The synergistic inhibition of breast cancer proliferation by combined treatment with 4EGI-1 and MK2206

Metadherin inhibits chemosensitivity of triple-negative breast cancer to paclitaxel via activation of AKT/GSK-3β signaling pathway

Triple-negative breast cancer (TNBC) has an aggressive clinical course, and paclitaxel (PTX)-based chemotherapy remains the main therapeutic drug. Metadherin (MTDH) acts as an oncogene that regulates proliferation, invasion, metastasis, and chemoresistance. This study aimed to investigate whether TNBC chemosensitivity to PTX was related to the MTDH/AKT/glycogen synthase kinase-3beta (GSK-3β) pathway. Clinical baseline characteristics and immunohistochemistry (IHC) were used to evaluate the expression and prognosis of MTDH and AKT (protein kinase B, PKB) in TNBC patient samples. MTDH shRNA, MTDH overexpression vector, MK-2206, and PTX intervention were used in cell models and mouse tumor-bearing models. Afterwards, mRNA and protein levels were assessed using quantitative real-time polymerase chain reaction and Western blot. Evaluate the level of tumor cell apoptosis and cell cycle using flow cytometry. Cell viability was detected using Cell Count Kit 8. The in vivo imaging system is used to analyze the growth of tumors. We found that higher expression of MTDH or AKT resulted in poorer disease-free survival and a lower Miller-Payne grade. MTDH promotes cell proliferation and increases p-AKT and p-GSK-3β expression in TNBC cells. Notably, suppression of AKT terminated MTDH overexpression-induced cell proliferation and apoptosis. MTDH knockdown or the AKT inhibitor MK2206 reduced the p-AKT and p-GSK-3β ratio, reduced cell viability and proliferation, increased cell apoptosis, and increased chemosensitivity to PTX. In vivo, xenograft tumors of an MTDH knockdown+MK2206 group treated with PTX were the smallest compared to other groups. In short, MTDH inhibits TNBC chemosensitivity to PTX by activating the AKT/GSK-3β signaling pathway.

Nonsense mutation suppression is enhanced by targeting different stages of the protein synthesis process

The introduction of premature termination codons (PTCs), as a result of splicing defects, insertions, deletions, or point mutations (also termed nonsense mutations), lead to numerous genetic diseases, ranging from rare neuro-metabolic disorders to relatively common inheritable cancer syndromes and muscular dystrophies. Over the years, a large number of studies have demonstrated that certain antibiotics and other synthetic molecules can act as PTC suppressors by inducing readthrough of nonsense mutations, thereby restoring the expression of full-length proteins. Unfortunately, most PTC readthrough-inducing agents are toxic, have limited effects, and cannot be used for therapeutic purposes. Thus, further efforts are required to improve the clinical outcome of nonsense mutation suppressors. Here, by focusing on enhancing readthrough of pathogenic nonsense mutations in the adenomatous polyposis coli (APC) tumor suppressor gene, we show that disturbing the protein translation initiation complex, as well as targeting other stages of the protein translation machinery, enhances both antibiotic and non-antibiotic-mediated readthrough of nonsense mutations. These findings strongly increase our understanding of the mechanisms involved in nonsense mutation readthrough and facilitate the development of novel therapeutic targets for nonsense suppression to restore protein expression from a large variety of disease-causing mutated transcripts.

Mechanistic insights into cancer drug resistance through optogenetic PI3K signaling hyperactivation

Hyperactivation of phosphatidylinositol 3-kinase (PI3K) signaling is a prominent feature in cancer cells. However, the mechanism underlying malignant behaviors in the state remains unknown. Here, we describe a mechanism of cancer drug resistance through the protein synthesis pathway, downstream of PI3K signaling. An optogenetic tool (named PPAP2) controlling PI3K signaling was developed. Melanoma cells stably expressing PPAP2 (A375-PPAP2) acquired resistance to a cancer drug in the hyperactivation state. Proteome analyses revealed that expression of the antiapoptotic factor tumor necrosis factor alpha-induced protein 8 (TNFAIP8) was upregulated. TNFAIP8 upregulation was mediated by protein translation from preexisting mRNA. These results suggest that cancer cells escape death via upregulation of TNFAIP8 expression from preexisting mRNA even though alkylating cancer drugs damage DNA.

