Albumin uptake in human podocytes: a possible role for the cubilin-amnionless (CUBAM) complex

Abstract Albumin re-uptake is a receptor-mediated pathway located in renal proximal tubuli. There is increasing evidence of glomerular protein handling by podocytes, but little is known about the mechanism behind this process. In this study, we found that human podocytes in vitro are committed to internalizing albumin through a receptor-mediated mechanism even after exposure to low doses of albumin. We show that these cells express cubilin, megalin, ClC-5, amnionless and Dab2, which are partners in the tubular machinery. Exposing human podocytes to albumin overload prompted an increase in CUBILIN, AMNIONLESS and CLCN5 gene expression. Inhibiting cubilin led to a reduction in albumin uptake, highlighting its importance in this mechanism. We demonstrated that human podocytes are committed to performing endocytosis via a receptor-mediated mechanism even in the presence of low doses of albumin. We also disclosed that protein overload first acts on the expression of the cubilin-amnionless (CUBAM) complex in these cells, then involves the ClC-5 channel, providing the first evidence for a possible role of the CUBAM complex in albumin endocytosis in human podocytes

Understanding the Pathophysiology of Nephrocalcinosis

Many in vitro and in vivo studies on the mechanisms underlying calcium nephrolithiasis have provided evidence of a frequently associated condition, i.e., a microscopic renal crystal deposition that can occur within the tubular lumen (intratubular nephrocalcinosis) or in the interstitium (interstitial nephrocalcinosis). Medullary nephrocalcinosis is the typical pattern seen in 98% of cases of human nephrocalcinosis, with calcification clustering around each renal pyramid. It is common in patients with metabolic conditions that predispose them to renal calcium stones. Cortical nephrocalcinosis is rare and usually results from severe destructive disease of the cortex. It has been described in chronic glomerulonephritis, but often in association with another factor, such as an increased calcium ingestion, acute cortical necrosis, chronic pyelonephritis or trauma. The most accredited hypothesis to explain the onset of interstitial nephrocalcinosis is purely physicochemical, relating to spontaneous Ca2PO4 crystallization in the interstitium due to oversaturation of Ca2PO4salts in this milieu. The theory that nephrocalcinosis is a process driven by osteogenic cells was first proposed by our group. We review nephrocalcinosis in terms of its definition, genetic associations, and putative mechanisms, pointing out how much evidence in the literature suggests that it may have some features in common with, and pathogenic links to vascular calcification

SerpinB3 and Yap Interplay Increases Myc Oncogenic Activity

SerpinB3 has been recently described as an early marker of liver carcinogenesis, but the potential mechanistic role of this serpin in tumor development is still poorly understood. Overexpression of Myc often correlates with more aggressive tumour forms, supporting its involvement in carcinogenesis. Yes-associated protein (Yap), the main effector of the Hippo pathway, is a central regulator of proliferation and it has been found up-regulated in hepatocellular carcinomas. The study has been designed to investigate and characterize the interplay and functional modulation of Myc by SerpinB3 in liver cancer. Results from this study indicate that Myc was up-regulated by SerpinB3 through calpain and Hippo-dependent molecular mechanisms in transgenic mice and hepatoma cells overexpressing human SerpinB3, and also in human hepatocellular carcinomas. Human recombinant SerpinB3 was capable to inhibit the activity of Calpain in vitro, likely reducing its ability to cleave Myc in its non oncogenic Myc-nick cytoplasmic form. SerpinB3 indirectly increased the transcription of Myc through the induction of Yap pathway. These findings provide for the first time evidence that SerpinB3 can improve the production of Myc through direct and indirect mechanisms that include the inhibition of generation of its cytoplasmic form and the activation of Yap pathway

Low P66shc with High SerpinB3 Levels Favors Necroptosis and Better Survival in Hepatocellular Carcinoma.

Cell proliferation and escape from apoptosis are important pathological features of hepatocellular carcinoma (HCC), one of the tumors with the highest mortality rate worldwide. The aim of the study was to evaluate the expression of the pro-apoptotic p66shc and the anti-apoptotic SerpinB3 in HCCs in relation to clinical outcome, cell fate and tumor growth. p66shc and SerpinB3 were evaluated in 67 HCC specimens and the results were correlated with overall survival. Proliferation and cell death markers were analyzed in hepatoma cells overexpressing SerpinB3, under different stress conditions. p66shc-/- mice and xenograft models were also used to assess the effects of p66shc and SerpinB3 on tumor growth. In patients with HCC, the best survival was observed in the subgroup with p66shc levels below median values and SerpinB3 levels above median values. Mice p66shc-/- showed high levels of SerpinB3, while in HepG2 cells overexpressing SerpinB3, p66shc expression was trivial. HepG2 overexpressing SerpinB3 cells were more prone to die after oxidizing treatments, such as diamide or high concentration H2O2. These cells injected in nude mice developed tumors five times smaller than those from control HepG2 cells. Tumors originating from HepG2 overexpressing SerpinB3 cells showed decreased activated Caspase-8, with concomitant increase of RIP3K and decreased levels of cleaved RIP3K, typical features of necroptosis. In conclusion, in patients affected by HCC, the pattern characterized by p66shc downregulation and elevated SerpinB3 levels was associated with markedly better survival. This pattern favored necroptosis in experimental high-stress conditions

SerpinB3 upregulates the Cyclooxygenase-2 / \u3b2-Catenin positive loop in colorectal cancer

Colorectal cancer is characterized by aberrant Cyclooxigenase-2 (COX-2) and \u3b2-Catenin pathways. Recently, the protease inhibitor SerpinB3 has been described overexpressed in more advanced stages of this tumor. Aim of the study was to explore the possible relationship between these molecules in this setting. We evaluated colorectal cancer specimens from 105 patients and a positive correlation between SerpinB3, COX-2 and \u3b2-Catenin expression was observed, with higher levels in tumor than in adjacent tissue. The highest levels were associated with pathologic parameters of poor prognosis, including vascular invasion, lymph node metastasis and perineural invasion. The molecular and protein profiles of COX-2 and \u3b2-Catenin were analyzed in cell lines with different expression of SerpinB3. In those with high expression of SerpinB3, COX-2 and \u3b2-Catenin were higher than in controls. Cells with high levels of SerpinB3 showed higher proliferation and invasion compared to controls. In conclusion, in colorectal cancer SerpinB3, COX-2 and \u3b2-Catenin are positively correlated and associated with more advanced tumor stage. The in vitro experimental results support a driving role of SerpinB3 in the upregulation of COX-2/ \u3b2-Catenin positive loop, associated with a more aggressive cellular phenotype