TRAF6 Silencing Attenuates Multiple Myeloma Cell Adhesion to Bone Marrow Stromal Cells

A comprehensive review of the PTEN/PI3K/Akt axis in multiple myeloma: From molecular interactions to potential therapeutic targets

Phosphatase and tensin homolog (PTEN), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt) signaling pathways contribute to the development of several cancers, including multiple myeloma (MM). PTEN is a tumor suppressor that influences the PI3K/Akt/mTOR pathway, which in turn impacts vital cellular processes like growth, survival, and treatment resistance. The current study aims to present the role of PTEN and PI3K/Akt/mTOR signaling in the development of MM and its response to treatment. In addition, the molecular interactions in MM that underpin the PI3K/Akt/mTOR pathway and address potential implications for the development of successful treatment plans are also discussed in detail. We investigate their relationship to both upstream and downstream regulators, highlighting new developments in combined therapies that target the PTEN/PI3K/Akt axis to overcome drug resistance, including the use of PI3K and mitogen-activated protein kinase (MAPK) inhibitors. We also emphasize that PTEN/PI3K/Akt pathway elements may be used in MM diagnosis, prognosis, and therapeutic targets.

Role of adhesion molecules in cancer and targeted therapy

Adhesion molecules mediate cell-to-cell and cell-to-extracellular matrix interactions and transmit mechanical and chemical signals among them. Various mechanisms deregulate adhesion molecules in cancer, enabling tumor cells to proliferate without restraint, invade through tissue boundaries, escape from immune surveillance, and survive in the tumor microenvironment. Recent studies have revealed that adhesion molecules also drive angiogenesis, reshape metabolism, and are involved in stem cell self-renewal. In this review, we summarize the functions and mechanisms of adhesion molecules in cancer and the tumor microenvironment, as well as the therapeutic strategies targeting adhesion molecules. These studies have implications for furthering our understanding of adhesion molecules in cancer and providing a paradigm for exploring novel therapeutic approaches.

The roles of E3 ubiquitin ligases in cancer progression and targeted therapy

Ubiquitination is one of the most important post-translational modifications which plays a significant role in conserving the homeostasis of cellular proteins. In the ubiquitination process, ubiquitin is conjugated to target protein substrates for degradation, translocation or activation, dysregulation of which is linked to several diseases including various types of cancers. E3 ubiquitin ligases are regarded as the most influential ubiquitin enzyme owing to their ability to select, bind and recruit target substrates for ubiquitination. In particular, E3 ligases are pivotal in the cancer hallmarks pathways where they serve as tumour promoters or suppressors. The specificity of E3 ligases coupled with their implication in cancer hallmarks engendered the development of compounds that specifically target E3 ligases for cancer therapy. In this review, we highlight the role of E3 ligases in cancer hallmarks such as sustained proliferation via cell cycle progression, immune evasion and tumour promoting inflammation, and in the evasion of apoptosis. In addition, we summarise the application and the role of small compounds that target E3 ligases for cancer treatment along with the significance of targeting E3 ligases as potential cancer therapy.

The ubiquitination-dependent and -independent functions of cereblon in cancer and neurological diseases

Cereblon (CRBN) mediates the teratogenic effect of thalidomide in zebrafish, chicken, and humans. It additionally modulates the anti-myeloma effect of the immunomodulatory drugs (IMiDs) thalidomide, lenalidomide, and pomalidomide. IMiDs bind to CRBN and recruit neo-substrates for their ubiquitination and proteasome-mediated degradation, which significantly expands the application of proteolysis-targeting chimeras (PROTACs) for targeted drug discovery. However, the underlying molecular mechanisms by which CRBN mediates the teratogenicity and anti-myeloma effect of IMiDs are not fully elucidated. Furthermore, the normal physiological functions of endogenous CRBN have not been extensively studied, which precludes the thorough assessment of side effects of the CRBN ligand-based PROTACs in the treatment of cancer and neurological diseases. To advance our understanding of the diverse functions of CRBN, in this review, we will survey the ubiquitination-dependent and -independent functions of CRBN, summarize recent advances in the discovery of constitutive and neo-substrates of CRBN, and explore the molecular functions of CRBN in cancer treatment and in the development of neurological diseases. We will also discuss the potential future directions towards the identification of CRBN substrates and interacting proteins, and CRBN-ligand-based drug discovery in the treatment of cancer and neurological diseases.

