Peroxiredoxin IV is an endoplasmic reticulum-localized enzyme forming oligomeric complexes in human cells

The peroxiredoxins are a ubiquitous family of proteins involved in protection against oxidative stress through the detoxification of cellular peroxides. In addition, the typical 2-Cys peroxiredoxins function in signalling of peroxide stress and as molecular chaperones, functions that are influenced by their oligomeric state. Of the human peroxiredoxins, Prx IV (peroxiredoxin IV) is unique in possessing an N-terminal signal peptide believed to allow secretion from the cell. Here, we present a characterization of Prx IV in human cells demonstrating that it is actually retained within the ER (endoplasmic reticulum). Stable knockdown of Prx IV expression led to detrimental effects on the viability of human HT1080 cells following treatment with exogenous H₂O₂. However, these effects were not consistent with a dose-dependent correlation between Prx IV expression and peroxide tolerance. Moreover, modulation of Prx IV expression showed no obvious effect on ER-associated stress, redox conditions or H₂O₂ turnover. Subsequent investigation demonstrated that Prx IV forms complex structures within the ER, consistent with the formation of homodecamers. Furthermore, Prx IV oligomeric interactions are stabilized by additional non-catalytic disulfide bonds, indicative of a primary role other than peroxide elimination.