p27Kip1 and p21Cip1 collaborate in the regulation of transcription by recruiting cyclin-Cdk complexes on the promoters of target genes

Strategy of combining CDK4/6 inhibitors with other therapies and mechanisms of resistance

Cell cycle-dependent protein kinase 4/6 (CDK4/6) is a crucial kinase that regulates the cell cycle, essential for cell division and proliferation. Hence, combining CDK4/6 inhibitors with other anti-tumor drugs is a pivotal clinical strategy. This strategy can efficiently inhibit the growth and division of tumor cells, reduce the side effects, and improve the quality of life of patients by reducing the dosage of combined anticancer drugs. Furthermore, the combination therapy strategy of CDK4/6 inhibitors could ameliorate the drug resistance of combined drugs and overcome the CDK4/6 resistance caused by CDK4/6 inhibitors. Various tumor treatment strategies combined with CDK4/6 inhibitors have entered the clinical trial stage, demonstrating their substantial clinical potential. This study reviews the research progress of CDK4/6 inhibitors from 2018 to 2022, the related resistance mechanism of CDK4/6 inhibitors, and the strategy of combination medication.

IRE1α pathway: A potential bone metabolism mediator

Osteoblasts and osteoclasts collaborate in bone metabolism, facilitating bone development, maintaining normal bone density and strength, and aiding in the repair of pathological damage. Endoplasmic reticulum stress (ERS) can disrupt the intracellular equilibrium between osteoclast and osteoblast, resulting in dysfunctional bone metabolism. The inositol-requiring enzyme-1α (IRE1α) pathway-the most conservative unfolded protein response pathway activated by ERS-is crucial in regulating cell metabolism. This involvement encompasses functions such as inflammation, autophagy, and apoptosis. Many studies have highlighted the potential roles of the IRE1α pathway in osteoblasts, chondrocytes, and osteoclasts and its implication in certain bone-related diseases. These findings suggest that it may serve as a mediator for bone metabolism. However, relevant reviews on the role of the IRE1α pathway in bone metabolism remain unavailable. Therefore, this review aims to explore recent research that elucidated the intricate roles of the IRE1α pathway in bone metabolism, specifically in osteogenesis, chondrogenesis, osteoclastogenesis, and osteo-immunology. The findings may provide novel insights into regulating bone metabolism and treating bone-related diseases.

Targeting PEG10 as a novel therapeutic approach to overcome CDK4/6 inhibitor resistance in breast cancer

BACKGROUND

Breast cancer is the global leading cancer burden in women and the hormone receptor-positive (HR+) subtype is a major part of breast cancer. Though cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors are highly effective therapy for HR+ subtype, acquired resistance is inevitable in most cases. Herein, we investigated the paternally expressed gene 10 (PEG10)-associated mechanism of acquired resistance to CDK4/6 inhibitors.

METHODS

Palbociclib-resistant cells were generated by exposing human HR+ breast cancer cell lines to palbociclib for 7-9 months. In vitro mechanistic study and in vivo xenograft assay were performed. For clinical relevance, public mRNA microarray data sets of early breast cancer were analyzed and PEG10 immunohistochemical staining was performed using pre-CDK4/6 inhibitor tumor samples.

RESULTS

We observed that PEG10 was significantly upregulated in palbociclib-resistant cells. Ectopic overexpression of PEG10 in parental cells caused CDK4/6 inhibitor resistance and enhanced epithelial-mesenchymal transition (EMT). On the contrary, PEG10-targeting siRNA or antisense oligonucleotides (ASOs) combined with palbociclib synergistically inhibited proliferation of palbociclib-resistant cells and growth of palbociclib-resistant xenograft in mice and suppressed EMT as well. The mechanistic study confirmed that high PEG10 expression suppressed p21, a natural CDK inhibitor, and SIAH1, a post-translational degrader of ZEB1, augmenting CDK4/6 inhibitor resistance. Then PEG10 siRNA combined with palbociclib suppressed cell cycle progression and EMT via activating p21 and SIAH1, respectively. Consequently, combined PEG10 inhibition and palbociclib overcame CDK4/6 inhibitor resistance. Furthermore, high PEG10 expression was significantly associated with a shorter recurrence-free survival (RFS) based on public mRNA expression data. In pre-CDK4/6 inhibitor treatment tissues, PEG10 positivity by IHC also showed a trend toward a shorter progression-free survival (PFS) with CDK4/6 inhibitor. These results support clinical relevance of PEG10 as a therapeutic target.

CONCLUSIONS

We demonstrated a novel PEG10-associated mechanism of CDK4/6 inhibitor resistance. We propose PEG10 as a promising therapeutic target for overcoming PEG10-associated resistance to CDK4/6 inhibitors.

Patterns of senescence and apoptosis during development of branchial arches, epibranchial placodes, and pharyngeal pouches

BACKGROUND

Many developmental processes are coregulated by apoptosis and senescence. However, there is a lack of data on the development of branchial arches, epibranchial placodes, and pharyngeal pouches, which harbor epibranchial signaling centers.

RESULTS

Using immunohistochemical, histochemical, and 3D reconstruction methods, we show that in mice, senescence and apoptosis together may contribute to the invagination of the branchial clefts and the deepening of the cervical sinus floor, in antagonism to the proliferation acting in the evaginating branchial arches. The concomitant apoptotic elimination of lateral line rudiments occurs in the absence of senescence. In the epibranchial placodes, senescence and apoptosis appear to (1) support invagination or at least indentation by immobilizing the margins of the centrally proliferating pit, (2) coregulate the number and fate of Pax8+ precursors, (3) progressively narrow neuroblast delamination sites, and (4) contribute to placode regression. Putative epibranchial signaling centers in the pharyngeal pouches are likely deactivated by rostral senescence and caudal apoptosis.

CONCLUSIONS

Our results reveal a plethora of novel patterns of apoptosis and senescence, some overlapping, some complementary, whose functional contributions to the development of the branchial region, including the epibranchial placodes and their signaling centers, can now be tested experimentally.

Tumor-Suppressive Functions of the Aryl Hydrocarbon Receptor (AhR) and AhR as a Therapeutic Target in Cancer

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor involved in regulating a wide range of biological responses. A diverse array of xenobiotics and endogenous small molecules bind to the receptor and drive unique phenotypic responses. Due in part to its role in mediating toxic responses to environmental pollutants, AhR activation has not been traditionally viewed as a viable therapeutic approach. Nonetheless, the expression and activation of AhR can inhibit the proliferation, migration, and survival of cancer cells, and many clinically approved drugs transcriptionally activate AhR. Identification of novel select modulators of AhR-regulated transcription that promote tumor suppression is an active area of investigation. The development of AhR-targeted anticancer agents requires a thorough understanding of the molecular mechanisms driving tumor suppression. Here, we summarized the tumor-suppressive mechanisms regulated by AhR with an emphasis on the endogenous functions of the receptor in opposing carcinogenesis. In multiple different cancer models, the deletion of AhR promotes increased tumorigenesis, but a precise understanding of the molecular cues and the genetic targets of AhR involved in this process is lacking. The intent of this review was to synthesize the evidence supporting AhR-dependent tumor suppression and distill insights for development of AhR-targeted cancer therapeutics.

Alcohol extracts of Chinese bayberry branch induce S-phase arrest and apoptosis in HepG2 cells

The alcohol extracts of Chinese bayberry (Myrica rubra) branches (MRBE) are rich in flavonoids which have a variety of medicinal benefits, but their effects on human HepG2 were unknown. In this study, the effects of MRBE on HepG2 cell growth and its potential for inhibiting cancer were explored. The results displayed that MRBE inhibited HepG2 proliferation both by arresting cells in S phase and promoting apoptosis. Quantitative reverse-transcription PCR (qRT-PCR), western blotting, and immunofluorescence showed that MRBE induced S-phase arrest by upregulating p21, which in turn downregulated cyclin and cyclin-dependent kinase messenger RNA (mRNA) and protein. Apoptosis was induced by blocking the expression of BCL-2 and suppression of the Raf/ERK1 signaling pathways. These results indicated that MRBE may have the potential for treatment of human liver cancer, highlighting novel approaches for developing new pharmacological tools for the treatment of this deadly type cancer. Meanwhile, it provides a new direction for the medicinal added values of Chinese bayberry, which helped to broaden the diversified development of its industry chain.

