p62 Promotes Amino Acid Sensitivity of mTOR Pathway and Hepatic Differentiation in Adult Liver Stem/Progenitor Cells

Liquid-liquid phase separation in diseases

Liquid-liquid phase separation (LLPS), an emerging biophysical phenomenon, can sequester molecules to implement physiological and pathological functions. LLPS implements the assembly of numerous membraneless chambers, including stress granules and P-bodies, containing RNA and protein. RNA-RNA and RNA-protein interactions play a critical role in LLPS. Scaffolding proteins, through multivalent interactions and external factors, support protein-RNA interaction networks to form condensates involved in a variety of diseases, particularly neurodegenerative diseases and cancer. Modulating LLPS phenomenon in multiple pathogenic proteins for the treatment of neurodegenerative diseases and cancer could present a promising direction, though recent advances in this area are limited. Here, we summarize in detail the complexity of LLPS in constructing signaling pathways and highlight the role of LLPS in neurodegenerative diseases and cancers. We also explore RNA modifications on LLPS to alter diseases progression because these modifications can influence LLPS of certain proteins or the formation of stress granules, and discuss the possibility of proper manipulation of LLPS process to restore cellular homeostasis or develop therapeutic drugs for the eradication of diseases. This review attempts to discuss potential therapeutic opportunities by elaborating on the connection between LLPS, RNA modification, and their roles in diseases.

Focusing on the role of protein kinase mTOR in endometrial physiology and pathology: insights for therapeutic interventions

The mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase crucial for cellular differentiation, proliferation, and autophagy. It shows a complex role in the endometrium, influencing both normal and pathogenic conditions. mTOR promotes the growth and maturation of endometrial cells, enhancing endometrial receptivity and decidualization. However, it also contributes to the development of endometriosis (EMs) and endometrial cancer (EC), thus emerging as a therapeutic target for these conditions. In this review, we summarize recent research progress on the mTOR signalling pathway in the endometrium. This provides insights into female endometrial structure and function and guides the prevention and treatment of related diseases.

Quinoline-based thiazolyl-hydrazones target cancer cells through autophagy inhibition

Heterocyclic pharmacophores such as thiazole and quinoline rings have a significant role in medicinal chemistry. They are considered privileged structures since they constitute several Food and Drug Administration (FDA)-approved drugs for cancer treatment. Herein, we report the synthesis, in silico evaluation of the ADMET profiles, and in vitro investigation of the anticancer activity of a series of novel thiazolyl-hydrazones based on the 8-quinoline (1a-c), 2-quinoline (2a-c), and 8-hydroxy-2-quinolyl moiety (3a-c). The panel of several human cancer cell lines and the nontumorigenic human embryonic kidney cell line HEK-293 were used to evaluate the compound-mediated in vitro anticancer activities, leading to [2-(2-(quinolyl-8-ol-2-ylmethylene)hydrazinyl)]-4-(4-methoxyphenyl)-1,3-thiazole (3c) as the most promising compound. The study revealed that 3c blocks the cell-cycle progression of a human colon cancer cell line (HCT-116) in the S phase and induces DNA double-strand breaks. Also, our findings demonstrate that 3c accumulates in lysosomes, ultimately leading to the cell death of the hepatocellular carcinoma cell line (Hep-G2) and HCT-116 cells, by the mechanism of autophagy inhibition.

p62/Sqstm1 rescue in muscle retards the progression of steatohepatitis in p62/Sqstm1-null mice fed a high-fat diet

Introduction: Obesity is a risk factor for many diseases because it leads to a reduction in skeletal muscle mass and promotes insulin resistance. p62/Sqstm1-knockout mice are a model of metabolic syndrome; show obesity, insulin resistance, and non-alcoholic fatty liver (NAFL); and develop non-alcoholic steatohepatitis (NASH) in response to the feeding of a high-fat diet (HFD). These phenotypes suggest that muscle p62 may prevent obesity-induced muscle dysfunction. In the present study, we aimed to determine the effects of muscle p62 on skeletal muscle mass, muscle strength, insulin resistance, and NASH pathology.

Methods: We generated muscle-specific p62 gene rescue mice (p62-mRes), which express p62 only in muscle and were derived from p62-knock out mice (p62^KIKI) using the cre/loxp system. p62^KIKI and p62-mRes mice were fed an HFD for 20 weeks and their phenotypes were compared.

