GSK3 regulates the expressions of human and mouse c-Myb via different mechanisms

Efficacy of Silkworm Pupae Extract on Muscle Strength and Mass in Middle-Aged and Older Individuals: A Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVES

We investigated the efficacy and safety of silkworm pupae extract (SWP) consumption for 12 weeks on muscle mass and strength in middle-aged and older individuals with relatively low skeletal muscle mass who do regular low-intensity exercise.

DESIGN

A randomized double-blinded placebo-controlled trial.

PARTICIPANTS

The study was conducted with 54 participants with relatively low skeletal muscle mass (SMM) (64.4 ± 6.1 years; body mass index, 23.8 ± 2.4 kg/m2).

INTERVENTION AND MEASUREMENTS

Participants were randomly assigned to one of two groups: 1000 mg of SWP/day plus regular exercise (SWP group, n=27) or placebo plus regular exercise (placebo group, n=27). All participants were required to engage in 30-60 minutes/day of walking for ≥3 days/week for 12 weeks. The primary outcome was knee extension/flexion strength (Nm), measured at the velocity of 60°/s. Secondary outcomes included body composition, biomarkers (creatine kinase and creatinine), handgrip strength, and quality of life questionnaire.

RESULTS

Both the intention-to-treat (ITT) and per-protocol (PP) analyses revealed no significant impact of SWP on knee strength compared to the placebo group over 12 weeks. On the other hand, the SWP group had significantly greater increases in right-handgrip strength by 1.94 kg (95% CI: 0.08-3.79; p = 0.041) and left-handgrip strength by 1.83 kg (0.25-3.41; p = 0.024) compared to the placebo group in the ITT population, after 12 weeks. Moreover, in the PP population, the SWP group revealed an even greater increase in right-handgrip strength by 2.07 kg (0.15-3. 98; p = 0.035) and left-handgrip strength by 2.21 kg (0.60-3.83; p = 0.008) for the 12-week period. However, this study resulted in a failure to detect significant differences in the body composition, biomarkers, quality of life questionnaire, physical activity, and caloric intake between the groups. None of the participants in the SWP group experienced any significant adverse events. In the placebo group, two participants experienced urticaria and allergic side effects, leading to their withdrawal from the study and two exhibited elevated levels of liver enzyme and increased diastolic blood pressure, respectively at 12 weeks.

CONCLUSION

SWP, in addition to low-intensity exercise, may enhance handgrip strengths in middle-aged and older adults with relatively lower SMM. Future studies need to use a large sample size over longer periods to validate our findings. This trial was registered at clinicaltrials.gov as NCT04994054.

Recent advances in SCF ubiquitin ligase complex: Clinical implications

F-box proteins, which are subunit recruiting modules of SCF (SKP1-Cullin 1-F-box protein) E3 ligase complexes, play critical roles in the development and progression of human malignancies through governing multiple cellular processes including cell proliferation, apoptosis, invasion and metastasis. Moreover, there are emerging studies that lead to the development of F-box proteins inhibitors with promising therapeutic potential. In this article, we describe how F-box proteins including but not restricted to well-established Fbw7, Skp2 and β-TRCP, are involved in tumorigenesis. However, in-depth investigation is required to further explore the mechanism and the physiological contribution of undetermined F-box proteins in carcinogenesis. Lastly, we suggest that targeting F-box proteins could possibly open new avenues for the treatment and prevention of human cancers.

Tetraspanin CD9 participates in dysmegakaryopoiesis and stromal interactions in primary myelofibrosis

Primary myelofibrosis is characterized by clonal myeloproliferation, dysmegakaryopoiesis, extramedullary hematopoiesis associated with myelofibrosis and altered stroma in the bone marrow and spleen. The expression of CD9, a tetraspanin known to participate in megakaryopoiesis, platelet formation, cell migration and interaction with stroma, is deregulated in patients with primary myelofibrosis and is correlated with stage of myelofibrosis. We investigated whether CD9 participates in the dysmegakaryopoiesis observed in patients and whether it is involved in the altered interplay between megakaryocytes and stromal cells. We found that CD9 expression was modulated during megakaryocyte differentiation in primary myelofibrosis and that cell surface CD9 engagement by antibody ligation improved the dysmegakaryopoiesis by restoring the balance of MAPK and PI3K signaling. When co-cultured on bone marrow mesenchymal stromal cells from patients, megakaryocytes from patients with primary myelofibrosis displayed modified behaviors in terms of adhesion, cell survival and proliferation as compared to megakaryocytes from healthy donors. These modifications were reversed after antibody ligation of cell surface CD9, suggesting the participation of CD9 in the abnormal interplay between primary myelofibrosis megakaryocytes and stroma. Furthermore, silencing of CD9 reduced CXCL12 and CXCR4 expression in primary myelofibrosis megakaryocytes as well as their CXCL12-dependent migration. Collectively, our results indicate that CD9 plays a role in the dysmegakaryopoiesis that occurs in primary myelofibrosis and affects interactions between megakaryocytes and bone marrow stromal cells. These results strengthen the "bad seed in bad soil" hypothesis that we have previously proposed, in which alterations of reciprocal interactions between hematopoietic and stromal cells participate in the pathogenesis of primary myelofibrosis.

