Chaperone-mediated autophagy promotes lung cancer cell survival through selective stabilization of the pro-survival protein, MCL1

Moringa oleifera and Autophagy: Evidence from In Vitro Studies on Chaperone-Mediated Autophagy in HepG2 Cancer Cells

Hepatocellular carcinoma (HCC) is the most prevalent primary liver cancer in Sub-Saharan African countries, including South Africa (SA). Given the limitations in current HCC therapeutics, there is an increasing need for alternative adjuvant therapeutic options. As such, several cell survival mechanisms, such as autophagy, have been identified as potential adjuvant therapeutic targets in HCC treatment. Of the three most established autophagic pathways, the upregulation of chaperone-mediated autophagy (CMA) has been extensively described in various cancer cells, including HCC cells. CMA promotes tumor growth and chemotherapeutic drug resistance, thus contributing to HCC tumorigenesis. Therefore, the modulation of CMA serves as a promising adjuvant target for current HCC therapeutic strategies. Phytochemical extracts found in the medicinal plant, Moringa oleifera (MO), have been shown to induce apoptosis in numerous cancer cells, including HCC. MO leaves have the greatest abundance of phytochemicals displaying anticancer potential. However, the potential interaction between the pro-apoptotic effects of MO aqueous leaf extract and the survival-promoting role of CMA in an in vitro model of HCC remains unclear. This review aims to summarize the latest findings on the role of CMA, and MO in the progression of HCC.

The Complex Role of Chaperone-Mediated Autophagy in Cancer Diseases

Chaperone-mediated autophagy (CMA) is a process that rapidly degrades proteins labeled with KFERQ-like motifs within cells via lysosomes to terminate their cellular functioning. Meanwhile, CMA plays an essential role in various biological processes correlated with cell proliferation and apoptosis. Previous studies have shown that CMA was initially found to be procancer in cancer cells, while some theories suggest that it may have an inhibitory effect on the progression of cancer in untransformed cells. Therefore, the complex relationship between CMA and cancer has aroused great interest in the application of CMA activity regulation in cancer therapy. Here, we describe the basic information related to CMA and introduce the physiological functions of CMA, the dual role of CMA in different cancer contexts, and its related research progress. Further study on the mechanism of CMA in tumor development may provide novel insights for tumor therapy targeting CMA. This review aims to summarize and discuss the complex mechanisms of CMA in cancer and related potential strategies for cancer therapy.

Chaperone-mediated autophagy promotes breast cancer angiogenesis via regulation of aerobic glycolysis

Evidence shows that chaperone-mediated autophagy (CMA) is involved in cancer cell pathogenesis and progression. However, the potential role of CMA in breast cancer angiogenesis remains unknown. We first manipulated CMA activity by knockdown and overexpressing of lysosome-associated membrane protein type 2A (LAMP2A) in MDA-MB-231, MDA-MB-436, T47D and MCF7 cells. We found that the tube formation, migration and proliferation abilities of human umbilical vein endothelial cells (HUVECs) were inhibited after cocultured with tumor-conditioned medium from breast cancer cells of LAMP2A knockdown. While the above changes were promoted after cocultured with tumor-conditioned medium from breast cancer cells of LAMP2A overexpression. Moreover, we found that CMA could promote VEGFA expression in breast cancer cells and in xenograft model through upregulating lactate production. Finally, we found that lactate regulation in breast cancer cells is hexokinase 2 (HK2) dependent, and knockdown of HK2 can significantly reduce the ability of CMA-mediated tube formation capacity of HUVECs. Collectively, these results indicate that CMA could promote breast cancer angiogenesis via regulation of HK2-dependent aerobic glycolysis, which may serve as an attractive target for breast cancer therapies.

