CELL BIOLOGY – IMMUNOLOGY – PATHOLOGY
Kidney International (1999) 55, 529–545; doi:10.1046/j.1523-1755.1999.00268.x
Direct lysosomal uptake of 
2-microglobulin contributes to chemically induced nephropathy
ANA MARIA CUERVO, HEINZ HILDEBRAND, ERNST M BOMHARD and J FRED DICE
Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts, USA, and Bayer AG, Toxicology, Wuppertal, Germany
Correspondence: Ana Maria Cuervo, M.D., Ph.D., Department of Physiology, Tufts University, School of Medicine, 136 Harrison Avenue, Boston, Massachusetts 02111, USA. E-mail: acuervo@opal.tufts.edu
Received 26 March 1998; Revised 24 August 1998; Accepted 24 August 1998.
Abstract
Direct lysosomal uptake of 
2-microglobulin contributes to chemically induced nephropathy.
Background
An abnormal accumulation of 
2-microglobulin (2
) in kidney lysosomes of male rats has been described in the nephropathy resulting from exposure to a variety of chemicals. The increment in lysosomal levels of 2 cannot be explained by a decrease in its proteolytic susceptibility. Because a portion of 2 resides in the cytosol of kidney cells, we decided to analyze whether this cytosolic form also contributes to the abnormal lysosomal accumulation of 2 after exposure to chemicals.
Methods
Intact kidney lysosomes were isolated from untreated or 2,2,4-trimethylpentane (TMP) treated rats, and their ability to take up 2 was compared.
Results
2 can be directly transported into isolated lysosomes in the presence of the heat shock cognate protein of 73 kDa (hsc73). 2 specifically binds to a lysosomal membrane glycoprotein of 96 kDa, previously identified as the receptor for the hsc73-mediated lysosomal pathway of protein degradation. In rats exposed to TMP, the specific lysosomal transport of 2 increases, as well as the ability of lysosomes to directly transport other substrates for this pathway. The increased lysosomal transport is mainly due to an increase in the levels of the receptor protein in the lysosomal membrane.
Conclusions
The hsc73-mediated lysosomal pathway contributes to the normal degradation of 2 in rat kidney and liver, and the activity of this pathway is increased after exposure to TMP. Our results suggest that the chemically induced accumulation of cytosolic 2 in lysosomes is mediated by an increased rate of direct uptake into lysosomes.
Keywords:
hyaline droplet nephropathy, lysosomes, heat shock protein, protein degradation, cathepsin, membrane transport
Abbreviations:
2, 2-microglobulin; ATP, adenosine triphosphate; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; hsc73, heat shock cognate protein of 73 kDa; k-FABP, kidney fatty acid-binding protein; lgp96, lysosomal glycoprotein of 96 kDa; MOPS, 3-(N-morpholino) propanesulfonic acid; RNase A, ribonuclease A; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TMP, 2,2, 4-trimethylpentane; TMP-2, 2,2, 4-trimethyl pentane-2-microglobulin conjugate
