A mechanism regulating proteolysis of specific proteins during renal tubular cell growth.
Growth factors suppress the degradation of cellular proteins in lysosomes in renal epithelial cells. Whether this process also involves specific classes of proteins that influence growth processes is unknown. We investigated chaperone-mediated autophagy, a lysosomal import pathway that depends on the 73-kDa heat shock cognate protein and allows the degradation of proteins containing a specific lysosomal import consensus sequence (KFERQ motif). Epidermal growth factor (EGF) or ammonia, but not transforming growth factor beta1, suppresses total protein breakdown in cultured NRK-52E renal epithelial cells. EGF or ammonia prolonged the half-life of glyceraldehyde-3-phosphate dehydrogenase, a classic substrate for chaperone-mediated autophagy, by more than 90%, whereas transforming growth factor beta1 did not. EGF caused a similar increase in the half-life of the KFERQ-containing paired box-related transcription factor, Pax2. The increase in half-life was accompanied by an increased accumulation of proteins with a KFERQ motif including glyceraldehyde-3-phosphate dehydrogenase and Pax2. Ammonia also increased the level of the Pax2 protein. Lysosomal import of KFERQ proteins depends on the abundance of the 96-kDa lysosomal glycoprotein protein (lgp96), and we found that EGF caused a significant decrease in lgp96 in cellular homogenates and associated with lysosomes. We conclude that EGF in cultured renal cells regulates the breakdown of proteins targeted for destruction by chaperone-mediated autophagy. Because suppression of this pathway results in an increase in Pax2, these results suggest a novel mechanism for the regulation of cell growth.
Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA.
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Franch
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Sooparb
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Du
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Brown
D020816:Amino Acid Motifs; D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000737:chemistry* / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006801:Humans; D007684:Kidney Tubules / Q000166:cytology* / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D051762:PAX2 Transcription Factor; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000737:chemistry* / Q000378:metabolism; D053773:Transforming Growth Factor beta1; D015854:Up-Regulation; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; C494373:Hspa8 protein, rat; D018832:Molecular Chaperones; D051762:PAX2 Transcription Factor; C497318:PAX2 protein, human; D011994:Recombinant Proteins; C508960:TGFB1 protein, human; C508962:Tgfb1 protein, rat; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D004815:Epidermal Growth Factor; D000641:Ammonia; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D001619:beta-N-Acetylhexosaminidases