Chaperone-mediated Autophagy Regulates Cell Growth by Targeting SMAD3 in Glioma

Previous studies suggest that the reduction of SMAD3 (mothers against decapentaplegic homolog 3) has a great impact on tumor development, but its exact pathological function remains unclear. In this study, we found that the protein level of SMAD3 was greatly reduced in human-grade IV glioblastoma tissues, in which LAMP2A (lysosome-associated membrane protein type 2A) was significantly up-regulated. LAMP2A is a key rate-limiting protein of chaperone-mediated autophagy (CMA), a lysosome pathway of protein degradation that is activated in glioma. We carefully analyzed the amino-acid sequence of SMAD3 and found that it contained a pentapeptide motif biochemically related to KFERQ, which has been proposed to be a targeting sequence for CMA. In vitro, we confirmed that SMAD3 was degraded in either serum-free or KFERQ motif deleted condition, which was regulated by LAMP2A and interacted with HSC70 (heat shock cognate 71 kDa protein). Using isolated lysosomes, amino-acid residues 75 and 128 of SMAD3 were found to be of importance for this process, which affected the CMA pathway in which SMAD3 was involved. Similarly, down-regulating SMAD3 or up-regulating LAMP2A in cultured glioma cells enhanced their proliferation and invasion. Taken together, these results suggest that excessive activation of CMA regulates glioma cell growth by promoting the degradation of SMAD3. Therefore, targeting the SMAD3-LAMP2A-mediated CMA-lysosome pathway may be a promising approach in anti-cancer therapy.

MicroRNA-106a regulates autophagy-related cell death and EMT by targeting TP53INP1 in lung cancer with bone metastasis

Bone metastasis is one of the most serious complications in lung cancer patients. MicroRNAs (miRNAs) play important roles in tumour development, progression and metastasis. A previous study showed that miR-106a is highly expressed in the tissues of lung adenocarcinoma with bone metastasis, but its mechanism remains unclear. In this study, we showed that miR-106a expression is dramatically increased in lung cancer patients with bone metastasis (BM) by immunohistochemical analysis. MiR-106a promoted A549 and SPC-A1 cell proliferation, migration and invasion in vitro. The results of bioluminescence imaging (BLI), micro-CT and X-ray demonstrated that miR-106a promoted bone metastasis of lung adenocarcinoma in vivo. Mechanistic investigations revealed that miR-106a upregulation promoted metastasis by targeting tumour protein 53-induced nuclear protein 1 (TP53INP1)-mediated metastatic progression, including cell migration, autophagy-dependent death and epithelial-mesenchymal transition (EMT). Notably, autophagy partially attenuated the effects of miR-106a on promoting bone metastasis in lung adenocarcinoma. These findings demonstrated that restoring the expression of TP53INP1 by silencing miR-106a may be a novel therapeutic strategy for bone metastatic in lung adenocarcinoma.

Role of chaperone-mediated autophagy in the pathophysiology including pulmonary disorders

Autophagy is a highly conserved mechanism of delivering cytoplasmic components for lysosomal degradation. Among the three major autophagic pathways, chaperone-mediated autophagy (CMA) is primarily characterized by its selective nature of protein degradation, which is mediated by heat shock cognate 71 kDa protein (HSC70: also known as HSPA8) recognition of the KFERQ peptide motif in target proteins. Lysosome-associated membrane protein type 2A (LAMP2A) is responsible for substrate binding and internalization to lysosomes, and thus, the lysosomal expression level of LAMP2A is a rate-limiting factor for CMA. Recent advances have uncovered not only physiological but also pathological role of CMA in multiple organs, including neurodegenerative disorders, kidney diseases, liver diseases, heart diseases, and cancers through the accumulation of unwanted proteins or increased degradation of target proteins with concomitant metabolic alterations resulting from CMA malfunction. With respect to pulmonary disorders, the involvement of CMA has been demonstrated in lung cancer and chronic obstructive pulmonary disease (COPD) pathogenesis through regulating apoptosis. Further understanding of CMA machinery may shed light on the molecular mechanisms of refractory disorders and lead to novel treatment modalities through CMA modulation.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

USP19 (ubiquitin specific peptidase 19) promotes TBK1 (TANK-binding kinase 1) degradation via chaperone-mediated autophagy