Human myeloma cell- and plasma-derived extracellular vesicles contribute to functional regulation of stromal cells

Circulating small extracellular vesicles (sEV) represent promising non-invasive biomarkers that may aid in the diagnosis and risk-stratification of multiple myeloma (MM), an incurable blood cancer. Here, we comprehensively isolated and characterized sEV from human MM cell lines (HMCL) and patient-derived plasma (psEV) by specific EV-marker enrichment and morphology. Importantly, we demonstrate that HMCL-sEV are readily internalised by stromal cells to functionally modulate proliferation. psEV were isolated using various commercial approaches and pre-analytical conditions (collection tube types, storage conditions) assessed for sEV yield and marker enrichment. Functionally, MM-psEV was shown to regulate stromal cell proliferation and migration. In turn, pre-educated stromal cells favour HMCL adhesion. psEV isolated from patients with both pre-malignant plasma cell disorders (monoclonal gammopathy of undetermined significance [MGUS]; smouldering MM [SMM]) and MM have a similar ability to promote cell migration and adhesion, suggesting a role for both malignant and pre-malignant sEV in disease progression. Proteomic profiling of MM-psEV (305 proteins) revealed enrichment of oncogenic factors implicated in cell migration and adhesion, in comparison to non-disease psEV. This study describes a protocol to generate morphologically-intact and biologically functional sEV capable of mediating the regulation of stromal cells, and a model for the characterization of tumour-stromal cross-talk by sEV in MM.

The Effect of miR-361-3p Targeting TRAF6 on Apoptosis of Multiple Myeloma Cells

microRNA-361-3p (miR-361-3p) is involved in the carcinogenesis of oral cancer and pancreatic catheter adenocarcinoma, and has anti-carcinogenic effects on non-small cell lung cancer (NSCLC). However, its effect on multiple myeloma (MM) is less reported. Here, we found that upregulating the expression of miR-361-3p inhibited MM cell viability and promoted MM apoptosis. We measured expressions of tumor necrosis factor receptor-associated factor 6 (TRAF6) and miR-361-3p in MM cells and detected the viability, colony formation rate, and apoptosis of MM cells. In addition, we measured expressions of apoptosis-related genes Bcl-2, Bax, and Cleaved caspase-3 (C caspase-3). The binding site between miR-361-3p and TRAF6 was predicted by TargetScan. Our results showed that miR-361-3p was low expressed in the plasma of MM patients and cell lines, while its overexpression inhibited viability and colony formation of MM cells and increased the cell apoptosis. Furthermore, TRAF6, which was predicted to be a target gene of miR-361-3p, was highexpressed in the plasma of patients and cell lines with MM. Rescue experiments demonstrated that the effect of TRAF6 on MM cells was opposite to that of miR-361-3p. Upregulation of miR-361-3p induced apoptosis and inhibited the proliferation of MM cells through targeting TRAF6, suggesting that miR-361-3p might be a potential target for MM therapy.

NOD-like receptor X1, tumor necrosis factor receptor-associated factor 6 and NF-κB are associated with clinicopathological characteristics in gastric cancer

Gastric cancer (GC) is a common cancer worldwide and its precise mechanism is largely unknown. The aim of the present study was to evaluate the expression levels of NOD-like receptor X1 (NLRX1), tumor necrosis factor receptor-associated factor 6 (TRAF6) and NF-κB in GC and normal gastric tissue samples to determine the association with the clinicopathological features of GC. GC and adjacent normal gastric tissues from 60 patients with GC were analyzed using immunohistochemistry and western blotting analysis. In addition, the association between NLRX1, TRAF6 and NF-κB expression levels were investigated by Spearman's correlation analysis. The results revealed that NLRX1 protein expression levels were downregulated in the GC tissues compared with the normal gastric tissues (P<0.05). Conversely, TRAF6 and NF-κB protein expression levels were upregulated in the GC tissues compared with the normal gastric tissues (P<0.05). A significant difference was identified between GC patients with high and low expression levels of each protein in the tumor size, vascular invasion, neural invasion, lymph node metastasis, differentiation, gross stage and clinical stage. In addition, a negative correlation was observed between NLRX1 and TRAF6, and NLRX1 and NF-κB expression levels, while a positive correlation was observed between TRAF6 and NF-κB expression levels. In conclusion, NLRX1 expression levels were discovered to be downregulated in GC tissues. The expression levels of NLRX1, TRAF6 and NF-κB were also significantly associated with the clinicopathological characteristics of GC, and the aforementioned results indicated that NLRX1 may be a biomarker in assessing GC.

