Investigation the Functional Role of Extracellular Matrix Protein, Nephronectin, in the Renal Proximal Tubular Cell Tight Junction Formation

Renal cell carcinoma (RCC) is the most lethal genitourinary cancer; more than one-fourth of patients have metastasis at its presentation. Patients undergoing radical nephrectomy frequently relapse with metastasis; the median survival for metastatic patients is only 8 months and 5-year survival rate less than 10%. Therefore, investigating the underlying mechanisms of RCC metastasis is needed for the improvement in therapeutic applications. It had been suggested the kidney regeneration process after acute kidney injury (AKI) presented similar features as the renal tubular cell malignancy. The extracellular matrix protein, nephronectin (NPNT) was expressed on the regenerating renal proximal tubular cells (RPTECs) after AKI. Embryos lacking a functional NPNT gene display server defects in the kidney development. However, little is known for its role in RPTEC and RCC. In our preliminary data, we had found NPNT were down-regulated in the RCC cell lines and clinical specimens. Silencing NPNT in RPTEC cell line, HK-2 cell, altered epithelial cell morphology into spindlelike shape and loss cell-cell contact, these phenomena mimic to epithelial-to-mesenchymal transition (EMT) process in the progression of cancer. Besides, intracellular cellular junction components, zonula occludens-1 and E-cadherin were also suppressed in NPNT knockdown cells. These evidences suggest NPNT may promote tight junction (TJ) formation in RPTEC. Therefore, in the current proposal, we will firstly evaluate the role of NPNT in RPTEC TJ formation and its underlying mechanisms. It is of note that tumor cells frequently show abnormal TJ function, decreased differentiation and cell polarity. Since NPNT may increase TJ formation, thereafter, we will further study whether NPNT can inhibit RCC cell motility and metastasis in a spontaneous metastatic RCC mouse model. Understanding the role of NPNT in regulating intracellular junction formation may largely increase our knowledge in the mechanisms of RCC metastasis.