Proteases involved in the metabolic degradation of human interleukin-1beta by rat kidney lysosomes

cDNA macroarray analysis of genes in renal epithelial cells exposed to calcium oxalate crystals

Kidney stone formation is a complex process, and numerous genes participate in this cascade. The binding and internalization of calcium oxalate monohydrate (COM) crystals, the most common crystal in renal stones by renal epithelial cells may be a critical step leading to kidney stone formation. Exposure to COM crystals alters the expression of various genes, but previous studies on gene expression have generally been limited. To obtain more detailed insight into gene expression, we examined gene expression profiles in renal epithelial cells exposed to COM crystals using cDNA macroarray. NRK-52E cells were exposed to COM crystals for 60 and 120 min. Poly (A)(+) RNA was isolated and converted into (32)P-labeled first-strand cDNA, then the cDNA probe was hybridized to the membrane. Hybridization images were scanned and the signal intensities were quantified. Expression of mRNA of 1,176 genes was analyzed with global sum normalization methods. Exposure to COM crystals altered the expression of some of the genes reported previously. Furthermore, novel genes were also identified. Over 20 genes were found to be regulated at least twofold. We performed a large-scale analysis of gene expression in renal epithelial cells exposed to COM crystals, and identified the genes differentially regulated. cDNA macroarray is a useful tool for evaluating gene expression in urolithiasis research.

Cathepsin D--many functions of one aspartic protease

For years, it has been held that cathepsin D (CD) is involved in rather non-specific protein degradation in a strongly acidic milieu of lysosomes. Studies with CD knock-out mice revealed that CD is not necessary for embryonal development, but it is indispensable for postnatal tissue homeostasis. Mutation that abolishes CD enzymatic activity causes neuronal ceroid lipofuscinosis (NCL) characterized by severe neurodegeneration, developmental regression, visual loss and epilepsy in both animals and humans. In the last decade, however, an increasing number of studies demonstrated that enzymatic function of CD is not restricted solely to acidic milieu of lysosomes with important consequences in regulation of apoptosis. In addition to CD enzymatic activity, it has been shown that apoptosis is also regulated by catalytically inactive mutants of CD which suggests that CD interacts with other important molecules and influences cell signaling. Moreover, procathepsin D (pCD), secreted from cancer cells, acts as a mitogen on both cancer and stromal cells and stimulates their pro-invasive and pro-metastatic properties. Numerous studies found that pCD/CD level represents an independent prognostic factor in a variety of cancers and is therefore considered to be a potential target of anti-cancer therapy. Studies dealing with functions of cathepsin D are complicated by the fact that there are several simultaneous forms of CD in a cell-pCD, intermediate enzymatically active CD and mature heavy and light chain CD. It became evident that these forms may differently regulate the above-mentioned processes. In this article, we review the possible functions of CD and its various forms in cells and organisms during physiological and pathological conditions.

Intracrystalline urinary proteins facilitate degradation and dissolution of calcium oxalate crystals in cultured renal cells

We have previously proposed that intracrystalline proteins would increase intracellular proteolytic disruption and dissolution of calcium oxalate (CaOx) crystals. Chauvet MC, Ryall RL. J Struct Biol 151: 12-17, 2005; Fleming DE, van Riessen A, Chauvet MC, Grover PK, Hunter B, van Bronswijk W, Ryall RL. J Bone Miner Res 18: 1282-1291, 2003; Ryall RL, Fleming DE, Doyle IR, Evans NA, Dean CJ, Marshall VR. J Struct Biol 134: 5-14, 2001. The aim of this investigation was to determine the effect of increasing concentrations of intracrystalline protein on the rate of CaOx crystal dissolution in Madin-Darby canine kidney (MDCKII) cells. Crystal matrix extract (CME) was isolated from urinary CaOx monohydrate (COM) crystals. Cold and [14C]oxalate-labeled COM crystals were precipitated from ultrafiltered urine containing 0-5 mg/l CME. Crystal surface area was estimated from scanning electron micrographs, and synchrotron X-ray diffraction was used to determine nonuniform strain and crystallite size. Radiolabeled crystals were added to MDCKII cells and crystal dissolution, expressed as radioactive label released into the medium, was measured. Increasing CME content did not significantly alter crystal surface area. However, nonuniform strain increased and crystallite size decreased in a dose-response manner, both reaching saturation at a CME concentration of 3 mg/ and demonstrating unequivocally the inclusion of increasing quantities of proteins in the crystals. This was confirmed by Western blotting. Crystal dissolution also followed saturation kinetics, increasing proportionally with final CME concentration and reaching a plateau at a concentration of approximately 2 mg/l. These findings were complemented by field emission scanning electron microscopy, which showed that crystal degradation also increased relative to CME concentration. Intracrystalline proteins enhance degradation and dissolution of CaOx crystals and thus may constitute a natural defense against urolithiasis. The findings have significant ramifications in biomineral metabolism and pathogenesis of renal stones.

