Fragile X mental retardation protein regulates skeletal muscle stem cell activity by regulating the stability of Myf5 mRNA.

BACKGROUND: Regeneration of adult tissues relies on adult stem cells that are primed to enter a differentiation program, while typically remaining quiescent. In mouse skeletal muscle, these features are reconciled by multiple translational control mechanisms that ensure primed muscle stem cells (MuSCs) are not activated. In quiescent MuSCs, this concept is illustrated by reversible microRNA silencing of Myf5 translation, mediated by microRNA-31 and fragile X mental retardation protein (FMRP). METHODS: In this work, we take advantage of FMRP knockout (Fmr1 -/- ) mice to support the role for FMRP in maintaining stem cell properties of the MuSC. We compare the activity of MuSCs in vivo after acute injury and engraftment, as well as ex vivo during culture. We use RNA immunoprecipitation and 3'UTR poly-adenine (poly(A)) length assays to assess the impact of FMRP on the stability of transcripts for myogenic regulatory factors. RESULTS: We show that RNA-binding FMRP is required to maintain the MuSC pool. More specifically, FMRP is required for stem cell properties of muscle stem cells, which include MuSC capacity to prime the myogenic program, their self-renewal, and their capacity to efficiently regenerate muscle. We provide evidence that FMRP regulation of MuSC activity occurs in part by the capacity of FMRP to directly bind Myf5 transcripts and impact rates of Myf5 deadenylation. CONCLUSIONS: Our results provide further evidence supporting a role for post-transcriptional silencing platforms by RNA-binding proteins in maintaining stemness properties of adult stem cells. In addition, deregulated MuSC activity in the absence of Fmr1 may have implications for fragile X syndrome, which is associated with muscle hypotonia during infancy.

Multiple myeloma cells promote migration of bone marrow mesenchymal stem cells by altering their translation initiation.

The role of the bone marrow microenvironment in multiple myeloma pathogenesis and progression is well recognized. Indeed, we have shown that coculture of bone marrow mesenchymal stem cells from normal donors and multiple myeloma cells comodulated translation initiation. Here, we characterized the timeline of mesenchymal stem cells conditioning by multiple myeloma cells, the persistence of this effect, and the consequences on cell phenotype. Normal donor mesenchymal stem cells were cocultured with multiple myeloma cell lines (U266, ARP1) (multiple myeloma-conditioned mesenchymal stem cells) (1.5 h,12 h, 24 h, 48 h, and 3 d) and were assayed for translation initiation status (eukaryotic translation initiation factor 4E; eukaryotic translation initiation factor 4G; regulators: mechanistic target of rapamycin, MNK, 4EBP; targets: SMAD family 5, nuclear factor κB, cyclin D1, hypoxia inducible factor 1, c-Myc) (immunoblotting) and migration (scratch assay, inhibitors). Involvement of mitogen-activated protein kinases in mesenchymal stem cell conditioning and altered migration was also tested (immunoblotting, inhibitors). Multiple myeloma-conditioned mesenchymal stem cells were recultured alone (1-7 d) and were assayed for translation initiation (immunoblotting). Quantitative polymerase chain reaction of extracted ribonucleic acid was tested for microRNAs levels. Mitogen-activated protein kinases were activated within 1.5 h of coculture and were responsible for multiple myeloma-conditioned mesenchymal stem cell translation initiation status (an increase of >200%, P < 0.05) and elevated migration (16 h, an increase of >400%, P < 0.05). The bone marrow mesenchymal stem cells conditioned by multiple myeloma cells were reversible after only 1 d of multiple myeloma-conditioned mesenchymal stem cell culture alone. Decreased expression of microRNA-199b and microRNA-125a (an increase of <140%, P < 0.05) in multiple myeloma-conditioned mesenchymal stem cells supported elevated migration. The time- and proximity-dependent conditioning of normal donor mesenchymal stem cells in our model points to a dynamic interaction between multiple myeloma cells and the bone marrow niche, which causes profound changes in the nonmalignant bone marrow constituents. Future studies are warranted to identify clinically relevant means of blocking this crosstalk and improving multiple myeloma therapy.

Phosphorylation of eIF2α Is a Translational Control Mechanism Regulating Muscle Stem Cell Quiescence and Self-Renewal.

