BCR-ABL/p62/SQSTM1: a cannibal embrace

Chemotherapy Resistance: Role of Mitochondrial and Autophagic Components

Simple Summary

Chemotherapy resistance is a common occurrence during cancer treatment that cancer researchers are attempting to understand and overcome. Mitochondria are a crucial intracellular signaling core that are becoming important determinants of numerous aspects of cancer genesis and progression, such as metabolic reprogramming, metastatic capability, and chemotherapeutic resistance. Mitophagy, or selective autophagy of mitochondria, can influence both the efficacy of tumor chemotherapy and the degree of drug resistance. Regardless of the fact that mitochondria are well-known for coordinating ATP synthesis from cellular respiration in cellular bioenergetics, little is known its mitophagy regulation in chemoresistance. Recent advancements in mitochondrial research, mitophagy regulatory mechanisms, and their implications for our understanding of chemotherapy resistance are discussed in this review.

Abstract

Cancer chemotherapy resistance is one of the most critical obstacles in cancer therapy. One of the well-known mechanisms of chemotherapy resistance is the change in the mitochondrial death pathways which occur when cells are under stressful situations, such as chemotherapy. Mitophagy, or mitochondrial selective autophagy, is critical for cell quality control because it can efficiently break down, remove, and recycle defective or damaged mitochondria. As cancer cells use mitophagy to rapidly sweep away damaged mitochondria in order to mediate their own drug resistance, it influences the efficacy of tumor chemotherapy as well as the degree of drug resistance. Yet despite the importance of mitochondria and mitophagy in chemotherapy resistance, little is known about the precise mechanisms involved. As a consequence, identifying potential therapeutic targets by analyzing the signal pathways that govern mitophagy has become a vital research goal. In this paper, we review recent advances in mitochondrial research, mitophagy control mechanisms, and their implications for our understanding of chemotherapy resistance.

Influence of Iron on Cytotoxicity and Gene Expression Profiles Induced by Arsenic in HepG2 Cells

The toxicity of arsenic (As) could be influenced by many environmental factors and elements. Iron (Fe) is one of the elements that could be involved in As-induced toxicity. In this study, the interactive effects of Fe and As in HepG2 cells were analyzed based on cytotoxicity and transcriptomic analyses. The results showed that Fe could decrease cell viability and increase mitochondrial depolarization induced by As exposure. Oxidative stress and damage have been proven to be one of the main mechanisms of As toxicity. Our results showed that Fe increased the generation of reactive oxygen species (ROS) and lipid peroxidation product malondialdehyde (MDA) induced by As exposure. Microarray analysis further verified that Fe increased the alteration of gene expression and biological processes related to oxidative stress, cell proliferation, and the apoptotic signaling pathway caused by As exposure. Both results of cytotoxicity and transcriptomic analyses suggest that an increase of Fe in the human body could increase the As-induced toxicity, which should be considered during the health risk assessment of As.

