Target Genes Regulated by MEK1/2 in Renal Epithelial Cells

Under physiological conditions, differentiated cells will usually maintain their specialized character while, during adaptation or reparative regeneration, conversion of cellular specificities can be observed. In pathological conditions, such as inflammation and carcinogenesis, even highly specialized cells can alter their properties leading to a deranged control of cell differentiation and/or proliferation. The mitogen-activated protein kinases (MAP kinases) ERK1 and ERK2 as well as their upstream activators MEK1 and MEK2 are important regulators of these processes. It is our aim to define those genes, which are differentially regulated by MEK1 and MEK2 and which are involved in the regulation of renal epithelial cell differentiation and proliferation. Based on the progress during the previous projects, it is our aim to transfer our knowledge about the function of the MAPK activators MEK1 and MEK2 for renal epithelial cell differentiation and proliferation to the human renal epithelial system and to perform studies both at the cellular as well as at the tissue level. Thus, it is the aim of the present grant proposal to ... 1. define MEK1- and/or MEK2-dependent genes (mechanisms) causally related to dedifferentiation, increased invasion and/or transformation of human proximal tubular cells. 2. study the hypothesis that MEK1 and MEK2 have different functions in human renal epithelial cells. 3. find possible therapeutic targets to interfere with the pathophysiological mechanisms leading to renal diseases, which are associated with alterations in epithelial cell differentiation and/or proliferation ... ..... in order to develop a novel renal tubule cell-specific gene therapy to inhibit unlimited cell proliferation and/or cell dedifferentiationransformation. Elucidating cellular signaling events and genes, which are regulated by these molecules, in human renal epithelial cells as well as in human tissue from patients with tubulointerstitial fibrosis and/or renal cell carcinoma should lead to the development of new strategies for therapeutic interventions, which attenuate or even prevent cellular alterations that finally lead to end-stage renal disease or malignant tumors derived from renal epithelia.

Renal tubulointerstitial fibrosis and tubular atrophy are two hallmarks during development and progression of chronic kidney disease eventually ending in end-stage renal failure, a condition, which necessitates patients to depend on live-saving but also life-long invasive therapies such as hemodialysis or renal transplantation. The final steps linked to the induction of renal fibrosis and tubular atrophy are characterized by an increase in number of a special cell type named activated (myo)fibroblasts. Although, in principle, these activated (myo)fibroblasts can be derived from different sites in kidneys, growing evidence suggests, that a large proportion of them originates from tubular epithelial cells by a process called epithelial-mesenchymal transition (EMT). During the two years of our present project we were able to establish human kidney-2 (HK-2) cells as a valuable cell model to study one of the earliest key events during induction of tubular EMT, namely loss of epithelial cell-cell adhesion, as well as to investigate one event, which is supposed to occur at later time points in the course of EMT, namely enhanced cell migration and invasion. We found that oncostatin M (OSM), which has unique biological activities in inflammation, meets some of those criteria, which have been established as key events during tubular EMT and, thus, represents a potential inducer of this mechanism leading to the development of renal fibrosis. Furthermore, the present grant enabled us to identify several genes regulated by distinct intracellular signals (MAP Kinases), which are likely to be involved in the induction of renal EMT. Studying the hypotheses derived from these results should ultimately lead to the development of new therapeutic strategies against renal fibrosis and chronic kidney disease.