Reduced expression of proteolipid protein 2 increases ER stress-induced apoptosis and autophagy in glioblastoma

Autophagy machinery in glioblastoma: The prospect of cell death crosstalk and drug resistance with bioinformatics analysis

Brain tumors are common malignancies with high mortality and morbidity in which glioblastoma (GB) is a grade IV astrocytoma with heterogeneous nature. The conventional therapeutics for the GB mainly include surgery and chemotherapy, however their efficacy has been compromised due to the aggressiveness of tumor cells. The dysregulation of cell death mechanisms, especially autophagy has been reported as a factor causing difficulties in cancer therapy. As a mechanism contributing to cell homeostasis, the autophagy process is hijacked by tumor cells for the purpose of aggravating cancer progression and drug resistance. The autophagy function is context-dependent and its role can be lethal or protective in cancer. The aim of the current paper is to highlight the role of autophagy in the regulation of GB progression. The cytotoxic function of autophagy can promote apoptosis and ferroptosis in GB cells and vice versa. Autophagy dysregulation can cause drug resistance and radioresistance in GB. Moreover, stemness can be regulated by autophagy and overall growth as well as metastasis are affected by autophagy. The various interventions including administration of synthetic/natural products and nanoplatforms can target autophagy. Therefore, autophagy can act as a promising target in GB therapy.

Reduced Proteolipid Protein 2 promotes endoplasmic reticulum stress-related apoptosis and increases drug sensitivity in acute myeloid leukemia

BACKGROUND

The Proteolipid Protein 2 (PLP2), a protein in the Endoplasmic Reticulum (ER) membrane, has been reported to be highly expressed in various tumors. Previous studies have demonstrated that the reduced PLP2 can induce apoptosis and autophagy through ER stress-related pathways, leading to a decreased proliferation and aggressiveness. However, there is no research literature on the role of PLP2 in Acute Myeloid Leukemia (AML).

METHODS

PLP2 expression, clinical data, genetic mutations, and karyotype changes from GEO, TCGA, and timer2.0 databases were analyzed through the R packages. The possible functions and pathways of cells were explored through GO, KEGG, and GSEA enrichment analysis using the clusterProfiler R package. Immuno-infiltration analysis was conducted using the Cibersort algorithm and the Xcell R package. RT-PCR and western blot techniques were employed to identify the PLP2 expression, examine the knockdown effects in THP-1 cells, and assess the expression of genes associated with endoplasmic reticulum stress and apoptosis. Flow cytometry was utilized to determine the apoptosis and survival rates of different groups.

RESULTS

PLP2 expression was observed in different subsets of AML and other cancers. Enrichment analyses revealed that PLP2 was involved in various tumor-related biological processes, primarily apoptosis and lysosomal functions. Additionally, PLP2 expression showed a strong association with immune cell infiltration, particularly monocytes. In vitro, the knockdown of PLP2 enhanced endoplasmic reticulum stress-related apoptosis and increased drug sensitivity in THP-1 cells.

CONCLUSIONS

PLP2 could be a novel therapeutic target in AML, in addition, PLP2 is a potential endoplasmic reticulum stress regulatory gene in AML.

PLP2 Could Be a Prognostic Biomarker and Potential Treatment Target in Glioblastoma Multiforme

Objective

This study aimed to discern the association between PLP2 expression, its biological significance, and the extent of immune infiltration in human GBM.

Methods

Utilizing the GEPIA2 and TCGA databases, we contrasted the expression levels of PLP2 in GBM against normal tissue. We utilized GEPIA2 and LinkedOmics for survival analysis, recognized genes co-expressed with PLP2 via cBioPortal and GEPIA2, and implemented GO and KEGG analyses. The STRING database facilitated the construction of protein-protein interaction networks. We evaluated the relationship of PLP2 with tumor immune infiltrates using ssGSEA and the TIMER 2.0 database. An IHC assay assessed PLP2 and PDL-1 expression in GBM tissue, and the Drugbank database aided in identifying potential PLP2-targeting compounds. Molecular docking was accomplished using Autodock Vina 1.2.2.