Results: HFD-feeding caused severe obesity in both p62^KIKI and p62-mRes mice, but there was no effect of muscle p62 on body mass. Limb skeletal muscle mass, grip strength, and the cross-sectional area of muscle fibers were higher in p62-mRes mice than in p62^KIKI. The glucose tolerance and insulin sensitivity of the p62-mRes mice were also superior. The protein expression of mechanistic target of rapamycin, which promotes muscle protein synthesis, and GLUT4, a glucose transporter in skeletal muscle, were higher in the p62-mRes mice. p62^KIKI mice developed severe NASH when fed an HFD, but the progression of NASH was retarded by p62 gene rescue in muscle, and the expression of Tgf-β1, which encodes a factor that promotes hepatic fibrosis, was reduced.

Conclusion: Rescue of muscle-specific p62 in the whole-body p62 knock-out mice ameliorates the insulin resistance and retards the progression of NASH caused by systemic p62 ablation.

Atg5 knockdown induces age-dependent cardiomyopathy which can be rescued by repeated remote ischemic conditioning

Altered autophagy is implicated in several human cardiovascular diseases. Remote ischemic conditioning (RIC) is cardioprotective in multiple cardiovascular injury models and modifies autophagy signaling, but its effect in cardiomyopathy induced by gene manipulation has not been reported. To investigate the cardiac effects of chronically reduced autophagy as a result of Atg5 knockdown and assess whether RIC can rescue the phenotype. Atg5 knockdown was induced with tamoxifen for 14 days in cardiac-specific conditional Atg5 flox mice. Autophagy proteins and cardiac function were evaluated by Western blot and echocardiography, respectively. RIC was induced by cyclical hindlimb ischemia and reperfusion using a tourniquet. RIC or sham procedure was performed daily during tamoxifen induction and, in separate experiments, chronically 3 times per week for 8 weeks. Cardiac responses were assessed by end of the study. Cardiac-specific knockdown of Atg5 reduced protein levels by 70% and was associated with a significant increase in mTOR, a reduction of LC3-II and increased upstream autophagy proteins including LC3-I, P62, and Beclin. The changes in biochemical markers were associated with development of an age-related cardiomyopathy during the 17-month follow-up indicated by increased heart weight body weight ratio, progressive decline in cardiac function, and premature death. RIC increased cardiac ATG5 and rescued some of the Atg5 knockdown-induced cardiomyopathy phenotype and associated morphological remodeling. We conclude that cardiac-specific Atg5 knockdown leads to the development of age-related cardiomyopathy. RIC reverses the molecular and structural phenotype when administered both acutely and chronically.

Amino acid levels determine metabolism and CYP450 function of hepatocytes and hepatoma cell lines

Predicting drug-induced liver injury in a preclinical setting remains challenging, as cultured primary human hepatocytes (PHHs), pluripotent stem cell-derived hepatocyte-like cells (HLCs), and hepatoma cells exhibit poor drug biotransformation capacity. We here demonstrate that hepatic functionality depends more on cellular metabolism and extracellular nutrients than on developmental regulators. Specifically, we demonstrate that increasing extracellular amino acids beyond the nutritional need of HLCs and HepG2 cells induces glucose independence, mitochondrial function, and the acquisition of a transcriptional profile that is closer to PHHs. Moreover, we show that these high levels of amino acids are sufficient to drive HLC and HepG2 drug biotransformation and liver-toxin sensitivity to levels similar to those in PHHs. In conclusion, we provide data indicating that extracellular nutrient levels represent a major determinant of cellular maturity and can be utilized to guide stem cell differentiation to the hepatic lineage.

SOX9: The master regulator of cell fate in breast cancer

SRY-related high-mobility group box 9 (SOX9) is an indispensable transcription factor that regulates multiple developmental pathways related to stemness, differentiation, and progenitor development. Previous studies have demonstrated that the SOX9 protein directs pathways involved in tumor initiation, proliferation, migration, chemoresistance, and stem cell maintenance, thereby regulating tumorigenesis as an oncogene. SOX9 overexpression is a frequent event in breast cancer (BC) subtypes. Of note, the molecular mechanisms and functional regulation underlying SOX9 upregulation during BC progression are still being uncovered. The focus of this review is to appraise recent advances regarding the involvement of SOX9 in BC pathogenesis. First, we provide a general overview of SOX9 structure and function, as well as its involvement in various kinds of cancer. Next, we discuss pathways of SOX9 regulation, particularly its miRNA-mediated regulation, in BC. Finally, we describe the involvement of SOX9 in BC pathogenesis via its regulation of pathways involved in regulating cancer hallmarks, as well as its clinical and therapeutic importance. In general, this review article aims to serve as an ample source of knowledge on the involvement of SOX9 in BC progression. Targeting SOX9 activity may improve therapeutic strategies to treat BC, but precisely inhibiting SOX9 using drugs and/or small peptides remains a huge challenge for forthcoming cancer research.

