Sall1 and Sall4 cooperatively interact with Myocd and SRF to promote cardiomyocyte proliferation by regulating CDK and cyclin genes

Sall1 and Sall4 (Sall1/4), zinc-finger transcription factors, are expressed in the progenitors of the second heart field (SHF) and in cardiomyocytes during the early stages of mouse development. To understand the function of Sall1/4 in heart development, we generated heart-specific Sall1/4 functionally inhibited mice by forced expression of the truncated form of Sall4 (ΔSall4) in the heart. The ΔSall4-overexpression mice exhibited a hypoplastic right ventricle and outflow tract, both of which were derived from the SHF, and a thinner ventricular wall. We found that the numbers of proliferative SHF progenitors and cardiomyocytes were reduced in ΔSall4-overexpression mice. RNA-sequencing data showed that Sall1/4 act upstream of the cyclin-dependent kinase (CDK) and cyclin genes, and of key transcription factor genes for the development of compact cardiomyocytes, including myocardin (Myocd) and serum response factor (Srf). In addition, ChIP-sequencing and co-immunoprecipitation analyses revealed that Sall4 and Myocd form a transcriptional complex with SRF, and directly bind to the upstream regulatory regions of the CDK and cyclin genes (Cdk1 and Ccnb1). These results suggest that Sall1/4 are critical for the proliferation of cardiac cells via regulation of CDK and cyclin genes that interact with Myocd and SRF.

The pathophysiology of the cell cycle in cancer and treatment strategies using various cell cycle checkpoint inhibitors

The cell cycle is the series of events that occur in a cell leading to its division and duplication. It can be divided into two main stages: interphase and mitosis. Interphase is the longest stage of the cell cycle and can be further divided into three phases: G1, S, and G2. During G1, the cell grows and prepares for DNA synthesis. In the S phase, DNA synthesis occurs, leading to the replication of the genetic material. In G2, the cell continues to grow and prepares for mitosis. After mitosis, the cell enters the final stage of the cell cycle, called cytokinesis, during which the cytoplasm is divided, resulting in two separate daughter cells. The cell cycle then begins again with interphase. Cell cycle dysregulation is a hallmark of cancer, and it can have several consequences that contribute to the development and progression of cancer. Cyclin inhibitors and checkpoint activators have shown promise in the treatment of cancer, particularly in combination with other therapies.

The Populus D-type cyclin gene PsnCYCD1;1 accelerates cell division and participates in secondary growth of vascular bundles in poplar

Plant growth and development rely heavily on cyclins, which compose an important class of cell division regulators. D-type cyclins (CYCDs) are responsible for the rate-limiting step of G1 cells. In the plant kingdom, despite the importance of CYCDs in herbaceous plants, there is little knowledge of these proteins in perennial woody plants. Here, a nucleus-localized cyclin gene, PsnCYCD1;1, was cloned from Populus. PsnCYCD1;1 was highly expressed in tissues with active cell division, especially the leaf buds, and could be induced by sucrose and phytohormones. Moreover, overexpression of PsnCYCD1;1 in poplar could stimulate cell division, resulting in the generation of small cells and causing severe morphological changes in the vascular bundles, resulting in "S"-shaped tortuous stems and curled leaves. Furthermore, transcriptomic analysis revealed that endogenous genes related to cell division and vascular cambium development were significantly upregulated in the transgenic plants. In addition, PsnCDKA1, PsnICK3 and PsnICK5 were identified as interacting proteins of PsnCYCD1;1 according to yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. Our study demonstrates that PsnCYCD1;1 accelerates plant cell division and participates in secondary growth of vascular bundles in poplar.

Cyclins and cyclin-dependent kinases: from biology to tumorigenesis and therapeutic opportunities

The discussion on cell proliferation cannot be continued without taking a look at the cell cycle regulatory machinery. Cyclin-dependent kinases (CDKs), cyclins, and CDK inhibitors (CKIs) are valuable members of this system and their equilibrium guarantees the proper progression of the cell cycle. As expected, any dysregulation in the expression or function of these components can provide a platform for excessive cell proliferation leading to tumorigenesis. The high frequency of CDK abnormalities in human cancers, together with their druggable structure has raised the possibility that perhaps designing a series of inhibitors targeting CDKs might be advantageous for restricting the survival of tumor cells; however, their application has faced a serious concern, since these groups of serine-threonine kinases possess non-canonical functions as well. In the present review, we aimed to take a look at the biology of CDKs and then magnify their contribution to tumorigenesis. Then, by arguing the bright and dark aspects of CDK inhibition in the treatment of human cancers, we intend to reach a consensus on the application of these inhibitors in clinical settings.

HUSH-mediated HIV silencing is independent of TASOR phosphorylation on threonine 819

BACKGROUND

TASOR, a component of the HUSH repressor epigenetic complex, and SAMHD1, a cellular triphosphohydrolase (dNTPase), are both anti-HIV proteins antagonized by HIV-2/SIVsmm Viral protein X. As a result, the same viral protein is able to relieve two different blocks along the viral life cell cycle, one at the level of reverse transcription, by degrading SAMHD1, the other one at the level of proviral expression, by degrading TASOR. Phosphorylation of SAMHD1 at T592 has been shown to downregulate its antiviral activity. The discovery that T819 in TASOR was lying within a SAMHD1 T592-like motif led us to ask whether TASOR is phosphorylated on this residue and whether this post-translational modification could regulate its repressive activity.

RESULTS

Using a specific anti-phospho-antibody, we found that TASOR is phosphorylated at T819, especially in cells arrested in early mitosis by nocodazole. We provide evidence that the phosphorylation is conducted by a Cyclin/CDK1 complex, like that of SAMHD1 at T592. While we could not detect TASOR in quiescent CD4 + T cells, TASOR and its phosphorylated form are present in activated primary CD4 + T lymphocytes. In addition, TASOR phosphorylation appears to be independent from TASOR repressive activity. Indeed, on the one hand, nocodazole barely reactivates HIV-1 in the J-Lat A1 HIV-1 latency model despite TASOR T819 phosphorylation. On the other hand, etoposide, a second cell cycle arresting drug, reactivates latent HIV-1, without concomitant TASOR phosphorylation. Furthermore, overexpression of wt TASOR or T819A or T819E similarly represses gene expression driven by an HIV-1-derived LTR promoter. Finally, while TASOR is degraded by HIV-2 Vpx, TASOR phosphorylation is prevented by HIV-1 Vpr, likely as a consequence of HIV-1 Vpr-mediated-G2 arrest.

CONCLUSIONS

Altogether, we show that TASOR phosphorylation occurs in vivo on T819. This event does not appear to correlate with TASOR-mediated HIV-1 silencing. We speculate that TASOR phosphorylation is related to a role of TASOR during cell cycle progression.

The role of cyclins in the development and progression of prostate cancer

The role of cyclins in hormone-dependent neoplasms is crucial in the development of the disease that is resistant to first-line therapy, as the example of breast cancer shows. However, in prostate cancer, cyclins are studied to a lesser extent. There are some well-described molecular pathways, including cyclins A1 and D1 signaling, however the role of other cyclins, e.g., D2, D3, E, and H, still requires further investigation. Recent studies indicate that cyclins regulate various cellular processes, not only the cell cycle. Furthermore, they remain in cross-talk with many other signaling pathways, e.g., MAPK/ERK, PI3K/Akt, and Notch. The androgen signaling axis, which is pivotal in prostate cancer progression, interferes with cyclin pathways at many levels. This article summarizes current knowledge on the influence of cyclins on prostate cancer progression by describing interactions between the androgen receptor and cyclins, as well as mechanisms underlying the development of resistance to currently used therapies.

