Kidney injury molecule-1 (KIM-1) is strongly upregulated in proximal tubular epithelial cells in various states characterized by epithelial cell dedifferentiation: ischemia, toxic renal injury, polycystic kidney disease and renal cell carcinoma. It is upregulated more than any other known protein with renal injury. KIM-1 protein is a Type I cell membrane glycoprotein containing extracellular immunoglobulin-like and mucin domains suggesting functional roles in cell-cell and/or cell-matrix interactions. We have cloned, and generated monoclonal and polyclonal antibodies to, the human, mouse and rat KIM-1. KIM-1 is upregulated in vitro in MDCK cells adjacent to a mechanical """"""""wound"""""""". The ectodomain of KIM-1 is cleaved and found in urine of patients with acute tubular necrosis or renal cell carcinoma. Gene transfer of KIM-1 in LLC-PK1 epithelial cells results in an increased number of cells with mesenchymal morphology and confers growth in soft agar. The goal of this proposal is to characterize the functional role of KIM-1 during the processes of adhesion and differentiation of epithelial cells. We hypothesize that KIM-1 reduces cell-cell and increases cell-matrix adhesion and potentiates epithelial to mesenchymal transition.
In Specific Aim 1, we will characterize the effects of KIM-1 on cell-cell and cell-matrix interactions of epithelial cells. In pilot experiments, we found decreased cell-cell aggregation of LLC-PK1 cells expressing KIM-1. CHO cells overexpressing KIM-1 """"""""scatter"""""""" on various matrix substrates. KIM-1 expression results in loss of E-cadherin and increased cell-matrix adhesion. The roles of ERM proteins, integrins, Rho, integrin-linked and mitogen-activated protein (MAP) kinases as effectors of KIM-1 actions on cell-cell and cell-matrix adhesion will be explored. The contributions of the extracellular and intracellular domains of KIM-1 and tyrosine phosphorylation of the intracellular domain of KIM-1 in KIM-l's effects on adhesion will be evaluated. In the second specific aim, we will analyze the role of KIM-1 in the processes associated with dedifferentiation of renal tubular epithelial cells that are important for repair of the epithelium with both positive and potentially negative consequences. We will explore the role of TGF-beta in potentiating the effects of KIM-1 on cell differentiation and epithelial to mesenchymal transition. A mechanism is proposed that implicates ERM proteins, Rho, integrin-linked and MAP family kinases as well as a-catenin and the transcription factor Snail, in the effect of KIM-1 on the differentiation status of the renal epithelial cell. KIM-1-expressing proximal tubules localize in areas of the kidney with increased fibrosis in a model of polycystic kidney disease and we will explore if there is an effect of KIM-1 expression on matrix protein production and extracellular matrix remodeling. Understanding the function of KIM-1 will provide important insight into the role of this protein in injury and repair processes of the kidney, and may identify KIM-1 as an important therapeutic target not only for acute and chronic renal disease but also for malignant transformation of the epithelial cell.
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