RKTG overexpression inhibits proliferation and induces apoptosis of human leukemia cells via suppression of the ERK and PI3K/AKT signaling pathways

Molecular mechanisms of ferroptosis and its roles in leukemia

Cell death is a complex process required to maintain homeostasis and occurs when cells are damage or reach end of life. As research progresses, it is apparent that necrosis and apoptosis do not fully explain the whole phenomenon of cell death. Therefore, new death modalities such as autophagic cell death, and ferroptosis have been proposed. In recent years, ferroptosis, a new type of non-apoptotic cell death characterized by iron-dependent lipid peroxidation and reactive oxygen species (ROS) accumulation, has been receiving increasing attention. Ferroptosis can be involved in the pathological processes of many disorders, such as ischemia-reperfusion injury, nervous system diseases, and blood diseases. However, the specific mechanisms by which ferroptosis participates in the occurrence and development of leukemia still need to be more fully and deeply studied. In this review, we present the research progress on the mechanism of ferroptosis and its role in leukemia, to provide new theoretical basis and strategies for the diagnosis and treatment of clinical hematological diseases.

Ferroptosis in acute leukemia

ABSTRACT

Ferroptosis is an iron-dependent cell death pathway that is different from apoptosis, pyroptosis, and necrosis. The main characteristics of ferroptosis are the Fenton reaction mediated by intracellular free divalent iron ions, lipid peroxidation of cell membrane lipids, and inhibition of the anti-lipid peroxidation activity of intracellular glutathione peroxidase 4 (GPX4). Recent studies have shown that ferroptosis can be involved in the pathological processes of many disorders, such as ischemia-reperfusion injury, nervous system diseases, and blood diseases. However, the specific mechanisms by which ferroptosis participates in the occurrence and development of acute leukemia still need to be more fully and deeply studied. This article reviews the characteristics of ferroptosis and the regulatory mechanisms promoting or inhibiting ferroptosis. More importantly, it further discusses the role of ferroptosis in acute leukemia and predicts a change in treatment strategy brought about by increased knowledge of the role of ferroptosis in acute leukemia.

Golgi Complex: A Signaling Hub in Cancer

The Golgi Complex is the central hub in the endomembrane system and serves not only as a biosynthetic and processing center but also as a trafficking and sorting station for glycoproteins and lipids. In addition, it is an active signaling hub involved in the regulation of multiple cellular processes, including cell polarity, motility, growth, autophagy, apoptosis, inflammation, DNA repair and stress responses. As such, the dysregulation of the Golgi Complex-centered signaling cascades contributes to the onset of several pathological conditions, including cancer. This review summarizes the current knowledge on the signaling pathways regulated by the Golgi Complex and implicated in promoting cancer hallmarks and tumor progression.

PAQR3 inhibits proliferation and aggravates ferroptosis in acute lymphoblastic leukemia through modulation Nrf2 stability

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is a usual hematological tumor, which was featured by malignant proliferation of lymphoid progenitor cells. Many important factors participate into the regulation of ALL, including proteins. PAQR3 (also named RKTG) has been proved to take part in many human cancers by acting as a tumor suppressor. PAQR3 has bee n shown to repress human leukemia cells proliferation and induce cell apoptosis, but its role and relevant regulatory mechanism on cell proliferation and ferroptosis in ALL needs more exploration.

METHODS

The genes expression was detected through quantitative reverse transcription polymerase chain reaction (mRNA) or western blot (protein). The cell proliferation was assessed through Cell Counting Kit-8 and 5-ethynyl-2-deoxyuridine assays. The levels of MDA, DCF, and intracellular free Fe in ALL cells were tested through the commercial kits. The cell apoptosis was determined through flow cytometry analysis. The binding ability of PAQR3 and nuclear factor erythroid 2-related factor 2 (Nrf2) was verified through pull down assay.

RESULTS

PAQR3 expression was firstly assessed in ALL patients and cell lines, and discovered to be downregulated. It was verified that PAQR3 suppressed ALL cells proliferation. Further experiments proved that PAQR3 aggravates ferroptosis in ALL. In addition, AQR3 bound with Nrf2, and modulated its expression through ubiquitination in ALL. Finally, through rescue assays, it was demonstrated that Nrf2 overexpression reversed the effects of PAQR3 on cell proliferation and ferroptosis.

CONCLUSION

Findings from our work uncovered that PAQR3 inhibited proliferation and aggravated ferroptosis in ALL through modulation Nrf2 stability. This study suggested that PAQR3 may serve as an effective biological marker for ALL treatment.

