Hypoxia and regulation of messenger RNA translation.

Poor oxygenation (hypoxia) influences important physiological and pathological conditions, including development, ischemia, stroke, and cancer. The influence of hypoxia is due in large part to changes in gene expression, which occur through changes in transcription and translation. In response to hypoxic conditions, cells reduce their overall rate of messenger RNA (mRNA) translation. However, individual mRNA species are effected to highly varying degrees, with some even translationally stimulated under these conditions. Regulation of translation in response to hypoxia thereby gives rise to differential gene expression. The ability of cells to regulate translation during hypoxia is important for their survival. In the first part of this chapter, we review the effects of hypoxia on overall and gene-specific mRNA translation efficiencies and summarize the molecular pathways activated by hypoxia that regulate mRNA translation. In the second part, we describe the methods employed to investigate overall and gene-specific translation, including radioactive metabolic labeling, polysome fractionation, and reporter assays. We have emphasized the qualitative and quantitative analysis of polysome profiles, which can yield interesting information regarding the mechanistic basis for (gene-specific) translational regulation.