CDK4/6 inhibitor resistance mechanisms and treatment strategies (Review)

In recent years, the incidence rate of breast cancer has increased year by year, and it has become a major threat to the health of women globally. Among all breast cancer subtypes, the hormone receptor (HR)⁺/human epidermal growth factor receptor 2 (HER2)⁻ luminal subtype breast cancer is the most common form of breast cancer. Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, the hotspots in the field of targeted therapy for breast cancer, have proved to exhibit a good effect on patients with HR⁺/HER2⁻ breast cancer in a number of clinical trials, but the problem of drug resistance is inevitable. At present, three specific CDK4/6 inhibitors (palbociclib, ribociclib and abemaciclib) have been approved by the USA Food and Drug Administration for the first-line treatment of HR⁺/HER2⁻ breast cancer. The drug resistance mechanisms of CDK4/6 inhibitors can be divided into cell cycle-specific resistance and cell cycle non-specific resistance. With the discovery of the drug resistance mechanism of CDK4/6 inhibitors, various targeted strategies have been proposed. The present review mainly discusses the mechanism of CDK4/6 inhibitors, drug resistance mechanisms and treatment strategies after resistance.

From cyclins to CDKIs: Cell cycle regulation of skeletal muscle stem cell quiescence and activation

After extensive proliferation during development, the adult skeletal muscle cells remain outside the cell cycle, either as post-mitotic myofibers or as quiescent muscle stem cells (MuSCs). Despite its terminally differentiated state, adult skeletal muscle has a remarkable regeneration potential, driven by MuSCs. Upon injury, MuSC quiescence is reversed to support tissue growth and repair and it is re-established after the completion of muscle regeneration. The distinct cell cycle states and transitions observed in the different myogenic populations are orchestrated by elements of the cell cycle machinery. This consists of i) complexes of cyclins and Cyclin-Dependent Kinases (CDKs) that ensure cell cycle progression and ii) their negative regulators, the Cyclin-Dependent Kinase Inhibitors (CDKIs). In this review we discuss the roles of these factors in developmental and adult myogenesis, with a focus on CDKIs that have emerging roles in stem cell functions.

The cyclin-dependent kinase inhibitor p27Kip1 interacts with the aryl hydrocarbon receptor and negatively regulates its transcriptional activity

p27^Kip1 functions to coordinate cell cycle progression through the inhibition of cyclin-dependent kinase (CDK) complexes. p27^Kip1 also exerts distinct activities beyond CDK-inhibition, including functioning as a transcriptional regulator. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor with diverse biological roles. The regulatory inputs that control AhR-mediated transcriptional responses are an active area of investigation. AhR was previously established as a direct regulator of p27^Kip1 transcription. Here, we report the physical interaction of AhR and p27^Kip1 and show that p27^Kip1 expression negatively regulates AhR-mediated transcription. p27^Kip1 knockout cells display increased AhR nuclear localisation and significantly higher expression of AhR target genes. This work thus identifies new regulatory cross-talk between p27^Kip1 and AhR.

Circular RNA circCRKL inhibits the proliferation of acute myeloid leukemia cells via the miR-196a-5p/miR-196b-5p/p27 axis

As a new type of non-coding RNA, the role of circular RNA (circRNA) in various diseases and tumors has received considerable attention. Studies have shown that circRNAs play an important role in the progression of acute myeloid leukemia (AML) via different mechanisms. However, the specific underlying molecular mechanism of circRNAs in the proliferation of AML cells remians unclear. This study aimed to clarify the biological role and mechanism of circCRKL in AML. The results indicated low circCRKL expression in AML cell lines and samples. Moreover, the overexpression of circCRKL inhibited the proliferation and colony-forming ability of AML cells, while its silencing promoted them. In addition, bioinformatics tools and luciferase assays revealed that circCRKL could sponge miR-196a-5p and miR-196b-5p to promote the expression of p27. Furthermore, circCRKL inhibited AML cell proliferation via the miR-196a-5p/miR-196b-5p/p27 axis, suggesting a potential new target for AML therapy.

Catalpol Protects ARPE-19 Cells against Oxidative Stress via Activation of the Keap1/Nrf2/ARE Pathway

Oxidative damage to retinal pigment epithelial (RPE) has been identified as one of the major regulatory factors in the pathogenesis of age-related macular degeneration (AMD). Catalpol is an iridoid glucoside compound that has been found to possess potential antioxidant activity. In the present study, we aimed to investigate the protective effect of catalpol on RPE cells under oxidative stress and to elucidate the potential molecular mechanism involved. We found that catalpol significantly attenuated hydrogen peroxide (H₂O₂)-induced cytotoxicity, G0/G1 phase cell cycle arrest, and apoptosis in RPE cells. The overproduction of reactive oxygen species (ROS) and malondialdehyde (MDA) stimulated by oxidative stress and the corresponding reductions in antioxidant glutathione (GSH) and superoxide dismutase (SOD) levels were largely reversed by catalpol pretreatment. Moreover, catalpol pretreatment markedly activated the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and its downstream antioxidant enzymes, catalase (CAT), heme oxygenase-1 (HO-1), and NADPH dehydrogenase (NQO1). It also increased the expression levels of cyclin E, Bcl-2, cyclin A, and cyclin-dependent kinase 2 (CDK2) and decreased the expression levels of Bax, Fas, cleaved PARP, p-p53, and p21 cleaved caspase-3, 8, and 9. The oxidative stress-induced formation of the Keap1/Nrf2 complex in the cytoplasm was significantly blocked by catalpol pretreatment. These results indicate that catalpol protected RPE cells from oxidative stress through a mechanism involving the activation of the Keap1/Nrf2/ARE pathways and the inactivation of oxidative stress-mediated pathways of apoptosis.

Establishing and maintaining fertility: the importance of cell cycle arrest

In this review, Frost et al. summarize the current knowledge on the Cip/Kip family of cyclin-dependent kinase inhibitors in mouse gonad development and highlight new roles for cell cycle inhibitors in controlling and maintaining female fertility.

Development of the ovary or testis is required to establish reproductive competence. Gonad development relies on key cell fate decisions that occur early in embryonic development and are actively maintained. During gonad development, both germ cells and somatic cells proliferate extensively, a process facilitated by cell cycle regulation. This review focuses on the Cip/Kip family of cyclin-dependent kinase inhibitors (CKIs) in mouse gonad development. We particularly highlight recent single-cell RNA sequencing studies that show the heterogeneity of cyclin-dependent kinase inhibitors. This diversity highlights new roles for cell cycle inhibitors in controlling and maintaining female fertility.

BET bromodomain-containing epigenetic reader proteins regulate vascular smooth muscle cell proliferation and neointima formation

AIMS

Recent studies revealed that the bromodomain and extra-terminal (BET) epigenetic reader proteins resemble key regulators in the underlying pathophysiology of cancer, diabetes, or cardiovascular disease. However, whether they also regulate vascular remodelling processes by direct effects on vascular cells is unknown. In this study, we investigated the effects of the BET proteins on human smooth muscle cell (SMC) function in vitro and neointima formation in response to vascular injury in vivo.

METHODS AND RESULTS

Selective inhibition of BETs by the small molecule (+)-JQ1 dose-dependently reduced proliferation and migration of SMCs without apoptotic or toxic effects. Flow cytometric analysis revealed a cell cycle arrest in the G0/G1 phase in the presence of (+)-JQ1. Microarray- and pathway analyses revealed a substantial transcriptional regulation of gene sets controlled by the Forkhead box O (FOXO1)1-transcription factor. Silencing of the most significantly regulated FOXO1-dependent gene, CDKN1A, abolished the antiproliferative effects. Immunohistochemical colocalization, co-immunoprecipitation, and promoter-binding ELISA assay data confirmed that the BET protein BRD4 directly binds to FOXO1 and regulates FOXO1 transactivational capacity. In vivo, local application of (+)-JQ1 significantly attenuated SMC proliferation and neointimal lesion formation following wire-induced injury of the femoral artery in C57BL/6 mice.

CONCLUSION

Inhibition of the BET-containing protein BRD4 after vascular injury by (+)-JQ1 restores FOXO1 transactivational activity, subsequent CDKN1A expression, cell cycle arrest and thus prevents SMC proliferation in vitro and neointima formation in vivo. Inhibition of BET epigenetic reader proteins might thus represent a promising therapeutic strategy to prevent adverse vascular remodelling.

