SEARCH · PubMed Health

Results for “Chaperone-Mediated Autophagy”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed2004

Mechanisms of chaperone-mediated autophagy.

Chaperone-mediated autophagy is one of several lysosomal pathways of proteolysis. This pathway is activated by physiological stresses such as prolonged starvation. Cytosolic proteins with particular peptide sequence motifs are recognized by a complex of molecular chaperones and delivered to lysosomes. No vesicular traffic is required for this protein degradation pathway, so it differs from microautophagy and macroautophagy. Protein substrates bind to a receptor in the lysosomal membrane, the lysosome-associated membrane protein (lamp) type 2a. Levels of lamp2a in the lysosomal membrane are controlled by alterations in the lamp2a half-life as well as by the dynamic distribution of the protein between the lysosomal membrane and the lumen. Substrate proteins are unfolded before transport into the lysosome lumen, and the transport of substrate proteins requires a molecular chaperone within the lysosomal lumen. The exact roles of this lysosomal chaperone remain to be defined. The mechanisms of chaperone-mediated autophagy are similar to mechanisms of protein import into mitochondria, chloroplasts, and the endoplasmic reticulum.

Amino Acid Motifs↗

PubMed2004

Suppression of chaperone-mediated autophagy in the renal cortex during acute diabetes mellitus.

BACKGROUND: In the renal hypertrophy that occurs in diabetes mellitus, decreased proteolysis may lead to protein accumulation, but it is unclear which proteins are affected. Because the lysosomal proteolytic pathway of chaperone-mediated autophagy is suppressed by growth factors in cultured cells, we investigated whether the abundance of substrates of this pathway increase in diabetic hypertrophy. METHODS: Rats with streptozotocin (STZ)-induced diabetes were pair-fed with vehicle-injected control rats. Proteolysis was measured as lysine release in renal cortical suspensions and protein synthesis as phenylalanine incorporation. Target proteins of chaperone-mediated autophagy were measured in cortical lysates and nuclear extracts by immunoblot analysis. Proteins that regulate chaperone-mediated autophagy [the lysosomal-associated membrane protein 2a (LAMP2a) or the heat shock cognate protein of 73 kD (hsc-73)] were measured in lysosomes isolated by density gradient centrifugation. RESULTS: Proteolysis decreased by 41% in diabetic rats; protein synthesis increased at 3 days, but returned to baseline by 7 days. The abundance of proteins containing that chaperone-mediated autophagy KFERQ signal motif increased 38% and individual KFERQ containing proteins [e.g., M2 pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and pax2] were more abundant. LAMP2a and hsc73 decreased by 25% and 81%, respectively, in cortical lysosomes from diabetic vs. control rats. CONCLUSION: The decline in proteolysis in acute diabetes mellitus is associated with an increase in proteins degraded by chaperone-mediated autophagy and a decrease in proteins which regulate this pathway. This study provides the first evidence that reduced chaperone-mediated autophagy contributes to accumulation of specific proteins in diabetic-induced renal hypertrophy.

Amino Acid Motifs↗

PubMed2000

Age-related decline in chaperone-mediated autophagy.

Intracellular protein degradation rates decrease with age in many tissues and organs. In cultured cells, chaperone-mediated autophagy, which is responsible for the selective degradation of cytosolic proteins in lysosomes, decreases with age. In this work we use lysosomes isolated from rat liver to analyze age-related changes in the levels and activities of the main components of chaperone-mediated autophagy. Lysosomes from "old" (22-month-old) rats show lower rates of chaperone-mediated autophagy, and both substrate binding to the lysosomal membrane and transport into lysosomes decline with age. A progressive age-related decrease in the levels of the lysosome-associated membrane protein type 2a that acts as a receptor for chaperone-mediated autophagy was responsible for decreased substrate binding in lysosomes from old rats as well as from late passage human fibroblasts. The cytosolic levels and activity of the 73-kDa heat-shock cognate protein required for substrate targeting to lysosomes were unchanged with age. The levels of lysosome-associated hsc73 were increased only in the oldest rats. This increase may be an attempt to compensate for reduced activity of the pathway with age.

