Signal Pathway of Hypoxia-Inducible Factor-1α Phosphorylation and its Interaction with von Hippel-Lindau Tumor Suppressor Protein During Ischemia in MiaPaCa-2 Pancreatic Cancer Cells

Abstract

Purpose and Experimental Design: Previously, we observed that the activation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH 2 -terminal kinase (JNK1) is mediated through the activation of apoptosis signal^regulating kinase 1 (ASK1) as a result of the reactive oxygen species^mediated dissociation of glutaredoxin and thioredoxin from ASK1. In this study, we examined whether p38 MAPK and JNK1are involved in the accumulation of hypoxia-inducible factor-1a (HIF-1a) during ischemia. Human pancreatic cancer MiaPaCa-2 cells were exposed to low glucose (0.1mmol/L) with hypoxia (0.1% O 2 ). Results and Conclusions: During ischemia, p38 MAPK and JNK1were activated in MiaPaCa-2 pancreatic cancer cells. The activated p38 MAPK, but not JNK1, phosphorylated HIF-1a. Data from in vivo binding assay of von Hippel-Lindau tumor suppressor protein with HIF-1a suggests that the p38-mediated phosphorylation of HIF-1a contributed to the inhibition of HIF-1a and von Hippel-Lindau tumor suppressor protein interaction during ischemia. SB203580, a specific inhibitor of p38 MAPK, inhibited HIF-1a accumulation during ischemia, probably resulting from the ubiquitination and degradation of HIF-1a.Pancreatic cancers are highly aggressive, and because there is no effective therapy for this cancer, one of the major causes of cancer death. Pancreatic cancer cells survive and proliferate even in the severe hypoxia and nutrient deprivation resulting from the poor blood supply in a tumor (1). When the tumor cells are exposed to hypoxic stress, hypoxia-inducible factor-1 (HIF-1) plays an important role in cancer angiogenesis and anaerobic metabolism (2). A previous study reported that pancreatic cancer cells with constitutive expression of HIF-1a were more resistant to apoptosis induced by hypoxia and glucose deprivation than those without constitutive expression of HIF-1a (3). Thus far, the role of oxygen in the regulation of intracellular levels of HIF-1a has been well studied (4). Under normoxic conditions, HIF-1a is rapidly degraded by the proteasome. This proteolytic regulation is mediated by hydroxylation of HIF-1a protein on proline residues 402 and 504 by specific HIF-prolyl hydroxylases in the presence of iron and oxygen (5 -7). The hydroxylated HIF-1a protein then interacts with the von Hippel-Lindau tumor suppressor protein (pVHL), which functions as an E3 ubiquitin ligase. Under hypoxic conditions, HIF-1a is not hydroxylated, resulting in the prevention of its interaction with pVHL and its subsequent ubiquitination and degradation. In addition to studies on hypoxia-induced stabilization of HIF-1a, there are several reports relating to up-regulation of HIF-1a through its phosphorylation by the following signal pathways: phosphoinositide-3-kinase/AKT signaling, mitogen-activated protein kinase (MAPK) signaling, and the signal pathway mediated by reactive oxygen species (ROS; refs. 8 -11). However, the exact regulatory mechanism of HIF-1a phosphorylation remains unknown.In the present study, we focused on the HIF-1a phos...

Endoplasmic Reticulum (ER) Stress and Hypoxia Response Pathways Interact to Potentiate Hypoxia-inducible Factor 1 (HIF-1) Transcriptional Activity on Targets Like Vascular Endothelial Growth Factor (VEGF)

“…However, unexpectedly, this induction occurred primarily via UPR-induced potentiation of HIF-1 transcriptional activity, an observation that was extended to an additional HIF target, BNIP3. We report that the UPR enhances the phosphorylation of HIF-1␣, which has been shown previously to enhance its activity (11).…”

Reactive Oxygen Species Regulate Hypoxia-Inducible Factor 1α Differentially in Cancer and Ischemia

“…Lending support to the model's finding that extracellular H 2 O 2 greatly determines the cellular hypoxic response, recent studies have indicated catalase added to cell medium has a strong effect on cell-cell communication in microglia via NO signaling (47). Furthermore, another study showed that an adenovirus containing catalase affected the activity of apoptosis signal-regulating kinase 1, another signaling molecule involved in hypoxia and ischemia, whose activity is dependent on H 2 O 2 and indirectly related to HIF1 (57).…”

Implication of VHL, ERK5, and HIF-1alpha in clear cell renal cell carcinoma: Molecular basis

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