TBK1 (TANK-binding kinase 1) is an essential receptor protein required for the innate immune response, but the mechanisms underlying TBK1 stability, especially those regulated via autophagy, remain poorly understood. Here, we demonstrate that USP19 (ubiquitin specific peptidase 19) interacts with and promotes TBK1 lysosomal degradation via chaperone-mediated autophagy (CMA). We observed that TBK1 had a canonical CMA motif, knocking down key proteins involved in CMA (HSPA8/HSC70 or LAMP2A) or inhibiting CMA-prevented USP19-mediated TBK1 degradation. Furthermore, USP19 deficiency in macrophages caused an elevation of TBK1 and the activation of the type-I interferon signaling pathway after vesicular stomatitis virus (VSV) infection. Consistently, macrophage-specific usp19 knockout in mice resulted in attenuated VSV replication and resistance to VSV infection in vivo. Altogether, our results suggest that USP19 is a key regulator of TBK1 and uncovers a previously uncharacterized role for USP19 in CMA-mediated TBK1 degradation and infectious diseases.

Acetylation-dependent regulation of TPD52 isoform 1 modulates chaperone-mediated autophagy in prostate cancer

Aberrant chaperone-mediated autophagy (CMA) activation has been suggested as a tumorigenesis-promoting event in various cancers, although its roles in prostate cancer (PCa) remain elusive. Emerging evidence indicates that TPD52 isoform 1, a prostate-specific and androgen-responsive gene, contributes to the malignant progression of PCa. Here, we demonstrate that TPD52 enhances CMA activation by interacting with HSPA8/HSC70 and enhancing substrate degradation in PCa. Elevation of TPD52 is essential for CMA-induced PCa cell proliferation and stress resistance in vitro and in vivo. Furthermore, TPD52 is acetylated by KAT2B at K163, which is a process that can be antagonized by HDAC2. Inactivation of HDAC2 results in elevated TPD52 acetylation, which compromises the interaction between TPD52 and HSPA8, leading to impaired CMA function and tumor growth in vivo. Taken together, our findings reveal that acetylation-dependent regulation of TPD52 modulates CMA oncogenic function in PCa, thereby suggesting the possibility of targeting the TPD52-mediated CMA pathway to control the progression of PCa.Abbreviations: CMA: chaperone-mediated autophagy; HDAC2: histone deacetylase 2; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; KAT2B: lysine acetyltransferase 2B; LAMP2A: lysosomal associated membrane protein 2A; PCa: prostate cancer; TPD52: tumor protein D52.

Inhibition of chaperone‑mediated autophagy reduces tumor growth and metastasis and promotes drug sensitivity in colorectal cancer

Chaperone-mediated autophagy (CMA) is a selective type of autophagy whereby a specific subset of intracellular proteins is targeted to the lysosome for degradation. The present study investigated the mechanisms underlying the response and resistance to 5-fluorouracil (5-FU) in colorectal cancer (CRC) cell lines. In engineered 5-FU-resistant CRC cell lines, a significant elevation of lysosome-associated membrane protein 2A (LAMP2A), which is the key molecule in the CMA pathway, was identified. High expression of LAMP2A was found to be responsible for 5-FU resistance and to enhance PLD2 expression through the activation of NF-κB pathway. Accordingly, loss or gain of function of LAMP2A in 5-FU-resistant CRC cells rendered them sensitive or resistant to 5-FU, respectively. Taken together, the results of the present study suggested that chemoresistance in patients with CRC may be mediated by enhancing CMA. Thus, CMA is a promising predictor of chemosensitivity to 5-FU treatment and anti-CMA therapy may be a novel therapeutic option for patients with CRC.

Chaperone Mediated Autophagy Substrates and Components in Cancer

Chaperone-mediated autophagy (CMA) represents a specific way of lysosomal protein degradation and contrary to macro and microautophagy is independent of vesicles formation. The role of CMA in different physiopathological processes has been studied for several years. In cancer, alterations of the CMA principal components, Hsc70 and Lamp2A protein and mRNA levels, have been described in malignant cells. However, changes in the expression levels of these CMA components are not always associated with changes in CMA activity and their biological significance must be carefully interpreted case by case. The objective of this review is to discuss whether altering the CMA activity, CMA substrates or CMA components is accurate to avoid cancer progression. In particular, this review will discuss about the evidences in which alterations CMA components Lamp2A and Hsc70 are associated or not with changes in CMA activity in different cancer types. This analysis will help to better understand the role of CMA activity in cancer and to elucidate whether CMA can be considered as target for therapeutics. Further, it will help to define whether the attention of the investigation should be focused on Lamp2A and Hsc70 because they can have an independent role in cancer progression beyond of their participation in altered CMA activity.