Age Factors↗

PubMed2026

Chaperone-mediated autophagy as a regulator of hallmarks of cancer.

Chaperone-mediated autophagy (CMA) is a selective lysosomal degradation pathway that maintains cellular homeostasis by degrading soluble proteins containing KFERQ-like motifs. Although CMA has traditionally been recognized for its role in protein quality control and cellular stress adaptation, increasing evidence shows that it is frequently altered in cancer, where it regulates multiple processes that promote tumor initiation, progression, and therapy resistance. The growing number of identified CMA substrates involved in cell proliferation, apoptosis, metabolism, DNA damage response, immune regulation, inflammation, and cellular plasticity suggests that CMA is much more than a protein degradation pathway; it is an important regulator of tumor adaptation. In this review, we bring together current evidence to provide a comprehensive understanding of how CMA contributes to the Hallmarks of Cancer, including sustained proliferative signaling, resistance to cell death, metabolic reprogramming, invasion and metastasis, immune evasion, and the enabling characteristics of genome instability and tumor-promoting inflammation. We further explore the emerging roles of CMA in cellular plasticity and cancer stem cell maintenance, two interconnected processes that drive tumor progression, metastasis, and therapeutic resistance. By integrating evidence from diverse tumor types, this review provides a comprehensive understanding of how CMA shapes multiple hallmarks of cancer by selectively degrading key regulatory proteins. Finally, we highlight the context-dependent roles of CMA, identify key gaps in our current understanding, and discuss the opportunities and challenges of targeting CMA for cancer therapy. Overall, this hallmark-based perspective provides an integrated understanding of how CMA contributes to multiple hallmarks of cancer and supports its potential as a therapeutic target.

autophagy↗

PubMed2000

Selective degradation of annexins by chaperone-mediated autophagy.

Annexins are a family of proteins that bind phospholipids in a calcium-dependent manner. Analysis of the sequences of the different members of the annexin family revealed the presence of a pentapeptide biochemically related to KFERQ in some annexins but not in others. Such sequences have been proposed to be a targeting sequence for chaperone-mediated autophagy, a lysosomal pathway of protein degradation that is activated in confluent cells in response to removal of serum growth factors. We demonstrate that annexins II and VI, which contain KFERQ-like sequences, are degraded more rapidly in response to serum withdrawal, while annexins V and XI, without such sequences, are degraded at the same rate in the presence and absence of serum. Using isolated lysosomes, only the annexins containing KFERQ-like sequences are degraded by chaperone mediated-autophagy. Annexins V and XI could associate with lysosomes but did not enter the lysosomes and were not proteolytic substrates. Furthermore, four annexins containing KFERQ-like sequences, annexins I, II, IV, and VI, are enriched in lysosomes with high chaperone-mediated autophagy activity as expected for substrate proteins. These results provide striking evidence for the importance of KFERQ motifs in substrates of chaperone-mediated autophagy.

Amino Acid Motifs↗

PubMed2025

Chaperone-mediated autophagy regulates neuronal activity by sex-specific remodelling of the synaptic proteome.

Chaperone-mediated autophagy (CMA) declines in ageing and neurodegenerative diseases. Loss of CMA in neurons leads to neurodegeneration and behavioural changes in mice but the role of CMA in neuronal physiology is largely unknown. Here we show that CMA deficiency causes neuronal hyperactivity, increased seizure susceptibility and disrupted calcium homeostasis. Pre-synaptic neurotransmitter release and NMDA receptor-mediated transmission were enhanced in CMA-deficient females, whereas males exhibited elevated post-synaptic AMPA-receptor activity. Comparative quantitative proteomics revealed sexual dimorphism in the synaptic proteins degraded by CMA, with preferential remodelling of the pre-synaptic proteome in females and the post-synaptic proteome in males. We demonstrate that genetic or pharmacological CMA activation in old mice and an Alzheimer's disease mouse model restores synaptic protein levels, reduces neuronal hyperexcitability and seizure susceptibility, and normalizes neurotransmission. Our findings unveil a role for CMA in regulating neuronal excitability and highlight this pathway as a potential target for mitigating age-related neuronal decline.