Autophagy is essential for the endothelial differentiation of breast cancer stem‑like cells

Blood vessels serve an important role in tumor growth and metastasis, and recent studies have shown that certain tumor cancer stem cells may differentiate into endothelial cells and contribute to angiogenesis. In the present study, vascular endothelial growth factor (VEGF) was used to induce endothelial differentiation of breast cancer stem‑like cells (BCSLCs), and methods including flow cytometry, western blotting and immunofluorescence were used to study the relationship between autophagy and the endothelial differentiation of BCSLCs. The results showed that BCSLCs could differentiate into endothelial cells under the induction of VEGF in vitro. Subsequently, the role of autophagy in the endothelial differentiation of BCSLCs was examined. Autophagic activity was measured during endothelial differentiation of BCSLCs, and the association between autophagy and endothelial differentiation was investigated using autophagy activators, autophagy inhibitors and autophagy related 5 (Atg5)‑knockdown BCSLCs. Autophagy was increased during endothelial differentiation of BCSLCs, and there was a positive association between autophagy and endothelial differentiation. The ability of cells to undergo endothelial differentiation was reduced in BCSLCs with Atg5 knockdown. Therefore, autophagy was essential for endothelial differentiation of BCSLCs, and the findings of the present study may highlight novel potential avenues for reducing angiogenesis and improving treatment of breast cancer.

A critical role of autophagy in regulating the mesenchymal transition of ductular cells in liver cirrhosis

Our previous studies have shown that autophagy mediates the link between ductular reaction (DR) and liver cirrhosis. Whether the subsequent fibrogenic response is regulated by increased autophagy in DR remains unclear. Here, using both human liver specimens and a rat model of liver cirrhosis induced by 2-acetylaminofluorene (AAF) and carbon tetrachloride (CCL4), we explored the involvement of autophagy in regulating mesenchymal transition of ductular cells. Ductular cells from AAF/CCL4 livers exhibited increased autophagy compared to those of normal livers. These cells showed morphological and functional characteristics of mesenchymal cells. Blocking autophagy using bafilomycin A1 or siRNA targeting ATG7 reduced the expression of mesenchymal markers in these ductular cells from AAF/CCL4 livers, indicating a role for autophagy in regulating the mesenchymal phenotype of ductular cells. Furthermore, we show that the mesenchymal transition in DR requires the activation of transforming growth factor-β (TGF-β) signaling in an autophagy-dependent manner. Importantly, in cirrhotic human livers, ductular cells that are positive for LC3B also showed increased expression of TGF-β and fibroblast-specific protein-1. Our data suggest activation of autophagy in ductular cells, and also demonstrate that it is required for the mesenchymal transition during the DR, processes that are critically involved in the pathogenesis of cirrhosis.

Regulation of death receptor signaling by the autophagy protein TP53INP2

TP53INP2 positively regulates autophagy by binding to Atg8 proteins. Here, we uncover a novel role of TP53INP2 in death-receptor signaling. TP53INP2 sensitizes cells to apoptosis induced by death receptor ligands. In keeping with this, TP53INP2 deficiency in cultured cells or mouse livers protects against death receptor-induced apoptosis. TP53INP2 binds caspase-8 and the ubiquitin ligase TRAF6, thereby promoting the ubiquitination and activation of caspase-8 by TRAF6. We have defined a TRAF6-interacting motif (TIM) and a ubiquitin-interacting motif in TP53INP2, enabling it to function as a scaffold bridging already ubiquitinated caspase-8 to TRAF6 for further polyubiquitination of caspase-8. Mutations of key TIM residues in TP53INP2 abrogate its interaction with TRAF6 and caspase-8, and subsequently reduce levels of death receptor-induced apoptosis. A screen of cancer cell lines showed that those with higher protein levels of TP53INP2 are more prone to TRAIL-induced apoptosis, making TP53INP2 a potential predictive marker of cancer cell responsiveness to TRAIL treatment. These findings uncover a novel mechanism for the regulation of caspase-8 ubiquitination and reveal TP53INP2 as an important regulator of the death receptor pathway.