Effects of SPATA6 on proliferation, apoptosis and steroidogenesis of Hu sheep Leydig cells in vitro

This study aimed to investigate the expression pattern of spermatogenesis associated protein 6 (SPATA6) in Hu sheep testis and to ascertain the effects of SPATA6 on sheep Leydig cells (LCs) function linked to spermatogenesis. In the present study, we detected a 1970 bp cDNA fragment of SPATA6 included a 1467 bp coding sequence which encoded 487 amino acids. Meanwhile, sheep SPATA6 shared 51.70%-97.41% amino acid sequences with its orthologs compared with other species. In addition, SPATA6 was highly expressed in testis and localized in cytoplasm and nucleus of LCs as well as spermatogenic cells at different stages. Compared to the negative control (NC), SPATA6 interference promoted apoptosis of LCs with the increase of BAX/BCL-2 mRNA and protein levels, while the results of SPATA6 overexpression were on the contrary. Meanwhile, cell cycle was blocked at G2/M phase and CDK1 and CCNB1 were down-regulated after SPATA6 interference. SPATA6 overexpression induced cell cycle transfer G0/G1 into S and G2/M phase with upregulation of CDK1, CDK4, CCND1 and CCND2. Moreover, the secretion of testosterone hormone and the expression of StAR in LCs with SPATA6 overexpression were significantly promoted. Overall, our data suggest that SPATA6 is an important functional molecule of spermatogenesis, via regulating the proliferation, apoptosis and testosterone biosynthesis of Hu sheep LCs. These findings will enhance the understanding of the roles of SPATA6 in sheep spermatogenesis.

Activation of DNA damage response signaling in mammalian cells by ionizing radiation

Cellular responses to DNA damage are fundamental to preserve genomic integrity during various endogenous and exogenous stresses. Following radiation therapy and chemotherapy, this DNA damage response (DDR) also determines development of carcinogenesis and therapeutic outcome. In humans, DNA damage activates a robust network of signal transduction cascades, driven primarily through phosphorylation events. These responses primarily involve two key non-redundant signal transducing proteins of phosphatidylinositol 3-kinase-like (PIKK) family - ATR and ATM, and their downstream kinases (hChk1 and hChk2). They further phosphorylate effectors proteins such as p53, Cdc25A and Cdc25C which function either to activate the DNA damage checkpoints and cell death mechanisms, or DNA repair pathways. Identification of molecular pathways that determine signaling after DNA damage and trigger DNA repair in response to differing types of DNA lesions allows for a far better understanding of the consequences of radiation and chemotherapy on normal and tumor cells. Here we highlight the network of DNA damage response pathways that are activated after treatment with different types of radiation. Further, we discuss regulation of cell cycle checkpoint and DNA repair processes in the context of DDR in response to radiation.

Cell cycle exit during bortezomib-induced osteogenic differentiation of mesenchymal stem cells was mediated by Xbp1s-upregulated p21Cip1 and p27Kip1

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into a variety of cell types. Bortezomib, the first approved proteasome inhibitor used for the treatment of multiple myeloma (MM), has been shown to induce osteoblast differentiation, making it beneficial for myeloma bone disease. In the present study, we aimed to investigate the effects and underlying mechanisms of bortezomib on the cell cycle during osteogenic differentiation. We confirmed that low doses of bortezomib can induce MSCs towards osteogenic differentiation, but high doses are toxic. In the course of bortezomib-induced osteogenic differentiation, we observed cell cycle exit characterized by G₀ /G₁ phase cell cycle arrest with a significant reduction in cell proliferation. Additionally, we found that the cell cycle exit was tightly related to the induction of the cyclin-dependent kinase inhibitors p21^Cip1 and p27^Kip1 . Notably, we further demonstrated that the up-regulation of p21^Cip1 and p27^Kip1 is transcriptionally dependent on the bortezomib-activated ER stress signalling branch Ire1α/Xbp1s. Taken together, these findings reveal an intracellular pathway that integrates proteasome inhibition, osteogenic differentiation and the cell cycle through activation of the ER stress signalling branch Ire1α/Xbp1s.

Artesunate promotes the proliferation of neural stem/progenitor cells and alleviates Ischemia-reperfusion Injury through PI3K/Akt/FOXO-3a/p27kip1 signaling pathway

Stroke is one of the leading causes of death worldwide that also result in long-term disability. Endogenous neural stem/progenitor cells (NSPCs) within subventricular (SVZ) and dentate gyrus (DG) zone, stimulated by cerebral infarction, can promote neural function recovery. However, the proliferation of eNSPCs triggered by ischemia is not enough to induce neural repair, which may contribute to the permanent disability in stroke patients. In this study, our results showed that following the treatment with artesunate (ART, 150 mg/kg), the functional recovery was significantly improved, the infarct volume was notably reduced, and the expression of Nestin, a proliferation marker of NSPCs in the infarcted cortex, was also increased. Additionally, the proliferative activity of NSPCs with or without oxygen-glucose deprivation/reperfusion was significantly promoted by ART treatment, and the therapeutic concentration was 0.8 μmol/L (without OGD/R) or 0.4 μmol/L (with OGD/R) in the in vitro model. Furthermore, the effects of ART can be abolished by the treatment of PI3K inhibitor wortmannin. The expression levels of related molecules in PI3K/Akt/FOXO-3a/p27^kip1 signaling pathway (p-AKT, p-FOXO-3a, p27^kip1) were examined using western blotting. The results suggested ART could inhibit the transcriptional function of FOXO-3a by inducing its phosphorylation, subsequently downregulating p27^kip1 and enhancing neural stem cell proliferation in the infarcted cortex via PI3K/AKT signaling, further alleviating ischemia-reperfusion injury after ischemic stroke.

The CDK inhibitor p57Kip2 enhances the activity of the transcriptional coactivator FHL2

The eukaryotic cell cycle is negatively regulated by cyclin-dependent kinase inhibitors (CKIs). p57^Kip2 is a member of the Cip/Kip family of CKIs and frequently inactivated by genomic mutations associated with human overgrowth disorders. There is increasing evidence for p57 to control cellular processes in addition to cell cycle and CDK regulation including transcription, apoptosis, migration or development. In order to obtain molecular insights to unknown functions of p57, we performed a protein interaction screen. We identified the transcription regulator four-and-a-half LIM-only protein 2 (FHL2) as a novel p57-binding protein. Co-immunoprecipitation and reporter gene assays were used to elucidate the physiological and functional relevance of p57/FHL2 interaction. We found in cancer cells that endogenous p57 and FHL2 are in a complex. We observed a substantial induction of established FHL2-regulated gene promoters by p57 in reporter gene experiments and detected strong induction of the intrinsic transactivation activity of FHL2. Treatment of cells with histone deacetylase (HDAC) inhibitors and binding of exogenous FHL2 to HDACs indicated repression of FHL2 transcription activity by HDACs. In the presence of the HDAC inhibitor sodium butyrate activation of FHL2 by p57 is abrogated suggesting that p57 shares a common pathway with HDAC inhibitors. p57 competes with HDACs for FHL2 binding which might partly explain the mechanism of FHL2 activation by p57. These results suggest a novel function of p57 in transcription regulation.

p27 as a Transcriptional Regulator: New Roles in Development and Cancer

p27 binds and inhibits cyclin-CDK to arrest the cell cycle. p27 also regulates other processes including cell migration and development independent of its cyclin-dependent kinase (CDK) inhibitory action. p27 is an atypical tumor suppressor-deletion or mutational inactivation of the gene encoding p27, CDKN1B, is rare in human cancers. p27 is rarely fully lost in cancers because it can play both tumor suppressive and oncogenic roles. Until recently, the paradigm was that oncogenic deregulation results from either loss of growth restraint due to excess p27 proteolysis or from an oncogenic gain of function through PI3K-mediated C-terminal p27 phosphorylation, which disrupts the cytoskeleton to increase cell motility and metastasis. In cancers, C-terminal phosphorylation alters p27 protein-protein interactions and shifts p27 from CDK inhibitor to oncogene. Recent data indicate p27 regulates transcription and acts as a transcriptional coregulator of cJun. C-terminal p27 phosphorylation increases p27-cJun recruitment to and action on target genes to drive oncogenic pathways and repress differentiation programs. This review focuses on noncanonical, CDK-independent functions of p27 in migration, invasion, development, and gene expression, with emphasis on how transcriptional regulation by p27 illuminates its actions in cancer. A better understanding of how p27-associated transcriptional complexes are regulated might identify new therapeutic targets at the interface between differentiation and growth control.

