Expression of mitogen-activated protein kinase family in rat renal development

Background. Among mitogen-activated protein kinase (MAPK) family members, e xtracellular signal-regulated kinase (ERK) promotes proliferation or differ entiation, whereas c-Jun N-terminal kinase (JNK) and p38 MAPK (p38) are tho ught to inhibit cell growth and induce apoptosis. MAPK phosphatase-1 (MKP-1 ) inactivates and modulates MAPKs. During renal development, large scale pr oliferation and apoptosis occur. We investigated the temporal and spatial e xpression patterns of MAPKs and MKP-1 in rat kidney during development. Methods. Western blot analysis and immunohistochemistry were performed in t he developing and mature kidney of the rat. Results. The expression of ERK, p38, and MKP-1 were high in developing kidn ey. On thf other hand, JNK was abundantly expressed in adult kidney. Active forms of ERK, p38, and JNK correlated with the protein expression levels. Immunohistochemical studies revealed that ERK was strongly expressed by bla stema cells, mesenchymal cells, and ureteric bud tips in nephrogenic zone o f embryonic kidney. In neonatal kidney, ERK was more abundant in the deep c ortex and the medulla corresponding to tubule maturation. p38 and MKP-1 wer e detected uniformly in mesenchymal cells, mesangial cells, and ureteric bu d epithelia of fetal kidney without an obvious correlation with the occurre nce of apoptosis. JNK was expressed by tubular cells and podocytes of adult kidney. Conclusions. ERK, p33, and MKP-1 are strongly expressed in developing kidne y, and JNK is detected predominantly in adult kidney. Both the temporal and spatial expression of ERK coincides with the maturation of the kidney.