Regulation of the cell cycle under anoxia stress in tail muscle and hepatopancreas of the freshwater crayfish, Orconectes virilis

Regulation of the cell cycle is an understudied response to oxygen deprivation among crustaceans. The virile crayfish, Orconectes virilis, is a freshwater crustacean that when challenged by environmental oxygen limitation undergoes metabolic rate depression (to ~30% of normal levels) and switches to anaerobic metabolism to generate energy. To understand how crayfish regulate the cell cycle in response to anoxia, key proteins involved in cell cycle control were analyzed in muscle and hepatopancreas. At the G1/S barrier, an overall upregulation of positive regulators of cell cycle progression was indicated by the responses of G1 cyclins (cyclin D and cyclin E) and Cyclin dependent kinases (CDK4, CDK6 and CDK2) under anoxia. Although the levels of Cyclin kinase inhibitors (CKIs) at this juncture were also upregulated (P15/16 and P21 (T145) in muscle and P16 (S152) in hepatopancreas), levels of a major regulator of this phase and driver to S-phase, E2F1, were significantly higher in both tissues in conjunction with deactivation of its inhibitor, Retinoblastoma (Rb) protein. At the G2/M barrier, expression profiles of the G2 cyclin B suggested cell cycle progression despite overall trend of higher activities of checkpoint kinases, (Chk1 (S317) and Chk2 (S19)), that also negatively regulate the cyclin B-CDK1 complex via CdC25C (cell division cycle 25) whose levels remained unchanged. Overall, the present study suggests continued cell cycle progression, albeit with potential deceleration, as indicated by checkpoint kinases and kinase inhibitor profiles that might play a role in protecting tissues from apoptotic damage under chronic anoxic stress.

CDK4/6 inhibitors sensitize gammaherpesvirus-infected tumor cells to T-cell killing by enhancing expression of immune surface molecules

BACKGROUND

The two oncogenic human gammaherpesviruses, Kaposi sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), both downregulate immune surface molecules, such as MHC-I, ICAM-1, and B7-2, enabling them to evade T-cell and natural killer cell immunity. Both also either encode for human cyclin homologues or promote cellular cyclin activity, and this has been shown to be important for proliferation and survival of gammaherpesvirus-induced tumors. CDK4/6 inhibitors, which are approved for certain breast cancers, have been shown to enhance expression of MHC-I in cell lines and murine models of breast cancer, and this was attributed to activation of interferons by endogenous retrovirus elements. However, it was not known if this would occur in gammaherpesvirus-induced tumors in which interferons are already activated.

METHODS

Multiple KSHV/EBV-infected cell lines were treated with CDK4/6 inhibitors. The growth of viable cells and expression of surface markers was assessed. T cell activation stimulated by the treated cells was assayed by a T-cell activation bioassay. Both viral and host gene expression was surveyed using RT-qPCR.

RESULTS

Three CDK4/6 inhibitors, abemaciclib, palbociclib, and ribociclib, inhibited cell growth in KSHV-induced primary effusion lymphoma (PEL) and EBV positive Burkitt's lymphoma (BL) cell lines, and KSHV-infected human umbilical vein endothelial cells (HUVECs). Moreover, CDK4/6 inhibitors increased mRNA and surface expression of MHC-I in all three and prevented downregulation of MHC-I surface expression during lytic replication in KSHV-infected cells. CDK4/6 inhibitors also variably increased mRNA and surface expression of ICAM-1 and B7-2 in the tested lines. Abemaciclib also significantly enhanced T-cell activation induced by treated PEL and BL cells. Certain gammaherpesvirus genes as well as endogenous retrovirus (ERV) 3-1 genes were enhanced by CDK4/6 inhibitors in most PEL and BL lines and this enhancement was associated with expression of gamma interferon-induced genes including MHC-I.

CONCLUSIONS

These observations provide evidence that CDK4/6 inhibitors can induce expression of surface immune markers MHC-I, B7-2, and ICAM-1 in gammaherpesvirus-infected cell lines and induce virus-specific immunity. They can thus thwart virus-induced immune evasion. These effects, along with their direct effects on KSHV- or EBV-induced tumors, provide a rational for the clinical testing of these drugs in these tumors.

The kinome, cyclins and cyclin-dependent kinases of pituitary adenomas, a look into the gene expression profile among tumors from different lineages

Background

Pituitary adenomas (PA) are the second most common intracranial tumors and are classified according to hormone they produce, and the transcription factors they express. The majority of PA occur sporadically, and their molecular pathogenesis is incompletely understood.

Methods

Here we performed transcriptome and proteome analysis of tumors derived from POU1F1 (GH-, TSH-, and PRL-tumors, N = 16), NR5A1 (gonadotropes and null cells adenomas, n = 17) and TBX19 (ACTH-tumors, n = 6) lineages as well as from silent ACTH-tumors (n = 3) to determine expression of kinases, cyclins, CDKs and CDK inhibitors.

Results

The expression profiles of genes encoding kinases were distinctive for each of the three PA lineage: NR5A1-derived tumors showed upregulation of ETNK2 and PIK3C2G and alterations in MAPK, ErbB and RAS signaling, POU1F1-derived adenomas showed upregulation of PIP5K1B and NEK10 and alterations in phosphatidylinositol, insulin and phospholipase D signaling pathways and TBX19-derived adenomas showed upregulation of MERTK and STK17B and alterations in VEGFA-VEGFR, EGF-EGFR and Insulin signaling pathways. In contrast, the expression of the different genes encoding cyclins, CDK and CDK inhibitors among NR5A1-, POU1F1- and TBX19-adenomas showed only subtle differences. CDK9 and CDK18 were upregulated in NR5A1-adenomas, whereas CDK4 and CDK7 were upregulated in POUF1-adenomas.

Conclusions

The kinome of PA clusters these lesions into three distinct groups according to the transcription factor that drives their terminal differentiation. And these complexes could be harnessed as molecular therapy targets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01206-y.

Degron Tagging Using mAID and SMASh Tags in RPE-1 Cells

Degron tags allow the precise and well-controlled analysis of essential genes by rapidly inducing degradation of the protein of interest. This is critical when the consequences of loss of gene function needs to be analyzed in a strictly defined time window such as a specific cell cycle phase. We have recently published the successful application of degron tags to analyze cell cycle genes such as CDC6, CCNA2, and CCNB1. A critical aspect of our approach was to combine two tags to generate a synergy in the degradation dynamics. Here we outline our approach and describe some of the essential steps to generate double-degron-tagged genes in RPE-1 cells. Similar procedures can easily be applied to other cell lines.

Pharmacological relevance of CDK inhibitors in Alzheimer's disease

Evidence suggests that cell cycle activation plays a role in the pathophysiology of neurodegenerative diseases. Alzheimer's disease is a progressive, terminal neurodegenerative disease that affects memory and other important mental functions. Intracellular deposition of Tau protein, a hyperphosphorylated form of a microtubule-associated protein, and extracellular aggregation of Amyloid β protein, which manifests as neurofibrillary tangles (NFT) and senile plaques, respectively, characterize this condition. In recent years, however, several studies have concluded that cell cycle re-entry is one of the key causes of neuronal death in the pathogenesis of Alzheimer's disease. The eukaryotic cell cycle is well-coordinated machinery that performs critical functions in cell replenishment, such as DNA replication, cell creation, repair, and the birth of new daughter cells from the mother cell. The complex interplay between the levels of various cyclins and cyclin-dependent kinases (CDKs) at different checkpoints is needed for cell cycle synchronization. CDKIs (cyclin-dependent kinase inhibitors) prevent cyclin degradation and CDK inactivation. Different external and internal factors regulate them differently, and they have different tissue expression and developmental functions. The checkpoints ensure that the previous step is completed correctly before starting the new cell cycle phase, and they protect against the transfer of defects to the daughter cells. Due to the development of more selective and potent ATP-competitive CDK inhibitors, CDK inhibitors appear to be on the verge of having a clinical impact. This avenue is likely to yield new and effective medicines for the treatment of cancer and other neurodegenerative diseases. These new methods for recognizing CDK inhibitors may be used to create non-ATP-competitive agents that target CDK4, CDK5, and other CDKs that have been recognized as important therapeutic targets in Alzheimer's disease treatment.

Identification of differentially abundant mRNA transcripts and autocrine/paracrine factors in oocytes and follicle cells of mud crabs

The late vitellogenic stage of the mud crab is characterized by large and obvious follicle cells as well as an enlarged oocyte nucleus and a prominent germinal vesicle (GV). The aim of this study was evaluation of functions of oocytes and follicle cells during meiosis as well as at identifying associated ovarian autocrine/paracrine factors using comparative transcriptomics. The results from the KEGG pathway analysis indicated DNA replication, nucleotide excision repair, spliceosome and the ribosome pathways were highly associated with oocyte maturation across both transcriptomes. In addition, there was a larger abundance of mRNA transcripts for cell cycle-related genes in the oocyte, as well as cyclin A, cyclin B and CKS1B in the GV than at the time of germinal vesicle breakdown (GVBD). These findings indicate these cell cycle-related genes might be involved in GVBD induction. Results when there was localization of ligands and the respective receptors of VEGF, TGFβ propeptide and BMP9/10 indicated these proteins might be autocrine/paracrine factors. Results from functional analysis of VEGF, TGFβ propeptide and BMP9/10 in oocyte maturation using RNA interference revealed that these proteins might be involved in oocyte maturation by regulating cyclin abundance. This is the first study on the functions of VEGF in oocyte maturation in invertebrates.