Dysfunction of chaperone-mediated autophagy in human diseases

Chaperone-mediated autophagy (CMA), one of the degradation pathways of proteins, is highly selective to substrates that have KFERQ-like motif. In this process, the substrate proteins are first recognized by the chaperone protein, heat shock cognate protein 70 (Hsc70), then delivered to lysosomal membrane surface where the single-span lysosomal receptor, lysosome-associated membrane protein type 2A (LAMP2A) can bind to the substrate proteins to form a 700 kDa protein complex that allows them to translocate into the lysosome lumen to be degraded by the hydrolytic enzymes. This degradation pathway mediated by CMA plays an important role in regulating glucose and lipid metabolism, transcription, DNA reparation, cell cycle, cellular response to stress and consequently, regulating many aging-associated human diseases, such as neurodegeneration, cancer and metabolic disorders. In this review, we provide an overview of current research on the functional roles of CMA primarily from a perspective of understanding and treating human diseases and also discuss its potential applications for diseases.

Long non-coding RNA SNHG20 promotes ovarian cancer development by targeting microRNA-338-3p to regulate MCL1 expression

Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs/miRs) were reported to be associated with the development of ovarian cancer (OC). Increasing evidence demonstrated that lncRNA SNHG20 and miR-338-3p were involved in OC. However, the functional mechanism of lncRNA SNHG20 and miR-338-3p in OC development remains unknown. The expression of SNHG20, miR-338-3p and myeloid cell leukemia 1 (MCL1) was detected by reverse transcription-quantitative PCR. MTT assay, flow cytometry and transwell migration and invasion assays were used to assess cell proliferation, apoptosis, migration and invasion, respectively. The relative protein expression was detected by western blot analysis. The interaction between miR-338-3p and SNHG20 or MCL1 was predicted by starBase v3.0, and subsequently confirmed by dual-luciferase reporter assay. Besides, mouse xenograft assay was carried out to explore the effect of SNHG20 on tumor growth in vivo. The levels of SNHG20 and MCL1 were upregulated, while miR-338-3p level was downregulated in OC tissues and cells. SNHG20 knockdown repressed OC cell proliferation, migration, invasion and epithelial-mesenchymal transition, and induced apoptosis. Interestingly, SNHG20 targeted miR-338-3p to regulate MCL1 expression. miR-338-3p depletion or MCL1 overexpression could reverse the effects of SNHG20 knockdown on OC cells. Besides, SNHG20 knockdown impeded tumor growth in vivo. In conclusion, the present study demonstrated that SNHG20 regulates OC development via modulation of the miR-338-3p/MCL1 axis, providing the theoretical basis for the treatment of OC.

Chaperone-mediated Autophagy Governs Progression of Papillary Thyroid Carcinoma via PPARγ-SDF1/CXCR4 Signaling

CONTEXT

Papillary thyroid carcinoma (PTC) is the most common endocrine malignancy. Chaperone-mediated autophagy (CMA), 1 type of autophagy, is thought to promote or suppress cancer development in different cancer types. However, the effect of CMA on PTC development and the underlying mechanisms remain unknown.

OBJECTIVE

To determine whether CMA plays implied critical roles in the development of PTC.

DESIGN

We investigated the association between CMA and PTC development in PTC tissues and normal thyroid tissues by detecting the key protein of CMA, lysosome-associated membrane protein type 2A (LAMP2A), using quantitative polymerase chain reaction (PCR) and immunohistochemistry, which were further validated in the TGCA dataset. The effect of CMA on PTC development was studied by cell proliferation, migration, and apoptosis assays. The underlying mechanisms of peroxisome proliferator-activated receptor γ (PPARγ)-stromal cell-derived factor 1 (SDF1)/ C-X-C motif chemokine receptor 4 (CXCR4) signaling were clarified by western blotting, quantitative PCR, and rescue experiments. Knockdown and tamoxifen were used to analyze the effect of estrogen receptor (ER) α on CMA.