Results

PLP2 expression was markedly higher in GBM tissues in comparison to normal tissues. High PLP2 expression correlated with a decrease in overall survival across two databases. Functional analyses highlighted a focus of PLP2 functions within leukocyte. Discrepancies in PLP2 expression were evident in immune infiltration, impacting CD4+ T cells, neutrophils, myeloid dendritic cells, and macrophages. There was a concomitant increase in PLP2 and PD-L1 expression in GBM tissues, revealing a link between the two. Molecular docking with ethosuximide and praziquantel yielded scores of -7.441 and -4.295 kcal/mol, correspondingly.

Conclusion

PLP2's upregulation in GBM may adversely influence the lifespan of GBM patients. The involvement of PLP2 in pathways linked to leukocyte function is suggested. The positive correlation between PLP2 and PD-L1 could provide insights into PLP2's role in glioma modulation. Our research hints at PLP2's potential as a therapeutic target for GBM, with ethosuximide and praziquantel emerging as potential treatment candidates, especially emphasizing the potential of these compounds in GBM treatment targeting PLP2.

MicroRNA-765 is upregulated in myelodysplastic syndromes and induces apoptosis via PLP2 inhibition in leukemia cells

Background

Epigenetic studies, particularly research on microRNA (miRNA), have flourished. The abnormal expression of miRNA contributes to the development of hematologic malignancies. miR-765 has been reported to inhibit cell proliferation by downregulating proteolipid protein 2 (PLP2), which causes apoptosis. We investigated miR-765 dysregulation in myelodysplastic syndromes (MDS).

Methods

We compared the expression profiles of miR-765 in 65 patients with MDS and 11 controls. Cell proliferation and apoptosis assays were performed to determine the in vitro effects of miR-765 on leukemia cells transfected with the miR-765 mimic. Reverse transcription quantitative PCR (RT-qPCR) and western blotting were performed to examine the targets of miR-765.

Results

We found that miR-765 levels were upregulated 10.2-fold in patients with MDS compared to controls. In refractory cytopenia with multilineage dysplasia, the percentage of patients with elevated miR-765 levels was significantly higher than in other forms of MDS. Experiments with leukemia cells revealed that transfection with a miR-765 mimic inhibited cell proliferation and induced apoptosis. RT-qPCR and western blotting demonstrated that the target of miR-765 was PLP2.

Conclusion

These findings imply that upregulation of miR-765 induces apoptosis via downregulation of PLP2 and may have a role in MDS pathogenesis.

CircKIF4A promotes glioma growth and temozolomide resistance by accelerating glycolysis

Circular RNAs (circRNAs) are a kind of noncoding RNAs that have different biological functions. CircRNAs play very important parts in the progression of cancers. Nevertheless, the exact mechanism and function of many circRNAs in glioma are not clear. In our study, circKIF4A was identified as a remarkably upregulated circRNA expressed in glioma tissues and cell lines. We performed loss-off function and gain-of-function experiments to inquire into the biological function of circKIF4A in the progression of glioma. We discovered that knockdown of circKIF4A remarkably decreased the proliferation and invasion ability of glioma cells. Moreover, subcutaneous tumorigenesis model and intracranial injection of orthotopic glioma model were established to investigate the functions of circKIF4A in vivo. Suppression of circKIF4A remarkably enhanced the sensitivity of glioma to temozolomide treatment. The glycolysis rate was accelerated by circKIF4A overexpression, which promoted glioma growth and temozolomide resistance. The glycolysis regulating enzyme ALDOA was regulated by circKIF4A through the mechanism of interactivity with miR-335-5p in glioma cells. In a word, our data showed that the upregulation of circKIF4A facilitates glioma progression by means of binding miR-335-5p and upregulating ALDOA expression.

PLP2 drives collective cell migration via ZO-1-mediated cytoskeletal remodeling at the leading edge in human colorectal cancer cells

Collective cell migration (CCM), in which cell-cell integrity remains preserved during movement, plays an important role in the progression of cancer. However, studies describing CCM in cancer progression are majorly focused on the effects of extracellular tissue components on moving cell plasticity. The molecular and cellular mechanisms of CCM during cancer progression remain poorly explored. Here, we report that proteolipid protein 2 (PLP2), a colonic epithelium-enriched transmembrane protein, plays a vital role in the CCM of invasive human colorectal cancer (CRC) epithelium by modulating leading-edge cell dynamics in 2D. The extracellular pool of PLP2, secreted via exosomes, was also found to contribute to the event. During CCM, the protein was found to exist in association with ZO-1 (also known as TJP1) and to be involved in the positioning of the latter at the migrating edge. PLP2-mediated positioning of ZO-1 at the leading edge further alters actin cytoskeletal organization that involves Rac1 activation. Taken together, our findings demonstrate that PLP2, via its association with ZO-1, drives CCM in CRC epithelium by modulating the leading-edge actin cytoskeleton, thereby opening up new avenues of cancer research. This article has an associated First Person interview with the first author of the paper.

