Dataset Information

PKB and megalin determine the survival or death of renal proximal tubule cells.

ABSTRACT: Renal proximal tubule cells have a remarkable ability to reabsorb large quantities of albumin through megalin-mediated endocytosis. This is an essential process for overall body homeostasis. Overstressing this endocytic system with a prolonged excess of albumin is injurious to proximal tubule cells. How these cells function and protect themselves from injury is unknown. Here, we show that megalin is the sensor that determines whether cells will be protected or injured by albumin. Megalin, through a novel mechanism, binds PKB in a D-3-phosphorylated phospholipid-insensitive manner, anchoring PKB in the luminal plasma membrane. Whereas low doses of albumin are protective, an overload of albumin decreases megalin expression followed by a reduction of plasma membrane PKB, PKB activity, and Bad phosphorylation induced by PKB. The result is albumin-induced apoptosis. These results reveal a model for PKB distribution in the plasma membrane and elucidate mechanisms involved in both the protective and toxic effects of albumin on proximal tubule cells. In addition, our findings suggest a mechanism for the progression of chronic kidney disease to end-stage renal disease.

SUBMITTER: Caruso-Neves C

PROVIDER: S-EPMC1693744 | biostudies-literature | 2006 Dec

REPOSITORIES: biostudies-literature

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PKB and megalin determine the survival or death of renal proximal tubule cells.

Caruso-Neves Celso C Pinheiro Ana Acacia S AA Cai Hui H Souza-Menezes Jackson J Guggino William B WB

Proceedings of the National Academy of Sciences of the United States of America 20061122 49

Renal proximal tubule cells have a remarkable ability to reabsorb large quantities of albumin through megalin-mediated endocytosis. This is an essential process for overall body homeostasis. Overstressing this endocytic system with a prolonged excess of albumin is injurious to proximal tubule cells. How these cells function and protect themselves from injury is unknown. Here, we show that megalin is the sensor that determines whether cells will be protected or injured by albumin. Megalin, throug ...[more]

PMID: 17121993

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Project description:Cystinosis is a lysosomal storage disorder caused by defects in CTNS, the gene that encodes the lysosomal cystine transporter cystinosin. Patients with nephropathic cystinosis are characterized by endocrine defects, defective proximal tubule cell (PTC) function, the development of Fanconi syndrome and, eventually, end-stage renal disease. Kidney disease is developed despite the use of cysteamine, a drug that decreases lysosomal cystine overload but fails to correct overload-independent defects. Chaperone-mediated autophagy (CMA), a selective form of autophagy, is defective in cystinotic mouse fibroblasts, and treatment with cysteamine is unable to correct CMA defects in vivo, but whether the vesicular trafficking mechanisms that lead to defective CMA in cystinosis are manifested in human PTCs is not currently known and whether PTC-specific mechanisms are corrected upon CMA upregulation remains to be elucidated. Here, using CRISPR-Cas9 technology, we develop a new human PTC line with defective cystinosin expression (CTNS-KO PTCs). We show that the expression and localization of the CMA receptor, LAMP2A, is defective in CTNS-KO PTCs. The expression of the lipidated form of LC3B, a marker for another form of autophagy (macroautophagy), is decreased in CTNS-KO PTCs indicating decreased autophagosome numbers under basal conditions. However, the autophagic flux is functional, as measured by induction by starvation or by blockage using the v-ATPase inhibitor bafilomycin A, and by degradation of the macroautophagy substrate SQSTM1 under starvation and proteasome-inhibited conditions. Previous studies showed that LAMP2A accumulates in Rab11-positive vesicles in cystinotic cells. Here, we show defective Rab11 expression, localization and trafficking in CTNS-KO PTCs as determined by confocal microscopy, immunoblotting and TIRFM. We also show that both Rab11 expression and trafficking in cystinotic PTCs are rescued by the upregulation of CMA using small-molecule CMA activators. Cystinotic PTCs are characterized by PTC de-differentiation accompanied by loss of the endocytic receptor megalin, and megalin recycling is regulated by Rab11. Here we show that megalin plasma membrane localization is defective in CTNS-KO PTCs and its expression is rescued by treatment with CMA activators. Altogether, our data support that CMA upregulation has the potential to improve PTC function in cystinosis.

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Dataset Information

PKB and megalin determine the survival or death of renal proximal tubule cells.

Publications

PKB and megalin determine the survival or death of renal proximal tubule cells.

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