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4-Hydroxynonenal (HNE) is a lipid peroxidation product that is able to modify proteins. HNE-modified proteins are degraded to a considerable extend by the proteasomal system. It is unclear whether the recognition of HNE-modified proteins is mediated by ubiquitin, or whether the ubiquitin-independent proteasomal pathway is involved. In this study we demonstrate that HNE-modified GAPDH is preferentially ubiquitinated in vitro. In an attempt to demonstrate the formation of poly-ubiquitinated HNE-modified proteins in living cells we explored E36 fibroblasts. A clear rise in HNE-protein modification could be demonstrated after HNE treatment of the cells. Using inhibitors, we could show that the ubiquitin-dependent, ubiquitin-independent, and the lysosomal pathways affect the presence of HNE-modified proteins. We conclude that, although several proteolytic pathways exist for the degradation of HNE-modified proteins, there is the possibility of involvement of ubiquitin-dependent degradation. [ABSTRACT FROM AUTHOR]