RESULTS

Our study confirmed that CMA, indicated by LAMP2A expression, was significantly increased in PTC tumor tissues and cell lines, and was associated with tumor size and lymph node metastasis of patients. Higher CMA in PTC promoted tumor cell proliferation and migration, thereby promoting tumor growth and metastasis. These effects of CMA on PTC were exerted by decreasing PPARγ protein expression to enhance SDF1 and CXCR4 expression. Furthermore, CMA was found positively regulated by ERα signaling in PTC.

CONCLUSION

Our investigation identified CMA regulated by ERα promoting PTC tumor progression that enhanced tumor cell proliferation and migration by targeting PPARγ-SDF1/CXCR4 signaling, representing a potential target for treatment of PTC.

Pros and Cons of Chaperone-Mediated Autophagy in Cancer Biology

Autophagy contributes to cellular quality control and energetics through lysosomal breakdown and recycling of essential cellular components. Chaperone-mediated autophagy (CMA) adds to these autophagic functions the ability to timely and selectively degrade single tagged proteins to terminate their cellular function and, in this way, participate in the regulation of multiple cellular processes. Many cancer cells upregulate CMA for protumorigenic and prosurvival purposes. However, growing evidence supports a physiological role for CMA in limiting malignant transformation. Understanding the mechanisms behind this functional switch of CMA from antioncogenic to pro-oncogenic is fundamental for targeting CMA in cancer treatment. We summarize current understanding of CMA functions in cancer biology and discuss the basis for its context-dependent dual role in oncogenesis.

Chaperone-mediated autophagy regulates apoptosis and the proliferation of colon carcinoma cells

Chaperone-mediated autophagy (CMA) is one of the three types of autophagy. In recent years, CMA has been shown to be associated with the pathogenesis of several types of cancer. However, whether CMA is involved in the pathogenesis of colorectal cancer (CRC) remains unclear. In this study, we investigated CMA activity in tissue specimens from CRC patients and mouse models of colitis-associated CRC (induced by administration of AOM plus DSS). In addition, we down-regulated CMA in CT26 colon carcinoma cells stably transfected with a vector expressing a siRNA targeting LAMP-2A, the limiting component in the CMA pathway, to explore the role of CMA in these cells. Apoptosis was detected using TUNEL assay, and the apoptosis-related proteins were detected using western blotting. Cell proliferation was assessed using MTT assay, Ki-67 labelling and western blotting for PCNA. We found that LAMP-2A expression was significantly increased in CRC patients and mouse models and varied according to the stage of the disease. Inhibition of CMA in CT26 cells facilitated apoptosis, as evidenced by increased TUNEL immunolabeling, increased expression of Bax and Bnip3, and decreased expression of Bcl-2. Cell proliferation assays showed that inhibition of CMA impeded the proliferation of CT26 cells. These data support the hypothesis that CMA is up-regulated in CRC, and inhibition of CMA may be a new therapeutic strategy for CRC patients.

Chaperone-mediated autophagy degradation of IGF-1Rβ induced by NVP-AUY922 in pancreatic cancer

Enhancement of insulin-like growth factor 1 receptor (IGF-IR) degradation by heat shock protein 90 (HSP90) inhibitor is a potential antitumor therapeutic strategy. However, very little is known about how IGF-IR protein levels are degraded by HSP90 inhibitors in pancreatic cancer (PC). We found that the HSP90α inhibitor NVP-AUY922 (922) effectively downregulated and destabilized the IGF-1Rβ protein, substantially reduced the levels of downstream signaling molecules (p-AKT, AKT and p-ERK1/2), and resulted in growth inhibition and apoptosis in IGF-1Rβ-overexpressing PC cells. Preincubation with a proteasome or lysosome inhibitor (MG132, 3 MA or CQ) mainly led to IGF-1Rβ degradation via the lysosome degradation pathway, rather than the proteasome-dependent pathway, after PC cells were treated with 922 for 24 h. These results might be associated with the inhibition of pancreatic cellular chymotrypsin-peptidase activity by 922 for 24 h. Interestingly, 922 induced autophagic flux by increasing LC3II expression and puncta formation. However, knockdown of the crucial autophagy component AGT5 and the chemical inhibitor 3 MA-blocked 922-induced autophagy did not abrogate 922-triggered IGF-1Rβ degradation. Furthermore, 922 could enhance chaperone-mediated autophagy (CMA) activity and promote the association between HSP/HSC70 and IGF-1Rβ or LAMP2A in coimmunoprecipitation and immunofluorescence analyses. Silencing of LAMP2A to inhibit CMA activity reversed 922-induced IGF-1Rβ degradation, suggesting that IGF-1Rβ degradation by 922 was partially dependent on the CMA pathway rather than macroautophagy. This finding is mirrored by the identification of the KFERQ-like motif in IGF-1Rβ. These observations support the potential application of 922 for IGF-1Rβ-overexpressing PC therapy and first identify the role of the CMA pathway in IGF-1Rβ degradation by an HSP90 inhibitor.