Oscillating waves of Fox, Cyclin and CDK gene expression indicate unique spatiotemporal control of cell cycling during nervous system development in onychophorans

Forkhead box (Fox) genes code for a class of transcription factors with many different fundamental functions in animal development including cell cycle control. Other important factors of cell cycle control are Cyclins and Cyclin-dependent kinases (CDKs). Here we report on the oscillating expression of three Fox genes, FoxM, FoxN14 (jumeaux) and FoxN23 (Checkpoint suppressor like-1), Cyclins and CDKs in an onychophoran, a representative of a relatively small group of animals that are closely related to the arthropods. Expression of these genes is in the form of several waves that start as dot-like domains in the center of each segment and then transform into concentric rings that run towards the periphery of the segments. This oscillating gene expression, however, occurs exclusively along the anterior-posterior body axis in the tissue ventral to the base of the appendages, a region where the central nervous system and the enigmatic ventral and preventral organs of the onychophoran develop. We suggest that the oscillating gene expression and the resulting waves of expression we report are likely correlated with cell cycle control during the development of the onychophoran nervous system. This intriguing patterning appears to be unique for onychophorans as it is not found in any of the arthropods we also investigated in this study, and is likely correlated with the slow embryonic development of onychophorans compared to arthropods.

Upregulation of KIF11 in TP53 Mutant Glioma Promotes Tumor Stemness and Drug Resistance

Glioma is the most common type of primary brain malignancy with high morbidity and mortality, but little is known about its pathological mechanisms. Kinesin family member 11 (KIF11) is a key driver of malignancy in glioblastoma, a grade IV glioma, but its involvement in glioma chemoresistance remains to be determined. We accessed the TCGA open datasets, collected glioma tumor tissue samples, and analyzed the expression of KIF11 in glioma patients. Meanwhile, the correlation between KIF11 and survival outcomes was determined by the Kaplan-Meier analysis. The role of KIF11 in glioma tumor cell function was assessed in an in vitro knockdown and overexpressing system. Here, we found that KIF11 was upregulated in glioma tumors and negatively correlated with overall survival outcomes via analyzing the open datasets. KIF11 was negatively correlated with TP53 expression. Furthermore, KIF11 promoted the stemness in glioma cells, accompanied by increased cell proliferation and chemoresistance. Mechanistically, we found that KIF11 promoted cell cycle progression via upregulating cyclin expression.

pombe CDK5 Orthologue Pef1 Cooperates with Three Cyclins, Clg1, Pas1 and Psl1, to Promote Pre-Meiotic DNA Replication

Meiosis is a specialized cell division process that mediates genetic information transfer to the next generation. Meiotic chromosomal segregation occurs when DNA replication is completed during the pre-meiotic S phase. Here, we show that Schizosaccharomyces pombe Pef1, an orthologue of mammalian cyclin-dependent kinase 5 (CDK5), is required to promote pre-meiotic DNA replication. We examined the efficiency of meiotic initiation using pat1-114 mutants and found that, meiotic nuclear divisions did not occur in the pef1Δ pat1-114 strain. Deletion of pef1 also suppressed the expression of DNA replication factors and the phosphorylation of Cdc2 Tyr-15. The double deletion of clg1 and psl1 arrested meiotic initiation in pat1-114 mutant cells, similar to that of pef1-deficient cells. Meiotic progression was also slightly delayed in the pas1-deficient strain. Our results reveal that Pef1 regulates cyclin-coordinated meiotic progression.

Cell Cycle Control: A System of Interlinking Oscillators

The cell cycle is the sequence of events through which a cell duplicates its genome, grows, and divides. Key cell cycle transitions are driven by oscillators comprising of protein kinases and their regulators. Different cell cycle oscillators are inextricably linked to ensure orderly activation of oscillators. A recurring theme in their regulation is the abundance of autoamplifying loops that ensure switch-like and unidirectional cell cycle transitions. The periodicity of many cell cycle oscillators is choreographed by inherent mechanisms that promote automatic inactivation, often involving dephosphorylation and ubiquitin-mediated protein degradation. These inhibitory signals are subsequently suppressed to enable the next cell cycle to occur. Although the activation and inactivation of cell cycle oscillators are in essence autonomous during the unperturbed cell cycle, a number of checkpoint mechanisms are able to halt the cell cycle until preconditions or defects are addressed. Together, these mechanisms orchestrate orderly progression of the cell cycle to produce more cells and to safeguard genome stability.

Plant cell cycle regulators: Mitogen-activated protein kinase, a new regulating switch?

Cell cycle is essential for the maintenance of genetic material and continuity of a species. Its regulation involves a complex interplay between multiple proteins with diverse molecular functions such as the kinases, transcription factors, proteases and phosphatases. Every step of this cycle requires a certain combination of these protein regulators which paves the way for the next stage. It is now evident that plants have their own unique features in the context of cell cycle regulation. Cell cycle in plants is not only necessary for maintenance of its physio-morphological parameter but it also regulates traits important for mankind like grain or fruit size. This makes it even more important to understand how plants regulate its cell cycle amidst various a/biotic stresses it is subjected to during its lifetime. The association of MAPK signaling pathways with every major developmental and stress response pathways in plants raises the question of its potential role in cell cycle regulation. There are number of cell cycle regulating proteins with putative sites for MAPK phosphorylation. The MAPK signaling pathway may directly or in a parallel pathway regulate the plant cell cycle. Unraveling the role of MAPK in cell cycle will open up new arenas to explore.

Role of cyclins and cyclin-dependent kinases in pluripotent stem cells and their potential as a therapeutic target

Over the last 15 years connections between cell cycle control, maintenance of pluripotency, and control of cell fate decisions have been firmly established. With the emergence of powerful tools, such as highly-specific small molecule inhibitors for cyclin-dependent protein kinase (CDK) activity and single-cell imaging technologies, the mechanistic links between cyclins, CDKs and regulation in PSCs in mechanistic detail has been made possible. In this review, we discuss new developments that mechanistically link the CDK regulatory network to control of cell fate decisions, including maintenance of the pluripotent state. Overall, these findings have potential to impact the translational applications of stem cells in regenerative medicine, drug discovery and cancer treatment.

The S. pombe CDK5 ortholog Pef1 regulates sexual differentiation through control of the TORC1 pathway and autophagy

In Schizosaccharomyces pombe, a general strategy for survival in response to environmental changes is sexual differentiation, which is triggered by TORC1 inactivation. However, mechanisms of TORC1 regulation in fission yeast remain poorly understood. In this study, we found that Pef1, which is an ortholog of mammalian CDK5, regulates the initiation of sexual differentiation through positive regulation of TORC1 activity. Conversely, deletion of pef1 leads to activation of autophagy and subsequent excessive TORC1 reactivation during the early phases of the nitrogen starvation response. This excessive TORC1 reactivation results in the silencing of the Ste11-Mei2 pathway and mating defects. Additionally, we found that pef1 genetically interacts with tsc1 and tsc2 for TORC1 regulation, and physically interacts with three cyclins, Clg1, Pas1 and Psl1. The double deletion of clg1 and pas1 promotes activation of autophagy and TORC1 during nitrogen starvation, similar to what is seen in pef1Δ cells. Overall, our work suggests that Pef1-Clg1 and Pef1-Pas1 complexes regulate initiation of sexual differentiation through control of the TSC-TORC1 pathway and autophagy.

