha mRNA levels, with subsequent inhibition of HIF-1 transcriptional activity. MDR1 and Bcl-2 gene expression was downmodulated by HIPK2 overexpression in cobalt-treated cells. Inhibition of HIF-1 transcriptional activity was dependent on HIPK2 catalytic activity. HIPK2 overexpression did not induce per se apoptosis of cobalt-treated cells, on the contrary it sensitized cobalt-treated cells to ADR-induced apoptosis, regardless of their p53 status.

CONCLUSION

The ability of HIPK2 to restore the apoptosis-inducing potential of chemotherapeutic drug in hypoxia-mimicking condition and therefore to sensitize chemoresistant tumor cells suggests that HIPK2 may induce fundamental alterations in cell signaling pathways, involving or not p53 function. Thus potential use of HIPK2 is promising for cancer treatment by potentiating cytotoxic therapies, regardless of p53 cell status.