Regulation of GATA-binding protein 2 levels via ubiquitin-dependent degradation by Fbw7: involvement of cyclin B-cyclin-dependent kinase 1-mediated phosphorylation of THR176 in GATA-binding protein 2

A GATA family transcription factor, GATA-binding protein 2 (GATA2), participates in cell growth and differentiation of various cells, such as hematopoietic stem cells. Although its expression level is controlled by transcriptional induction and proteolytic degradation, the responsible E3 ligase has not been identified. Here, we demonstrate that F-box/WD repeat-containing protein 7 (Fbw7/Fbxw7), a component of Skp1, Cullin 1, F-box-containing complex (SCF)-type E3 ligase, is an E3 ligase for GATA2. GATA2 contains a cell division control protein 4 (Cdc4) phosphodegron (CPD), a consensus motif for ubiquitylation by Fbw7, which includes Thr(176). Ectopic expression of Fbw7 destabilized GATA2 and promoted its proteasomal degradation. Substitution of threonine 176 to alanine in GATA2 inhibited binding with Fbw7, and the ubiquitylation and degradation of GATA2 by Fbw7 was suppressed. The CPD kinase, which mediates the phosphorylation of Thr(176), was cyclin B-cyclin-dependent kinase 1 (CDK1). Moreover, depletion of endogenous Fbw7 stabilized endogenous GATA2 in K562 cells. Conditional Fbw7 depletion in mice increased GATA2 levels in hematopoietic stem cells and myeloid progenitors at the early stage. Increased GATA2 levels in Fbw7-conditional knock-out mice were correlated with a decrease in a c-Kit high expressing population of myeloid progenitor cells. Our results suggest that Fbw7 is a bona fide E3 ubiquitin ligase for GATA2 in vivo.

FBW7 increases drug sensitivity to cisplatin in human nasopharyngeal carcinoma by downregulating the expression of multidrug resistance-associated protein

F-box/WD repeat-containing protein 7 (FBW7) is a member of the F-box protein family that regulates cell cycle progression and cell growth and differentiation. FBW7 also functions as a tumor suppressor. A cisplatin (CDDP)-based multidrug chemotherapy regimen is standard for nasopharyngeal carcinoma (NPC), but drug resistance is an increasing problem. Here, we evaluated the relationship between FBW7 and multidrug resistance-associated protein (MRP), and its correlation with drug resistance in NPC, and explored the mechanism underlying drug resistance to CDDP in this disease. We used cell viability assays, Western blotting, and small interfering RNA (siRNA) interference to investigate the underlying mechanism underlying CDDP resistance in a NPC cell line. The expression of FBW7 and MRP was detected by Western blotting after siRNA interference in the CDDP-resistant NPC cell line, CNE2-CDDP. The 3-(4 5-dimethyl-2-thiazolyl)-2 5-diphenyl-2-H-tetrazolium bromide (MTT) assay was used to evaluate drug sensitivity of various types of antitumor drugs, including paclitaxel (PCX), CDDP, fluorouracil (5-FU), and vincristine (VCR). We found that siRNA-mediated upregulation of FBW7 significantly increased CDDP chemosensitivity. The IC50 values of CDDP in siRNA-FBW7-CNE2-CDDP and FBW7-CNE2-CDDP-NC cells were 2.485 ± 0.155 and 4.867 ± 0.442 μmol/mL, respectively. The IC50 values of PCX, CDDP, 5-FU, and VCR were significantly decreased in siRNA-FBW7-CNE2 than in FBW7-CNE2-NC (3.46 ± 0.14 vs. 46.21 ± 6.03 μmol/mL; 3.76 ± 0.54 vs. 39.45 ± 0.96 μmol/mL; 2.14 ± 1.67 vs. 28.76 ± 1.89 μmol/mL; 4.43 ± 0.89 vs. 87.90 ± 3.45 μmol/mL, respectively). The IC50 of CDDP was significantly less in siRNA-FBW7-CNE2-CDDP than in FBW7-CNE2-CDDP-NC. The level of FBW7 expression in CNE2 cells was correlated with CDDP chemosensitivity. siRNA-mediated upregulation of FBW7 expression downregulated the expression of MRP, significantly increasing drug sensitivity in CNE2 cells.

