Autophagy is a mechanism by which cellular material is delivered to lysosomes for degradation, leading to the basal turnover of cell components and providing energy and macromolecular precursors. Autophagy has opposing, context-dependent roles in cancer, and interventions to both stimulate and inhibit autophagy have been proposed as cancer therapies. This has led to the therapeutic targeting of autophagy in cancer to be sometimes viewed as controversial. In this Review, we suggest a way forwards for the effective targeting of autophagy by understanding the context-dependent roles of autophagy and by capitalizing on modern approaches to clinical trial design.

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Targeting autophagy in cancer

Autophagy, as a type II programmed cell death, plays crucial roles with autophagy-related (ATG) proteins in cancer. Up to now, the dual role of autophagy both in cancer progression and inhibition remains controversial, in which the numerous ATG proteins and their core complexes including ULK1/2 kinase core complex, autophagy-specific class III PI3K complex, ATG9A trafficking system, ATG12 and LC3 ubiquitin-like conjugation systems, give multiple activities of autophagy pathway and are involved in autophagy initiation, nucleation, elongation, maturation, fusion and degradation. Autophagy plays a dynamic tumor-suppressive or tumor-promoting role in different contexts and stages of cancer development. In the early tumorigenesis, autophagy, as a survival pathway and quality-control mechanism, prevents tumor initiation and suppresses cancer progression. Once the tumors progress to late stage and are established and subjected to the environmental stresses, autophagy, as a dynamic degradation and recycling system, contributes to the survival and growth of the established tumors and promotes aggressiveness of the cancers by facilitating metastasis. This indicates that regulation of autophagy can be used as effective interventional strategies for cancer therapy.

https://link.springer.com/content/pdf/10.1186/s12943-020-1138-4.pdf

Autophagy and autophagy-related proteins in cancer

Tumorigenic and Immunosuppressive Effects of Endoplasmic Reticulum Stress in Cancer

Evolutionarily conserved across eukaryotic cells, macroautophagy (herein autophagy) is an intracellular catabolic degradative process targeting damaged and superfluous cellular proteins, organelles, and other cytoplasmic components. Mechanistically, it involves formation of double-membrane vesicles called autophagosomes that capture cytosolic cargo and deliver it to lysosomes, wherein the breakdown products are eventually recycled back to the cytoplasm. Dysregulation of autophagy often results in various disease manifestations, including neurodegeneration, microbial infections, and cancer. In the case of cancer, extensive attention has been devoted to understanding the paradoxical roles of autophagy in tumor suppression and tumor promotion. In this review, while we summarize how this self-eating process is implicated at various stages of tumorigenesis, most importantly, we address the link between autophagy and hallmarks of cancer. This would eventually provide a better understanding of tumor dependence on autophagy. We also discuss how therapeutics targeting autophagy can counter various transformations involved in tumorigenesis. Finally, this review will provide a novel insight into the mutational landscapes of autophagy-related genes in several human cancers, using genetic information collected from an array of cancers.

Dual role of autophagy in hallmarks of cancer.

The lysosome has long been viewed as the recycling center of the cell. However, recent discoveries have challenged this simple view and have established a central role of the lysosome in nutrient-dependent signal transduction. The degradative role of the lysosome and its newly discovered signaling functions are not in conflict but rather cooperate extensively to mediate fundamental cellular activities such as nutrient sensing, metabolic adaptation, and quality control of proteins and organelles. Moreover, lysosome-based signaling and degradation are subject to reciprocal regulation. Transcriptional programs of increasing complexity control the biogenesis, composition, and abundance of lysosomes and fine-tune their activity to match the evolving needs of the cell. Alterations in these essential activities are, not surprisingly, central to the pathophysiology of an ever-expanding spectrum of conditions, including storage disorders, neurodegenerative diseases, and cancer. Thus, unraveling the functions of th...

The Lysosome as a Regulatory Hub

Induction of cell death and inhibition of cell survival are the main principles of cancer therapy. Resistance to chemotherapeutic agents is a major problem in oncology, which limits the effectiveness of anticancer drugs. A variety of factors contribute to drug resistance, including host factors, specific genetic or epigenetic alterations in the cancer cells and so on. Although various mechanisms by which cancer cells become resistant to anticancer drugs in the microenvironment have been well elucidated, how to circumvent this resistance to improve anticancer efficacy remains to be defined. Autophagy, an important homeostatic cellular recycling mechanism, is now emerging as a crucial player in response to metabolic and therapeutic stresses, which attempts to maintain/restore metabolic homeostasis through the catabolic lysis of excessive or unnecessary proteins and injured or aged organelles. Recently, several studies have shown that autophagy constitutes a potential target for cancer therapy and the induction of autophagy in response to therapeutics can be viewed as having a prodeath or a prosurvival role, which contributes to the anticancer efficacy of these drugs as well as drug resistance. Thus, understanding the novel function of autophagy may allow us to develop a promising therapeutic strategy to enhance the effects of chemotherapy and improve clinical outcomes in the treatment of cancer patients.