Chaperone-Mediated Autophagy and Its Emerging Role in Hematological Malignancies

Chaperone-mediated autophagy (CMA) ensures the selective degradation of cellular proteins endowed with a KFERQ-like motif by lysosomes. It is estimated that 30% of all cellular proteins can be directed to the lysosome for CMA degradation, but only a few substrates have been formally identified so far. Mechanistically, the KFERQ-like motifs present in substrate proteins are recognized by the molecular chaperone Hsc70c (Heat shock cognate 71 kDa protein cytosolic), also known as HSPA8, and directed to LAMP2A, which acts as the CMA receptor at the lysosomal surface. Following linearization, the protein substrate is next transported to the lumen of the lysosomes, where it is degraded by resident proteases, mainly cathepsins and eventually recycled to sustain cellular homeostasis. CMA is induced by different stress conditions, including energy deprivation that also activates macro-autophagy (MA), that may make it difficult to decipher the relative impact of both pathways on cellular homeostasis. Besides common inducing triggers, CMA and MA might be induced as compensatory mechanisms when either mechanism is altered, as it is the often the case in different pathological settings. Therefore, CMA activation can compensate for alterations of MA and vice versa. In this context, these compensatory mechanisms, when occurring, may be targeted for therapeutic purposes. Both processes have received particular attention from scientists and clinicians, since modulation of MA and CMA may have a profound impact on cellular proteostasis, metabolism, death, differentiation, and survival and, as such, could be targeted for therapeutic intervention in degenerative and immune diseases, as well as in cancer, including hematopoietic malignancies. The role of MA in cancer initiation and progression is now well established, but whether and how CMA is involved in tumorigenesis has been only sparsely explored. In the present review, we encompass the description of the mechanisms involved in CMA, its function in the physiology and pathogenesis of hematopoietic cells, its emerging role in cancer initiation and development, and, finally, the potential therapeutic opportunity to target CMA or CMA-mediated compensatory mechanisms in hematological malignancies.

Xanthohumol, a Prenylated Flavonoid from Hops, Induces Caspase-Dependent Degradation of Oncoprotein BCR-ABL in K562 Cells

BCR-ABL oncoprotein drives the initiation, promotion, and progression of chronic myelogenous leukemia (CML). Tyrosine kinase inhibitors are the first choice for CML therapy, however, BCR-ABL mediated drug resistance limits its clinical application and prognosis. A novel promising therapeutic strategy for CML therapy is to degrade BCR-ABL using small molecules. Antioxidant xanthohumol (XN) is a hop-derived prenylated flavonoid with multiple bioactivities. In this study, we showed XN could inhibit the proliferation, induce S phase cell cycle arrest, and stimulate apoptosis in K562 cells. XN degraded BCR-ABL in a concentration- and time-dependent manner, and the involved degradation pathway was caspase activation, while not autophagy induction or ubiquitin proteasome system (UPS) activation. Moreover, we revealed for the first time that XN could inhibit the UPS and autophagy in K562 cells, and the inhibitory effect of XN on autophagy could attenuate imatinib-induced autophagy and enhance the therapeutic efficiency of imatinib in K562 cells. Our present findings identified XN act as a degrader of BCR-ABL in K562 cells, and XN had potential to be developed as an alternate agent for CML therapy.

Autophagy, a key mechanism of oncogenesis and resistance in leukemia

Autophagy is a lysosomal pathway involved in degradation of intracellular material. It appears as an adaptation mechanism that is essential for cellular homeostasis in response to various stress conditions. Over the past decade, many studies have linked alteration of autophagy with cancer initiation and progression, autoimmune, inflammatory, metabolic, and degenerative diseases. This review highlights recent findings on the impact of autophagy on leukemic transformation of normal hematopoietic stem cells and summarizes its role on leukemic cell response to chemotherapy.

The PRKAA1/AMPKα1 pathway triggers autophagy during CSF1-induced human monocyte differentiation and is a potential target in CMML

Autophagy is induced during differentiation of human monocytes into macrophages that is mediated by CSF1/CSF-1/M-CSF (colony stimulating factor 1 [macrophage]). However, little is known about the molecular mechanisms that link CSF1 receptor engagement to the induction of autophagy. Here we show that the CAMKK2-PRKAA1-ULK1 pathway is required for CSF1-induced autophagy and human monocyte differentiation. We reveal that this pathway links P2RY6 to the induction of autophagy, and we decipher the signaling network that links the CSF1 receptor to P2RY6-mediated autophagy and monocyte differentiation. In addition, we show that the physiological P2RY6 ligand UDP and the specific P2RY6 agonist MRS2693 can restore normal monocyte differentiation through reinduction of autophagy in primary myeloid cells from some but not all chronic myelomonocytic leukemia (CMML) patients. Collectively, our findings highlight an essential role for PRKAA1-mediated autophagy during differentiation of human monocytes and pave the way for future therapeutic interventions for CMML.