Aberrant regulation of FBW7 in cancer

FBW7 (F-box and WD repeat domain-containing 7) or Fbxw7 is a tumor suppressor, which promotes the ubiquitination and subsequent degradation of numerous oncoproteins including Mcl-1, Cyclin E, Notch, c- Jun, and c-Myc. In turn, FBW7 is regulated by multiple upstream factors including p53, C/EBP-δ, EBP2, Pin1, Hes-5 and Numb4 as well as by microRNAs such as miR-223, miR-27a, miR-25, and miR-129-5p. Given that the Fbw7 tumor suppressor is frequently inactivated or deleted in various human cancers, targeting FBW7 regulators is a promising anti-cancer therapeutic strategy.

Situational awareness: regulation of the myb transcription factor in differentiation, the cell cycle and oncogenesis

This review summarizes the mechanisms that control the activity of the c-Myb transcription factor in normal cells and tumors, and discusses how c-Myb plays a role in the regulation of the cell cycle. Oncogenic versions of c-Myb contribute to the development of leukemias and solid tumors such as adenoid cystic carcinoma, breast cancer and colon cancer. The activity and specificity of the c-Myb protein seems to be controlled through changes in protein-protein interactions, so understanding how it is regulated could lead to the development of novel therapeutic strategies.

SCF(FBXW7α) modulates the intra-S-phase DNA-damage checkpoint by regulating Polo like kinase-1 stability

The intra-S-checkpoint is essential to control cell progression through S phase under normal conditions and in response to replication stress. When DNA lesions are detected, replication fork progression is blocked allowing time for repair to avoid genomic instability and the risk of cancer. DNA replication initiates at many origins of replication in eukaryotic cells, where a series of proteins form pre-replicative complexes (pre-RCs) that are activated to become pre-initiation complexes and ensure a single round of replication in each cell cycle. PLK1 plays an important role in the regulation of DNA replication, contributing to the regulation of pre-RCs formation by phosphorylating several proteins, under both normal and stress conditions. Here we report that PLK1 is ubiquitinated and degraded by SCFFBXW7α/proteasome. Moreover, we identified a new Cdc4 phosphodegron in PLK1, conserved from yeast to humans, whose mutation prevents PLK1 destruction. We established that endogenous SCFFBXW7α degrades PLK1 in the G1 and S phases of an unperturbed cell cycle and in S phase following UV irradiation. Furthermore, we showed that FBXW7α overexpression or UV irradiation prevented the loading of proteins onto chromatin to form pre-RCs and, accordingly, reduced cell proliferation. We conclude that PLK1 degradation mediated by SCFFBXW7α modulates the intra-S-phase checkpoint.

Stress-induced phosphorylation of Thr486 in c-Myb by p38 mitogen-activated protein kinases attenuates conjugation of SUMO-2/3

c-Myb plays an essential role in regulation of properly balanced hematopoiesis through transcriptional regulation of genes directly controlling cellular processes such as proliferation, differentiation, and apoptosis. The transcriptional activity and protein levels of c-Myb are strictly controlled through post-translational modifications such as phosphorylation, acetylation, ubiquitination, and SUMOylation. Conjugation of small ubiquitin-like modifier (SUMO) proteins has been shown to suppress the transcriptional activity of c-Myb. SUMO-1 modifies c-Myb under physiological conditions, whereas SUMO-2/3 conjugation was reported in cells under stress. Because stress also activates several cellular protein kinases, we investigated whether phosphorylation of c-Myb changes in stressed cells and whether a mutual interplay exists between phosphorylation and SUMOylation of c-Myb. Here we show that several types of environmental stress induce a rapid change in c-Myb phosphorylation. Interestingly, the phosphorylation of Thr(486), located in close proximity to SUMOylation site Lys(499) of c-Myb, is detected preferentially in nonSUMOylated protein and has a negative effect on stress-induced SUMOylation of c-Myb. Stress-activated p38 MAPKs phosphorylate Thr(486) in c-Myb, attenuate its SUMOylation, and increase its proteolytic turnover. Stressed cells expressing a phosphorylation-deficient T486A mutant demonstrate decreased expression of c-Myb target genes Bcl-2 and Bcl-xL and accelerated apoptosis because of increased SUMOylation of the mutant protein. These results suggest that phosphorylation-dependent modulation of c-Myb SUMOylation may be important for proper response of cells to stress. In summary, we have identified a novel regulatory interplay between phosphorylation and SUMOylation of c-Myb that regulates its activity in stressed cells.

