Poly C Binding Protein 1 Regulates p62/SQSTM1 mRNA Stability and Autophagic Degradation to Repress Tumor Progression

RNA binding proteins in senescence: A potential common linker for age-related diseases?

Aging represents the major risk factor for the onset and/or progression of various disorders including neurodegenerative diseases, metabolic disorders, and bone-related defects. As the average age of the population is predicted to exponentially increase in the coming years, understanding the molecular mechanisms underlying the development of aging-related diseases and the discovery of new therapeutic approaches remain pivotal. Well-reported hallmarks of aging are cellular senescence, genome instability, autophagy impairment, mitochondria dysfunction, dysbiosis, telomere attrition, metabolic dysregulation, epigenetic alterations, low-grade chronic inflammation, stem cell exhaustion, altered cell-to-cell communication and impaired proteostasis. With few exceptions, however, many of the molecular players implicated within these processes as well as their role in disease development remain largely unknown. RNA binding proteins (RBPs) are known to regulate gene expression by dictating at post-transcriptional level the fate of nascent transcripts. Their activity ranges from directing primary mRNA maturation and trafficking to modulation of transcript stability and/or translation. Accumulating evidence has shown that RBPs are emerging as key regulators of aging and aging-related diseases, with the potential to become new diagnostic and therapeutic tools to prevent or delay aging processes. In this review, we summarize the role of RBPs in promoting cellular senescence and we highlight their dysregulation in the pathogenesis and progression of the main aging-related diseases, with the aim of encouraging further investigations that will help to better disclose this novel and captivating molecular scenario.

Different Roles of Apoptosis and Autophagy in the Development of Human Colorectal Cancer

Colorectal cancer (CRC) remains a major life-threatening malignancy, despite numerous therapeutic and screening attempts. Apoptosis and autophagy are two processes that share common signaling pathways, are linked by functional relationships and have similar protein components. During the development of cancer, the two processes can trigger simultaneously in the same cell, causing, in some cases, an inhibition of autophagy by apoptosis or apoptosis by autophagy. Malignant cells that have accumulated genetic alterations can take advantage of any alterations in the apoptotic process and as a result, progress easily in the cancerous transformation. Autophagy often plays a suppressive role during the initial stages of carcinogenicity, while in the later stages of cancer development it can play a promoting role. It is extremely important to determine the regulation of this duality of autophagy in the development of CRC and to identify the molecules involved, as well as the signals and the mechanisms behind it. All the reported experimental results indicate that, while the antagonistic effects of autophagy and apoptosis occur in an adverse environment characterized by deprivation of oxygen and nutrients, leading to the formation and development of CRC, the effects of promotion and collaboration usually involve an auxiliary role of autophagy compared to apoptosis. In this review, we elucidate the different roles of autophagy and apoptosis in human CRC development.

Borax regulates iron chaperone- and autophagy-mediated ferroptosis pathway in glioblastoma cells

Glioblastoma (GBM) is classified as a stage-IV glioma. Unfortunately, there are currently no curative treatments for GBM. Poly(rC)-binding protein 1 (PCBP1) is a cytosolic iron chaperone with diverse functions. PCBP1 is also known to regulate autophagy, but the role of PCBP1 in ferroptosis, iron-dependent cell death pathway, remains unrevealed in GBM cells. Here, we investigated the effects of borax, a boron compound, on the ferroptosis signaling pathway mediated by PCBP1 and autophagy. The study analyzed cell viability, proliferation, and cell cycle on U87-MG and HMC3 cells to investigate the effects of borax. After determining the cytotoxic concentrations of borax, morphological analyzes and measurement of PCBP1, Beclin1, malondialdehyde (MDA), glutathione (GSH), glutathione peroxidase 4 (GPx4) and acyl-CoA synthetase long chain family member 4 (ACSL4) levels were performed. Finally, expression levels of PCBP1, Beclin1, GPx4 and ACSL4, and caspase-3/7 activity were determined. We found that borax reduced U87-MG cell viability in a concentration- and time-dependent manner. Additionally, borax altered cell proliferation and remarkably reduced S phase in the U87-MG cells and exhibited selectivity by having an opposite effect on normal cells (HMC3). According to DAPI staining, borax caused nuclear deficits in U87-MG cells. The result showed that borax in U87-MG cells induced reduction of the PCBP1, GSH, and GPx4 and enhancement of Beclin1, MDA, and ACSL4. Furthermore, borax triggered apoptosis by activating caspase 3/7 in U87-MG cells. Our study indicated that the borax has potential as an anticancer treatment for GBM via regulating PCBP1/Beclin1/GPx4/ACSL4 signaling pathways.

