Cyclin D1 inhibits mitochondrial activity in B cells

Beyond cell cycle regulation: The pleiotropic function of CDK4 in cancer

CDK4, along with its regulatory subunit, cyclin D, drives the transition from G1 to S phase, during which DNA replication and metabolic activation occur. In this canonical pathway, CDK4 is essentially a transcriptional regulator that acts through phosphorylation of retinoblastoma protein (RB) and subsequent activation of the transcription factor E2F, ultimately triggering the expression of genes involved in DNA synthesis and cell cycle progression to S phase. In this review, we focus on the newly reported functions of CDK4, which go beyond direct regulation of the cell cycle. In particular, we describe the extranuclear roles of CDK4, including its roles in the regulation of metabolism, cell fate, cell dynamics and the tumor microenvironment. We describe direct phosphorylation targets of CDK4 and decipher how CDK4 influences these physiological processes in the context of cancer.

Pharmacodynamics of Cyclin D1 Degradation in Ovarian Cancer Xenografts with Repeated Oral SHetA2 Dosing

SHetA2 is a promising, orally active small molecule with anticancer properties that target heat shock proteins. In this study, we aimed to investigate the pharmacodynamic (PD) effects of SHetA2 using preclinical in vitro and in vivo models of ovarian cancer and establish a physiologically based pharmacokinetic (PBPK)/PD model to describe their relationships with SHetA2 concentrations in mice. We found that daily oral administration of 60 mg/kg SHetA2 for 7 days resulted in consistent plasma PK and tissue distribution, achieving tumor drug concentrations required for growth inhibition in ovarian cancer cell lines. SHetA2 effectively induced cyclin D1 degradation in cancer cells in a dose-dependent manner, with up to 70% reduction observed and an IC50 of 4~5 µM. We identified cyclin D1 as a potential PD marker for SHetA2, based on a well-correlated time profile with SHetA2 PK. Additionally, we examined circulating levels of ccK18 as a non-invasive PD marker for SHetA2-induced apoptotic activity and found it unsuitable due to high variability. Using a PBPK/PD model, we depicted SHetA2 levels and their promoting effects on cyclin D1 degradation in tumors following multiple oral doses. The model suggested that twice-daily dosing regimens would be effective for sustained reduction in cyclin D1 protein. Our study provides valuable insights into the PK/PD of SHetA2, facilitating future clinical trial designs and dosing schedules.

Metabolic and DNA checkpoints for the enhancement of Al tolerance

Acidic soils are a major limiting factor for food production in many developing countries. High concentrations of soluble Al cations, particularly Al³⁺, inhibit cell division and root elongation in plants. Al³⁺ damages several biomolecules, including DNA, impairing gene expression and cell cycle progression. Notably, the loss-of-function mutants of DNA checkpoints may mediate Al tolerance. Furthermore, mitochondrial organic acids play key roles in neutralizing Al³⁺ within the cell and around the rhizosphere. Here, we provide knowledge synthesis on interactions between checkpoints related to mitochondrial organic acid homeostasis and DNA integrity mediating Al tolerance in land plants. These interactions, coupled with remarkable advances in tools related to metabolism and cell cycle, may facilitate the development of next-generation productive crops under Al toxicity.

Targeting Reactive Oxygen Species Metabolism to Induce Myeloma Cell Death

Multiple myeloma (MM) is a common hematological disease characterized by the accumulation of clonal malignant plasma cells in the bone marrow. Over the past two decades, new therapeutic strategies have significantly improved the treatment outcome and patients survival. Nevertheless, most MM patients relapse underlying the need of new therapeutic approaches. Plasma cells are prone to produce large amounts of immunoglobulins causing the production of intracellular ROS. Although adapted to high level of ROS, MM cells die when exposed to drugs increasing ROS production either directly or by inhibiting antioxidant enzymes. In this review, we discuss the efficacy of ROS-generating drugs for inducing MM cell death and counteracting acquired drug resistance specifically toward proteasome inhibitors.

Mitochondrial protein import dysfunction: mitochondrial disease, neurodegenerative disease and cancer

The majority of proteins localised to mitochondria are encoded by the nuclear genome, with approximately 1500 proteins imported into mammalian mitochondria. Dysfunction in this fundamental cellular process is linked to a variety of pathologies including neuropathies, cardiovascular disorders, myopathies, neurodegenerative diseases and cancer, demonstrating the importance of mitochondrial protein import machinery for cellular function. Correct import of proteins into mitochondria requires the co-ordinated activity of multimeric protein translocation and sorting machineries located in both the outer and inner mitochondrial membranes, directing the imported proteins to the destined mitochondrial compartment. This dynamic process maintains cellular homeostasis, and its dysregulation significantly affects cellular signalling pathways and metabolism. This review summarises current knowledge of the mammalian mitochondrial import machinery and the pathological consequences of mutation of its components. In addition, we will discuss the role of mitochondrial import in cancer, and our current understanding of the role of mitochondrial import in neurodegenerative diseases including Alzheimer's disease, Huntington's disease and Parkinson's disease.