Regeneration of adult tissues depends on somatic stem cells that remain quiescent yet are primed to enter a differentiation program. The molecular pathways that prevent activation of these cells are not well understood. Using mouse skeletal muscle stem cells as a model, we show that a general repression of translation, mediated by the phosphorylation of translation initiation factor eIF2α at serine 51 (P-eIF2α), is required to maintain the quiescent state. Skeletal muscle stem cells unable to phosphorylate eIF2α exit quiescence, activate the myogenic program, and differentiate, but do not self-renew. P-eIF2α ensures in part the robust translational silencing of accumulating mRNAs that is needed to prevent the activation of muscle stem cells. Additionally, P-eIF2α-dependent translation of mRNAs regulated by upstream open reading frames (uORFs) contributes to the molecular signature of stemness. Pharmacological inhibition of eIF2α dephosphorylation enhances skeletal muscle stem cell self-renewal and regenerative capacity.

Secretome of human bone marrow mesenchymal stem cells: an emerging player in lung cancer progression and mechanisms of translation initiation.

Non-small cell lung cancer (NSCLC) remains the most common cause of cancer-related death worldwide. Patients presenting with advanced-stage NSCLC have poor prognosis, while metastatic spread accounts for >70 % of patient's deaths. The major advances in the treatment of lung cancer have brought only minor improvements in survival; therefore, novel strategic treatment approaches are urgently needed. Accumulating data allocate a central role for the cancer microenvironment including mesenchymal stem cells (MSCs) in acquisition of drug resistance and disease relapse. Furthermore, studies indicate that translation initiation factors are over expressed in NSCLC and negatively impact its prognosis. Importantly, translation initiation is highly modulated by microenvironmental cues. Therefore, we decided to examine the effect of bone marrow MSCs (BM-MSCs) from normal donors on NSCLC cell lines with special emphasis on translation initiation mechanism in the crosstalk. We cultured NSCLC cell lines with BM-MSC conditioned media (i.e., secretome) and showed deleterious effects on the cells' proliferation, viability, death, and migration. We also demonstrated reduced levels of translation initiation factors implicated in cancer progression [eukaryotic translation initiation factor 4E (eIF4E) and eukaryotic translation initiation factor 4GI (eIF4GI)], their targets, and regulators. Finally, we outlined a mechanism by which BM-MSCs' secretome affected NSCLC's mitogen-activated protein kinase (MAPK) signaling pathway, downregulated the cell migration, and diminished translation initiation factors' levels. Taken together, our study demonstrates that there is direct dialogue between the BM-MSCs' secretome and NSCLC cells that manipulates translation initiation and critically affects cell fate. We suggest that therapeutic approach that will sabotage this dialogue, especially in the BM microenvironment, may diminish lung cancer metastatic spread and morbidity and improve the patient's life quality.

Multiple myeloma and bone marrow mesenchymal stem cells' crosstalk: Effect on translation initiation.

Multiple myeloma (MM) malignant plasma cells reside in the bone marrow (BM) and convert it into a specialized pre-neoplastic niche that promotes the proliferation and survival of the cancer cells. BM resident mesenchymal stem cells (BM-MSCs) are altered in MM and in vitro studies indicate their transformation by MM proximity is within hours. The response time frame suggested that protein translation may be implicated. Thus, we assembled a co-culture model of MM cell lines with MSCs from normal donors (ND) and MM patients to test our hypothesis. The cell lines (U266, ARP-1) and BM-MSCs (ND, MM) were harvested separately after 72 h of co-culture and assayed for proliferation, death, levels of major translation initiation factors (eIF4E, eIF4GI), their targets, and regulators. Significant changes were observed: BM-MSCs (ND and MM) co-cultured with MM cell lines displayed elevated proliferation and death as well as increased expression/activity of eIF4E/eIF4GI; MM cell lines co-cultured with MM-MSCs also displayed higher proliferation and death rates coupled with augmented translation initiation factors; in contrast, MM cell lines co-cultured with ND-MSCs did not display elevated proliferation only death and had no changes in eIF4GI levels/activity. eIF4E expression was increased in one of the cell lines. Our study demonstrates that there is direct dialogue between the MM and BM-MSCs populations that includes translation initiation manipulation and critically affects cell fate. Future research should be aimed at identifying therapeutic targets that may be used to minimize the collateral damage to the cancer microenvironment and limit its recruitment into the malignant process. © 2015 Wiley Periodicals, Inc.

Multiple myeloma proteostasis can be targeted via translation initiation factor eIF4E.