Translational Regulation by eIFs and RNA Modifications in Cancer

Translation is a fundamental process in all living organisms that involves the decoding of genetic information in mRNA by ribosomes and translation factors. The dysregulation of mRNA translation is a common feature of tumorigenesis. Protein expression reflects the total outcome of multiple regulatory mechanisms that change the metabolism of mRNA pathways from synthesis to degradation. Accumulated evidence has clarified the role of an increasing amount of mRNA modifications at each phase of the pathway, resulting in translational output. Translation machinery is directly affected by mRNA modifications, influencing translation initiation, elongation, and termination or altering mRNA abundance and subcellular localization. In this review, we focus on the translation initiation factors associated with cancer as well as several important RNA modifications, for which we describe their association with cancer.

A biphenyl inhibitor of eIF4E targeting an internal binding site enables the design of cell-permeable PROTAC-degraders

The eukaryotic translation initiation factor 4E (eIF4E) is the master regulator of cap-dependent protein synthesis. Overexpression of eIF4E is implicated in diseases such as cancer, where dysregulation of oncogenic protein translation is frequently observed. eIF4E has been an attractive target for cancer treatment. Here we report a high-resolution X-ray crystal structure of eIF4E in complex with a novel inhibitor (i4EG-BiP) that targets an internal binding site, in contrast to the previously described inhibitor, 4EGI-1, which binds to the surface. We demonstrate that i4EG-BiP is able to displace the scaffold protein eIF4G and inhibit the proliferation of cancer cells. We provide insights into how i4EG-BiP is able to inhibit cap-dependent translation by increasing the eIF4E-4E-BP1 interaction while diminishing the interaction of eIF4E with eIF4G. Leveraging structural details, we designed proteolysis targeted chimeras (PROTACs) derived from 4EGI-1 and i4EG-BiP and characterized these on biochemical and cellular levels. We were able to design PROTACs capable of binding eIF4E and successfully engaging Cereblon, which targets proteins for proteolysis. However, these initial PROTACs did not successfully stimulate degradation of eIF4E, possibly due to competitive effects from 4E-BP1 binding. Our results highlight challenges of targeted proteasomal degradation of eIF4E that must be addressed by future efforts.

Thiocoraline mediates drug resistance in MCF-7 cells via PI3K/Akt/BCRP signaling pathway

Thiocoraline, a depsipeptide bisintercalator with potent antitumor activity, was first isolated from marine actinomycete Micromonospora marina. It possesses an intense toxicity to MCF-7 cells at nanomolar concentrations in a dose-dependent manner evaluated by MTT assay and crystal violet staining. We established a human breast thiocoraline-resistant cancer subline of MCF-7/thiocoraline (MCF-7/T) to investigate the expression variation of breast cancer resistance proteins (BCRP) and its subsequent influence on drug resistance. Colony-forming assay showed that the MCF-7 cells proliferated faster than the MCF-7/T cells in vitro. Western blot analysis demonstrated that thiocoraline increased the phosphorylation of Akt. Additionally, the sensitivity of tumor cells to thiocoraline was reduced with a concurrent rise in phosphorylation level of Akt and of BCRP expression.These studies indicated that thiocoraline probably mediated the drug resistance via PI3K/Akt/BCRP signaling pathway. MK-2206 dihydrochloride, a selective phosphorylation inhibitor of Akt, significantly decreased MCF-7 cell viability under exposure to thiocoraline compared to the control. However, it was not obviously able to decrease MCF-7/T cell viability when cells were exposed to thiocoraline.

4EGI-1 represses cap-dependent translation and regulates genome-wide translation in malignant pleural mesothelioma

Deregulation of cap-dependent translation has been implicated in the malignant transformation of numerous human tissues. 4EGI-1, a novel small-molecule inhibitor of cap-dependent translation, disrupts formation of the eukaryotic initiation factor 4F (eIF4F) complex. The effects of 4EGI-1-mediated inhibition of translation initiation in malignant pleural mesothelioma (MPM) were examined. 4EGI-1 preferentially inhibited cell viability and induced apoptosis in MPM cells compared to normal mesothelial (LP9) cells. This effect was associated with hypophosphorylation of 4E-binding protein 1 (4E-BP1) and decreased protein levels of the cancer-related genes, c-myc and osteopontin. 4EGI-1 showed enhanced cytotoxicity in combination with pemetrexed or gemcitabine. Translatome-wide polysome microarray analysis revealed a large cohort of genes that were translationally regulated upon treatment with 4EGI-1. The 4EGI-1-regulated translatome was negatively correlated to a previously published translatome regulated by eIF4E overexpression in human mammary epithelial cells, which is in agreement with the notion that 4EGI-1 inhibits the eIF4F complex. These data indicate that inhibition of the eIF4F complex by 4EGI-1 or similar translation inhibitors could be a strategy for treating mesothelioma. Genome wide translational profiling identified a large cohort of promising target genes that should be further evaluated for their potential significance in the treatment of MPM.