Altered iron metabolism as a target for ferroptosis induction in head and neck cancer

Iron is a mineral micronutrient essential for survival and vital functions in many biological processes in living organisms. Iron plays a crucial role as a cofactor of iron-sulfur clusters in energy metabolism and biosynthesis by binding with enzymes and transferring electrons to targets. Iron can also impair cellular functions by damaging organelles and nucleic acids by producing free radicals from redox cycling. Iron-catalyzed reaction products can induce active-site mutations in tumorigenesis and cancer progression. However, the boosted pro-oxidant iron form may contribute to cytotoxicity by increasing soluble radicals and highly reactive oxygen species via the Fenton reaction. An increased redox-active labile iron pool is required for tumor growth and metastasis, but the increased cytotoxic lipid radicals also lead to regulated cell death, such as ferroptosis. Therefore, this may be a major target for selectively killing cancer cells. This review intends to understand altered iron metabolism in cancers and discuss iron-related molecular regulators highly associated with iron-induced cytotoxic radical production and ferroptosis induction, focusing on head and neck cancer.

SH3BGRL Suppresses Liver Tumor Progression through Enhanced ATG5-Dependent Autophagy

SH3BGRL, an adaptor protein, is upregulated in breast cancers and indicates its tumorigenic role. But the function of SH3BGRL in other types of cancers is largely unknown. Here, we modulate SH3BGRL expression level in two liver cancer cells and conduct both in vitro and in vivo analyses of SH3BGRL in cell proliferation and tumorigenesis. Results demonstrate that SH3BGRL notably inhibits cell proliferation and arrests the cell cycle in both LO2 and HepG2 cells. Molecularly, SH3BGRL upregulates the expression of ATG5 from proteasome degradation as well as the inhibitions of Src activation and its downstream ERK and AKT signaling pathways, which eventually enhance autophagic cell death. The xenograft mouse model reveals that SH3BGRL overexpression can efficiently suppress tumorigenesis in vivo, while the additional silencing ATG5 in SH3BGRL-overexpressing cells attenuates the inhibitory effect of SH3BGRL on both hepatic tumor cell proliferation and tumorigenicity in vivo. The relevance of SH3BGRL downregulation in liver cancers and their progression is validated based on the large-scale tumor data. Taken together, our results clarify the suppressive role of SH3BGRL in tumorigenesis of liver cancer, which would be of help to the diagnosis of liver cancer, while either promoting the autophagy of liver cancer cells or inhibiting the downstream signaling induced from SH3BGRL downregulation would be a promising therapy.

The RNA-binding protein PCBP1 represses lung adenocarcinoma progression by stabilizing DKK1 mRNA and subsequently downregulating β-catenin

Background

PolyC-RNA-binding protein 1 (PCBP1) functions as a tumour suppressor and RNA regulator that is downregulated in human cancers. Here, we aimed to reveal the biological function of PCBP1 in lung adenocarcinoma (LUAD).

Methods

First, PCBP1 was identified as an important biomarker that maintains LUAD through The Cancer Genome Atlas (TCGA) project screening and confirmed by immunohistochemistry and qPCR. Via colony formation, CCK8, IncuCyte cell proliferation, wound healing and Transwell assays, we confirmed that PCBP1 was closely related to the proliferation and migration of LUAD cells. The downstream gene DKK1 was discovered by RNA sequencing of PCBP1 knockdown cells. The underlying mechanisms were further investigated using western blot, qPCR, RIP, RNA pulldown and mRNA stability assays.