The coming of age of chaperone-mediated autophagy

Chaperone-mediated autophagy (CMA) was the first studied process that indicated that degradation of intracellular components by the lysosome can be selective - a concept that is now well accepted for other forms of autophagy. Lysosomes can degrade cellular cytosol in a nonspecific manner but can also discriminate what to target for degradation with the involvement of a degradation tag, a chaperone and a sophisticated mechanism to make the selected proteins cross the lysosomal membrane through a dedicated translocation complex. Recent studies modulating CMA activity in vivo using transgenic mouse models have demonstrated that selectivity confers on CMA the ability to participate in the regulation of multiple cellular functions. Timely degradation of specific cellular proteins by CMA modulates, for example, glucose and lipid metabolism, DNA repair, cellular reprograming and the cellular response to stress. These findings expand the physiological relevance of CMA beyond its originally identified role in protein quality control and reveal that CMA failure with age may aggravate diseases, such as ageing-associated neurodegeneration and cancer.

Sorting nexin 10 controls mTOR activation through regulating amino-acid metabolism in colorectal cancer

Amino-acid metabolism plays a vital role in mammalian target of rapamycin (mTOR) signaling, which is the pivot in colorectal cancer (CRC). Upregulated chaperone-mediated autophagy (CMA) activity contributes to the regulation of metabolism in cancer cells. Previously, we found that sorting nexin 10 (SNX10) is a critical regulator in CMA activation. Here we investigated the role of SNX10 in regulating amino-acid metabolism and mTOR signaling pathway activation, as well as the impact on the tumor progression of mouse CRC. Our results showed that SNX10 deficiency promoted colorectal tumorigenesis in male FVB mice and CRC cell proliferation and survival. Metabolic pathway analysis of gas chromatography–mass spectrometry (GC-MS) data revealed unique changes of amino-acid metabolism by SNX10 deficiency. In HCT116 cells, SNX10 knockout resulted in the increase of CMA and mTOR activation, which could be abolished by chloroquine treatment or reversed by SNX10 overexpression. By small RNA interference (siRNA), we found that the activation of mTOR was dependent on lysosomal-associated membrane protein type-2A (LAMP-2A), which is a limiting factor of CMA. Similar results were also found in Caco-2 and SW480 cells. Ultra-high-performance liquid chromatography–quadrupole time of flight (UHPLC-QTOF) and GC-MS-based untargeted metabolomics revealed that 10 amino-acid metabolism in SNX10-deficient cells were significantly upregulated, which could be restored by LAMP-2A siRNA. All of these amino acids were previously reported to be involved in mTOR activation. In conclusion, this work revealed that SNX10 controls mTOR activation through regulating CMA-dependent amino-acid metabolism, which provides potential target and strategy for treating CRC.

Targeting Chaperone-Mediated Autophagy for Disease Therapy

PURPOSE OF THE REVIEW

To reason that targeting chaperone-mediated autophagy (CMA) represents a promising approach for disease therapy, we will summarize advances in researches on the relationship between CMA and diseases and discuss relevant strategies for disease therapy by targeting the CMA process.

RECENT FINDINGS

CMA is a unique kind of selective autophagy in lysosomes. Under physiological conditions, CMA participates in the maintenance of cellular homeostasis by protein quality control, bioenergetics, and timely regulated specific substrate-associated cellular processes. Under pathological conditions, CMA interplays with various disease conditions. CMA makes adaptive machinery to address stress, while disease-associated proteins alter CMA which is involved in pathogeneses of diseases. As more proteins are identified as CMA substrates and regulators, dysregulation of CMA has been implicated in an increasing number of diseases, while rectifying CMA alteration may be a benefit for these diseases.