BAP31: Physiological functions and roles in disease

B-cell receptor-associated protein 31 (BAP31 or BCAP31) is a ubiquitously expressed transmembrane protein found mainly in the endoplasmic reticulum (ER), including in mitochondria-associated membranes (MAMs). It acts as a broad-specificity membrane protein chaperone and quality control factor, which can promote different fates for its clients, including ER retention, ER export, ER-associated degradation (ERAD), or evasion of degradation, and it also acts as a MAM tetherer and regulatory protein. It is involved in several cellular processes - it supports ER and mitochondrial homeostasis, promotes proliferation and migration, plays several roles in metabolism and the immune system, and regulates autophagy and apoptosis. Full-length BAP31 can be anti-apoptotic, but can also mediate activation of caspase-8, and itself be cleaved by caspase-8 into p20-BAP31, which promotes apoptosis by mobilizing ER calcium stores at MAMs. BAP31 loss-of-function mutations is the cause of 'deafness, dystonia, and central hypomyelination' (DDCH) syndrome, characterized by severe neurological symptoms and early death. BAP31 is furthermore implicated in a growing number of cancers and other diseases, and several viruses have been found to target it to promote their survival or life cycle progression. The purpose of this review is to provide an overview and examination of the basic properties, functions, mechanisms, and roles in disease of BAP31.

PLP2 Expression as a Prognostic and Therapeutic Indicator in High-Risk Multiple Myeloma

Multiple myeloma (MM) is a devastating cancer with a highly heterogeneous outcome. Because of the heterogeneity of myeloma cells, risk stratification is important for making therapeutic regimens. Nevertheless, no immunohistochemical predictive and prognostic marker has been constructed yet. In the present study, we explored the prognostic value of proteolipid protein 2 (PLP2) in MM patients using immunohistochemistry (IHC). We assessed PLP2 expression in bone marrow (BM) biopsy specimens obtained from 87 newly diagnosed MM (NDMM) patients. Correlations between PLP2 expression and clinicopathological features were analyzed. PLP2 expression was present in high-risk MM patients, which was increased with disease progression and poor prognosis. PLP2 was increasing in parallel with high beta-2 microglobulin (β2-MG) and lactate dehydrogenase (LDH). Furthermore, MM patients with low PLP2 expression could achieve a favorable treatment response. PLP2 may be a novel biomarker for prognostic prediction and a therapeutic target for anti-MM treatments.

Reduced expression of proteolipid protein 2 increases ER stress-induced apoptosis and autophagy in glioblastoma

Proteolipid protein 2 (PLP2) is an integral ion channel membrane protein of the endoplasmic reticulum. The protein has been shown to be highly expressed in many cancer types, but its importance in glioma progression is poorly understood. Using publicly available datasets (Rembrandt, TCGA and CGGA), we found that the expression of PLP2 was significantly higher in high‐grade gliomas than in low‐grade gliomas. We confirmed these results at the protein level through IHC staining of high‐grade (n = 56) and low‐grade glioma biopsies (n = 16). Kaplan‐Meier analysis demonstrated that increased PLP2 expression was associated with poorer patient survival. In functional experiments, siRNA and shRNA PLP2 knockdown induced ER stress and increased apoptosis and autophagy in U87 and U251 glioma cell lines. Inhibition of autophagy with chloroquine augmented apoptotic cell death in U87‐ and U251‐siPLP2 cells. Finally, intracranial xenografts derived from U87‐ and U251‐shPLP2 cells revealed that loss of PLP2 reduced glioma growth in vivo. Our results therefore indicate that increased PLP2 expression promotes GBM growth and that PLP2 represents a potential future therapeutic target.