Animals↗

PubMed2000

Import of a cytosolic protein into lysosomes by chaperone-mediated autophagy depends on its folding state.

We have analyzed the folding state of cytosolic proteins imported in vitro into lysosomes, using an approach originally developed by Eilers and Schatz, (Eilers, M., and Schatz, G. (1986) Nature 322, 228-232) to investigate protein import into mitochondria. The susceptibility toward proteases of mouse dihydrofolate reductase (DHFR), synthesized in a coupled transcription-translation system with rabbit reticulocytes, decreased in the presence of its substrate analogue, methotrexate. This analogue complexes with high affinity with the in vitro synthesized DHFR and locks it into a protease-resistant folded conformation. DHFR was taken up by freshly isolated rat liver lysosomes and methotrexate reduced this uptake by about 80%. A chimeric DHFR protein, which carries the N-terminal presequence of subunit 9 of ATP synthase preprotein from Neurospora crassa fused to its N terminus, was taken up by lysosomes more efficiently. Again, methotrexate abolished the lysosomal uptake of the fusion protein, which was partially restored by washing of methotrexate from DHFR or by adding together methotrexate and dihydrofolate, the natural substrate of DHFR. Immunoblot analysis with anti-DHFR of liver lysosomes and of other fractions, isolated from rats starved for 88 h and treated with lysosomal inhibitors, suggests that DHFR is degraded by chaperone-mediated autophagy. Competition with ribonuclease A and stimulation by ATP/Mg(2+) and the heat shock cognate protein of 73 kDa show that the lysosomal uptake of the fusion protein also occurs by this pathway. It is concluded that the lysosomal uptake of cytosolic proteins by chaperone-mediated autophagy mainly occurs by passage of the unfolded proteins through the lysosomal membrane. Therefore, this mechanism is different from protein transport into peroxisomes, but similar to the import of proteins into the endoplasmic reticulum and mitochondria.

Animals↗

PubMed2026

Dynamic evolution of chaperone-mediated autophagy is associated with tumor microenvironment remodeling and prognostic stratification in lung adenocarcinoma: insights from single-cell transcriptomics, ensemble machine learning, and experimental validation.

BACKGROUND: Lung adenocarcinoma (LUAD) shows prognostic heterogeneity, and tumor-node-metastasis (TNM) staging is limited for individualized management. Chaperone-mediated autophagy (CMA) maintains proteostasis, but its role during adenocarcinoma in situ (AIS)-minimally invasive adenocarcinoma (MIA)-invasive adenocarcinoma (IAC) progression remains unclear. METHODS: Single-cell RNA sequencing (scRNA-seq) data from GSE189357 and bulk transcriptomes from The Cancer Genome Atlas (TCGA)-LUAD and Gene Expression Omnibus (GEO) cohorts were integrated. CMA activity, cell-cell communication, weighted gene co-expression network analysis (WGCNA), tumor-normal differential expression, machine-learning survival modeling, tumor microenvironment (TME) features, drug sensitivity, and EPC1 function were analyzed. RESULTS: CMA-high tumor epithelial cells increased from AIS (58.1%) to MIA (65.7%) but declined in IAC (44.4%; p < 0.001). CMA-low cells preferentially received fibroblast-derived extracellular matrix cues. A CMA-negatively correlated module identified 69 core genes. Random survival forest (RSF) performed best among 117 machine-learning combinations (mean concordance index > 0.873). High-risk patients had worse survival across cohorts, and the risk score was independently associated with overall survival (hazard ratio = 16.013, 95% confidence interval: 9.579-26.768, p < 0.001). High-risk tumors showed proliferative activation and M0 macrophage enrichment, whereas low-risk tumors showed stronger immune-related signaling. EPC1 overexpression suppressed malignant phenotypes in A549 cells. CONCLUSION: CMA dynamics are associated with stromal and immune remodeling during LUAD progression. A CMA-based model provides robust prognostic stratification and may offer a basis for future TME-guided studies.

Chaperone-mediated autophagy↗

PubMed2003

Cathepsin A regulates chaperone-mediated autophagy through cleavage of the lysosomal receptor.

