The HIF-1 transcription factor drives hypoxic gene expression changes that are thought to be adaptive for cells exposed to a reduced-oxygen environment. For example, HIF-1 induces the expression of glycolytic genes. It is presumed that increased glycolysis is necessary to produce energy when low oxygen will not support oxidative phosphorylation at the mitochondria. However, we find that while HIF-1 stimulates glycolysis, it also actively represses mitochondrial function and oxygen consumption by inducing pyruvate dehydrogenase kinase 1 (PDK1). PDK1 phosphorylates and inhibits pyruvate dehydrogenase from using pyruvate to fuel the mitochondrial TCA cycle. This causes a drop in mitochondrial oxygen consumption and results in a relative increase in intracellular oxygen tension. We show by genetic means that HIF-1-dependent block to oxygen utilization results in increased oxygen availability, decreased cell death when total oxygen is limiting, and reduced cell death in response to the hypoxic cytotoxin tirapazamine.

Macroautophagy (called autophagy hereafter) is a catabolic process activated by various types of stress, most notably by nutrient deprivation. The autophagic degradation of intracellular macromolecules provides metabolic support for the cell; however, this physiological process can also initiate a form of cell death (type 2 programmed cell death). Here we report that oxygen deprivation can activate the autophagic pathway in human cancer cell lines. We observed that hypoxia induced distinct cellular changes characteristic of autophagy such as an increase in cytoplasmic acidic vesicles, and processing and cellular localization of microtubule-associated protein-1 light chain 3. Oxygen deprivation-induced autophagy did not require nutrient deprivation, hypoxia-inducible factor-1 (HIF-1) activity, or expression of the HIF-1 target gene BNIP3 (Bcl-2 adenovirus E1a nineteen kilodalton interacting protein 3) or BNIP3L (BNIP3 like protein). Hypoxia-induced autophagy involved the activity of 5 0 -AMP-activated protein kinase (AMPK). Finally, we determined that cells lacking the autophagy gene ATG5 were unable to activate the autophagic machinery in hypoxia, had decreased oxygen consumption and increased glucose uptake under hypoxia, had increased survival in hypoxic environments, and exhibited accelerated growth as xenografted tumors. Together, these findings suggest that the autophagic degradation of cellular macromolecules contributes to the energetic balance governed by AMPK, and that suppression of autophagy in transformed cells can increase both resistance to hypoxic stress and tumorigenicity. Low oxygen tension is a common characteristic of several pathophysiological conditions including cancer. Hypoxia in solid tumors is associated with resistance to radiotherapy and poor prognosis. 1 One consequence of tumor hypoxia can be cell death. 2,3 However, several groups have shown that in general tumor cells are well adapted to moderate hypoxia, provided that there are no additional stresses such as glucose deprivation. However, extreme hypoxia is able to activate apoptosis through a hypoxia-inducible factor-1 (HIF-1)-independent process. 4-6 Interestingly, forced normoxic expression of HIF-1 target gene BNIP3 (Bcl-2 adenovirus E1a nineteen kilodalton interacting protein 3) has been reported to cause mitochondrial dysfunction and cell death in some, but not all, experimental settings. 5,7,8 Recent studies have also implicated BNIP3 in ceramide-and arsenic trioxide-induced autophagy 9,10 and in a model of ischemia/reperfusion cell death. 11 5 0 -AMP-activated protein kinase (AMPK) is a major regulator of energy homeostasis. 12 Increases in the AMP/ ATP ratio lead to activation of AMPK, which in turn promotes energy-producing catabolic processes and attenuation of energy-consuming anabolic processes. 13 One major downstream pathway for this effect is through tuberous sclerosis complex (TSC) and mammalian target of rapamycin (mTOR). 14 Hypoxia is a potent stimulus of AMPK, which is independent of HIF activity, and can occur ...

In an empirical examination of the link between product involvement and brand loyalty, a convenience sample of 253 students were asked to complete a questionnaire relating to two products which had been found in preliminary qualitative research to be associated with contrasted levels of involvement. The factor structure of involvement was found to vary between the two product categories (sneakers and pens). Furthermore, the link between product involvement and brand loyalty was found to involve different aspects of product involvement for each of the products concerned. Hence, future researchers in the area should be mindful that product involvement and brand loyalty are not universal constructs: they should be examined within specific consumer and product parameters.

Poorly formed tumor blood vessels lead to regions of microenvironmental stress due to depletion of oxygen and glucose and accumulation of waste products (acidosis). These conditions contribute to tumor progression and correlate with poor patient prognosis. Here we show that the microenvironmental stresses found in the solid tumor are able to inhibit the canonical Wnt/␤-catenin signaling pathway. However, tumor cells harboring common ␤-catenin pathway mutations, such as loss of adenomatous polyposis coli, are insensitive to this novel hypoxic effect. The underlying mechanism responsible is hypoxia-induced endoplasmic reticulum (ER) stress that inhibits normal Wnt protein processing and secretion. ER stress causes dissociation between GRP78/BiP and Wnt, an interaction essential for its correct posttranslational processing. Microenvironmental stress can therefore block autocrine and paracrine signaling of the Wnt/␤-catenin pathway and negatively affect tumor growth. This study provides a general paradigm relating oxygen status to ER function and growth factor signaling.Tumor hypoxia is found in regions that are distant from the supporting tumor vasculature (6). These microenvironments can also suffer from low levels of nutrients (hypoglycemia) and high levels of waste products (acidosis). The net result is a stressful environment that can adversely effect tumor cell proliferation and survival and select for aggressive clonogens (12). Cells respond to these stresses through the induction of both HIF-1-dependent and HIF-1-independent mechanisms (8). Recent data from model tumors has identified how the endoplasmic reticulum (ER) can be stressed by severe hypoxia and how an incomplete response to this stress can inhibit tumor cell growth and survival (5,19,30). One potential mechanism by which ER stress could inhibit tumor formation would be through the inhibition of secreted growth factors, blocking autocrine and paracrine signaling of many molecules promoting proliferation and survival.Wnt genes encode a family of secreted cysteine-rich glycoproteins that plays a significant role in development and homeostasis (21). Wnt proteins can bind to the Frizzled transmembrane receptors and activate different intracellular signaling pathways, such as the "canonical pathway." Here, the key element is stabilization and nuclear translocation of ␤-catenin which then dimerizes with T-cell-specific transcription factor/lymphoid enhancer-binding factor 1 (TCF/LEF) transcription factors to transactivate target genes. In the absence of Wnt ligand, ␤-catenin is phosphorylated by a cytosolic multiprotein complex, which includes adenomatous polyposis coli (APC), axin, and glycogen synthase kinase 3 (GSK-3) and is thus targeted for degradation by the proteasome. Loss of APC, or even mutation of the phosphorylation sites in ␤-catenin itself, leads to a constitutively stable and active ␤-catenin (11, 29). In colorectal cancer, more than 90% of tumor samples have canonical Wnt pathway activating mutations. However, it is extremely rare to fin...

Higher maternal folate concentrations during late pregnancy were associated with longer gestational age and tended to be associated with a lower risk of preterm birth in this multiethnic Asian population. In contrast, the results of our study suggested little or no benefit of higher folate concentrations for reducing the risk of SGA or of higher vitamin B-6 and vitamin B-12 concentrations for reducing the risk of preterm birth or SGA.