Identification of changes in the transcriptome profile of human hepatoma HepG2 cells stimulated with interleukin-1 beta

Interleukin-1 (IL-1) is the principal pro-inflammatory cytokine participating in the initiation of acute phase response. Human hepatoma HepG2 cells were exposed to 15 ng/ml of IL-1beta for times ranging from 1 to 24 h and the total RNA was isolated. Then cDNA was obtained and used for differential display with 10 arbitrary primers and 9 oligo(dT) primers designed by Clontech. Validation of observed changes of differentially expressed known genes was carried out by RT-PCR or Northern blot analysis. Out of 90 cDNA strands modulated by IL-1, 46 have been successfully reamplified and their sequencing indicates that they represent 36 different cDNA templates. By GenBank search, 26 cDNA clones were identified as already known genes while 10 showed no homology to any known gene. The identified transcripts modulated by IL-1 in HepG2 cells code for intracellular proteins of various function: trafficking/motor proteins (3 genes), proteins participating in the translation machinery or posttranscriptional/posttranslational modifications (7 genes), proteases (1 gene), proteins involved in metabolism (6 genes), activity modulators (3 genes), proteins of the cell cycle machinery (2 genes) and those functionally unclassified (4 genes). Majority of genes responded to IL-1 within 1 to 6 h (early genes), while two were late response genes (12-24 h) and four showed prolonged response over the whole 24-h period. Most of the observed changes of expression were in the range of two- to threefold increase in comparison to control untreated cells. Among identified genes, no typical secretory acute phase protein was found. The obtained results suggest that IL-1 affects the expression of several genes in HepG2 cells, especially those engaged in the synthesis and modifications of proteins.

Intrarenal handling of recombinant human interleukin-1alpha in rats: mechanism for proximal tubular protein reabsorption

The intrarenal distribution of recombinant human interleukin (IL)-la was studied in Sprague-Dawley male rats by immunohistochemical staining. The effects of the concurrent administration of various proteins or synthetic polypeptides on the urinary excretion of IL-1alpha were also studied to clarify the mechanism(s) for the reabsorption of IL-la in the renal tubules. Microscopic immunohistochemistry showed that IL-1alpha distributed to early proximal convoluted tubules but not to glomeruli, Henle's loops, distal tubules, or collecting ducts. Electron microscopic immunohistochemistry showed that IL-la was taken up into the endocytic vesicle located close to the apical membrane of the proximal tubular epithelial cells, then accumulated in lysosomes. Urinary excretion of intravenous IL-la at 500 microg/kg was extremely low, accounting for only 0.014% of the dose administered. The coadministration of intravenous human serum albumin did not affect the urinary excretion of IL-1alpha, whereas trypsinogen, myoglobin, and trypsin inhibitor dose-dependently produced an increase in the excretion of IL-la, the potency of which was greatest in that order. Poly-L-lysine, but not poly-L-glutamic acid dose-dependently increased the urinary excretion of IL-1alpha. These results indicate that most of the glomerular filtrated IL-1alpha could be easily reabsorbed into the proximal tubular cells via endocytosis, and the reabsorption was inhibited by coadministered low molecular weight proteins, particularly basic proteins. This result suggests that scavengers with a negative charge and broad binding ability for glomerular filtered proteins exist on the surface of the apical membrane of proximal tubular cells and play an important role in the reabsorption of filtered proteins.