Intensive protein synthesis is a unique and differential trait of the multiple myeloma (MM) cells. Previously we showed that tetraspanin overexpression in MM cell lines attenuated mTOR and PI3K cascades, induced protein synthesis, activated unfolded protein response (UPR), and caused autophagic death, all suggesting breach of proteostasis. Here we assessed the role of translation initiation in the tetraspanin­induced MM cell death with emphasis on eIF4E translation initiation factor. We showed tetraspanins attenuated peIF4E and its targets [c­Myc, cyclin D1 (cycD1)]; eIF4E attenuation was Akt-dependent. eIF4E inhibition in MM cells [bone marrow (BM), lines] by siRNA and/or the anti­viral drug and competitive eIF4E inhibitor ribavirin (RBV) deleteriously affected MM cells in a similar manner to the overexpression of tetraspanins. Furthermore, combined application of RBV and velcade had a synergistic anti­MM effect. Our results demonstrate that breach of proteostasis via eIF4E inhibition is an attractive therapeutic approach that may be relatively easily achieved by employing RBV, making this strategy readily translatable into the clinic.

Combined inhibition of Hsp90 and the proteasome affects NSCLC proteostasis and attenuates cell migration.

Lung cancer remains the most common cause of cancer-related death worldwide. This malignancy is a complex disease, and it is important to identify potential biological targets, the blockade of which would affect multiple downstream signaling cascades. A growing number of reports recognize novel therapeutic targets in the protein homeostasis network responsible for generating and protecting the protein fold. The heat shock protein 90 (Hsp90) is an essential molecular chaperon involved in the posttranslational folding and stability of proteins. It is required for conformational maturation of multiple oncogenic kinases that drive signal transduction and proliferation of cancer cells. However, in the case of unfolded protein accumulation endoplasmic reticulum (ER) stress is induced and several response pathways such as proteasome functions are activated. The ubiquitin-proteasome system orchestrates the turnover of innumerable cellular proteins. Here, we suggest that the therapeutic efficacy of Hsp90 inhibition may be augmented by coadministering proteasome inhibitor on human non-small-cell lung cancer (NSCLC) cell lines. Indeed, we showed that coadministration of the Hsp90 inhibitor 17-demethoxygeldanamycin (17-DMAG) and proteasome inhibitor (velcade) induced ER stress evidenced by increased unfolded protein response markers. The consequences were evident in multiple aspects of the NSCLC phenotype: reduced viability and cell count, increased apoptotic cell death, and most profoundly, synergistically decreased cell motility. Our findings provide proof-of-concept that targeting ER homeostasis is therapeutically beneficial in NSCLC cell lines.

Targeting eIF4GI translation initiation factor affords an attractive therapeutic strategy in multiple myeloma.

BACKGROUND: Deregulation of protein synthesis is integral to the malignant phenotype and translation initiation is the rate limiting stage. Therefore, eIF4F translation initiation complex components are attractive therapeutic targets. METHODS: Protein lysates of myeloma cells (cell lines/patients' bone marrow samples) untreated/treated with bevacizumab were assayed for eIF4GI expression, regulation (NQO1/proteosome dependent fragmentation) (WB, Dicumarol, qPCR) and targets (WB). eIF4GI was inhibited by knockdown and 4EGI-1. Cells were tested for viability (ELISA), death (FACS) and eIF4GI targets (WB). RESULTS: Previously, we have shown that manipulation of VEGF in myeloma cells attenuated eIF4E dependent translation initiation. Here we assessed the significance of eIF4GI to MM cells. We demonstrated increased expression of eIF4GI in myeloma cells and its attenuation upon VEGF inhibition attributed to elevated NQO1/proteasome dependent fragmentation and diminished mRNA levels. Knockdown of eIF4GI was deleterious to myeloma cells phenotype and expression of specific molecular targets (SMAD5/ERα/HIF1α/c-Myc). Finally, we showed that the small molecule 4EGI-1 inhibits eIF4GI and causes a reduction in expression of its molecular targets in myeloma. CONCLUSION: Our findings substantiate that translation initiation of particular targets in MM is contingent on the function of eIF4GI, critical to cell phenotype, and mark it as a viable target for pharmacological intervention.

ER homeostasis and motility of NSCLC cell lines can be therapeutically targeted with combined Hsp90 and HDAC inhibitors.