Cell Cycle Deficits in Neurodegenerative Disorders: Uncovering Molecular Mechanisms to Drive Innovative Therapeutic Development

Cell cycle dysregulation has been implicated in the pathogenesis of neurodegenerative disorders. Specialised function obligates neuronal cells to subsist in a quiescent state of cell cycle once differentiated and therefore the circumstances and mechanisms underlying aberrant cell cycle activation in post-mitotic neurons in physiological and disease conditions remains an intriguing area of research. There is a strict requirement of concurrence to cell cycle regulation for neurons to ensure intracellular biochemical conformity as well as interrelationship with other cells within neural tissues. This review deliberates on various mechanisms underlying cell cycle regulation in neuronal cells and underscores potential implications of their non-compliance in neural pathology. Recent research suggests that successful duplication of genetic material without subsequent induction of mitosis induces inherent molecular flaws that eventually assert as apoptotic changes. The consequences of anomalous cell cycle activation and subsequent apoptosis are demonstrated by the increased presence of molecular stress response and apoptotic markers. This review delineates cell cycle events under normal physiological conditions and deficits amalgamated by alterations in protein levels and signalling pathways associated with cell-division are analysed. Cell cycle regulators essentially, cyclins, CDKs, cip/kip family of inhibitors, caspases, bax and p53 have been identified to be involved in impaired cell cycle regulation and associated with neural pathology. The pharmacological modulators of cell cycle that are shown to impart protection in various animal models of neurological deficits are summarised. Greater understanding of the molecular mechanisms that are indispensable to cell cycle regulation in neurons in health and disease conditions will facilitate targeted drug development for neuroprotection.

Analysis of localization of cell-cycle regulators in Neurospora crassa

Most fungi are multinucleated organisms. In some fungi, they have asynchronous nuclei in the same cytoplasm. We analyzed a cell-cycle regulation mechanism using a model fungus Neurospora crassa, which can make heterokaryon cells. G1/S cyclin CLN-1 and cyclin-dependent kinase CDC-2 were tagged with different fluorescence in different strains and expressed. By forming a heterokaryon strain of these, two different fluorescence-tagged proteins were expressed in the same cytoplasm. CDC-2 was localized in all nuclei, whereas CLN-1 was not detected in most of the nuclei and was dispersed in the cytoplasm with small granular clusters. This indicates that in multinucleated fungi, cell-cycle regulators, similar to other proteins, are shared around the nuclei regardless of different cell-cycle stages. Moreover, each nucleus can select and use a special cell-cycle regulator only when it is necessary. Fungal nuclei may have a novel pickup mechanism of necessary proteins from their cytoplasm at the point of use.

Cyclin A triggers Mitosis either via the Greatwall kinase pathway or Cyclin B

Two mitotic cyclin types, cyclin A and B, exist in higher eukaryotes, but their specialised functions in mitosis are incompletely understood. Using degron tags for rapid inducible protein removal, we analyse how acute depletion of these proteins affects mitosis. Loss of cyclin A in G2-phase prevents mitotic entry. Cells lacking cyclin B can enter mitosis and phosphorylate most mitotic proteins, because of parallel PP2A:B55 phosphatase inactivation by Greatwall kinase. The final barrier to mitotic establishment corresponds to nuclear envelope breakdown, which requires a decisive shift in the balance of cyclin-dependent kinase Cdk1 and PP2A:B55 activity. Beyond this point, cyclin B/Cdk1 is essential for phosphorylation of a distinct subset of mitotic Cdk1 substrates that are essential to complete cell division. Our results identify how cyclin A, cyclin B and Greatwall kinase coordinate mitotic progression by increasing levels of Cdk1-dependent substrate phosphorylation.

The prognostic significance of CDKN2A homozygous deletion in IDH-mutant lower-grade glioma and glioblastoma: a systematic review of the contemporary literature

BACKGROUND

The most recent cIMPACT-NOW update highlighted the homozygous deletion of the Cyclin Dependent Kinase Inhibitor 2A (CDKN2A) gene as a clinically important molecular alteration in IDH-mutant glioma. Correspondingly, we systematically reviewed the contemporary literature to affirm the contemporary stance of the literature on the prognostic significance of this alteration in this setting based on the current World Health Organization (WHO) Grade classification.

METHODS

A systematic search of seven electronic databases from inception to February 2020 was conducted following PRISMA guidelines. Articles were screened against pre-specified criteria to include lower-grade glioma (LGG, WHO Grade II/III) and glioblastoma (GBM, WHO Grade IV) separately. Progression free survival (PFS) and overall survival (OS) from Kaplan-Meier and multivariable analyses were outcomes of interest.

RESULTS

Nine institutional studies describing 2193 IDH-mutant gliomas satisfied criteria for evaluation, with 1756 (80%) LGG and 437 (20%) GBM. When reported, the proportion of CDKN2A homozygous deleted gliomas ranged from 9 to 43%, with a median incidence of 22%. For LGG, Kaplan-Meier analyses demonstrated shorter PFS in the presence of CDKN2A homozygous deletion in three studies (median values, 31 versus 91 months), and shorter OS in five studies (median values, 61 versus 154 months). For GBM, Kaplan-Meier analyses demonstrated shorter PFS in the presence of CDKN2A homozygous deletion in two studies (median values, 16 versus 30 months), and shorter OS in four studies (median values, 38 versus 86 months). By multivariable analyses, CDKN2A homozygous deletion was a predictor of significantly shorter PFS and OS in both LGG and GBM across all included studies.

CONCLUSIONS

The CDKN2A homozygous deletion is an important prognostic factor for survival outcomes of IDH-mutant glioma patients across multiple histologic WHO grades with specific molecular features likely dependent on IDH-mutant status. Greater understanding of how identifying this deletion can assist in the stratification of management for these tumors to optimize clinical course is required.

Melatonin modulates proliferation of pancreatic stellate cells through caspase-3 activation and changes in cyclin A and D expression

In this study, the effects of melatonin (1 μM-1 mM) on pancreatic stellate cells (PSC) have been examined. Cell viability and proliferation, caspase-3 activation, and the expression of cyclin A and cyclin D were analyzed. Our results show that melatonin decreased PSC viability in a time- and concentration-dependent manner. This effect was not inhibited by treatment of cells with MT1, MT2, calmodulin, or ROR-alpha inhibitors prior to melatonin addition. Activation of caspase-3 in response to melatonin was detected. The expression of cyclin A and cyclin D was decreased in cells treated with melatonin. Finally, changes in BrdU incorporation into the newly synthesized DNA of proliferating cells were also observed in the presence of melatonin. We conclude that melatonin, at pharmacological concentrations, modulates proliferation of PSC through activation of apoptosis and involving crucial regulators of the cell cycle. These actions might not require specific melatonin receptors. Our observations suggest that melatonin, at high doses, could potentially exert anti-fibrotic effects and, thus, could be taken into consideration as supportive treatment in the therapy of pancreatic diseases.

Inhibition of PI3K/AKT molecular pathway mediated by membrane estrogen receptor GPER accounts for cryptotanshinone induced antiproliferative effect on breast cancer SKBR-3 cells

Background

Breast cancer is the most frequently diagnosed malignancy among women and the second leading cause of cancer death worldwide. Among which nuclear estrogen receptor (nER) negative breast cancer is always with much poor prognosis. Recently, membrane G protein coupled estrogen receptor (GPER), a newly recognized estrogen receptor has been documented to take essential part in the development and treatment of breast cancer. The present study was designed to investigate the anti nER negative breast cancer effect of cryptotanshinone (CPT), an important active compound of traditional Chinese medicine Danshen and its possible molecular pathway.

Methods

The following in vitro tests were performed in nER negative but GPER positive breast cancer SKBR-3 cells. The effect of CPT on cell proliferation rate and cell cycle distribution was evaluated by MTT cell viability test and flow cytometry assay respectively. The role of PI3K/AKT pathway and the mediated function of GPER were tested by western blot and immunofluorescence. Technique of gene silence and the specific GPER agonist G-1 and antagonist G-15 were employed in the experiments to further verify the function of GPER in mediating the anticancer role of CPT.

Results

The results showed that proliferation of SKBR-3 cells could be blocked by CPT in a time and dose dependent manner. CPT could also exert antiproliferative activities by arresting cell cycle progression in G1 phase and down regulating the expression level of cyclin A, cyclin B, cyclin D and cyclin-dependent kinase 2 (CDK2). The antiproliferative effect of CPT was further enhanced by G-1 and attenuated by G-15. Results of western blot and immunofluorescence showed that expression of PI3K and p-AKT could be downregulated by CPT and such effects were mediated by GPER which were further demonstrated by gene silence test.

Conclusion

The current study showed that the antiproliferative action of CPT on SKBR-3 cells was realized by inhibition of GPER mediated PI3K/AKT pathway. These findings provide further validation of GPER serving as useful therapeutic target.

Mammalian cell cycle cyclins

Proper progression throughout the cell division cycle depends on the expression level of a family of proteins known as cyclins, and the subsequent activation of cyclin-dependent kinases (Cdks). Among the numerous members of the mammalian cyclin family, only a few of them, cyclins A, B, C, D and E, are known to display critical roles in the cell cycle. These functions will be reviewed here with a special focus on their relevance in different cell types in vivo and their implications in human disease.