Clb3-centered regulations are recurrent across distinct parameter regions in minimal autonomous cell cycle oscillator designs

Some biological networks exhibit oscillations in their components to convert stimuli to time-dependent responses. The eukaryotic cell cycle is such a case, being governed by waves of cyclin-dependent kinase (cyclin/Cdk) activities that rise and fall with specific timing and guarantee its timely occurrence. Disruption of cyclin/Cdk oscillations could result in dysfunction through reduced cell division. Therefore, it is of interest to capture properties of network designs that exhibit robust oscillations. Here we show that a minimal yeast cell cycle network is able to oscillate autonomously, and that cyclin/Cdk-mediated positive feedback loops (PFLs) and Clb3-centered regulations sustain cyclin/Cdk oscillations, in known and hypothetical network designs. We propose that Clb3-mediated coordination of cyclin/Cdk waves reconciles checkpoint and oscillatory cell cycle models. Considering the evolutionary conservation of the cyclin/Cdk network across eukaryotes, we hypothesize that functional ("healthy") phenotypes require the capacity to oscillate autonomously whereas dysfunctional (potentially "diseased") phenotypes may lack this capacity.

p57Kip2 is a master regulator of human adipose derived stem cell quiescence and senescence

Although human adipose derived stem cells (hADSCs) hold great promises for regenerative medicine, their key biological properties remain poorly understood. In particular, proliferation defects resulted from deep quiescence (dormancy) and senescence represent a major hurdle in hADSC production and clinical application. We have developed a model system for mechanistic dissection of hADSC quiescence and senescence. p57^Kip2, a major CDK inhibitor, was highly expressed in quiescent and senescent hADSCs but its level quickly declined upon stem cell activation. p57^Kip2 overexpression induced quiescence in spite of proliferative signals and its knockdown promoted cell cycle reentry even with induction of quiescence presumably through modulating the CDK2-CyclinE1 complex. Given its key role in quiescence and senescence, p57^Kip2 may be exploited for innovative strategies to amplify hADSCs of high quality for clinics.

Roles of vitamin D and its receptor in the proliferation and apoptosis of luteinised granulosa cells in the goat

The objective of this study was to investigate the dose-dependent effect of 1α,25-(OH)2VD3 (Vit D3) on invitro proliferation of goat luteinised granulosa cells (LGCs) and to determine the underlying mechanisms of its action by overexpressing and silencing vitamin D receptor (VDR) in LGCs. Results showed that VDR was prominently localised in GCs and theca cells (TCs) and its expression increased with follicle diameter, but was lower in atretic follicles than in healthy follicles. The proliferation rate of LGCs was significantly higher in the Vit D3-treated groups than in the control group, with the highest proliferation rate observed in the 10nM group; this was accompanied by changes in the expression of cell cycle-related genes. These data indicate that Vit D3 affects LGC proliferation in a dose-dependent manner. Contrary to the VDR knockdown effects, its overexpression upregulated and downregulated cell cycle- and apoptosis-related genes respectively; moreover, supplementation with 10nM of Vit D3 significantly enhanced these effects. These results suggest that changes in VDR expression patterns in LGCs may be associated with follicular development by regulation of cell proliferation and apoptosis. These findings will enhance the understanding of the roles of Vit D3 and VDR in goat ovarian follicular development.

Transcriptional activation of CBFβ by CDK11p110 is necessary to promote osteosarcoma cell proliferation

BACKGROUND

Aberrant expression of cyclin-dependent protein kinases (CDK) is a hallmark of cancer. CDK11 plays a crucial role in cancer cell growth and proliferation. However, the molecular mechanisms of CDK11 and CDK11 transcriptionally regulated genes are largely unknown.

METHODS

In this study, we performed a global transcriptional analysis using gene array technology to investigate the transcriptional role of CDK11 in osteosarcoma. The promoter luciferase assay, chromatin immunoprecipitation assay, and Gel Shift assay were used to identify direct transcriptional targets of CDK11. Clinical relevance and function of core-binding factor subunit beta (CBFβ) were further accessed in osteosarcoma.

RESULTS

We identified a transcriptional role of protein-DNA interaction for CDK11p110, but not CDK11p58, in the regulation of CBFβ expression in osteosarcoma cells. The CBFβ promoter luciferase assay, chromatin immunoprecipitation assay, and Gel Shift assay confirmed that CBFβ is a direct transcriptional target of CDK11. High expression of CBFβ is associated with poor outcome in osteosarcoma patients. Expression of CBFβ contributes to the proliferation and metastatic behavior of osteosarcoma cells.

CONCLUSIONS

These data establish CBFβ as a mediator of CDK11p110 dependent oncogenesis and suggest that targeting the CDK11- CBFβ pathway may be a promising therapeutic strategy for osteosarcoma treatment.

Characterization of the human E2F4 promoter region and its response to 12-O-tetradecanoylphorbol-13-acetate

The E2F transcription factors (TFs), which control the progression of the cell cycle in response to DNA-damage and various stresses, are known to interact with a tumour suppressor, Retinoblastoma 1 (RB1). We previously showed that the response of the human RB1 promoter to a 12-O-tetradecanoylphorbol-13-acetate (TPA) in HL-60 cells is mediated by a duplicated GGAA motif, which is also present in the 5'-upstream of the E2F family genes. The motifs are especially rich in the 5'-upstream of the E2F4 gene. In the present study, we constructed luciferase (Luc) expression vectors containing a 466 bp of the 5'-upstream of the human E2F4 gene. The transfection of this plasmid and deletion/mutation-introduced derivatives into HL-60 cells and a Luc reporter assay showed that duplicated and triplicated GGAA (TTCC) motifs in the E2F4 promoter respond to TPA. As expected, electrophoretic mobility shift assay indicated that SPI1 (PU.1) binds to the GGAA motif-containing element. A quantitative RT-PCR and western blotting showed that the E2F4 transcripts and its encoding proteins accumulate during the differentiation of HL-60 into macrophage-like cells. In contrast, the expression of the E2F1 gene and the protein, which possibly acts as a cell cycle accelerator, was greatly diminished.

Cold-inducible RNA-binding protein (CIRP) induces translation of the cell-cycle inhibitor p27Kip1

The CDK inhibitor p27^Kip1 plays a central role in controlling cell proliferation and cell-cycle exit. p27^Kip1 protein levels oscillate during cell-cycle progression and are regulated by mitogen or anti-proliferative signaling. The abundance of the protein is frequently determined by post-transcriptional mechanisms including ubiquitin-mediated proteolysis and translational control. Here, we report that the cold-inducible RNA-binding protein (CIRP) selectively binds to the 5′ untranslated region of the p27^Kip1 mRNA. CIRP is induced, modified and relocalized in response to various stress stimuli and can regulate cell survival and cell proliferation particularly during stress. Binding of CIRP to the 5′UTR of the p27^Kip1 mRNA significantly enhanced reporter translation. In cells exposed to mild hypothermia, the induction of CIRP correlated with increased translation of a p27^Kip1 5′UTR reporter and with the accumulation of p27^Kip1 protein. shRNA-mediated CIRP knockdown could prevent the induction of translation. We found that p27^Kip1 is central for the decreased proliferation at lower temperature, since p27^Kip1 KO mouse embryonic fibroblasts (MEFs) hardly increased their doubling time in hypothermic conditions, whereas wild-type MEFs significantly delayed proliferation in response to cold stress. This suggests that the CIRP-dependent p27^Kip1 upregulation during mild hypothermia contributes to the cold shock-induced inhibition of cell proliferation.

The Molecular Mechanisms of Protective Role of Se on the G0/G1 Phase Arrest Caused by AFB1 in Broiler's Thymocytes

This research was designed to explore the protective effects of sodium selenite on G₀/G₁ phase arrest induced by AFB₁ in thymocytes of broilers. Two hundred eighty-eight Cobb broilers were divided into control group, + Se group (0.4 mg/kg Se), AFB₁ group (0.6 mg/kg AFB₁), and AFB₁ + Se group (0.6 mg/kg AFB₁ + 0.4 mg/kg Se). The results revealed that 0.4 mg/kg Se supplement in diets could improve the AFB₁-induced histological lesions in the thymus consisting of the more vacuoles and nuclear debris in thymic cortical area. The results of flow cytometric detect showed that 0.4 mg/kg Se relieved the G₀/G₁ phase arrest caused by AFB₁ in thymocytes. The results of transcription levels of ATM, p53, p21, p27, p15, p16, CyclinD₁, CyclinE, Cdk6, Cdk2, and PCNA genes by qRT-PC, and protein expression level of PCNA by immunohistochemistry demonstrated that 0.4 mg/kg Se could reduce the adverse effects of AFB₁ on these parameters. In conclusion, Se could relieve AFB₁-induced G₀/G₁ phase arrest by p15 (or p16)-CyclinD₁/Cdk6, ATM-p53-p21-CyclinE/Cdk2, p27-CyclinE/Cdk2 pathways.