BACKGROUND AND OBJECTIVE: Lung cancer remains the most common cause of cancer-related death in the world for which novel systemic treatments are urgently needed. Protein homeostasis that regulates protein levels and their fold is critical for cancer cell proliferation and survival. A complex network of cellular organelles and signaling cascades is involved in control of protein homeostasis including endoplasmic reticulum (ER). Thus, proteins in control of ER homeostasis are increasingly recognized as potential therapeutic targets. Molecular chaperone heat shock protein 90 (Hsp90) and histone deacetylase (HDAC) play an important role in ER homeostasis. Previous studies demonstrate that Hsp90 and HDAC inhibitors are individually functional against lung cancer. In this work we suggested that combined Hsp90 and HDAC inhibitors may elevate ER stress thereby enhancing the anti non small lung cancer (NSCLC) activity. METHODS AND RESULTS: Using an in vitro cell line model we demonstrated that 17-DMAG (HSP90 inhibitor) co-administration with PTACH (HDAC inhibitor) caused elevated ER stress (immunoblotting) (more than 110%↑, p < 0.05) accompanied by apoptotic cell death (Annexin V) (7-21%↑, p < 0.05). Moreover, 17-DMAG/PTACH treated cells lost the ability to migrate (scratch test) (57-85%↓ of scratch closure, p < 0.05). CONCLUSIONS: Our findings provide proof-of-concept that targeting ER homeostasis is therapeutically beneficial in lung cancer cell lines. Indeed, the elevated ER stress caused by 17-DMAG/PTACH combined treatment leads to increased cell death of NSCLC cell lines compared to the application of the drugs separately.

Tetraspanins stimulate protein synthesis in myeloma cell lines.

Intensive protein synthesis is a unique and differential trait of multiple myeloma (MM) cells. Previously we showed that tetraspanin (CD81, CD82) overexpression in MM cell lines attenuated Akt/mTOR cascades, activated UPR, and caused autophagic death, suggesting breach of protein homeostasis. Here, we explored the role of protein synthesis in the tetraspanin-induced MM cell death. Contrary to attenuation of the major metabolic regulator, mTOR we determined elevated steady-state levels of protein in CD81N1/CD82N1 transfected MM lines (RPMI-8226, CAG). Elevated levels of immunoglobulins supported increased protein production in RPMI-8226. Changes in cell morphology consistent with elevated protein synthesis were also determined (cell, nuclei, and nucleoli sizes and ratios). Increased levels of phospho-rpS6 and decreased levels of phospho-AMPK were consistent with increased translation but independent of mTOR. Involvement of p38 and its role in tetraspanin induced translation and cell death were demonstrated. Microarray analyses of tetraspanin transfected MM cell lines revealed activation of protein synthesis signaling cascades and signals implicated in ribosome biogenesis (snoRNAs). Finally, we showed tetraspanins elevated protein synthesis was instrumental to MM cells' death. This work explores and demonstrates that excessive protein translation can be detrimental to MM cell lines and therefore may present a therapeutic target. Proteostasis is particularly important in MM because it integrates the high levels of protein production unique to myeloma cells with critically important microenvironmental cues. We suggest that increasing translation may be the path of least resistance in MM and thus may afford a novel platform for strategically designed therapy.

Bevacizumab attenuates major signaling cascades and eIF4E translation initiation factor in multiple myeloma cells.

Multiple myeloma (MM), a malignancy of plasma cells, remains fatal despite introduction of novel therapies, partially due to humoral factors, including vascular endothelial growth factor (VEGF), in their microenvironment. The aim of this study was to explore the efficacy of anti-VEGF treatment with bevacizumab directly on MM cells. Particular attention was directed to the affect of VEGF inhibition on protein translation initiation. Experiments were conducted on MM cells (lines, bone marrow (BM) samples) cultured on plastic. Inhibition of VEGF was achieved with the clinically employed anti-VEGF antibody, bevacizumab, as a platform and its consequences on viability, proliferation, and survival was assessed. VEGF downstream signals of established importance to MM cell biology were assayed as well, with particular emphasis on translation initiation factor eIF4E. We showed that blocking VEGF is deleterious to the MM cells and causes cytostasis. This was evidenced in MM cell lines, as well as in primary BM samples (BM MM). A common bevacizumab-induced attenuation of critical signaling effectors was determined: VEGFR1, mTOR, c-Myc, Akt, STAT3, (cell lines) and eIF4E translation initiation factor (lines and BM). ERK1/2 displayed a variegated response to bevacizumab (lines). Utilizing a constitutively Akt-expressing MM model, we showed that the effect of bevacizumab on viability and eIF4E status is Akt-dependent. Of note, the effect of bevacizumab was achieved with high concentrations (2 mg/ml), but was shown to be specific. These findings demonstrate that bevacizumab has a direct influence on major pathways critically activated in MM that is independent from its established effect on angiogenesis. The cytostatic effect of VEGF inhibition on MM cells underscores its potential in combined therapy, and our findings, regarding its influence on translation initiation, suggest that drugs that unbalance cellular proteostasis may be particularly effective.

