Expression and localization of diacylglycerol kinase isozymes and enzymatic features in rat lung

Diacylglycerol kinase (DGK) catalyzes phosphorylation of diacylglycerol to generate phosphatidic acid, and both molecules are known to serve as second messengers as well as important intermediates for the synthesis of various lipids. In this study, we investigated the spatiotemporal expression patterns of DGK isozymes together with the developmental changes of the mRNA expression and enzymatic property in rat lung. Northern blot and RT-PCR analyses showed that mRNAs for DGKalpha, -epsilon, and -zeta were detected in the lung. By immunohistochemical examination, DGKalpha and -zeta were shown to be coexpressed in alveolar type II cells and macrophages. Interestingly, these isozymes were localized at distinct subcellular locations, i.e., DGKalpha in the cytoplasm and DGKzeta in the nucleus, suggesting different roles for these isozymes. In the developing lung, the expression for DGKalpha and -zeta was transiently elevated on embryonic day 21 (E21) to levels approximately two- to threefold higher than on postnatal day 0 (P0). On the other hand, the expression for DGKepsilon was inversely elevated approximately twofold on P0 compared with that on E21. These unique changes in the expression pattern during the perinatal period suggest that each isozyme may play a distinct role in the adaptation of the lung to air or oxygen breathing at birth.