lncRNA CADM1-AS1 inhibits cell-cycle progression and invasion via PTEN/AKT/GSK-3β axis in hepatocellular carcinoma

Purpose: CADM1-AS1 (cell adhesion molecule 1 antisense RNA 1, long non-coding RNA), was firstly characterized in renal clear cell carcinoma, and exhibits a tumor suppressor role. However, its clinical relevance and exact effects in hepatocellular carcinoma (HCC) remain unknown. Therefore, in this study, we aimed to assess the clinical significance and function of CADM1-AS1 in HCC. Methods: We detected CADM1-AS1 expression in liver cancer tissue samples and cell lines, and analyzed the association between CADM1-AS1 expression and clinical parameters in 90 liver cancer patients. Moreover, we conducted gain-of-function and loss-of-function studies in liver cancer cell to explore the biological function and molecular mechanism of CADM1-AS1. Results: CADM1-AS1 expression was reduced in HCC. Clinical data showed that this downregulation was associated with advanced tumor stage, high TNM stage and reduced survival in HCC patients. CADM1-AS1 overexpression inhibited HCC cells proliferation, migration and invasion, while inducing G0/G1 phase arrest. Meanwhile, we revealed that CADM1-AS1 inhibited the phosphorylation of AKT and GSK-3β. Furthermore, our study showed that CADM1-AS1 decreased the cell cycle associated proteins expression of cyclinD, cyclinE, CDK2 CDK4, CDK6, and enhanced the levels of p15, p21 and p27. More importantly, SC79, a specific activator for AKT;, apparently attenuated the effects of CADM1-AS1 on above cell-cycle associated proteins, confirming that CADM1-AS1 inhibited cell cycles through the AKT signaling pathway. And we also found the CADM1-AS1 has antitumor effect in vivo by a xenograft HCC mouse model. In conclusion, the present findings show that the CADM1-AS1 inhibits proliferation of HCC by inhibiting AKT/GSK-3β signaling pathway, then upregulate p15, p21, p27 expression and downregulate cyclin, CDK expression to inhibit the G0/G1 to S phase transition both in vitro and in vivo. Conclusion: CADM1-AS1 functions as a tumor-suppressive lncRNA. This study reveals a molecular pathway involving PTEN/AKT/GSK-3β which regulates HCC cell-cycle progression.

Nuclear co-expression of p21 and p27 induced effective cell-cycle arrest in T24 cells treated with BCG

A proposed mechanism underlying the effect of bacillus Calmette-Guérin (BCG) treatment for bladder cancer cells is as follows: BCG-induced crosslinking of cell-surface receptors results in the activation of signaling cascades, including cell-cycle regulators. However, the clinical significance of cell-cycle regulators such as p21 and p27 is controversial. Here we investigated the relationship between BCG exposure and p21 and p27. We used confocal laser microscopy to examine the expression levels of pKi67, p21 and p27 in T24 cells (derived from human urothelial carcinoma) exposed six times to BCG. We performed dual immunofluorescence staining methods for p21 and p27 and observed the localization of nuclear and cytoplasm expressions. We investigated the priority of p27 over p21 regarding nuclear expression by using p27 Stealth RNAi™ (p27-siRNA). With 2-h BCG exposure, the nuclear-expression level of p21 and p27 was highest, while pKi67 was lowest. The percentage of double nuclear-expression of p21 and p27 in BCG cells was significantly higher than that in control cells during the 1st to 6th exposure (P < 0.05), and the expression of pKi67 showed the opposite of this pattern. Approximately 10% of the nuclear p21 was independent of p27, whereas the cytoplasmic p21 was dependent on p27. Our results suggested that the nuclear co-expression of p21 and p27 caused effective cell-cycle arrest, and thus the evaluation of the nuclear co-expression of p21 and p27 might help determine the effectiveness of BCG treatment.

Tsantan Sumtang Alleviates Chronic Hypoxia-Induced Pulmonary Hypertension by Inhibiting Proliferation of Pulmonary Vascular Cells

Hypoxia-induced pulmonary hypertension (HPH) is a severe condition associated with significant morbidity and mortality in people living at high altitude. Tsantan Sumtang, a traditional Tibetan medicine, has been routinely used for the treatment of cardiopyretic disease, as well as stenocardia. Interestingly, our previous research found that Tsantan Sumtang improved HPH in rats maintaining in a hypobaric chamber. We performed a series of experiments to test the indexes of vasoconstriction and vascular remodeling, the key pathophysiological characteristics of HPH. Our results showed that Tsantan Sumtang relaxed noradrenaline (NE)-precontracted rat pulmonary artery rings in a concentration-dependent manner in vitro. The PGI2-cAMP (prostaglandin I2-cyclic adenosine monophosphate) pathway, NO-cGMP (nitric oxide-cyclic guanosine monophosphate) pathway, and the opening of K⁺ channels (inward rectifier K⁺ channels, large conductance Ca²⁺-activated K⁺ channels, and voltage-dependent K⁺ channels) might play major roles in the vasorelaxation effect. In vivo, the administration of Tsantan Sumtang resulted in a substantial decrease in the rat mean pulmonary artery pressure (mPAP) and the right ventricular hypertrophy index (RVHI). The reduction of thickness of small pulmonary arterial wall and the WT% (the ratio of the vascular wall thickness to the vascular diameter) were observed. The smooth muscle muscularization of the arterials was alleviated by Tsantan Sumtang treatment at the same time. Tsantan Sumtang also reduced remodeling of pulmonary arterioles by suppressing the expression of proliferating cell nuclear antigen (PCNA), α-smooth muscle actin (α-SMA), cyclin D1, and cyclin-dependent kinase 4 (CDK4) through inhibition of p27Kip1 degradation. Therefore, Tsantan Sumtang could be applied as a preventative medication for HPH, which would be a new use for this traditional medicine.

Mechanisms associated to apoptosis of cancer cells by phenolic extracts from two canned common beans varieties (Phaseolus vulgaris L.)

Two varieties of common beans (Phaseolus vulgaris L.), Bayo Victoria and Negro 8025, were evaluated to determine the effect on cellular viability and mechanisms involved in apoptosis pathways, using a cellular model with HT-29 cells. Aqueous methanolic (50:50) extracts from cooked beans were analyzed for phenolic composition, identifying greater diversity of phenolic compounds in Bayo Victoria extracts. However, Negro 8025 showed greater phenolic content and cytotoxicity effects at lower media inhibitory concentrations, and greater effectiveness to activate apoptotic pathways. Proteins related to the arrest of cell cycle were modulated by both bean cultivars. Qualitative analysis by HPLC-PAD and HPLC-MS systems of phenolic compounds in common bean extracts showed mainly hydroxybenzoic and hydroxycinnamic acids, flavonols, and monomeric flavan-3-ols. Bioactive phenolics such as catechin, kaempferol, and ferulic acid were found in both cultivars as well anticancer phytochemicals such as quercetin, protocatechuic acid, myricetin, naringenin and their derivatives, and procyanidins. PRACTICAL APPLICATIONS: Polyphenols in common beans (Phaseolus vulgaris L.) cultivars processed by canning display chemoprotective potential as they activate mechanisms involved in apoptosis pathways. Phenolics in common beans modulate 28 proteins related to apoptotic processes. Therefore, a diet including canned beans (particularly darker varieties) might represent health benefits and cancer-preventive effects.

Delivery of a TNF-α-derived peptide by nanoparticles enhances its antitumor activity by inducing cell-cycle arrest and caspase-dependent apoptosis

Prostate cancer is the second-most common malignancy of the male genitourinary system. TNF-α has attracted intense attention as a potential therapeutic agent against various cancers. However, its therapeutic application is restricted by short half life and severe toxic side-effects. In this study, we constructed a stable nanodrug, called TNF-α-derived polypeptide (P16)-conjugated, chitosan (CTS)-modified selenium nanoparticle (SC; SCP), which is composed of SC as a slow-release carrier conjugated to P16. SCP had significant inhibitory effects on multiple types of tumor cells, especially DU145 prostate cancer cells, but not on RWPE-1 normal human prostate epithelial cells. SCP could induce G0/G1 cell-cycle arrest and apoptosis in DU145 cells more effectively than could P16 and TNF-α. In DU145 xenograft tumor models, SCP exerted much stronger antitumor effects than P16 or estramustine (the clinical drug for prostate cancer) but caused fewer toxic side-effects. In addition, SCP significantly inhibited proliferation and accelerated apoptosis in DU145 xenograft tumors. Further mechanistic studies revealed that SCP exerted antitumor effects via activation of the p38 MAPK/JNK pathway, thus inducing G0/G1 cell-cycle arrest and caspase-dependent apoptosis. These findings suggest that SCP may represent a potential long-lasting therapeutic agent for human prostate cancer with fewer side effects.-Yan, Q., Chen, X., Gong, H., Qiu, P., Xiao, X., Dang, S., Hong, A., Ma, Y. Delivery of a TNF-α-derived peptide by nanoparticles enhances its antitumor activity by inducing cell-cycle arrest and caspase-dependent apoptosis.