Bronchoscopic balloon dilatation of tracheobronchial stenosis: long-term follow-up.

OBJECTIVES: Bronchoscopic balloon dilatation (BBD) has become a valuable tool in the treatment of tracheobronchial stenosis (TBS). The objective of this study was to assess the short- and long-term effects of BBD. METHODS: A retrospective study that included all patients with confirmed, symptomatic stenosis, who underwent BBD between 2002 and 2008. A total of 92 BBD procedures were performed in 35 patients at our institute. Lung function studies were recorded for all patients before, immediately after and 1 month following the BBD. Long-term follow-up was for a mean of 33+/-4 months. RESULTS: All patients had initial success, including increased airway dimensions and symptom relief. No complications were noted related to BBD. Forced expiratory volume after one second (FEV(1)) was significantly increased after BBD (10.5%, p=0.03). These effects persisted for at least 1 month. Long-term follow-up, however, demonstrated the need for stent placement in 25 of 35 patients (71%), 210+/-91 days after BBD. Ten of 35 patients died 456+/-119 days after BBD due to progression of primary disease; all deaths were unrelated to the BBD procedures. CONCLUSIONS: BBD is a safe method that offers immediate symptomatic relief in both tracheal and bronchial stenosis. However, BBD is a temporary measure, as many patients will require definitive or additional treatment with laser or stent placement.

Tetraspanins affect myeloma cell fate via Akt signaling and FoxO activation.

Myeloma cell interface with microenvironmental components is critical to cell growth and survival and perceived as a major obstacle for effective disease treatment. Hence, molecules that facilitate cell-cell and cell-ECM interactions are particularly important. We have previously shown that re-expression of membranal microdomain organizers, tetraspanins CD81 and CD82, caused myeloma cell death. Herein we demonstrate that the anti-myeloma effect of CD81/CD82 involves a down-regulation of Akt, activation of FoxO transcription factors and a decrease in active mTOR and mTOR/rictor. We go on to show in a breast cancer cell line model that Akt dependent cells are more sensitive to the tetraspanin overexpression. Moreover, expression of a constitutively active Akt increased survival of CD81/CD82 transfected myeloma cell lines. Akt and mTOR afford attractive therapeutic targets in cancer yet, due to pathways' interactions, inhibitors of mTOR frequently activate Akt and vise versa. Our results demonstrate co-repression of both by CD81/CD82 implying that tetraspanins may serve as "switches" modulating pathways rather than blocking a single factor and constitute a promising therapeutic strategy in Akt dependent pathological conditions. The possibility that the tetraspanins affect metabolic control is broached as well.

Promoter hypermethylation of tetraspanin members contributes to their silencing in myeloma cell lines.

Multiple myeloma (MM) cell interactions with their microenvironment modulate acquired drug resistance and disease progression. Indeed, reported aberrant gene methylation underscores the possible role of epigenetic events in MM's molecular profile. Membranal tetraspanins are often inversely correlated with cancer prognosis and metastasis, however mutations were unidentified hitherto. Their promoter characteristics and frequent down-regulation conform to transcriptional silencing by chromatin remodeling. We delineated the baseline expression of select tetraspanins in MM cell lines (RPMI 8226, U266, ARP1, ARK, CAG and EBV transformed ARH77) and fresh bone marrow samples (n = 9) for the first time and determined reduced expression of CD9, CD81 and absence of CD82. Thus, we aimed to assess their promoter methylation status. Indeed, we established CD9, CD81 and CD82 promoter methylation in MM cell lines employing methyl-specific-PCR of bisulfite modified G-DNA and PCR of G-DNA digested with methylation-sensitive restriction enzyme (Hin6I). Re-transcription of assayed genes in the cell lines following de-methylation [5-aza-2'-deoxycytidine (5-aza-dC)] confirmed the mechanistic significance of methylation to their regulation. Combined de-methylation and de-acetylation [Trichostatin A (TsA)] induced synergistic elevation of CD82 mRNA. We conclude that chromatin remodeling contributes to tetraspanin silencing in MM.