Transcriptional adaptations to hypoxia are mediated by hypoxia-inducible factor (HIF)-1, a heterodimer of HIF-␣ and aryl hydrocarbon receptor nuclear translocator subunits. The HIF-1␣ and HIF-2␣ subunits both undergo rapid hypoxia-induced protein stabilization and bind identical target DNA sequences. When coexpressed in similar cell types, discriminating control mechanisms may exist for their regulation, explaining why HIF-1␣ and HIF-2␣ do not substitute during embryogenesis. We report that, in a human lung epithelial cell line (A549), HIF-1␣ and HIF-2␣ proteins were similarly induced by acute hypoxia (4 h, 0.5% O 2 ) at the translational or posttranslational level. However, HIF-1␣ and HIF-2␣ were differentially regulated by prolonged hypoxia (12 h, 0.5% O 2 ) since HIF-1␣ protein stimulation disappeared because of a reduction in its mRNA stability, whereas HIF-2␣ protein stimulation remained high and stable. Prolonged hypoxia also induced an increase in the quantity of natural antisense HIF-1␣ (aHIF), whose gene promoter contains several putative hypoxia response elements to which (as we confirm here) the HIF-1␣ or HIF-2␣ protein can bind. Finally, transient transfection of A549 cells by dominant-negative HIF-2␣, also acting as a dominant-negative for HIF-1␣, prevented both the decrease in the HIF-1␣ protein and the increase in the aHIF transcript. Taken together, these data indicate that, during prolonged hypoxia, HIF-␣ proteins negatively regulate HIF-1␣ expression through an increase in aHIF and destabilization of HIF-1␣ mRNA. This transregulation between HIF-1␣ and HIF-2␣ during hypoxia likely conveys target gene specificity.

Inkjet printing is emerging at the forefront of biosensor fabrication technologies. Parallel advances in both ink chemistry and printers have led to a biosensor manufacturing approach that is simple, rapid, flexible, high resolution, low cost, efficient for mass production, and extends the capabilities of devices beyond other manufacturing technologies. Here we review for the first time the factors behind successful inkjet biosensor fabrication, including printers, inks, patterning methods, and matrix types. We discuss technical considerations that are important when moving beyond theoretical knowledge to practical implementation. We also highlight significant advances in biosensor functionality that have been realised through inkjet printing. Finally, we consider future possibilities for biosensors enabled by this novel combination of chemistry and technology.