Role of p27Kip1 as a transcriptional regulator

The protein p27Kip1 is a member of the Cip/Kip family of cyclin-dependent kinase (Cdk) inhibitors. It interacts with both the catalytic and the regulatory subunit (cyclin) and introduces a region into the catalytic cleave of the Cdk inducing its inactivation. Its inhibitory capacity can be modulated by specific tyrosine phosphorylations. p27Kip1 also behaves as a transcriptional regulator. It associates with specific chromatin domains through different transcription factors. ChIP on chip, ChIP-seq and expression microarray analysis allowed the identification of the transcriptional programs regulated by p27Kip1. Thus, important cellular functions as cell division cycle, respiration, RNA processing, translation and cell adhesion, are under p27Kip1 regulation. Moreover, genes involved in pathologies as cancer and neurodegeneration are also regulated by p27Kip1, suggesting its implication in these pathologies. The carboxyl moiety of p27Kip1 can associate with different proteins, including transcriptional regulators. In contrast, its NH2-terminal region specifically interacts with cyclin-Cdk complexes. The general mechanistic model of how p27Kip1 regulates transcription is that it associates by its COOH region to the transcriptional regulators on the chromatin and by the NH2-domain to cyclin-Cdk complexes. After Cdk activation it would phosphorylate the specific targets on the chromatin leading to gene expression. This model has been demonstrated to apply in the transcriptional regulation of p130/E2F4 repressed genes involved in cell cycle progression. We summarize in this review our current knowledge on the role of p27Kip1 in the regulation of transcription, on the transcriptional programs under its regulation and on its relevance in pathologies as cancer and neurodegeneration.

Low-intensity pulsed ultrasound promotes Schwann cell viability and proliferation via the GSK-3β/β-catenin signaling pathway

Background: It has been reported that ultrasound enhances peripheral nerve regeneration, but the mechanism remains elusive. Low-intensity pulsed ultrasound (LIPUS) has been reported to enhance proliferation and alter protein production in various types of cells. In this study, we detected the effects of LIPUS on Schwann cells. Material and methods: Schwann cells were separated from new natal Sprague-Dawley rat sciatic nerves and were cultured and purified. The Schwann cells were treated by LIPUS for 10 minutes every day, with an intensity of 27.37 mW/cm2. After treatment for 5 days, MTT, EdU staining, and flow cytometry were performed to examine cell viability and proliferation. Neurotrophic factors, including FGF, NGF, BDNF, and GDNF, were measured by western blot and real-time PCR. GSK-3β, p-GSK-3β, β-catenin and Cyclin D1 protein levels were detected using a western blot analysis. The expression of Cyclin D1 was also detected by immunofluorescence. Results: MTT and EdU staining showed that LIPUS increased the Schwann cells viability and proliferation. Compared to the control group, LIPUS increased the expression of growth factors and neurotrophic factors, including FGF, NGF, BDNF, GDNF, and Cyclin D1. Meanwhile, GSK-3β activity was inhibited in the LIPUS group as demonstrated by the increased level of p-GSK-3β and the ratio of the p-GSK-3β/GSK-3β level. The mRNA and protein expressions of β-catenin were increased in the LIPUS group. However, SB216763, a GSK-3β inhibitor, reversed the effects of LIPUS on Schwann cells. Conclusion: LIPUS promotes Schwann cell viability and proliferation by increasing Cyclin D1 expression via enhancing the GSK-3β/β-catenin signaling pathway.

p27Kip1 regulates alpha-synuclein expression

Alpha-synuclein (α-SYN) is the main component of anomalous protein aggregates (Lewy bodies) that play a crucial role in several neurodegenerative diseases (synucleinopathies) like Parkinson’s disease and multiple system atrophy. However, the mechanisms involved in its transcriptional regulation are poorly understood. We investigated here the role of the cyclin-dependent kinase (Cdk) inhibitor and transcriptional regulator p27^Kip1 (p27) in the regulation of α-SYN expression. We observed that selective deletion of p27 by CRISPR/Cas9 technology in neural cells resulted in increased levels of α-SYN. Knock-down of the member of the same family p21^Cip1 (p21) also led to increased α-SYN levels, indicating that p27 and p21 collaborate in the repression of α-SYN transcription. We demonstrated that this repression is mediated by the transcription factor E2F4 and the member of the retinoblastoma protein family p130 and that it is dependent of Cdk activity. Chromatin immunoprecipitation analysis revealed specific binding sites for p27, p21 and E2F4 in the proximal α-SYN gene promoter. Finally, luciferase assays revealed a direct action of p27, p21 and E2F4 in α-SYN gene expression. Our findings reveal for the first time a negative regulatory mechanism of α-SYN expression, suggesting a putative role for cell cycle regulators in the etiology of synucleinopathies.

Halofuginone and artemisinin synergistically arrest cancer cells at the G1/G0 phase by upregulating p21Cip1 and p27Kip1

Combinational drug therapy is one of the most promising strategies in modern anticancer research. Traditional Chinese medicine (TCM) formulas represent a wealth of complex combinations proven successful over centuries of clinical application. One such formula used to treat a variety of diseases, including cancer, contains two herbs, whose main active components are Halofuginone (HF) and Artemisinin (ATS). Here we studied the anticancer synergism of HF and ATS in various cancer cell lines and in a xenograft nude mice model. We found that the HF-ATS combination arrested more cells at the G1/G0 phase than either one alone, with the concomitant increased levels of CDK2 inhibitors, p21^Cip1 and p27^Kip1. By knocking down p21^Cip1 and p27^Kip1 separately or simultaneously in HCT116 cells and MCF-7 cells, we found that p21^Cip1 was required for HF induced G1/G0 arrest, whereas p21^Cip1 and p27^Kip1 were both required for ATS or HF-ATS combination-mediated cell cycle arrest. Moreover, HF-ATS combination synergistically inhibited tumor growth in xenograft nude mice, and this was associated with the increased levels of p21^Cip1 and p27^Kip1. Collectively, these data indicate that the upregulation of p21^Cip1 and p27^Kip1 contributes to the synergistic anticancer effect of the HF-ATS combination.

YBX1 regulates tumor growth via CDC25a pathway in human lung adenocarcinoma

Y-box binding protein 1 (YBX1) is involved in the multi-tumor occurrence and development. However, the regulation of YBX1 in lung tumorigenesis and the underlying mechanisms, especially its relationship with CDC25a, was remains unclear. In this study, we analyzed the expression and clinical significance of YBX1 and CDC25a in lung adenocarcinoma and identified their roles in the regulation of lung cancer growth. The retrospective analysis of 116 patients with lung adenocarcinoma indicated that YBX1 was positively correlated with CDC25a expression. The Cox-regression analysis showed only high-ranking TNM stage and low CDC25a expression were an independent risk factor of prognosis in enrolled patients. High expression of YBX1 or CDC25a protein was also observed in lung adenocarcinoma cells compared with HLF cells. ChIP assay demonstrated the binding of endogenous YBX1 to the CDC25a promoter region. Overexpression of exogenous YBX1 up-regulated the expression of the CDC25a promoter-driven luciferase. By contrast, inhibition of YBX1 by siRNA markedly decreased the capability of YBX1 binding to CDC25a promoter in A549 and H322 cells. Inhibition of YBX1 expression also blocked cell cycle progression, suppressed cell proliferation and induced apoptosis via the CDC25a pathway in vitro. Moreover, inhibition of YBX1 by siRNA suppressed tumorigenesis in a xenograft mouse model and down-regulated the expression of YBX1, CDC25a, Ki67 and cleaved caspase 3 in the tumor tissues of mice. Collectively, these results demonstrate inhibition of YBX1 suppressed lung cancer growth partly via the CDC25a pathway and high expression of YBX1/CDC25a predicts poor prognosis in human lung adenocarcinoma.