PAQR3 protects against oxygen-glucose deprivation/reperfusion-induced injury through the ERK signaling pathway in N2A cells

Cerebral ischemia-reperfusion injury is pivotal in the development of multiple-subcellular organelle and tissue injury after acute ischemic stroke. Recently, the Golgi apparatus (GA) has been shown to be a key subcellular organelle that plays an important role in neuroprotection against oxygen-glucose deprivation/reperfusion (OGD/R) injury. PAQR3, a scaffold protein exclusively localized in the GA, was originally discovered as a potential tumor suppressor protein. PAQR3 acts as a spatial regulator of Raf-1 that binds Raf-1 and sequesters it to the GA, where it negatively modulates the Ras/Raf/MEK/ERK signaling pathway in tumor models. Studies suggest that suppression of the ERK pathway can alleviate OGD/R-induced cell apoptosis. However, whether PAQR3 has potential effects on ischemic stroke and the underlying mechanism(s) remain unexplored. The current study is the first to show that PAQR3 was significantly downregulated in mouse neuroblastoma (N2A) cells upon OGD/R exposure, both at the mRNA and protein levels. Compared to that in controls, the mRNA level of PAQR3 began to decline at 0 h (0 h) after reperfusion, while the protein level began to decline at 4 h. Furthermore, overexpression of PAQR3 reduced OGD/R-induced apoptosis. The mRNA and protein levels of total ERK1 and ERK2 were unaltered, while activated p-ERK1 and p-ERK2 were decreased in N2A cells transfected with a PAQR3 expression vector after OGD for 4 h plus 24 h of reperfusion. Collectively, these data indicated that increased PAQR3 expression protected against OGD/R-induced apoptosis possibly by inhibiting the ERK signaling pathway. Therefore, PAQR3 might be a new attractive target in the treatment of OGD/R insult, and the underlying mechanism will pave the way for its potential experimental and clinical application.

Characterization of the Golgi scaffold protein PAQR3, and its role in tumor suppression and metabolic pathway compartmentalization

The Golgi apparatus is critical in the compartmentalization of signaling cascades originating from the cytoplasmic membrane and various organelles. Scaffold proteins, such as progestin and adipoQ receptor (PAQR)3, specifically regulate this process, and have recently been identified in the Golgi apparatus. PAQR3 belongs to the PAQR family, and was recently described as a tumor suppressor. Accumulating evidence demonstrates PAQR3 is downregulated in different cancers to suppress its inhibitory effects on malignant potential. PAQR3 functions biologically through the pathological regulation of altered signaling pathways. Significant cell proliferation networks, including Ras proto-oncogene (Ras)/mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), insulin, and vascular endothelial growth factor, are closely controlled by PAQR3 for physiologically relevant effects. Meanwhile, genetic/epigenetic susceptibility and environmental factors, may have functions in the downregulation of PAQR3 in human cancers. This study aimed to assess the subcellular localization of PAQR3 and determine its topological features and functional domains, summarizing its effects on cell signaling compartmentalization. The pathophysiological functions of PAQR3 in cancer pathogenesis, metabolic diseases, and developmental ailments were also highlighted.

Selected Golgi-Localized Proteins and Carcinogenesis: What Do We Know?

The role of the Golgi apparatus in carcinogenesis still remains unclear. A number of structural and functional cis-, medial-, and trans-Golgi proteins as well as a complexity of metabolic pathways which they mediate may indicate a central role of the Golgi apparatus in the development and progression of cancer. Pleiotropy of cellular function of the Golgi apparatus makes it a "metabolic heart" or a relay station of a cell, which combines multiple signaling pathways involved in carcinogenesis. Therefore, any damage to or structural abnormality of the Golgi apparatus, causing its fragmentation and/or biochemical dysregulation, results in an up- or downregulation of signaling pathways and may in turn promote tumor progression, as well as local nodal and distant metastases. Three alternative or parallel models of spatial and functional Golgi organization within tumor cells were proposed: (1) compacted Golgi structure, (2) normal Golgi structure with its increased activity, and (3) the Golgi fragmentation with ministacks formation. Regardless of the assumed model, the increased activity of oncogenesis initiators and promoters with inhibition of suppressor proteins results in an increased cell motility and migration, increased angiogenesis, significantly activated trafficking kinetics, proliferation, EMT induction, decreased susceptibility to apoptosis-inducing factors, and modulating immune response to tumor cell antigens. Eventually, this will lead to the increased metastatic potential of cancer cells and an increased risk of lymph node and distant metastases. This chapter provided an overview of the current state of knowledge of selected Golgi proteins, their role in cytophysiology as well as potential involvement in tumorigenesis.