Cyclin D-CDK4/6 functions in cancer

The mammalian cell cycle is driven by a complex of cyclins and their associated cyclin-dependent kinases (CDKs). Abnormal dysregulation of cyclin-CDK is a hallmark of cancer. D-type cyclins and their associated CDKs (CDK4 and CDK6) are key components of cell cycle machinery in driving G1 to S phase transition via phosphorylating and inactivating the retinoblastoma protein (RB). A body of evidence shows that the cyclin Ds-CDKs axis plays a critical role in cancer through various aspects, such as control of proliferation, senescence, migration, apoptosis, and angiogenesis. CDK4/6 dual-inhibitors show significant efficacy in pre-clinical or clinical cancer therapies either as single agents or in combination with hormone, chemotherapy, irradiation or immune treatments. Of note, as the associated partner of D-type cyclins, CDK6 shows multiple distinct functions from CDK4 in cancer. Depletion of the individual CDK may provide a therapeutic strategy for patients with cancer.

Sexual cell cycle initiation is regulated by CDK19 and CYC9 in Tetrahymena thermophila

To investigate the mechanisms underlying initiation of the sexual cell cycle in eukaryotes, we have focused on cyclins and cyclin-dependent kinases (CDKs) in the well-studied model ciliate, Tetrahymena thermophila We identified two genes, CDK19 and CYC9, which are highly co-expressed with the mating-associated factors MTA, MTB and HAP2. Both CDK19 and CYC9 were found to be essential for mating in T. thermophila Subcellular localization experiments suggested that these proteins are located at the oral area, including the conjugation junction area, and that CDK19 or CYC9 knockout prevents mating. We found that CDK19 and CYC9 form a complex, and also identified several additional subunits, which may have regulatory or constitutive functions. RNA sequencing analyses and cytological experiments showed that mating is abnormal in both ΔCDK19 and ΔCYC9, mainly at the entry to the co-stimulation stage. These results indicate that the CDK19-CYC9 complex initiates the sexual cell cycle in T. thermophila.

Exposure to radioactive rocks from the Egyptian eastern desert attenuates the efficiency of the immune organs and induces apoptosis of blood lymphocytes in rat model

Exposure to ionizing radiation emitted from natural sources induces many health hazards. The response to ionizing radiation involves a number of mediators including inflammatory cytokines and free radicals which mediate immunosuppression. The present study aimed to monitor the impact of exposure to natural radioactive rocks from the Egyptian eastern desert on the primary immune organs. Therefore, three experimental groups (15 rats per group) were used: group I included the control non-irradiated rats; group II included rats that were exposed for 28 consecutive days to natural radioactive rocks from the Egyptian eastern desert (IR/R group); and group III (positive control group) included rats that were exposed to high dose of γ-rays (4 Gy/14 days for 28 days) (IR/γR group). We found that rats of both the IR/R and IR/γR groups exhibited pathological alterations in the architecture of the primary immune organs (bone marrow and thymus). Additionally, the levels of C-reactive protein (CRP), proinflammatory cytokines (IL-1β, IL-6 and TNF-α), and reactive oxygen species (ROS) were significantly increased in the IR/R and IR/γR groups compared to the control group. Furthermore, rats from the IR/R and IR/γR groups exhibited significant increase in the activity of caspase-3 and caspase-9 and subsequently exhibited a significant increase in the apoptosis of PBMCs compared with the control group. Most importantly, apoptosis induction in the PBMCs was associated with increased expression of cyclin B1 and decreased expression of cyclin D1 and survivin compared with the control non-irradiated group. Taken together, our data demonstrated that consecutive exposure to natural radioactive rocks from the Egyptian eastern desert could dampen the immune response through damaging the architectures of the immune system and mediating serious health problems to the population inhabiting this region.

Cyclin-dependent kinase inhibition: an opportunity to target protein-protein interactions

Cyclin-dependent kinases (CDKs) play an integral part in cellular activities. To date, most of the activities have been evaluated in the cell cycle and transcription. Several diseases are affected by abnormalities in CDKs, related-pathways, or proteins that regulate CDK activity. CDKs are primarily dependent on activation by binding other proteins, namely Cyclins. In addition, phosphorylation of key CDK residues also plays a major part in CDK activity. To date, the most successful drugs have been developed against CDK4 and CDK6 and are FDA approved for use in advanced breast cancer. However, this is likely only a small fraction of the potential for targeting CDKs as a strategy against cancer and other diseases. Based on the extensive protein-protein interactions made by CDKs with other proteins (Cyclins and others), there are numerous possibilities for targeting strategies against protein-protein interactions. Here we describe the predominant roles of CDKs in the cell, key interacting proteins, significant 3-dimensional structural characteristics, and summarize the work-to-date in inhibition of CDKs.

The atypical cyclin-like protein Spy1 overrides p53-mediated tumour suppression and promotes susceptibility to breast tumourigenesis

Background

Breast cancer is the most common cancer to affect women and one of the leading causes of cancer-related deaths. Proper regulation of cell cycle checkpoints plays a critical role in preventing the accumulation of deleterious mutations. Perturbations in the expression or activity of mediators of cell cycle progression or checkpoint activation represent important events that may increase susceptibility to the onset of carcinogenesis. The atypical cyclin-like protein Spy1 was isolated in a screen for novel genes that could bypass the DNA damage response. Clinical data demonstrates that protein levels of Spy1 are significantly elevated in ductal and lobular carcinoma of the breast. We hypothesized that elevated Spy1 would override protective cell cycle checkpoints and support the onset of mammary tumourigenesis.

Methods

We generated a transgenic mouse model driving expression of Spy1 in the mammary epithelium. Mammary development, growth characteristics and susceptibility to tumourigenesis were studied. In vitro studies were conducted to investigate the relationship between Spy1 and p53.

Results

We found that in the presence of wild-type p53, Spy1 protein is held ‘in check’ via protein degradation, representing a novel endogenous mechanism to ensure protected checkpoint control. Regulation of Spy1 by p53 is at the protein level and is mediated in part by Nedd4. Mutation or abrogation of p53 is sufficient to allow for accumulation of Spy1 levels resulting in mammary hyperplasia. Sustained elevation of Spy1 results in elevated proliferation of the mammary gland and susceptibility to tumourigenesis.

Conclusions

This mouse model demonstrates for the first time that degradation of the cyclin-like protein Spy1 is an essential component of p53-mediated tumour suppression. Targeting cyclin-like protein activity may therefore represent a mechanism of re-sensitizing cells to important cell cycle checkpoints in a therapeutic setting.

Greatwall-Endosulfine: A Molecular Switch that Regulates PP2A/B55 Protein Phosphatase Activity in Dividing and Quiescent Cells

During the cell cycle, hundreds of proteins become phosphorylated and dephosphorylated, indicating that protein kinases and protein phosphatases play a central role in its regulation. It has been widely recognized that oscillation in cyclin-dependent kinase (CDK) activity promotes DNA replication, during S-phase, and chromosome segregation, during mitosis. Each CDK substrate phosphorylation status is defined by the balance between CDKs and CDK-counteracting phosphatases. In fission yeast and animal cells, PP2A/B55 is the main protein phosphatase that counteracts CDK activity. PP2A/B55 plays a key role in mitotic entry and mitotic exit, and it is regulated by the Greatwall-Endosulfine (ENSA) molecular switch that inactivates PP2A/B55 at the onset of mitosis, allowing maximal CDK activity at metaphase. The Greatwall-ENSA-PP2A/B55 pathway is highly conserved from yeast to animal cells. In yeasts, Greatwall is negatively regulated by nutrients through TORC1 and S6 kinase, and couples cell growth, regulated by TORC1, to cell cycle progression, driven by CDK activity. In animal cells, Greatwall is phosphorylated and activated by Cdk1 at G2/M, generating a bistable molecular switch that results in full activation of Cdk1/CyclinB. Here we review the current knowledge of the Greatwall-ENSA-PP2A/B55 pathway and discuss its role in cell cycle progression and as an integrator of nutritional cues.

A bidirectional effect of Rac1 inhibition-Protects radiation-induced intestinal injury while inhibits tumor

AIMS

To investigate whether Rac1 inhibition can alleviate radiation-induced intestinal injury (RIII), meanwhile exist no protection on tumors.