ChIP-Seq analysis identifies p27(Kip1)-target genes involved in cell adhesion and cell signalling in mouse embryonic fibroblasts

The protein p27^Kip1 (p27), a member of the Cip-Kip family of cyclin-dependent kinase inhibitors, is involved in tumorigenesis and a correlation between reduced levels of this protein in human tumours and a worse prognosis has been established. Recent reports revealed that p27 also behaves as a transcriptional regulator. Thus, it has been postulated that the development of tumours with low amounts of p27 could be propitiated by deregulation of transcriptional programs under the control of p27. However, these programs still remain mostly unknown. The aim of this study has been to define the transcriptional programs regulated by p27 by first identifying the p27-binding sites (p27-BSs) on the whole chromatin of quiescent mouse embryonic fibroblasts. The chromatin regions associated to p27 have been annotated to the most proximal genes and it has been considered that the expression of these genes could by regulated by p27. The identification of the chromatin p27-BSs has been performed by Chromatin Immunoprecipitation Sequencing (ChIP-seq). Results revealed that p27 associated with 1839 sites that were annotated to 1417 different genes being 852 of them protein coding genes. Interestingly, most of the p27-BSs were in distal intergenic regions and introns whereas, in contrast, its association with promoter regions was very low. Gene ontology analysis of the protein coding genes revealed a number of relevant transcriptional programs regulated by p27 as cell adhesion, intracellular signalling and neuron differentiation among others. We validated the interaction of p27 with different chromatin regions by ChIP followed by qPCR and demonstrated that the expressions of several genes belonging to these programs are actually regulated by p27. Finally, cell adhesion assays revealed that the adhesion of p27^-/- cells to the plates was much higher that controls, revealing a role of p27 in the regulation of a transcriptional program involved in cell adhesion.

Hesperidin induces apoptosis and G0/G1 arrest in human non-small cell lung cancer A549 cells

Lung cancer has high incidence and mortality rates worldwide. In the present study, the mechanisms by which hesperidin decreases the viability and induces the apoptosis of human non-small cell lung cancer (NSCLC) A549 cells were investigated. Initially, MTT and flow cytometric assays were performed to evaluate the effects of hesperidin on the viability and apoptosis of A549 cells and human normal lung epithelial BEAS-2B cells. The results revealed that hesperidin has no negative effects on the human normal lung epithelial BEAS-2B cells and the viability of cells treated with various concentrations of hesperidin was inhibited in a time- and dose-dependent manner compared with the control groups. Subsequently, the expression levels of proteins involved in the mitochondria-associated apoptotic pathway were studied by western blot analysis. Hesperidin was identified to induce A549 cell apoptosis by downregulating the levels of B-cell lymphoma-2 (Bcl-2) and Bcl extra large protein and simultaneously upregulating the levels of Bcl-2-associated X protein, BH3 interacting-domain death agonist (Bid), tBid, cleaved caspase-9, cleaved caspase-3 and cleaved poly(adenosine diphosphate ribose)polymerase. The effect of hesperidin on the cell cycle was assessed by flow cytometry. Hesperidin was observed to cause G0/G1 arrest of A549 cells by decreasing the expression of cyclin D1 and increasing the expression of p21 and p53. In summary, it was demonstrated that hesperidin induced apoptosis through the mitochondrial apoptotic pathway and induced G0/G1 arrest in human NSCLC A549 cells. Therefore, hesperidin may be developed as a potential therapeutic drug for the treatment of NSCLC.

The α-melanocyte stimulating hormone/peroxisome proliferator activated receptor-γ pathway down-regulates proliferation in melanoma cell lines

Background

The α-Melanocyte Stimulating Hormone (αMSH)/Melanocortin-1 receptor (MC1R) interaction promotes melanogenesis through the cAMP/PKA pathway. The direct induction of this pathway by Forskolin (FSK) is also known to enhance melanocyte proliferation. αMSH acts as a mitogenic agent in melanocytes and its effect on proliferation of melanoma cells is less known. We previously identified the αMSH/Peroxisome Proliferator Activated Receptor (PPARγ) pathway as a new pathway on the B16-F10 mouse melanoma cell line. αMSH induced the translocation of PPARγ into the nucleus as an active transcription factor. This effect was independent of the cAMP/PKA pathway and was mediated by the activation of the PI(4,5)P2/PLC pathway, a pathway which we have described to be triggered by the αMSH-dependent MC1R stimulation. Moreover, in the same study, preliminary experiments showed that mouse melanoma cells responded to αMSH by reducing proliferation and that PPARγ was involved in this effect. Due to its key role in the control of cell proliferation, PPARγ agonists are used in therapeutic models for different forms of cancer, including melanoma. The purpose of this study was: (a) to confirm the different proliferative behavior in response to αMSH in healthy and in melanoma condition; (b) to verify whether the cAMP/PKA pathway and the PLC/PPARγ pathway could exert an antagonistic function in the control of proliferation; (c) to deepen the knowledge of the molecular basis responsible for the down-proliferative response of melanoma cells after exposure to αMSH.

Methods

We employed B16-F10 cell line, a human melanoma cell line (Mel 13) and two primary cultures of human melanocytes (NHM 1 and NHM 2, respectively), all expressing a wild type MC1R and responding to the αMSH in terms of pigmentation. We evaluated cell proliferation through: a) cell counting, b) cell cycle analysis c) protein expression of proliferation modulators (p27, p21, cyclin D1 and cyclin E).

Results

The αMSH acted as a mitogenic agent in primary cultures of human melanocytes, whereas it determined a slow down of proliferation in melanoma cell lines. FSK, as an inducer of the cAMP/PKA pathway, reproduced the αMSH mediated effect on proliferation in NHMs but it did not mimic the αMSH effect on proliferation in B16-F10 and Mel 13 melanoma cell lines. Meanwhile, 3 M3-FBS (3 M3), as an inducer of PI(4,5)P2/PLC pathway, reproduced the αMSH proliferative effect. Further experiments, treating melanoma cell lines with αMSH in the presence/absence of GW9662, as an inhibitor of PPARγ, confirmed the key role of this transcription factor in decreasing cell proliferation in response to the hormone exposure.

Conclusions

In both melanoma cell lines, αMSH determined the reduction of proliferation through the PI(4,5)P2/PLC pathway, employing PPARγ as an effector element. These evidence could offer perspectives for new therapeutic approaches for melanoma.

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0611-4) contains supplementary material, which is available to authorized users.

p27Kip1, PCAF and PAX5 cooperate in the transcriptional regulation of specific target genes

The cyclin-dependent kinase inhibitor p27^Kip1 (p27) also behaves as a transcriptional repressor. Data showing that the p300/CBP-associated factor (PCAF) acetylates p27 inducing its degradation suggested that PCAF and p27 could collaborate in the regulation of transcription. However, this possibility remained to be explored. We analyzed here the transcriptional programs regulated by PCAF and p27 in the colon cancer cell line HCT116 by chromatin immunoprecipitation sequencing (ChIP-seq). We identified 269 protein-encoding genes that contain both p27 and PCAF binding sites being the majority of these sites different for PCAF and p27. PCAF or p27 knock down revealed that both regulate the expression of these genes, PCAF as an activator and p27 as a repressor. The double knock down of PCAF and p27 strongly reduced their expression indicating that the activating role of PCAF overrides the repressive effect of p27. We also observed that the transcription factor Pax5 interacts with both p27 and PCAF and that the knock down of Pax5 induces the expression of p27/PCAF target genes indicating that it also participates in the transcriptional regulation mediated by p27/PCAF. In summary, we report here a previously unknown mechanism of transcriptional regulation mediated by p27, Pax5 and PCAF.

A novel deubiquitinase inhibitor b-AP15 triggers apoptosis in both androgen receptor-dependent and -independent prostate cancers

Prostate cancer (PCa) remains a leading cause of cancer-related death in men. Especially, a subset of patients will eventually progress to the metastatic castrate-resistant prostate cancer (CRPC) which is currently incurable. Deubiquitinases (DUBs) associated with the 19S proteasome regulatory particle are increasingly emerging as significant therapeutic targets in numerous cancers. Recently, a novel small molecule b-AP15 is identified as an inhibitor of the USP14/UCHL5 (DUBs) of the 19S proteasome, resulting in cell growth inhibition and apoptosis in several human cancer cell lines. Here, we studied the therapeutic effect of b-AP15 in PCa, and our results indicate that (i) b-AP15 decreases viability, proliferation and triggers cytotoxicity to both androgen receptor-dependent and -independent PCa cells in vitro and in vivo, associated with caspase activation, inhibition of mitochondria function, increased reactive oxygen species (ROS) generation and endoplasmic reticulum (ER) stress; (ii) pan-caspase inhibitor z-VAD-FMK and ROS scavenger N-acetyl-L-cysteine (NAC) efficiently block apoptosis but not proteasome inhibition induced by exposure of b-AP15; (iii) treatment with b-AP15 in androgen-dependent prostate cancer (ADPC) cells down-regulates the expression of androgen receptor (AR), which is degraded via the ubiquitin proteasome system. Hence, the potent anti-tumor effect of b-AP15 on both androgen receptor-dependent and -independent PCa cells identifies a new promising therapeutic strategy for prostate cancer.