The relationship between TRAF6 and tumors

Tumor necrosis factor receptor (TNFR)-related factors (TRAFs) are important linker molecules in the tumor necrosis factor superfamily (TNFSF) and the Toll-like/interleukin-1 receptor (TLR/ILR) superfamily. There are seven members: TRAF1-TRAF7, among those members, tumor necrosis factor receptor-associated factor 6 (TRAF6) is upregulated in various tumors, which has been related to tumorigenesis and development. With the in-depth study of the relationship between TRAF6 and different types of tumors, TRAF6 has oncogenic characteristics involved in tumorigenesis, tumor development, invasion, and metastasis through various signaling pathways, therefore, targeting TRAF6 has provided a novel strategy for tumor treatment. This review summarizes and analyzes the role of TRAF6 in tumorigenesis and tumor development in combination with the current research on TRAF6 and tumors.

Ex Vivo Models Simulating the Bone Marrow Environment and Predicting Response to Therapy in Multiple Myeloma

Multiple myeloma (MM) remains incurable despite the abundance of novel drugs. As it has been previously shown, preclinical 2D models fail to predict disease progression due to their inability to simulate the microenvironment of the bone marrow. In this review, we focus on 3D models and present all currently available ex vivo MM models that fulfil certain criteria, such as development of complex 3D environments using patients' cells and ability to test different drugs in order to assess personalized MM treatment efficacy of various regimens and combinations. We selected models representing the top-notch ex vivo platforms and evaluated them in terms of cost, time-span, and feasibility of the method. Finally, we propose where such a model can be more informative in a patient's treatment timeline. Overall, advanced 3D preclinical models are very promising as they may eventually offer the opportunity to precisely select the optimal personalized treatment for each MM patient.

Resveratrol induces depletion of TRAF6 and suppresses prostate cancer cell proliferation and migration

Although the early diagnosis of prostate cancer (PCa) enhances life expectancy with a 5-year survival rate of 100 %, metastasized-PCa is the fundamental reason for death by PCa, hence requires an advanced and target-directed treatment strategy. Metastasis is considered to be initiated with the epithelial-mesenchymal transition (EMT) event in which tumor cells change their epithelial characteristics into mesenchymal form and exacerbates the cancer progression. Herein, we investigated the effect and mechanism of resveratrol function in PCa cell proliferation and migration and reported that TNF-receptor associated factor 6 (TRAF6), an unconventional E3 ligase, is a key mediator of resveratrol function to inhibit PCa cell growth and proliferation and targeted for lysosomal degradation by resveratrol. MTT and cell counting demonstrated that resveratrol inhibited the viability and proliferation in DU145 and PC3 cells. Resveratrol (50 μM) mediated the degradation of TRAF6 which in turn facilitated repression of the NF-κB pathway. Also, wound healing and transwell migration assays and level of EMT-related proteins showed that resveratrol used TRAF6, at least in part to inhibit cell migration. Overexpression of TRAF6 augmented EMT in PCa by upregulating the expression of transcription factor SLUG. Moreover, TRAF6 overexpression was closely associated with EMT process through the NF-κB pathway. Our exploration exhibited that resveratrol may inhibit EMT through the TRAF6/NF-κB/SLUG axis. Altogether, this study represents that TRAF6 acts as an intermediary of resveratrol action to suppress PCa cell proliferation and migration, and concerns future attention to obtain as a therapeutic target for the treatment of PCa.

Rapamycin Attenuates High Glucose-Induced Inflammation Through Modulation of mTOR/NF-κB Pathways in Macrophages

Background: The NLRP3 inflammasome is one of the key contributors to impaired wound healing in diabetes. In this study, we assessed the role of rapamycin on high glucose-induced inflammation in THP-1-derived macrophages and investigated the underlying signaling mechanisms. Methods: THP-1-derived macrophages were treated with high glucose to induce NLRP3 inflammasome activation. The cells were pretreated with rapamycin, BAY 11-7082, or PDTC before exposure to HG. mTOR, NF-κB, and NLRP3 inflammasome expression were measured by western blotting. Results: We found that rapamycin reduced NLRP3 inflammasome activation in macrophages. Rapamycin reduced NLRP3 inflammasome activation by inhibiting mTOR phosphorylation and NF-κB activation. Moreover, mTOR siRNA inhibited NF-κB activation, leading to the suppression of NLRP3 inflammasome activation. Conclusion: Rapamycin can ameliorate high glucose-induced NLRP3 inflammasome activation by attenuating the mTOR/NF-κB signaling pathway in macrophages. Rapamycin may act as a possible therapeutic option for high glucose-induced inflammatory response in impaired wound healing in the future.