Targeting self-renewal pathways in myeloid malignancies

A fundamental property of hematopoietic stem cells (HSCs) is the ability to self-renew. This is a complex process involving multiple signal transduction cascades which control the fine balance between self-renewal and differentiation through transcriptional networks. Key activators/regulators of self-renewal include chemokines, cytokines and morphogens which are expressed in the bone marrow niche, either in a paracrine or autocrine fashion, and modulate stem cell behaviour. Increasing evidence suggests that the downstream signaling pathways induced by these ligands converge at multiple levels providing a degree of redundancy in steady state hematopoiesis. Here we will focus on how these pathways cross-talk to regulate HSC self-renewal highlighting potential therapeutic windows which could be targeted to prevent leukemic stem cell self-renewal in myeloid malignancies.

Novel players in multiple myeloma pathogenesis: role of protein kinases CK2 and GSK3

Multiple myeloma (MM) is an incurable plasma cell malignancy, which causes a significant morbidity due to organ damage and bone tissue destruction. In recent years, novel drugs have become available for MM therapy thanks to a more deepened knowledge of this disease's pathogenesis. The perspective of employing targeted therapies has considerably changed the expectations on the clinical outcome for patients affected by this malignancy and among the targetable molecules identified for MM therapy are several protein kinases, which have been proven to play relevant roles in supporting malignant plasma cell growth by regulating critical signaling cascades and by sustaining oncogenic mechanisms. Protein kinase CK2 (formerly known as casein kinase 2) and GSK3 (glycogen synthase kinase 3) are two multifaceted serine-threonine kinases whose task in the pathogenesis of malignant cell growth is increasingly emerging both in solid and blood tumors. In hematologic malignancies, CK2 and GSK3 have been shown to play an oncogenic function in chronic and acute leukemias as well as in MM. They have been demonstrated to act by impinging on pivotal signaling pathways that control malignant clone growth. We will herein briefly review the more recent advancements on the role of these two kinases in regulating the NF-κB, STAT3 and endoplasmic reticulum (ER) stress/unfolded protein response (UPR) signaling in MM and discuss the rationale of using small selective inhibitors as a therapeutic strategy to hamper the growth of malignant plasma cells or to improve the MM-associated bone disease.

Tumor suppressor functions of FBW7 in cancer development and progression

FBW7 (F-box and WD repeat domain-containing 7) has been characterized as an onco-suppressor protein in human cancers. Recent studies have also shown that FBW7 exerts its anti-tumor function primarily by promoting the degradation of various oncoproteins, through which FBW7 regulates cellular proliferation, differentiation and causes genetic instability. In this review, we will discuss the role of FBW7 downstream substrates and how dysregulation of Fbw7-mediated proteolysis of these substrates contributes to tumorigenesis. Additionally, we will also summarize the currently available various Fbw7-knockout mouse models that support Fbw7 as a tumor suppressor gene in the development and progression of human malignancies.

The two faces of FBW7 in cancer drug resistance

Chemotherapy is an important therapeutic approach for cancer treatment. However, drug resistance is an obstacle that often impairs the successful use of chemotherapies. Therefore, overcoming drug resistance would lead to better therapeutic outcomes for cancer patients. Recently, studies by our own and other groups have demonstrated that there is an intimate correlation between the loss of the F-box and WD repeat domain-containing 7 (FBW7) tumor suppressor and the incurring drug resistance. While loss of FBW7 sensitizes cancer cells to certain drugs, FBW7-/- cells are more resistant to other types of chemotherapies. FBW7 exerts its tumor suppressor function by promoting the degradation of various oncoproteins that regulate many cellular processes, including cell cycle progression, cellular metabolism, differentiation, and apoptosis. Since loss of the FBW7 tumor suppressor is linked to drug resistance, FBW7 may represent a novel therapeutic target to increase drug sensitivity of cancer cells to conventional chemotherapeutics. This paper thus focuses on the new functional aspects of FBW7 in drug resistance.