Protective protein/cathepsin A (PPCA) has a serine carboxypeptidase activity of unknown physiological function. We now demonstrate that this protease activity triggers the degradation of the lysosome-associated membrane protein type 2a (lamp2a), a receptor for chaperone-mediated autophagy (CMA). Degradation of lamp2a is important because its level in the lysosomal membrane is a rate-limiting step of CMA. Cells defective in PPCA show reduced rates of lamp2a degradation, higher levels of lamp2a and higher rates of CMA. Restoration of PPCA protease activity increases rates of lamp2a degradation, reduces levels of lysosomal lamp2a and reduces rates of CMA. PPCA associates with lamp2a on the lysosomal membrane and cleaves lamp2a near the boundary between the luminal and transmembrane domains. In addition to the well-studied role of PPCA in targeting and protecting two lysosomal glycosidases, we have defined a role for the proteolytic activity of this multifunctional protein.

Amino Acid Sequence↗

PubMed2000

Unique properties of lamp2a compared to other lamp2 isoforms.

Lamp2a acts as a receptor in the lysosomal membrane for substrate proteins of chaperone-mediated autophagy. Using antibodies specific for the cytosolic tail of lamp2a and others recognizing all lamp2 isoforms, we found that in rat liver lamp2a represents 25% of lamp2s in the lysosome. We show that lamp2a levels in the lysosomal membrane in rat liver and fibroblasts in culture directly correlate with rates of chaperone-mediated autophagy in a variety of physiological and pathological conditions. The concentration of other lamp2s in the lysosomal membrane show no correlation under the same conditions. Furthermore, substrate proteins bind to lamp2a but not to other lamp2s. Four positively-charged amino acids uniquely present in the cytosolic tail of lamp2a are required for the binding of substrate proteins. Lamp2a also distributes to an unique subpopulation of perinuclear lysosomes in cultured fibroblasts in response to serum withdrawal, and lamp2a, more than other lamp2s, tends to multimerize. These characteristics may be important for lamp2a to act as a receptor for chaperone-mediated autophagy.

Animals↗

PubMed2001

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.

Amino Acid Motifs↗

PubMed2002

Pathways of proteolysis affecting renal cell growth.

PURPOSE OF REVIEW: Although the suppression of protein breakdown plays a major role in the growth of the adult kidney in conditions that cause renal hypertrophy, the pathways responsible for controlling proteolysis and the substrates being destroyed have only recently been investigated. This review focuses on the role of the ubiquitin-proteasome pathway in regulating specific substrates during kidney growth, and the role of the lysosomal pathways in the suppression of general protein breakdown and of the substrates of chaperone-mediated autophagy. RECENT FINDINGS: New insights into the regulation of specific ubiquitin ligases demonstrate how the cell controls the destruction of particular substrates important for growth, including hypoxia-inducible factors and the cell cycle inhibitor, p27. In cell culture, growth factors suppress the lysosomal pathway of chaperone-mediated autophagy leading to the accumulation of specific cytoplasmic proteins containing KFERQ motifs. In a variety of systems, including cultured renal tubular cells, phosphoinositol 3 kinase activity and its downstream mediators control lysosomal proteolysis. SUMMARY: Specific ubiquitin ligases and the pathways that control their substrate recognition may be key signalling intermediaries for cell growth, but global alterations in lysosomal pathways account for the decrease in general proteolysis. Functional KFERQ motifs mark proteins that are important in renal growth, including enzymes responsible for the characteristic shift to glycolytic metabolism during growth, transcription factors, and signalling molecules. As altering phosphoinositol 3 kinase changes patterns of vesicular trafficking, it is possible that the regulation of intracellular trafficking may underlie the changes seen in lysosomal proteolysis with growth.

Animals↗

PubMed2000

Regulation of lamp2a levels in the lysosomal membrane.