MATERIALS AND METHODS

Rac1 inhibition was achieved by its specific inhibitor, NSC23766. Mice were pretreated with different intraperitoneal injections, which were normal saline for NS group (N = 9), and 2.5 mg/kg and 5 mg/kg of NSC23766 for Low-Dose group (N = 9) and High-Dose group (N = 9), respectively. After total body irritation (10Gy), small intestinal tissues were collected for Hematoxylin-Eosin (H&E) staining and Terminal-deoxynucleotidyl Transferase Mediated dUTP Nick End Labeling (TUNEL). Intestinal epithelial and tumor cell lines, namely MODE-k and CT-26, were used to further study the role of Rac1 inhibition on radiation damage. Flow cytometry was used to detect changes in reactive oxygen species production, cell cycles and mitochondrial membrane potential, the latter was also checked by fluorescence microscope. Changes of protein-expression associated with apoptosis and cell cycles were detected by Western blotting to explain the possible molecular mechanism.

KEY FINDINGS

Height of intestine villi and depth of crypt were higher (P < 0.01) and apoptosis ratio lower (P < 0.01) in High-Dose group compared with those in NS group. After radiation, Rac1 inhibition pre-treatment improved the vitality (P < 0.01) and reduced the apoptosis (P < 0.01) in MODE-k while yielded opposite results in CT-26, and reduced ROS production of MODE-k (P < 0.01) while had little effect on that of CT-26. Rac1 inhibition differently affected the cell cycles of normal cells and that of tumor cells.

SIGNIFICANCE

Inhibition of Rac1 could alleviate RIII, meanwhile assist the killing effect of radiation on tumor cells.

Cyclin B3 is dispensable for mouse spermatogenesis

Cyclins, as regulatory partners of cyclin-dependent kinases (CDKs), control the switch-like cell cycle transitions that orchestrate orderly duplication and segregation of genomes. Compared to mitosis, relatively little is known about how cyclin-CDK complexes control meiosis, the specialized cell division that generates gametes for sexual production. Mouse cyclin B3 was previously shown to have expression restricted to the beginning of meiosis, making it a candidate to regulate meiotic events. Indeed, female mice lacking cyclin B3 are sterile because oocytes arrest at the metaphase-to-anaphase transition of meiosis I. However, whether cyclin B3 functions during spermatogenesis was untested. Here, we found that males lacking cyclin B3 are fertile and show no detectable defects in spermatogenesis based on histological analysis of seminiferous tubules. Cytological analysis further showed no detectable defects in homologous chromosome synapsis or meiotic progression, and suggested that recombination is initiated and completed efficiently. Moreover, absence of cyclin B3 did not exacerbate previously described meiotic defects in mutants deficient for cyclin E2, suggesting a lack of redundancy between these cyclins. Thus, unlike in females, cyclin B3 is not essential for meiosis in males despite its prominent meiosis-specific expression.

Identification of novel PCTAIRE-1/CDK16 substrates using a chemical genetic screen

PCTAIRE-1 (also known as cyclin-dependent protein kinase (CDK) 16), is a Ser/Thr kinase that has been implicated in many cellular processes, including cell cycle, spermatogenesis, neurite outgrowth, and vesicle trafficking. Most recently, it has been proposed as a novel X-linked intellectual disability (XLID) gene, where loss-of-function mutations have been identified in human patients. The precise molecular mechanisms that regulate PCTAIRE-1 remained largely obscure, and only a few cellular targets/substrates have been proposed with no clear functional significance. We and others recently showed that cyclin Y binds and activates PCTAIRE-1 via phosphorylation and 14-3-3 binding. In order to understand the physiological role that PCTAIRE-1 plays in brain, we have performed a chemical genetic screen in vitro using an engineered PCTAIRE-1/cyclin Y complex and mouse brain extracts. Our screen has identified potential PCTAIRE-1 substrates (AP2-Associated Kinase 1 (AAK1), dynamin 1, and synaptojanin 1) in brain that have been shown to regulate crucial steps of receptor endocytosis, and are involved in control of neuronal synaptic transmission. Furthermore, mass spectrometry and protein sequence analyses have identified potential PCTAIRE-1 regulated phosphorylation sites on AAK1 and we validated their PCTAIRE-1 dependence in a cellular study and/or brain tissue lysates. Our results shed light onto the missing link between PCTAIRE-1 regulation and proposed physiological functions, and provide a basis upon which to further study PCTAIRE-1 function in vivo and its potential role in neuronal/brain disorders.

Proliferating cell nuclear antigen associates to protein complexes containing cyclins/cyclin dependent kinases susceptible of inhibition by KRPs during maize germination

The Proliferating Cell Nuclear Antigen, PCNA, has roles in both G1 and S phases of the cell cycle. Here we show that maize PCNA can be found in cells in structures of a trimer or a dimer of trimer, in complexes of high molecular mass that change in size as germination proceeds, co-eluting with cell cycle proteins as CycD3;1 and CDKs (A/B1;1). Using different methodological strategies, we show that PCNA actually interacts with CycD3;1, CDKA, CDKB1;1, KRP1;1 and KRP4;1, all of which contain PIP or PIP-like motifs. Anti-PCNA immunoprecipitates show kinase activity that is inhibited by KRP1;1 and KRP4;2, indicating the formation of quaternary complexes PCNA-CycD/CDKs-KRPs in which PCNA would act as a platform. This inhibitory effect seems to be differential during the germination process, more pronounced as germination advances, suggesting a complex regulatory mechanism in which PCNA could bind different sets of cyclins/CDKs, some more susceptible to inhibition by KRPs than others.

Cell cycle, energy metabolism and DNA repair pathways in cancer cells are suppressed by Compound Kushen Injection

BACKGROUND

In this report we examine candidate pathways perturbed by Compound Kushen Injection (CKI), a Traditional Chinese Medicine (TCM) that we have previously shown to alter the gene expression patterns of multiple pathways and induce apoptosis in cancer cells.

METHODS

We have measured protein levels in Hep G2 and MDA-MB-231 cells for genes in the cell cycle pathway, DNA repair pathway and DNA double strand breaks (DSBs) previously shown to have altered expression by CKI. We have also examined energy metabolism by measuring [ADP]/[ATP] ratio (cell energy charge), lactate production and glucose consumption. Our results demonstrate that CKI can suppress protein levels for cell cycle regulatory proteins and DNA repair while increasing the level of DSBs. We also show that energy metabolism is reduced based on reduced glucose consumption and reduced cellular energy charge.

RESULTS

Our results validate these pathways as important targets for CKI. We also examined the effect of the major alkaloid component of CKI, oxymatrine and determined that it had no effect on DSBs, a small effect on the cell cycle and increased the cell energy charge.

CONCLUSIONS

Our results indicate that CKI likely acts through the effect of multiple compounds on multiple targets where the observed phenotype is the integration of these effects and synergistic interactions.

Mass Cytometric Cell Cycle Analysis

The regulated proliferation of cells is a critical factor in tumor progression, antineoplastic therapies, immune system regulation, and the cellular developmental of multicellular organisms. While measurement of cell cycle state by fluorescent flow cytometry is well established, mass cytometry allows the cell cycle to be measured along with large numbers of other antigens enabling characterization of the complex interactions between the cell cycle and wide variety of cellular processes. This method describes the use of mass cytometry for the analysis of cell cycle state for cells from three different sources: in vitro cultured cell lines, ex vivo human blood or bone marrow, and in vivo labeling of murine tissues. The method utilizes incorporation of 5-Iodo-2'-deoxyuridine (IdU), combined with measurement of phosphorylated retinoblastoma protein (pRb), Cyclin B1, and phosphorylated Histone H3 (pHH3). These measurements can be integrated into a gating strategy that enables clear separation of all five phases of the cell cycle.