Results

We demonstrate that PCBP1 is downregulated in LUAD tumour tissues. The reduction in PCBP1 promotes the proliferation, migration and invasion of LUAD in vitro and in vivo. Mechanistically, the RNA-binding protein PCBP1 represses LUAD by stabilizing DKK1 mRNA. Subsequently, decreased expression of the DKK1 protein relieves the inhibitory effect on the Wnt/β-catenin signalling pathway. Taken together, these results show that PCBP1 acts as a tumour suppressor gene, inhibiting the tumorigenesis of LUAD.

Conclusions

We found that PCBP1 inhibits LUAD development by upregulating DKK1 to inactivate the Wnt/β-catenin pathway. Our findings highlight the potential of PCBP1 as a promising therapeutic target.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03552-y.

Strain-Specific Behavior of Mycobacterium tuberculosis in Interruption of Autophagy Pathway in Human Alveolar Type II Epithelial A549 Cells

Background:

Autophagy induction has been shown to differ in magnitude depending on the mycobacterial species. However, few studies have investigated the specific autophagic capacity of different Mtb strains in ATs. This study aimed to elucidate the host autophagic response to different Mtb strains in ATs responsible for TB in the capital of Iran, Tehran.

Methods:

A549 cells were infected with three different Mtb clinical isolates (Beijing, NEW1, and CAS1/Delhi) and the reference strain H37Rv. Following RNA extraction, the expression of eight ATG genes, four mycobacterial genes, and three miRNAs was evaluated using quantitative RT-PCR.

Results:

The results revealed that all four strains influenced the autophagy pathway in various ways at different magnitudes. The Beijing and H37Rv strains could inhibit autophagosome formation, whereas the CAS and NEW1 strains induced autophagosome formation. The expression of genes involved in the fusion of autophagosomes to lysosomes (LAMP1) indicated that all the studied strains impaired the autophagolysosomal fusion; this result is not unexpected as Mtb can block the autophagolysomal fusion. In addition, the Beijing and H37RV strains prevented the formation of autophagic vacuoles, besides mycobacterial targeting of lysosomes and protease activity.

Conclusion:

This preliminary study improved our understanding of how Mtb manages to overcome the host immune system, such as autophagy, and evaluated the genes used by specific strains during this process. Further studies with a large number of Mtb strains, encompassing the other main Mtb lineages, are inevitable.

Poly(rC) binding protein 1 benefits coxsackievirus B3 infection via suppressing the translation of p62/SQSTM1

Coxsackievirus B3 (CVB3) is a positive single-strand RNA virus causing myocarditis, pancreatitis and meningitis. During CVB3 infection, various host cellular components, including proteins and non-coding RNAs, interact with the virus and affect viral infection. Poly(rC) binding protein 1 (PCBP1) is a multifunctional RNA binding protein regulating transcription, translation and mRNA stability of a variety of genes. In this study, we observed a significant reduction of PCBP1 protein during CVB3 infection. By bioinformatic prediction and luciferase-assay verification, we confirmed that the expression of PCBP1 was directly inhibited by miR-21, a microRNA upregulated during CVB3 infection. Furthermore, we found that overexpression of PCBP1 promoted CVB3 infection and knocking down of PCBP1 inhibited it. In the subsequent mechanism study, our results revealed that PCBP1 blocked the translation of p62/SQSTM1 (sequestosome 1), an autophagy-receptor protein suppressing CVB3 replication, by interacting with the cis-element in the 5' untranslational region (5' UTR) of p62/SQSTM1. In summary, our studies have identified PCBP1 as a beneficial factor for CVB3 infection. These findings may deepen the understanding of host-virus interactions and provide a potential target for intervention of CVB3 infection.

