We have discovered that multiple basolateral pathways mediate EGF receptor sorting in renal epithelial cells. The polycystic kidney disease allele in the BPK mouse model, Bicc1, interferes with one specific EGF receptor pathway, causing nonpolar delivery of the receptor without affecting overall cell polarity.

No abstract

Familial prion disorders are believed to result from spontaneous conversion of mutant prion protein (PrP M ) to the pathogenic isoform (PrP Sc ). While most familial cases are heterozygous and thus express the normal (PrP C ) and mutant alleles of PrP, the role of PrP C in the pathogenic process is unclear. Plaques from affected cases reveal a heterogeneous picture; in some cases only PrP M is detected, whereas in others both PrP C and PrP M are transformed to PrP Sc . To understand if the coaggregation of PrP C is governed by PrP mutations or is a consequence of the cellular compartment of PrP M aggregation, we coexpressed PrP M and PrP C in neuroblastoma cells, the latter tagged with green fluorescent protein (PrP C-GFP ) for differentiation. Two PrP M forms (PrP 231T , PrP 217R/231T ) that aggregate spontaneously in the endoplasmic reticulum (ER) were generated for this analysis. We report that PrP C-GFP aggregates when coexpressed with PrP 231T or PrP 217R/231T , regardless of sequence homology between the interacting forms. Furthermore, intracellular aggregates of PrP 231T induce the accumulation of a C-terminal fragment of PrP, most likely derived from a potentially neurotoxic transmembrane form of PrP ( Ctm PrP) in the ER. These findings have implications for prion pathogenesis in familial prion disorders, especially in cases where transport of PrP M from the ER is blocked by the cellular quality control.

Transmissible Spongiform Encephalopathies are fatal neurodegenerative disorders of humans and animals that are familial, sporadic, and infectious in nature. Familial disorders of humans include Gerstmann-Straussler-Scheinker disease (GSS), familial Creutzfeldt-Jakob disease (CJD), and fatal familial insomnia, and result from point mutations in the prion protein gene. Although neurotoxicity in familial cases is believed to result from a spontaneous change in conformation of mutant prion protein (PrP) to the pathogenic PrP-scrapie (PrPSc) form, emerging evidence indicates otherwise. We have investigated the processing and metabolism of mutant PrP D202N (PrP202N) in cell models to elucidate possible mechanisms of cytotoxicity. In this report, we demonstrate that PrP202N expressed in human neuroblastoma cells fails to achieve a mature conformation following synthesis and accumulates in the endoplasmic reticulum as 'curly' aggregates. In addition, PrP202N cells show increased sensitivity to free radicals, indicating that neuronal susceptibility to oxidative damage may account for the neurotoxicity observed in cases of GSS resulting from PrP D202N mutation.

Prion diseases or transmissible spongiform encephalopathies are neurodegenerative disorders that are genetic, sporadic, or infectious. The pathogenetic event common to all prion disorders is a change in conformation of the cellular prion protein (PrPC) to the scrapie isoform (PrPSc), which, unlike PrPC, aggregates easily and is partially resistant to protease digestion. Although PrPSc is believed to be essential for the pathogenesis and transmission of prion disorders, the mechanism by which PrPSc deposits cause neurodegeneration is unclear. It has been proposed that in some cases of prion disorders, a transmembrane form of PrP, termed CtmPrP may be the mediator of neurodegenerative changes rather than PrPSc per se. In order to understand the underlying cellular processes by which PrPSc mediates neurodegeneration, we have investigated the mechanism of neurotoxicity by a beta-sheet rich peptide of PrP in a cell model. We show that exposure of human neuronal cell lines NT-2 and M17 to the prion peptide 106-126 (PrP106-126) catalyzes the aggregation of endogenous cellular prion protein (PrPC) to an amyloidogenic form that shares several characteristics with PrPSc. Intracellular accumulation of these PrPSc-like forms upregulates the synthesis of CtmPrP, which is proteolytically cleaved in the endoplasmic reticulum and the truncated C-terminal fragment is transported to the cell surface. In addition, we have isolated mutant NT-2 and neuroblastoma cells that are resistant to toxicity by PrP106-126 to facilitate further characterization of the biochemical pathways of PrP106-126 neurotoxicity. The PrP106-126-resistant phenotype of these cells could result from aberrant binding or internalization of the peptide, or due to an abnormality in the downstream pathway(s) of neuronal toxicity. Thus, our data suggest that PrPSc aggregation occurs by a process of 'nucleation' on a pre-existing 'seed' of PrP. Furthermore, the PrP106-126-resistant cells reported here will provide a unique opportunity for identifying the cellular and biochemical pathways that mediate neurotoxicity by PrPSc.