Low-Dose Paclitaxel Inhibits Tumor Cell Growth by Regulating Glutaminolysis in Colorectal Carcinoma Cells

Paclitaxel (PTX) is a natural alkaloid isolated from the bark of a tree, Taxus brevifolia, and is currently used to treat a variety of tumors. Recently, it has been found that low-dose PTX is a promising treatment for some cancers, presenting few side effects. However, antitumor mechanisms of low-dose PTX (<1 nM) have rarely been illuminated. Here we report a new antitumor mechanism of low-dose PTX in colorectal carcinoma cells. We treated colorectal carcinoma HCT116 cells with PTX at 0.1 and 0.3 nM for 0, 1, 2, or 3 days, and found that low-dose PTX inhibits cell growth without altering cell morphology and cell cycle. There was a significant decrease of pH in culture media with 0.3 nM PTX for 3 days. Also, lactate production was significantly increased in a dose- and time-dependent manner. Furthermore, expression of glutaminolysis-related genes GLS, SLC7A11 and SLC1A5 were significantly decreased in the colorectal carcinoma cells treated with low-dose PTX. Meanwhile, protein expression levels of p53 and p21 increased significantly in colorectal carcinoma cells so treated. In summary, low-dose PTX down-regulated glutaminolysis-related genes and increased their lactate production, resulting in decreased pH of tumor microenvironments and inhibition of tumor cell growth. Up-regulation of p53 and p21 in colorectal carcinoma cells treated with low-dose PTX also contributed to inhibition of tumor cell growth.

Complex regulation of LCoR signaling in breast cancer cells

Ligand-dependent corepressor (LCoR) is a transcriptional repressor of ligand-activated estrogen receptors (ERs) and other transcription factors that acts both by recruiting histone deacetylases and C-terminal binding proteins. Here, we first studied LCOR gene expression in breast cancer cell lines and tissues. We detected two mRNAs variants, LCoR and LCoR2 (which encodes a truncated LCoR protein). Their expression was highly correlated and localized in discrete nuclear foci. LCoR and LCoR2 strongly repressed transcription, inhibited estrogen-induced target gene expression and decreased breast cancer cell proliferation. By mutagenesis analysis, we showed that the helix-turn-helix domain of LCoR is required for these effects. Using in vitro interaction, coimmunoprecipitation, proximity ligation assay and confocal microscopy experiments, we found that receptor-interacting protein of 140 kDa (RIP140) is a LCoR and LCoR2 partner and that this interaction requires the HTH domain of LCoR and RIP140 N- and C-terminal regions. By increasing or silencing LCoR and RIP140 expression in human breast cancer cells, we then showed that RIP140 is necessary for LCoR inhibition of gene expression and cell proliferation. Moreover, LCoR and RIP140 mRNA levels were strongly correlated in breast cancer cell lines and biopsies. In addition, RIP140 positively regulated LCoR expression in human breast cancer cells and in transgenic mouse models. Finally, their expression correlated with overall survival of patients with breast cancer. Taken together, our results provide new insights into the mechanism of action of LCoR and RIP140 and highlight their strong interplay for the control of gene expression and cell proliferation in breast cancer cells.

Honokiol Induces Apoptosis, G1 Arrest, and Autophagy in KRAS Mutant Lung Cancer Cells

Aberrant signaling transduction induced by mutant KRAS proteins occurs in 20∼30% of non-small cell lung cancer (NSCLC), however, a direct and effective pharmacological inhibitor targeting KRAS has not yet reached the clinic to date. Honokiol, a small molecular polyphenol natural biophenolic compound derived from the bark of magnolia trees, exerts anticancer activity, however, its mechanism remains unknown. In this study, we sought to investigate the in vitro effects of honokiol on NSCLC cell lines harboring KRAS mutations. Honokiol was shown to induce G1 arrest and apoptosis to inhibit the growth of KRAS mutant lung cancer cells, which was weakened by an autophagy inhibitor 3-methyladenine (3-MA), suggesting a pro-apoptotic role of honokiol-induced autophagy that was dependent on AMPK-mTOR signaling pathway. In addition, we also discovered that Sirt3 was significantly up-regulated in honokiol treated KRAS mutant lung cancer cells, leading to destabilization of its target gene Hif-1α, which indicated that the anticancer property of honokiol maybe regulated via a novel mechanism associated with the Sirt3/Hif-1α. Taken together, these results broaden our understanding of the mechanisms on honokiol effects in lung cancer, and reinforce the possibility of its potential anticancer benefit as a popular Chinese herbal medicine (CHM).

p27Kip1 represses the Pitx2-mediated expression of p21Cip1 and regulates DNA replication during cell cycle progression

The tumor suppressor p21 regulates cell cycle progression and peaks at mid/late G1. However, the mechanisms regulating its expression during cell cycle are poorly understood. We found that embryonic fibroblasts from p27 null mice at early passages progress slowly through the cell cycle. These cells present an elevated basal expression of p21 suggesting that p27 participates to its repression. Mechanistically, we found that p27 represses the expression of Pitx2 (an activator of p21 expression) by associating with the ASE-regulatory region of this gene together with an E2F4 repressive complex. Furthermore, we found that Pitx2 binds to the p21 promoter and induces its transcription. Finally, silencing Pitx2 or p21 in proliferating cells accelerates DNA replication and cell cycle progression. Collectively, these results demonstrate an unprecedented connection between p27, Pitx2 and p21 relevant for the regulation of cell cycle progression and cancer and for understanding human pathologies associated with p27 germline mutations.

Loss of p27Kip¹ promotes metaplasia in the pancreas via the regulation of Sox9 expression

p27^Kip1 (p27) is a negative regulator of proliferation and a tumor suppressor via the inhibition of cyclin-CDK activity in the nucleus. p27 is also involved in the regulation of other cellular processes, including transcription by acting as a transcriptional co-repressor. Loss of p27 expression is frequently observed in pancreatic adenocarcinomas in human and is associated with decreased patient survival. Similarly, in a mouse model of K-Ras-driven pancreatic cancer, loss of p27 accelerates tumor development and shortens survival, suggesting an important role for p27 in pancreatic tumorigenesis. Here, we sought to determine how p27 might contribute to early events leading to tumor development in the pancreas. We found that K-Ras activation in the pancreas causes p27 mislocalization at pre-neoplastic stages. Moreover, loss of p27 or expression of a mutant p27 that does not bind cyclin-CDKs causes the mislocalization of several acinar polarity markers associated with metaplasia and induces the nuclear expression of Sox9 and Pdx1 two transcription factors involved in acinar-to-ductal metaplasia. Finally, we found that p27 directly represses transcription of Sox9, but not that of Pdx1. Thus, our results suggest that K-Ras activation, the earliest known event in pancreatic carcinogenesis, may cause loss of nuclear p27 expression which results in derepression of Sox9, triggering reprogrammation of acinar cells and metaplasia.

Cyclin-Dependent Kinases as Coregulators of Inflammatory Gene Expression

Cyclin-dependent kinases (CDKs) exert a variety of functions through regulation of the cell cycle and gene expression, thus implicating them in diverse biological processes. Recent studies have deciphered the molecular mechanisms employed by nuclear CDKs to support the expression of inflammatory mediators. Induced transcription of many proinflammatory genes is increased during the G1 phase of the cell cycle in a CDK-dependent manner. This process involves the cytokine-induced recruitment of CDK6 to the nuclear chromatin fraction where it associates with transcription factors of the NF-κB, STAT, and AP-1 families. The ability of CDK6 to trigger the expression of VEGF-A and p16(INK4A) and to recruit the NF-κB subunit p65 to its target sites is largely independent of its kinase function. The involvement of CDKs in proinflammatory gene expression also allows therapeutic targeting of their functions to interfere with tumor-promoting inflammation or chronic inflammatory diseases.