Sparstolonin B (SsnB) attenuates liver fibrosis via a parallel conjugate pathway involving P53-P21 axis, TGF-beta signaling and focal adhesion that is TLR4 dependent

SsnB previously showed a promising role to lessen liver inflammation observed in a mouse model of NAFLD. Since NAFLD can progress to fibrosis, studies were designed to unravel its role in attenuating NAFLD associated fibrosis. Using both in vivo and in vitro approaches, the study probed the possible mechanisms that underlined the role of SsnB in mitigating fibrosis. Mechanistically, SsnB, a TLR4 antagonist, decreased TLR4-PI3k akt signaling by upregulating PTEN protein expression. It also decreased MDM2 protein activation and increased p53 and p21 gene and protein expression. SsnB also downregulated pro-fibrogenic hedgehog signaling pathway, inhibited hepatic stellate cell proliferation and induced apoptosis in hepatic stellate cells, a mechanism that was LPS dependent. Further, SsnB decreased fibrosis by antagonizing TLR4 induced TGFβ signaling pathway. Alternatively, SsnB augmented BAMBI (a TGFβ pseudo-receptor) expression in mice liver by inhibiting TLR4 signaling pathway and thus reduced TGFβ signaling, resulting in decreased hepatic stellate cell activation and extracellular matrix deposition. In vitro experiments on human hepatic stellate cell line showed that SsnB increased gene and protein expression of BAMBI. It also decreased nuclear co-localization of phospho SMAD2/3 and SMAD4 protein and thus attenuated TGFβ signaling in vitro. We also observed a significant decrease in phosphorylation of SMAD2/3 protein, decreased STAT3 activation, alteration of focal adhesion protein and stress fiber disassembly upon SsnB administration in hepatic stellate cells which further confirmed the antagonistic effect of SsnB on TLR4-induced fibrogenesis.

A putative cyclin, SiPHO80 from root endophytic fungus Serendipita indica regulates phosphate homeostasis, salinity and heavy metal toxicity tolerance

Serendipita indica previously known as Piriformospora indica is an arbuscular mycorrhizal fungi (AMF) like endophytic fungus which can be cultivated axenically and colonizes an array of plants, thereby promoting their growth and confers biotic and abiotic stress tolerance to the colonized host plant. It efficiently sequestrates heavy metals and defends host plant against heavy metal-induced toxicity. In the present study, SiPHO80, a homologue of S. cerevisiae PHO80 was isolated from S. indica and functionally characterized in S. cerevisiae. SiPHO80 has conserved 'cyclin box' domain and closely related to negative regulator cyclin of the wood decaying fungi. In S. indica, its expression gets upregulated in phosphate-rich media. The regulation of Pi homeostasis which was disrupted in S. cerevisiae Δpho80 grown under high Pi condition was restored upon complementation with SiPHO80. Also, the expression of SiPHO80 in Δpho80 mutant restored osmotolerance and heavy metal tolerance. This is the first report of a cyclin which is involved in Pi homeostasis, salt tolerance, heavy metal toxicity tolerance in any plant growth promoting endophytic fungi.

ANGPTL2 deletion inhibits osteoclast generation by modulating NF-κB/MAPKs/Cyclin pathways

Osteoclasts are multinucleated cells essential for bone-resorption. Successful repair of bone defciencies still remains a great challenge worldwide. The signaling factor angiopoietin-like protein 2 (ANGPTL2), one of eight ANGPTL proteins, functions in maintenance of tissue homeostasis partly through regulating inflammation. In the study, ANGPTL2 expression was promoted during osteoclast development and that suppressing ANGPTL2 alleviated osteoclast production regulated by macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). The results suggested that ANGPTL2 knockdown inhibited M-CSF-caused proliferation of osteoclast precursor cells. Further, ANGPTL2 silence reduced nuclear factor of activated T cell c 1 (NFATC1) and NFATC4 expressions in M-CSF-treated cells, along with decreased Runx2, OPN and Colla1. Moreover, silencing ANGPTL2 down-regulated M-CSF-promoted expressions of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and chemoattractant protein-1 (CCL-2). Consistently, ANGPTL2 knockdown reduced M-CSF-enhanced activation of IKKα, IκBα and nuclear factor κB (NF-κB) and mitogen-activated protein kinases (MAPKs) (p38 MAPK, ERK1/2 MAPK and JNK MAPK). Additionally, knockdown of ANGPTL2 inhibited the induction of Cyclin D1, Cyclin D2 and Cyclin E1 due to M-CSF exposure. In vivo, we confirmed that ANGPTL2 knockout (KO) mice were protected against osteoporosis induced by ovariectomy (OVX), as proved by the improved bone loss and bone mineral density (BMD). Decreased expression of NFATCs was also observed in OVX-induced mice in the absence of ANGPTL2. Elevated release of pro-inflammatory cytokines was abrogated by ANGPTL2 knockout in femoral heads of mice with OVX operation, accompanied with a significant reduction of phosphorylated NF-κB and MAPKs signaling pathways. And down-regulated expression of Cyclin D1, Cyclin D2 and Cyclin E1 was observed in OVX-operated mice with ANGPTL2 knockout. Therefore, our study indicated that ANGPTL2 played an essential role in osteoclast generation through regulating the proliferation and inflammation of osteoclast lineage cells, providing new insights into the therapeutic strategy to alleviate bone loss.

Phosphorylation of Drosophila Brahma on CDK-phosphorylation sites is important for cell cycle regulation and differentiation

The SWI/SNF ATP-dependent chromatin-remodeling complex is an important evolutionarily conserved regulator of cell cycle progression. It associates with the Retinoblastoma (pRb)/HDAC/E2F/DP transcription complex to modulate cell cycle-dependent gene expression. The key catalytic component of the SWI/SNF complex in mammals is the ATPase subunit, Brahma (BRM) or BRG1. BRG1 was previously shown to be phosphorylated by the G₁-S phase cell cycle regulatory kinase Cyclin E/CDK2 in vitro, which was associated with the bypass of G₁ arrest conferred by BRG1 expression. However, it is unknown whether direct Cyclin E/CDK2-mediated phosphorylation of BRM/BRG1 is important for G₁-S phase cell cycle progression and proliferation in vivo. Herein, we demonstrate for the first time the importance of CDK-mediated phosphorylation of Brm in cell proliferation and differentiation in vivo using the Drosophila melanogaster model organism. Expression of a CDK-site phospho-mimic mutant of Brm, brm-ASP (all the potential CDK sites are mutated from Ser/Thr to Asp), which acts genetically as a brm loss-of-function allele, dominantly accelerates progression into the S phase, and bypasses a Retinoblastoma-induced developmental G₁ phase arrest in the wing epithelium. Conversely, expression of a CDK-site phospho-blocking mutation of Brm, brm-ALA, acts genetically as a brm gain-of-function mutation, and in a Brm complex compromised background reduces S phase cells. Expression of the brm phospho-mutants also affected differentiation and Decapentaplegic (BMP/TGFβ) signaling in the wing epithelium. Altogether our results show that CDK-mediated phosphorylation of Brm is important in G₁-S phase regulation and differentiation in vivo.

ABBREVIATIONS

A-P: Anterior-Posterior; BAF: BRG1-associated factor; BMP: Bone Morphogenetic Protein; Brg1: Brahma-Related Gene 1; Brm: Brahma; BSA: Bovine Serum Albumin; CDK: Cyclin dependent kinase dpp: decapentaplegic; EdU: 5-Ethynyl 2'-DeoxyUridine; EGFR: Epidermal Growth Factor Receptor; en: engrailed; GFP: Green Fluorescent Protein; GST: Glutathione-S-Transferase; HDAC: Histone DeACetylase; JNK: c-Jun N-terminal Kinase; Mad: Mothers Against Dpp; MAPK: Mitogen Activated Protein Kinase; MB:: Myelin Basic Protein; nub: nubbin; pH3: phosphorylated Histone H3; PBS: Phosphate Buffered Saline; PBT: PBS Triton; PFA: ParaFormAldehydep; Rb: Retinoblastoma protein; PCV: Posterior Cross-Vein; Snr1: Snf5-Related 1; SWI/SNF: SWitch/Sucrose Non-Fermentable; TGFβ: Transforming Growth Factor β; TUNEL: TdT-mediated dUTP Nick End Labelling; Wg: Wingless; ZNC: Zone of Non-Proliferating Cells.

The Temporal Regulation of S Phase Proteins During G1

Successful DNA replication requires intimate coordination with cell-cycle progression. Prior to DNA replication initiation in S phase, a series of essential preparatory events in G₁ phase ensures timely, complete, and precise genome duplication. Among the essential molecular processes are regulated transcriptional upregulation of genes that encode replication proteins, appropriate post-transcriptional control of replication factor abundance and activity, and assembly of DNA-loaded protein complexes to license replication origins. In this chapter we describe these critical G₁ events necessary for DNA replication and their regulation in the context of both cell-cycle entry and cell-cycle progression.

Beating the odds: programming proliferation in the mammalian heart

The heart is one of the least regenerative organs in the human body; adult cardiac myocytes divide at extremely low frequency. Therefore, meaningful induction of cardiac regeneration requires in-depth understanding of myocyte cell-cycle control. Recent insights into how myocytes can be coaxed into duplicating in vivo might inform emerging therapeutics.