The selective degradation of cytosolic proteins in lysosomes by chaperone-mediated autophagy depends, at least in part, on the levels of a substrate receptor at the lysosomal membrane. We have previously identified this receptor as the lysosome-associated membrane protein type 2a (lamp2a) and showed that levels of lamp2a at the lysosomal membrane directly correlate with the activity of the proteolytic pathway. Here we show that levels of lamp2a at the lysosomal membrane are mainly controlled by changes in its half-life and its distribution between the lysosomal membrane and the matrix. The lysosomal degradation of lamp2a requires the combined action of at least two different proteolytic activities at the lysosomal membrane. Lamp2a is released from the membrane by the action of these proteases, and then the truncated lamp2a is rapidly degraded within the lysosomal matrix. Membrane degradation of lamp2a is a regulated process that is inhibited in the presence of substrates for chaperone-mediated autophagy and under conditions that activate that type of autophagy. Uptake of substrate proteins also results in transport of some intact lamp2a from the lysosomal membrane into the matrix. This fraction of lamp2a can be reinserted back into the lysosomal membrane. The traffic of lamp2a through the lysosomal matrix is not mediated by vesicles, and lamp2a reinsertion requires the lysosomal membrane potential and protein components of the lysosomal membrane. The distribution of lamp2a between the lysosomal membrane and matrix is a dynamic process that contributes to the regulation of lysosomal membrane levels of lamp2a and consequently to the activity of the chaperone-mediated autophagic pathway.

3T3 Cells↗

PubMed2003

At the acidic edge: emerging functions for lysosomal membrane proteins.

It has recently become clear that lysosomes have more complex functions than simply being the end-point on a degradative pathway. Similarly, it is now emerging that there are interesting functions for the limiting membranes around these organelles and their associated proteins. Although it has been known for several decades that the lysosomal membrane contains several highly N-glycosylated proteins, including the lysosome-associated membrane proteins LAMP-1 and LAMP-2 and lysosomal integral membrane protein-2/lysosomal membrane glycoprotein-85 (LIMP-2/LGP85), specific functions of these proteins have only recently begun to be recognized. Although the normal functions of LAMP-1 can be substituted by the structurally related LAMP-2, LAMP-2 itself has more specific tasks. Knockout of LAMP-2 in mice has revealed roles for LAMP-2 in lysosomal enzyme targeting, autophagy and lysosomal biogenesis. LAMP-2 deficiency in humans leads to Danon disease, a fatal cardiomyopathy and myopathy. Furthermore, there is evidence that LAMP-2 functions in chaperone-mediated autophagy. LIMP-2/LGP85 also seems to have specific functions in maintaining endosomal transport and lysosomal biogenesis. The pivotal function of lysosomal membrane proteins is also highlighted by the recent identification of disease-causing mutations in cystine and sialic acid transporter proteins, leading to nephropathic cystinosis and Salla disease.

Animals↗

PubMed2004

Disturbed cholesterol traffic but normal proteolytic function in LAMP-1/LAMP-2 double-deficient fibroblasts.

Mice double deficient in LAMP-1 and -2 were generated. The embryos died between embryonic days 14.5 and 16.5. An accumulation of autophagic vacuoles was detected in many tissues including endothelial cells and Schwann cells. Fibroblast cell lines derived from the double-deficient embryos accumulated autophagic vacuoles and the autophagy protein LC3II after amino acid starvation. Lysosomal vesicles were larger and more peripherally distributed and showed a lower specific density in Percoll gradients in double deficient when compared with control cells. Lysosomal enzyme activities, cathepsin D processing and mannose-6-phosphate receptor expression levels were not affected by the deficiency of both LAMPs. Surprisingly, LAMP-1 and -2 deficiencies did not affect long-lived protein degradation rates, including proteolysis due to chaperone-mediated autophagy. The LAMP-1/2 double-deficient cells and, to a lesser extent, LAMP-2 single-deficient cells showed an accumulation of unesterified cholesterol in endo/lysosomal, rab7, and NPC1 positive compartments as well as reduced amounts of lipid droplets. The cholesterol accumulation in LAMP-1/2 double-deficient cells could be rescued by overexpression of murine LAMP-2a, but not by LAMP-1, highlighting the more prominent role of LAMP-2. Taken together these findings indicate partially overlapping functions for LAMP-1 and -2 in lysosome biogenesis, autophagy, and cholesterol homeostasis.