SUMMARY

Alterations of CMA in diseases mainly including neurodegenerative diseases and many cancers raise the possibility of targeting CMA to recover cellular homeostasis as one potential strategy for therapy of relevant diseases.

Chaperone-mediated autophagy: Advances from bench to bedside

Protein homeostasis or proteostasis is critical for proper cellular function and survival. It relies on the balance between protein synthesis and degradation. Lysosomes play an important role in degrading and recycling intracellular components via autophagy. Among the three types of lysosome-based autophagy pathways, chaperone-mediated autophagy (CMA) selectively degrades cellular proteins with KFERQ-like motif by unique machinery. During the past several years, significant advances have been made in our understanding of how CMA itself is modulated and what physiological and pathological processes it may be involved in. One particularly exciting discovery is how other cellular stress organelles such as ER signal to CMA. As more proteins are identified as CMA substrates, CMA function has been associated with an increasing number of important cellular processes, organelles, and diseases, including neurodegenerative diseases. Here we will summarize the recent advances in CMA biology, highlight ER stress-induced CMA, and discuss the role of CMA in diseases.

Chaperone-mediated autophagy and endosomal microautophagy: Joint by a chaperone

A variety of mechanisms deliver cytosolic materials to the lysosomal compartment for degradation through autophagy. Here, we focus on two autophagic pathways, the chaperone-mediated autophagy and the endosomal microautophagy that rely on the cytosolic chaperone hsc70 for substrate targeting. Although hsc70 participates in the triage of proteins for degradation by different proteolytic systems, the common characteristic shared by these two forms of autophagy is that hsc70 binds directly to a specific five-amino acid motif in the cargo protein for its autophagic targeting. We summarize the current understanding of the molecular machineries behind each of these types of autophagy.

Molecular control of chaperone-mediated autophagy

Chaperone-mediated autophagy (CMA) is a selective form of autophagy in which cytosolic proteins bearing a pentapeptide motif biochemically related to the KFERQ sequence, are recognized by the heat shock protein family A member 8 (HSPA8) chaperone, delivered to the lysomal membrane, and directly translocated across the lysosomal membrane by a protein complex containing lysosomal associated membrane protein 2a (Lamp2a). Since its discovery over two decades ago, the importance of this pathway in cell proteostasis has been made increasingly apparent. Deregulation of this pathway has been implicated in a variety of diseases and conditions, including lysosomal storage diseases, cancer, neurodegeneration and even aging. Here, we describe the main molecular features of the pathway, its regulation, cross-talk with other degradation pathways and importance in disease.

Staphylococcal lipoteichoic acid promotes osteogenic differentiation of mouse mesenchymal stem cells by increasing autophagic activity

This study sought to explore the effect of staphylococcal lipoteichoic acid (LTA) on autophagy in mouse mesenchymal stem cells (MSCs), and then influence osteogenesis through the change of autophagy. C3H10T1/2 cells were induced by osteogenic medium with the treatment of LTA at different concentrations (1, 5, 10 μg/mL); 3-methyladenine (3-MA) were used as the autophagy inhibitor, and rapamycin (rapamycin, Rap) were used to activate autophagy; the effects on osteogenesis were detected by alkaline phosphatase staining, alizarin red staining, real-time quantitative PCR, and western blotting; autophagic activity was investigated by the expression of LC3-Ⅱand p62 proteins. Compared with control group, the expression of osteogenesis markers was significantly up-regulated with the LTA treatment on the mRNA and protein level; the positive rate of alkaline phosphatase was enhanced in the LTA groups; and the formation of calcium nodules was increased simultaneously. The expression of LC3-Ⅱ protein was increased in LTA groups, while the expression of p62 protein was decreased. Inhibition of autophagy significantly reduced the effect of LTA on osteogenesis of MSCs; the promotion of LTA on osteogenic differentiation was further enhanced when adding rapamycin to activate autophagic activity. It provides new insight of prevention and treatment for bone infection.