Figure 3. Hepsin and prostasin interact with uromodulin to induce its cleavage and polymerisation.

(A) Immunofluorescence analysis (extended focus image) showing uromodulin on the surface of HEK293 cells. The protein is not assembled into polymers when expressed in this cellular system. Scale bar, 21 µm. (B) Representative Western blot analysis of N-deglycosylated uromodulin secreted by MDCK and HEK293 cells. HEK293 cells only secrete the longer polymerisation-incompetent uromodulin isoform (black arrowhead), while MDCK cells also secrete the shorter one (white arrowhead). (C) Schematic representation of the selection process employed to identify candidate enzymes for the secretion of the short uromodulin isoform. Only membrane-bound serine proteases specifically expressed by MDCK cells and by the TAL segment of the nephron, but not by HEK293 cells, were selected. (D) Representative Western blot analysis of N-deglycosylated uromodulin secreted by HEK293 cells expressing wild-type or catalytically inactive human hepsin or prostasin, as indicated. Only wild-type proteases promote the secretion of the short uromodulin isoform by these cells (white arrowhead). (E) Immunofluorescence analysis (extended focus image) showing uromodulin on the surface of HEK293 cells expressing wild-type or catalytically inactive hepsin or prostasin, as indicated. Uromodulin polymerisation is induced only when wild-type proteases are expressed. Scale bar, 21 µm. (F) Representative Western blot analysis of uromodulin immunoprecipitation (upper panels) from lysates of HEK293 cells expressing hepsin or prostasin, as indicated. Both enzymes are co-immunoprecipitated when uromodulin is co-expressed in HEK293 cells (lower panels). The arrowheads point at hepsin and prostasin specific bands.

DOI: http://dx.doi.org/10.7554/eLife.08887.009

Figure 3—figure supplement 1. Hepsin and prostasin expression in MDCK and HEK293 cells.

(A) RT-PCR analysis showing gene expression of candidate proteases hepsin (HPN) and prostasin (PRSS8) in MDCK and HEK293 cells. Constructs containing coding sequences of the human proteases were used as PCR positive controls (C+). Expression of GAPDH is shown as a cDNA positive control. PRSS8 and HPN are exclusively expressed in MDCK cells, confirming data obtained from available transcriptomes. (B) Representative Western blot analysis of uromodulin, hepsin and prostasin in lysates of transfected HEK293 cells. Wild-type proteases as well as catalytically inactive enzymes were expressed in HEK293 cells, as indicated. Protein disulfide-isomerase (Pdi) is shown as a loading control. The arrowhead points at hepsin specific band.

DOI: http://dx.doi.org/10.7554/eLife.08887.010