The switch of cellular metabolism from mitochondrial respiration to glycolysis is the hallmark of cancer cells and associated with tumor malignancy. However, the mechanism of this metabolic switch remains largely unknown. Herein, we reported that hypoxia-inducible factor-1 (HIF-1) induced pyruvate dehydrogenase kinase-3 (PDK3) expression leading to inhibition of mitochondrial respiration. Promoter activity assay, small interference RNA knockdown assay, and chromatin immunoprecipitation assay demonstrated that hypoxia-induced PDK3 gene activity was regulated by HIF-1 at the transcriptional level. Forced expression of PDK3 in cancer cells resulted in increased lactic acid accumulation and drugs resistance, whereas knocking down PDK3 inhibited hypoxia-induced cytoplasmic glycolysis and cell survival. These data demonstrated that increased PDK3 expression due to elevated HIF-1␣ in cancer cells may play critical roles in metabolic switch during cancer progression and chemoresistance in cancer therapy.

Huntington disease (HD) is a dominantly inherited neurodegenerative disorder characterized by dysregulation of various genes. Recently, microRNAs (miRNAs) have been reported to be involved in this dysregulation, suggesting that manipulation of appropriate miRNA regulation may have a therapeutic benefit. Here, we report the beneficial effects of miR-196a (miR196a) on HD in cell, transgenic mouse models, and human induced pluripotent stem cells derived from one individual with HD (HD-iPSCs). In the in vitro results, a reduction of mutant HTT and pathological aggregates, accompanying the overexpression of miR-196a, was observed in HD models of human embryonic kidney cells and mouse neuroblastoma cells. In the in vivo model, HD transgenic mice overexpressing miR-196a revealed the suppression of mutant HTT in the brain and also showed improvements in neuropathological progression, such as decreases of nuclear, intranuclear, and neuropil aggregates and late-stage behavioral phenotypes. Most importantly, miR-196a also decreased HTT expression and pathological aggregates when HD-iPSCs were differentiated into the neuronal stage. Mechanisms of miR-196a in HD might be through the alteration of ubiquitin-proteasome systems, gliosis, cAMP response element-binding protein pathway, and several neuronal regulatory pathways in vivo. Taken together, these results show that manipulating miR-196a provides beneficial effects in HD, suggesting the potential therapeutical role of miR-196a in HD.

Hypoxia inducible factor-1 (HIF-1) is the master transcriptional regulator of the cellular response to altered oxygen levels. HIF-1α protein is elevated in most solid tumors and contributes to poor disease outcome by promoting tumor progression, metastasis, and resistance to chemotherapy. To date, the relationship between HIF-1 and these processes, particularly chemoresistance, has remained largely unexplored. Here, we show that expression of the MAPK-specific phosphatase dual-specificity phosphatase-2 (DUSP2) is markedly reduced or completely absent in many human cancers and that its level of expression inversely correlates with that of HIF-1α and with cancer malignancy. Analysis of human cancer cell lines indicated that HIF-1α inhibited DUSP2 transcription, which resulted in prolonged phosphorylation of ERK and, hence, increased chemoresistance. Knockdown of DUSP2 increased drug resistance under normoxia, while forced expression of DUSP2 abolished hypoxia-induced chemoresistance. Further, reexpression of DUSP2 during cancer progression caused tumor regression and markedly increased drug sensitivity in mice xenografted with human tumor cell lines. Furthermore, a variety of genes involved in drug response, angiogenesis, cell survival, and apoptosis were found to be downregulated by DUSP2. Our results demonstrate that DUSP2 is a key downstream regulator of HIF-1-mediated tumor progression and chemoresistance. DUSP2 therefore may represent a novel drug target of particular relevance in tumors resistant to conventional chemotherapy.

De novo biosynthesis of pyrimidine nucleotides provides essential precursors for DNA synthesis and cell proliferation. The first three steps of de novo pyrimidine biosynthesis are catalyzed by a multifunctional enzyme known as CAD (carbamoyl phosphate synthetase-aspartate carbamoyltransferase-dihydroorotase). In this work, a decrease in CAD expression is detected in numerous cell lines and primary culture human stromal cells incubated under hypoxia or desferrioxamine (DFO)-induced HIF-1α accumulation. A putative hypoxia response element (HRE) binding matrix is identified by analyzing human cad-gene promoter using a bioinformatic approach. Promoter activity assays, using constructs harboring the cad promoter (−710/+122) and the −67/HRE fragment (25-bases), respectively, demonstrate the suppression of reporter-gene expression under hypoxia. Suppression of cad-promoter activity is substantiated by forced expression of wild-type HIF-1α but abolished by overexpression of dominant-negative HIF-1α. A chromatin immunoprecipitation assay provides further evidence that HIF-1α binds to the cad promoter in vivo. These data demonstrate that the cad-gene expression is repressed by HIF-1α, which represents a functional link between hypoxia and cell-cycle arrest.

Purpose: The first step of metastasis is the detachment of cancer cells from the surrounding matrix and neighboring cells; however, how cancer cells accomplish this process remains unclear. Thus, we aimed to investigate the underlying mechanism that controls the early event of metastasis. Experimental Design: One hundred and thirty-seven paired colorectal carcinoma and normal colon tissues were examined by immunohistochemical staining and Western blot for the expression of CD151, a member of the tetraspanin family that plays important roles in cell adhesion and motility. The effect of CD151 on cancer cell adhesion was investigated under normoxia and hypoxia conditions. Results: The level of CD151 was down-regulated in colon cancer compared with the paired normal counterparts. Expression of CD151was negatively regulated by hypoxia inducible factor1^dependent hypoxic stress. Suppression of CD151by hypoxia caused the detachment of cancer cells from the surrounding matrix and neighboring cells whereas restoration of CD151expression during reoxygenation facilitated the adhesion capacity. Clinical examination further showed that metastasized cancer cells expressed a greater level of CD151 compared with that of primary tumor. Conclusion: Regulation of CD151 by oxygen tension may play an important role in cancer metastasis by regulating the detachment from the primary site and homing in the secondary site.Cancer metastasis is a complex, multistep process with mechanisms largely unknown despite intensive investigation in the past. The first step of metastasis is the detachment of cancer cells from the surrounding matrix and neighboring cells. Adhesions between normal epithelial cells and cell-matrix are strong so local cell invasion is not able to occur. Therefore, the necessary early event in cancer invasion and metastasis is the conversion of the stationary phenotype to the migratory phenotype. This can be achieved by down-regulation of cell adhesion molecules such as cadherins and integrins. Indeed, studies have revealed that loss or down-regulation of E-cadherin and one or more of the integrins is a common feature of several epithelial malignancies (1, 2). Nonetheless, the underlying mechanisms of causing the down-regulation of these molecules are not yet clear. In addition, whether there are other molecules that also control cancer cell adhesion needs to be elucidated.Many factors have been identified as playing important roles in the regulation of cancer metastasis. Among these, hypoxia is the most common and critical one. Because oxygen can only diffuse for 150 to 200 Am, cells will face the hypoxic stress when distances of cells from a capillary exceed this range. Owing to the rapid growing nature, cancer cells of solid tumors frequently encounter reduced oxygen tension. The hypoxic stress will force cancer cells to develop necessary processes such as induction of angiogenesis, metabolic switch, and migration to avoid cell death. These responses to hypoxia are mainly mediated through genes regulated by t...