Aldehyde dehydrogenase 3B1: Characterization and role in oxidative stress

Aldehyde dehydrogenase (ALDH) enzymes are critical in the detoxification of aldehydes. The human genome contains 19 ALDH genes, mutations in which are the basis of several diseases. The purpose of this study was to characterize ALDH3B1 and investigate its physiological significance. First, the human ALDH3B1 protein sequence was analyzed and catalytic activity towards various aldehyde substrates was investigated. Second, enzyme kinetics of purified ALDH3B1, protein and mRNA expression, and the subcellular localization and protective role in transfected HEK293 cells were extensively investigated. Finally, the cellular- and subcellular-specific localization of ALDH3B1 in normal and cancerous human tissues was examined immunohistochemically. Results show that ALDH3B1 has high sequence homology with ALDH3 isozymes and contains the residues essential for catalysis and cofactor binding. Cell lysates of ALDH3B1-expressing Sf9 cells are catalytically active towards medium- and long-chain aliphatic aldehydes and the aromatic benzaldehyde. Purified ALDH3B1 has high affinity for hexanal, octanal, 4-hydroxy-2-nonenal and benzaldehyde. Low affinity is seen towards short-chain aldehydes including acetaldehyde and malondialdehyde. ALDH3B1 mRNA is high in testis, lung, kidney and ovary. ALDH3B1 protein is highly expressed in these tissues and the liver. ALDH3B1 appears to be predominantly cytosolic, with greater concentration at the plasma membrane. ALDH3B1-transfected HEK293 cells are significantly protected from the lipid peroxidation-derived octanal, trans-2-octenal, 4-hydroxy-2-nonenal and hexanal. ALDH3B1 is expressed in a tissue- and cell-specific manner including in hepatocytes, proximal convoluted tubule cells, cerebellar astrocytes, bronchiole ciliated cells and testis efferent ductule ciliated cells. ALDH3B1 expression is up-regulated in a high percentage of tumors (lung > breast = ovarian > colon). Collectively, the results of this study support a pathophysiological role for ALDH3B1 in protecting cells from the damaging effects of oxidative stress through the detoxification of lipid peroxidation-derived aldehydes. The specificity of ALDH3B1 distribution may prove to be directly related to the functional role of this enzyme in human tissues. Increased ALDH3B1 expression in tumor cells may confer a growth advantage or be the result of increased oxidative stress. This study shows for the first time the expression, functionality and protective role of ALDH3B1 and indicates a potential physiological role of ALDH3B1 against oxidative stress.