CDK1 inhibition facilitates formation of syncytiotrophoblasts and expression of human Chorionic Gonadotropin

AIMS

The human placental syncytiotrophoblast (STB) cells play essential roles in embryo implantation and nutrient exchange between the mother and the fetus. STBs are polyploid which are formed by fusion of diploid cytotrophoblast (CTB) cells. Abnormality in STBs formation can result in pregnancy-related disorders. While a number of genes have been associated with CTB fusion the initial events that trigger cell fusion are not well understood. Primary objective of this study was to enhance our understanding about the molecular mechanism of placental cell fusion.

METHODS

FACS and microscopic analysis was used to optimize Forskolin-induced fusion of BeWo cells (surrogate of CTBs) and subsequently, changes in the expression of different cell cycle regulator genes were analyzed through Western blotting and qPCR. Immunohistochemistry was performed on the first trimester placental tissue sections to validate the results in the context of placental tissue. Effect of Cyclin Dependent Kinase 1 (CDK1) inhibitor, RO3306, on BeWo cell fusion was studied by microscopy and FACS, and by monitoring the expression of human Chorionic Gonadotropin (hCG) by Western blotting and qPCR.

RESULTS

The data showed that the placental cell fusion was associated with down regulation of CDK1 and its associated cyclin B, and significant decrease in DNA replication. Moreover, inhibition of CDK1 by an exogenous inhibitor induced placental cell fusion and expression of hCG.

CONCLUSION

Here, we report that the placental cell fusion can be induced by inhibiting CDK1. This study has a high therapeutic significance to manage pregnancy related abnormalities.

Progesterone arrested cell cycle progression through progesterone receptor isoform A in pancreatic neuroendocrine neoplasm

In pancreatic neuroendocrine neoplasms (Pan-NEN) progesterone signaling has been shown to have both inhibitory and stimulatory effects on cell proliferation. The ability of progesterone to inhibit tumor proliferation is of particular interest and is suggested to be mediated through the less abundantly expressed progesterone receptor (PR) isoform A (PRA). To date the mechanistic processes underlying this inhibition of proliferation remain unclear. To examine the mechanism of PRA actions, the human Pan-NEN cell line QGP-1, that endogenously expresses PR isoform B (PRB) without PRA, was transfected with PRA. PRA transfection suppressed the majority of cell cycle related genes increased by progesterone including cyclin A2 (CCNA2), cyclin B1 (CCNB1), cyclin-dependent kinase 1 (CDK1) and cyclin-dependent kinase 2 (CDK2). Importantly, following progesterone administration cell cycle distribution was shifted to S and G2/M phases in the naïve cell line but in PRA-transfected cells, this effect was suppressed. To see if these mechanistic insights were confirmed in patient samples PRA, PRB, CCNA2, CCNB, CDK1 and CDK2 immunoreactivities were assessed in Pan-NEN cases. Higher levels of cell cycle markers were associated with higher WHO grade tumors and correlations between the markers suggested formation of cyclin/CDK activated complexes in S and G2/M phases. PRA expression was associated with inverse correlation of all cell cycle markers. Collectively, these results indicate that progesterone signals through PRA negatively regulates cell cycle progression through suppressing S and G2/M phases and downregulation of cell cycle phases specific cyclins/CDKs.

Lineage- and stage-specific expressed CYCD7;1 coordinates the single symmetric division that creates stomatal guard cells

Plants, with cells fixed in place by rigid walls, often utilize spatial and temporally distinct cell division programs to organize and maintain organs. This leads to the question of how developmental regulators interact with the cell cycle machinery to link cell division events with particular developmental trajectories. In Arabidopsis leaves, the development of stomata, two-celled epidermal valves that mediate plant-atmosphere gas exchange, relies on a series of oriented stem cell-like asymmetric divisions followed by a single symmetric division. The stomatal lineage is embedded in a tissue in which other cells transition from proliferation to postmitotic differentiation earlier, necessitating stomatal lineage-specific factors to prolong competence to divide. We show that the D-type cyclin, CYCD7;1, is specifically expressed just prior to the symmetric guard cell-forming division, and that it is limiting for this division. Further, we find that CYCD7;1 is capable of promoting divisions in multiple contexts, likely through RBR1-dependent promotion of the G1/S transition, but that CYCD7;1 is regulated at the transcriptional level by cell type-specific transcription factors that confine its expression to the appropriate developmental window.

Cell Cycle Analysis by Mass Cytometry

The regulated progression of cells through the cell cycle during proliferation is a critical factor in tumor progression, anti-neoplastic therapy response, immune system regulation, and developmental biology. While flow cytometric measurement of cell cycle progression is well established, mass cytometry assays allow the cell cycle to be measured along with up to 39 other antigens enabling characterization of the complex interactions between the cell cycle and a wide variety of cellular processes. This method describes the use of mass cytometry for the analysis of cell cycle state for cells from three different sources: in vitro cultured cell lines, ex vivo human blood or bone marrow, and in vivo labeling and ex vivo analysis of murine tissues. The method utilizes incorporation of 5-Iodo-2'-deoxyuridine (IdU), combined with measurement of phosphorylated retinoblastoma protein (pRb), cyclin B1, and phosphorylated histone H3 (p-HH3). These measurements can be integrated into a gating strategy that allows for clear separation of all five phases of the cell cycle.

The tomato B-type cyclin gene, SlCycB2, plays key roles in reproductive organ development, trichome initiation, terpenoids biosynthesis and Prodenia litura defense

Cyclins exist extensively in various plant species. Among them, B-type cyclins play important roles in the transition of G2-to-M. However, few B-type cyclins have been reported to participate in reproductive organ development and trichome formation. In this study, transgene analysis showed that SlCycB2 overexpression caused abnormal flower with the unclosed stamen, shortened style and aberrant pollen. In addition, nearly all non-glandular trichomes, as well as the glandular ones were disappeared. On the contrary, suppression of SlCycB2 could promote type III and type V trichomes formation. Detection of secondary metabolites indicated that the production of monoterpene and sesquiterpene were significantly decreased in SlCycB2-OE plants, which thus resulted in the reduction of the defense against Prodenia litura. Transcriptome profile demonstrated that the differentially expressed genes mainly participate in the biosynthesis of terpenes, cutin, suberine and wax. Furthermore, we identified several homologs of SlCycB2, SlCycB3, NtCycB2, AtCycB2, which have similar regulatory functions in trichome formation. These results indicate that SlCycB2 plays a critical role in reproductive organ development, multicellular trichome initiation, secondary metabolite biosynthesis and Prodenia litura defense in tomato. The similar roles of its homologs in multicellular trichome formation suggest that Solanaceous species may share common regulatory pathway.

Breast cancer in young women and prognosis: How important are proliferation markers?

AIM

Compared to middle-aged women, young women with breast cancer have a higher risk of systemic disease. We studied expression of proliferation markers in relation to age and subtype and their association with long-term prognosis.

METHODS

Distant disease-free survival (DDFS) was studied in 504 women aged <40 years and 383 women aged ≥40 years from a population-based cohort. Information on patient characteristics, treatment and follow-up was collected from medical records. Tissue microarrays were produced for analysis of oestrogen receptor, progesterone receptor (PR), Her2, Ki-67 and cyclins.

RESULTS

Young women with luminal tumours had significantly higher expression of Ki-67 and cyclins. Proliferation markers were prognostic only within this subtype. Ki-67 was a prognostic indicator only in young women with luminal PR+ tumours. The optimal cut-off for Ki-67 varied by age. High expression of cyclin E1 conferred a better DDFS in women aged <40 years with luminal PR- tumours (hazard ratio [HR] 0.47 [0.24-0.92]). Age <40 years was an independent risk factor of DDFS exclusively in women with luminal B PR+ tumours (HR 2.35 [1.22-4.50]). Young women with luminal B PR- tumours expressing low cyclin E1 had a six-fold risk of distant disease compared with luminal A (HR 6.21 [2.17-17.6]).

CONCLUSIONS

The higher expression of proliferation markers in young women does not have a strong impact on prognosis. Ki-67 is only prognostic in the subgroup of young women with luminal PR+ tumours. The only cyclin adding prognostic value beyond subtype is cyclin E1. Age is an independent prognostic factor only in women with luminal B PR+ tumours.