Animals↗

PubMed2026

Hepatitis C Virus Enhances Lysosome-Associated Membrane Protein 2 A Transcription Through Nuclear Factor Erythroid 2-Related Factor 2 to Support Viral Replication.

Hepatitis C virus (HCV) establishes persistent infection by rewiring host stress-response pathways. Chaperone-mediated autophagy (CMA) contributes to HCV replication, but it remains unclear whether HCV regulates lysosome-associated membrane protein 2 A (LAMP-2A), the rate-limiting receptor for CMA. Here, we examined LAMP-2A regulation in HCV-infected Huh-7.5 cells. HCV infection increased LAMP-2A promoter activity, mRNA, and protein abundance, indicating transcriptional upregulation. Among candidate stress-responsive transcription factors, nuclear factor erythroid 2-related factor 2 (NRF2), hypoxia-inducible factor 1α (HIF-1α), and nuclear factor of activated T cells 1 (NFAT1) were elevated in infected cells. However, promoter mutagenesis identified NRF2 as the principal direct regulator. Mutation of the NRF2-responsive antioxidant response element markedly reduced basal and HCV-induced LAMP-2A promoter activity. Chromatin immunoprecipitation assays revealed NRF2 association with the LAMP-2A promoter, and HCV infection increased nuclear accumulation and Ser40 phosphorylation of NRF2. Functionally, shRNA-mediated knockdown of LAMP-2A reduced intracellular HCV RNA and protein levels. These findings identify an NRF2-LAMP-2A regulatory axis engaged during HCV infection and support a model in which HCV upregulates LAMP-2A to establish a cellular environment favorable for viral replication.

Hepacivirus↗

PubMed2001

A molecular chaperone complex at the lysosomal membrane is required for protein translocation.

A group of cytosolic proteins are targeted to lysosomes for degradation in response to serum withdrawal or prolonged starvation by a process termed chaperone-mediated autophagy. In this proteolytic pathway little is known about how proteins are translocated across lysosomal membranes. We now show that an isoform of the constitutively expressed protein of the heat shock family of 70 kDa (Hsc70) is associated with the cytosolic side of the lysosomal membrane where it binds to substrates of this proteolytic pathway. Results from coimmunoprecipitation and colocalization studies indicate that this molecular chaperone forms complexes with other molecular chaperones and cochaperones, including Hsp90, Hsp40, the Hsp70-Hsp90 organizing protein (Hop), the Hsp70-interacting protein (Hip), and the Bcl2-associated athanogene 1 protein (BAG-1). Antibodies against Hip, Hop, Hsp40 and Hsc70 block transport of protein substrates into purified lysosomes.

Biological Transport↗

PubMed2001

Starvation-induced lysosomal degradation of aldolase B requires glutamine 111 in a signal sequence for chaperone-mediated transport.

Aldolase B is an abundant cytosolic protein found in all eukaryotic cells. Like many glycolytic enzymes, this protein was sequestered into lysosomes for degradation during nutrient starvation. We report here that the degradation of recombinant aldolase B was enhanced two-fold when rat and human hepatoma cells were starved for amino acid and serum. In addition, starvation-induced degradation of aldolase B was inhibited by chloroquine, an inhibitor of lysosomal proteinases and by 3-methyladenine, an inhibitor of autophagy. Aldolase B has three lysosomal targeting motifs (Q(12)KKEL, Q(58)FREL, and IKLDQ(111)) that have been proposed to interact with hsc73 thereby initiating its transport into lysosomes. In this study, we have mutated the essential glutamine residues in each of these hsc73-binding motifs in order to evaluate their roles in the lysosomal degradation of aldolase B during starvation. We have found that when glutamines 12 or 58 are mutated to asparagines enhanced degradation of aldolase B proceeded normally. However, when glutamine 111 was mutated to an asparagine or a threonine, starvation-induced degradation was completely suppressed. These mutations did not appear to alter the tertiary structure of aldolase B since enzymatic activity was not affected. Our results suggest that starvation-induced lysosomal degradation of aldolase B requires both autophagy and glutamine 111. We discuss the possible roles for autophagy and hsc73-mediated transport in the lysosomal sequestration of aldolase B.

Amino Acid Motifs↗