Poly(rC)-binding protein 1 represses ferritinophagy-mediated ferroptosis in head and neck cancer

A cytosolic iron chaperone poly(rC)-binding protein 1 (PCBP1) is a multifunctional RNA-binding protein involving gene transcription, RNA regulation, and iron loading to ferritins. PCBP1 is also known to repress autophagy, but the role of PCBP1 in ferritinophagy and ferroptosis remains unrevealed. Therefore, we examined the role of PCBP1 in ferritinophagy-mediated ferroptosis in head and neck cancer (HNC) cells. The effects of system xc^– cystine/glutamate antiporter (xCT) inhibitors and PCBP1 gene silencing/overexpression were tested on HNC cell lines and mouse tumor xenograft models. These effects were analyzed by assessing cell viability and death, lipid reactive oxygen species and iron production, lipid, malondialdehyde, mRNA/protein expression, and autophagy flux assays. Interaction between PCBP1 and BECN1 mRNA was also examined by luciferase and RNA-protein pull-down assays. PCBP1 gene silencing increased autophagosome generation and autophagic flux. Conversely, PCBP1 upregulation inhibited autophagy activation via direct binding to the CU-rich elements on the 3′-untranslated region (3′-UTR) of BECN1 mRNA. The internal deletion or mutation of the 3′-UTR F2 region recovered BECN1 mRNA stability repressed by PCBP1, resulting in enhanced ferritinophagy-mediated ferroptosis. Besides, PCBP1 knockdown promoted polyunsaturated fatty acid peroxidation by increasing ALOX15 expression. Further, excess iron accumulation caused mitochondrial dysfunction in PCBP1-suppressed cells. A ferroptosis inducer sulfasalazine significantly suppressed tumor growth in mice with the transplantation of PCBP1-silenced HNC. Our data suggest that the dual functions of PCBP1 repressing BECN1 and ALOX15 mRNAs contribute to attenuating cancer susceptibility to ferroptosis inducers.

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PCBP1 expression is related to head and neck cancer survival and response to ferroptosis inducers.

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Knockdown of PCBP1 increased ferroptosis sensitivity by inducing an increased labile iron pool.

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PCBP1 negatively regulated ferritinophagy by the 3′-UTR binding of BECN1 mRNA.

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Knockdown of PCBP1 increased lipid peroxidation by ALOX15 expression.

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PCBP1 depletion promoted ferroptosis susceptibility in vitro and in vivo.

Low-Intensity Focused Ultrasound Targeted Microbubble Destruction Enhanced Paclitaxel Sensitivity by Decreasing Autophagy in Paclitaxel-Resistant Ovarian Cancer

Ultrasound targeted microbubble destruction (UTMD) was introduced as a promising method to improve anti-tumor therapeutic efficacy, while minimizing side effects to healthy tissues. Nevertheless, the acoustical phenomenon behind the UTMD as well as the exact mechanisms of autophagy action involved in the increased anti-cancer response are still not fully understood. Therefore, we examined the drug resistance-reversing effects of low-intensity focused ultrasound with microbubble (LIFU+MB) in paclitaxel (PTX)-resistant ovarian cancer cells. Cell viability was evaluated using CCK8 (Cell Counting Kit-8), apoptosis was detected by flow cytometry, quantitative real-time PCR and Western blot were used to detect the expressions of mRNA and protein, and autophagy was observed by transmission electron microscopy (TEM). We revealed that the level of autophagy was increased (p < 0.05) in PTX-resistant ovarian cancer cells. Treatment of LIFU+MB combined with PTX can notably inhibit proliferation as well as increase apoptosis (p < 0.01) in drug-resistant cells. We proposed that LIFU+MB might affect the sensitivity of ovarian cancer cells to PTX by modulating autophagy. To verify the hypothesis, we analyzed the autophagy level of drug-resistant cells after the treatment of LIFU+MB and found that autophagy was significantly inhibited. Altogether, our findings demonstrated that LIFU+MB could reverse PTX resistance in ovarian cancer via inhibiting autophagy, which provides a novel strategy to improve chemosensitivity in ovarian cancer.