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Autophagy and chemotherapy resistance: a promising therapeutic target for cancer treatment

The novel proteasome subunit Adrm1 located on the 20q13 amplicon was differentially expressed in colorectal cancer by semiquantitative RT-PCR. Adrm1 mRNA was overexpressed in 46.2% (18/39) colorectal cancer tissues compared to their matched normal mucosa and significantly correlated with lymph node metastasis of colorectal cancer (P=0.037). Knockdown of Adrm1 by shRNA in human colon carcinoma RKO cells inhibited their anchorage-independent growth, cell migration as well as cell proliferation through inducing apoptosis and cell cycle arrest at the G1 phase. In addition, stable RNA interference of Adrm1 gene synergistic with 5-Fu treatment suppressed RKO cell growth in vitro. Collectively, these data suggested that Adrm1 is potentially oncogenic and may play an important role in colon tumorigenesis. Regiment with combined application of Adrm1 RNA interference and chemotherapy may emerge as a novel therapeutic strategy for Adrm1 overexpressed colorectal cancer.

https://www.spandidos-publications.com/10.3892/or_00000254/download

Knockdown of the novel proteasome subunit Adrm1 located on the 20q13 amplicon inhibits colorectal cancer cell migration, survival and tumorigenicity.

Colorectal cancer (CRC) is still the third most common cancer and the second most common causes of cancer-related death around the world. Metformin, a biguanide, which is widely used for treating diabetes mellitus, has recently been shown to have a suppressive effect on CRC risk and mortality, but not all laboratory studies suggest that metformin has antineoplastic activity. Here, we investigated the effect of metformin and AMPK activator AICAR on CRC cells proliferation. As a result, metformin did not inhibit cell proliferation or induce apoptosis for CRC cell lines in vitro and in vivo. Different from metformin, AICAR emerged antitumor activity and sensitized anticancer effect of 5-FU on CRC cells in vitro and in vivo. In further analysis, we show that AMPK activation may be a key molecular mechanism for the additive effect of AICAR. Taken together, our results suggest that metformin has not antineoplastic activity for CRC cells as a single agent but AMPK activator AICAR can induce apoptosis and enhance the cytotoxic effect of 5-FU through AMPK activation.

Use of metformin alone is not associated with survival outcomes of colorectal cancer cell but AMPK activator AICAR sensitizes anticancer effect of 5-fluorouracil through AMPK activation.

Transforming growth factor-beta-induced (TGFBI) serves as a linker protein and plays a role in the activation of morphogenesis, cell proliferation, adhesion, migration, differentiation and inflammation. High expression levels of the human TGFBI gene are correlated with numerous human malignancies. In order to explore the roles of TGFBI in the tumor progression of colorectal cancer, colorectal cancer specimens from 115 patients with strict follow-up were selected for the analysis of TGFBI by immunohistochemistry. The correlations between TGFBI expression and the clinicopathological features of colorectal cancers were evaluated. In the colorectal cancer tissues, TGFBI was mainly localized in the cytoplasm and stroma and scarcely in the nucleus. TGFBI expression in the cytoplasm and stroma was not found to be associated with age, gender, tumor histopathological grading, PT category and tumor location (P > 0.05 for each). However, high TGFBI expression in the cytoplasm and stroma correlated with lymph node metastasis, distant metastasis and Dukes stage (P < 0.05 for each). The survival rate was significantly lower in patients with high TGFBI expression than in those with low TGFBI expression. Furthermore, we found that tumor node metastasis (TNM) staging (HR: 2.963; 95% CI: 1.573-1.664; P = 0.000), differentiation (HR: 1.574; 95% CI: 1.001-2.476; P = 0.049) and high TGFBI cytoplasmic expression (HR: 3.332; 95% CI: 1.410-7.873; P = 0.000) proved to be independent prognostic factors for survival in colorectal cancer. In conclusion, TGFBI plays an important role in the progression of colorectal cancers and it is an independent poor prognostic factor for colorectal cancer patients.

TGFBI protein high expression predicts poor prognosis in colorectal cancer patients.

The proteasome subunit PSMA7 located on the 20q13 amplicon was found to be differentially expressed in colorectal cancer by semiquantitative RT-PCR. PSMA7 mRNA was overexpressed in 37.5% (12/32) colorectal cancer tissues while it was either of a low level or not expressed in matched normal mucosa. The aim of this study was to examine the PSMA7 protein expression in 62 colorectal cancer primary sites, 34 lymph node metastatic sites and 13 liver metastatic sites by immunohistochemistry and clarify the correlations of this expression with the clinicopathological parameters. PSMA7 high expression was detected in 38.8% (24/62) colorectal cancer primary sites, 52.9% (18/34) lymph node metastatic sites and 100% (13/13) liver metastatic sites but not in the normal colorectal tissues. The PSMA7 high expression was significantly correlated with liver metastasis (P=0.028). Survival was significantly lower in patients with a PSMA7 high expression than in those with a PSMA7 low expression (P=0.0012). Moreover, in multivariate analysis, the PSMA7 expression demonstrated an independent prognostic factor (P=0.004, relative risk 5.057; 95% confidence interval, 1.682-15.201). These results indicated that PSMA7 may play an important role in colorectal cancer progression and provide a unique target site for the development of therapeutic drugs. The evaluation of PSMA7 expression in primary colorectal cancer at the time of surgery may be a valuable tool for defining patients with a high risk of developing liver metastasis.

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Chao He

Papers

Autophagy and chemotherapy resistance: a promising therapeutic target for cancer treatment

Knockdown of the novel proteasome subunit Adrm1 located on the 20q13 amplicon inhibits colorectal cancer cell migration, survival and tumorigenicity.

Use of metformin alone is not associated with survival outcomes of colorectal cancer cell but AMPK activator AICAR sensitizes anticancer effect of 5-fluorouracil through AMPK activation.

TGFBI protein high expression predicts poor prognosis in colorectal cancer patients.

The proteasome subunit PSMA7 located on the 20q13 amplicon is overexpressed and associated with liver metastasis in colorectal cancer.