Differential regulation of mTORC1 and mTORC2 is critical for 8-Br-cAMP-induced decidualization

Human endometrium decidualization, a differentiation process involving biochemical and morphological changes, is a prerequisite for embryo implantation and successful pregnancy. Here, we show that the mammalian target of rapamycin (mTOR) is a crucial regulator of 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP)-induced decidualization in human endometrial stromal cells. The level of mSin1 in mTOR complex 2 (mTORC2) and DEPTOR in mTOR complex 1 (mTORC1) decreases during 8-Br-cAMP-induced decidualization, resulting in decreased mTORC2 activity and increased mTORC1 activity. Notably, DEPTOR displacement increases the association between raptor and insulin receptor substrate-1 (IRS-1), facilitating IRS-1 phosphorylation at serine 636/639. Finally, both S473 and T308 phosphorylation of Akt are reduced during decidualization, followed by a decrease in forkhead box O1 (FOXO1) phosphorylation and an increase in the mRNA levels of the decidualization markers prolactin (PRL) and insulin-like growth factor-binding protein-1 (IGFBP-1). Taken together, our findings reveal a critical role for mTOR in decidualization, involving the differential regulation of mTORC1 and mTORC2.

Autophagic Regulation of p62 is Critical for Cancer Therapy

Sequestosome1 (p62/SQSTM 1) is a multidomain protein that interacts with the autophagy machinery as a key adaptor of target cargo. It interacts with phagophores through the LC3-interacting (LIR) domain and with the ubiquitinated protein aggregates through the ubiquitin-associated domain (UBA) domain. It sequesters the target cargo into inclusion bodies by its PB1 domain. This protein is further the central hub that interacts with several key signaling proteins. Emerging evidence implicates p62 in the induction of multiple cellular oncogenic transformations. Indeed, p62 upregulation and/or reduced degradation have been implicated in tumor formation, cancer promotion as well as in resistance to therapy. It has been established that the process of autophagy regulates the levels of p62. Autophagy-dependent apoptotic activity of p62 is recently being reported. It is evident that p62 plays a critical role in both autophagy and apoptosis. Therefore in this review we discuss the role of p62 in autophagy, apoptosis and cancer through its different domains and outline the importance of modulating cellular levels of p62 in cancer therapeutics.

Targeting the phosphatidylinositol 3-kinase/Akt/mechanistic target of rapamycin signaling pathway in B-lineage acute lymphoblastic leukemia: An update

Despite considerable progress in treatment protocols, B-lineage acute lymphoblastic leukemia (B-ALL) displays a poor prognosis in about 15-20% of pediatric cases and about 60% of adult patients. In addition, life-long irreversible late effects from chemo- and radiation therapy, including secondary malignancies, are a growing problem for leukemia survivors. Targeted therapy holds promising perspectives for cancer treatment as it may be more effective and have fewer side effects than conventional therapies. The phosphatidylinositol 3-phosphate kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) signaling pathway is a key regulatory cascade which controls proliferation, survival and drug-resistance of cancer cells, and it is frequently upregulated in the different subtypes of B-ALL, where it plays important roles in the pathophysiology, maintenance and progression of the disease. Moreover, activation of this signaling cascade portends a poorer prognosis in both pediatric and adult B-ALL patients. Promising preclinical data on PI3K/Akt/mTOR inhibitors have documented their anticancer activity in B-ALL and some of these novel drugs have entered clinical trials as they could lead to a longer event-free survival and reduce therapy-associated toxicity for patients with B-ALL. This review highlights the current status of PI3K/Akt/mTOR inhibitors in B-ALL, with an emphasis on emerging evidence of the superior efficacy of synergistic combinations involving the use of traditional chemotherapeutics or other novel, targeted agents.

Autophagy in Stem Cell Biology: A Perspective on Stem Cell Self-Renewal and Differentiation

Autophagy is a highly conserved cellular process that degrades modified, surplus, or harmful cytoplasmic components by sequestering them in autophagosomes which then fuses with the lysosome for degradation. As a major intracellular degradation and recycling pathway, autophagy is crucial for maintaining cellular homeostasis, as well as for remodeling during normal development. Impairment of this process has been implicated in various diseases, in the pathogenic response to bacterial and viral infections, and in aging. Pluripotent stem cells, with their ability to self-replicate and to give rise to any specialized cell type, are very valuable resources for cell-based medical therapies and open a number of promising avenues for studying human development and disease. It has been suggested that autophagy is vital for the maintenance of cellular homeostasis in stem cells, and subsequently more in-depth knowledge about the regulation of autophagy in stem cell biology has been acquired recently. In this review, we describe the most significant advances in the understanding of autophagy regulation in hematopoietic and mesenchymal stem cells, as well as in induced pluripotent stem cells. In particular, we highlight the roles of various autophagy activities in the regulation of self-renewal and differentiation of these stem cells.