LncRNA EIF1AX-AS1 promotes endometrial cancer cell apoptosis by affecting EIF1AX mRNA stabilization

Long non-coding RNAs (lncRNAs) have been found to play an important role in the occurrence and development of endometrial carcinoma (EC). Here, using RNA sequencing analysis, we systemically screened and identified the lncRNA EIF1AX-AS1, which is aberrantly down-regulated in clinical EC tissues and closely correlated with tumor type. EIF1AX-AS1 markedly inhibited EC cell proliferation and promoted apoptosis in vitro and in vivo. Mechanistically, EIF1AX-AS1 interacts with EIF1AX mRNA and poly C binding protein 1 (PCBP1), which promote eukaryotic translation initiation factor 1A, X-linked (EIF1AX) mRNA degradation. Intriguingly, interaction with IRES-related proteins Y-box binding protein 1 (YBX-1), EIF1AX promotes c-Myc translation through the internal ribosome enter site pathway. c-Myc promotes EIF1AX transcription and thus forms a feed-forward loop to regulate EC cell proliferation. Taken together, these data reveal new insights into the biology driving EC proliferation and highlights the potential of lncRNAs as biomarkers for prognosis and future therapeutic targets for cancer.

Tumorigenic bacteria in colorectal cancer: mechanisms and treatments

Colorectal cancer (CRC) is the third most common and the second most fatal cancer. In recent years, more attention has been directed toward the role of gut microbiota in the initiation and development of CRC. Some bacterial species, such as Fusobacterium nucleatum, Escherichia coli, Bacteroides fragilis, Enterococcus faecalis, and Salmonella sp. have been associated with CRC, based upon sequencing studies in CRC patients and functional studies in cell culture and animal models. These bacteria can cause host DNA damage by genotoxic substances, including colibactin secreted by pks + Escherichia coli, B. fragilis toxin (BFT) produced by Bacteroides fragilis, and typhoid toxin (TT) from Salmonella. These bacteria can also indirectly promote CRC by influencing host-signaling pathways, such as E-cadherin/β-catenin, TLR4/MYD88/NF-κB, and SMO/RAS/p38 MAPK. Moreover, some of these bacteria can contribute to CRC progression by helping tumor cells to evade the immune response by suppressing immune cell function, creating a proinflammatory environment, or influencing the autophagy process. Treatments with the classical antibacterial drugs, metronidazole or erythromycin, the antibacterial active ingredients, M13@ Ag (electrostatically assembled from inorganic silver nanoparticles and the protein capsid of bacteriophage M13), berberine, and zerumbone, were found to inhibit tumorigenic bacteria to different degrees. In this review, we described progress in elucidating the tumorigenic mechanisms of several CRC-associated bacteria, as well as progress in developing effective antibacterial therapies. Specific bacteria have been shown to be active in the oncogenesis and progression of CRC, and some antibacterial compounds have shown therapeutic potential in bacteria-induced CRC. These bacteria may be useful as biomarkers or therapeutic targets for CRC.

Identification of PCBP1 as a Novel Modulator of Mammalian Circadian Clock

The circadian clock governs our daily cycle of behavior and physiology. Previous studies have identified a handful of core clock components and hundreds of circadian modifiers. Here, we report the discovery that poly(C)-binding protein 1 (PCBP1), displaying a circadian expression pattern, was a novel circadian clock regulator. We found that knocking down PCBP1 resulted in period shortening in human U2OS cells, and that manipulations of PCBP1 expression altered the activity of CLOCK/BMAL1 in an E-box-based reporter assay. Further mechanistic study demonstrated that this clock function of PCBP1 appears to work by enhancing the association of Cryptochrome 1 (CRY1) with the CLOCK/BMAL1 complex, thereby negatively regulating the latter’s activation. Co-immunoprecipitation of PCBP1 and core clock molecules confirmed the interactions between PCBP1 and CRY1, and a time-course qPCR assay revealed the rhythmic expression of PCBP1 in mouse hearts in vivo. Given that the RNA interference of mushroom-body expressed (mub), the poly(rC) binding protein (PCBP) homolog of Drosophila, in the clock neurons also led to a circadian phenotype in the locomotor assay, our study deemed PCBP1 a novel clock modifier whose circadian regulatory mechanism is conserved during evolution.