Metabolic Effects of Recurrent Genetic Aberrations in Multiple Myeloma

Oncogene activation and malignant transformation exerts energetic, biosynthetic and redox demands on cancer cells due to increased proliferation, cell growth and tumor microenvironment adaptation. As such, altered metabolism is a hallmark of cancer, which is characterized by the reprogramming of multiple metabolic pathways. Multiple myeloma (MM) is a genetically heterogeneous disease that arises from terminally differentiated B cells. MM is characterized by reciprocal chromosomal translocations that often involve the immunoglobulin loci and a restricted set of partner loci, and complex chromosomal rearrangements that are associated with disease progression. Recurrent chromosomal aberrations in MM result in the aberrant expression of MYC, cyclin D1, FGFR3/MMSET and MAF/MAFB. In recent years, the intricate mechanisms that drive cancer cell metabolism and the many metabolic functions of the aforementioned MM-associated oncogenes have been investigated. Here, we discuss the metabolic consequences of recurrent chromosomal translocations in MM and provide a framework for the identification of metabolic changes that characterize MM cells.

Ursolic Acid Regulates Cell Cycle and Proliferation in Colon Adenocarcinoma by Suppressing Cyclin B1

Aims: The biological functions of cyclin B1 (CCNB1) in colon adenocarcinoma (COAD) will be explored in this study. Furthermore, the therapeutic effects and potential molecular mechanisms of ursolic acid (UA) in COAD cells will also be investigated in vitro.

Methods: COAD data were obtained from Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases. Differentially expressed genes (DEGs) were determined with differential analysis. The biological functions of CCNB1 were analyzed through the GeneCards, the Search Tool for the Retrieval of Interacting Genes (STRING), and the Database for Annotation, Visualization, and Integrated Discovery (DAVID) databases. Therapeutic effects of UA on COAD cell lines HCT-116 and SW-480 were analyzed by CCK-8 and high-content screening (HCS) imaging assay. Flow cytometry was utilized to detect cell cycle changes of SW-480 and HCT-116 cells. Levels of mRNA and expression proteins of HCT-116, SW-480, and normal colon epithelial cells NCM-460 were determined by qRT-PCR and western blot.

Results: CCNB1 was highly expressed and acted as an oncogene in COAD patients. CCNB1 and its interacting genes were significantly enriched in the cell cycle pathway. UA effectively inhibited the proliferation and injured COAD cells. In addition, UA arrested cell cycle of COAD cells in S phase. With regard to the molecular mechanisms of UA, we demonstrated that UA can significantly downregulate CCNB1 and its interacting genes and proteins, including CDK1, CDC20, CCND1, and CCNA2, which contributed to cell cycle blocking and COAD treatment.

Conclusion: Results from this study revealed that UA possesses therapeutic effects on COAD. The anti-COAD activities of UA are tightly related to suppression of CCNB1 and its interacting targets, which is crucial in abnormal cell cycle process.

The multifaceted role of cell cycle regulators in the coordination of growth and metabolism

Adapting to changes in nutrient availability and environmental conditions is a fundamental property of cells. This adaptation requires a multi‐directional coordination between metabolism, growth, and the cell cycle regulators (consisting of the family of cyclin‐dependent kinases (CDKs), their regulatory subunits known as cyclins, CDK inhibitors, the retinoblastoma family members, and the E2F transcription factors). Deciphering the mechanisms accountable for this coordination is crucial for understanding various patho‐physiological processes. While it is well established that metabolism and growth affect cell division, this review will focus on recent observations that demonstrate how cell cycle regulators coordinate metabolism, cell cycle progression, and growth. We will discuss how the cell cycle regulators directly regulate metabolic enzymes and pathways and summarize their involvement in the endolysosomal pathway and in the functions and dynamics of mitochondria.

Cyclin D1 targets hexokinase 2 to control aerobic glycolysis in myeloma cells

Cancer cells are characterized by the Warburg effect, a shift from mitochondrial respiration to oxidative glycolysis. We report here the crucial role of cyclin D1 in promoting this effect in a cyclin-dependent kinase (CDK)4/6-independent manner in multiple myeloma (MM) cells. We show that the cyclin D1 oncoprotein targets hexokinase 2 (HK2), a major glycolysis regulator, through two original molecular mechanisms in the cytoplasmic and nuclear compartments. In the cytoplasm, cyclin D1 binds HK2 at the outer mitochondrial membrane, and in the nucleus, it binds hypoxia-inducible factor-1α (HIF1α), which regulates HK2 gene transcription. We also show that high levels of HK2 expression are correlated with shorter event-free survival (EFS) and overall survival (OS) in MM patients. HK2 may therefore be considered as a possible target for antimyeloma therapy.

The double dealing of cyclin D1

The cell cycle is tightly regulated by cyclins and their catalytic moieties, the cyclin-dependent kinases (CDKs). Cyclin D1, in association with CDK4/6, acts as a mitogenic sensor and integrates extracellular mitogenic signals and cell cycle progression. When deregulated (overexpressed, accumulated, inappropriately located), cyclin D1 becomes an oncogene and is recognized as a driver of solid tumors and hemopathies. Recent studies on the oncogenic roles of cyclin D1 reported non-canonical functions dependent on the partners of cyclin D1 and its location within tumor cells or tissues. Support for these new functions was provided by various mouse models of oncogenesis. Finally, proteomic and transcriptomic data identified complex cyclin D1 networks. This review focuses on these aspects of cyclin D1 pathophysiology, which may be crucial for targeted therapy.Abbreviations: aa, amino acid; AR, androgen receptor; ATM, ataxia telangectasia mutant; ATR, ATM and Rad3-related; CDK, cyclin-dependent kinase; ChREBP, carbohydrate response element binding protein; CIP, CDK-interacting protein; CHK1/2, checkpoint kinase 1/2; CKI, CDK inhibitor; DDR, DNA damage response; DMP1, cyclin D-binding myb-like protein; DSB, double-strand DNA break; DNA-PK, DNA-dependent protein kinase; ER, estrogen receptor; FASN, fatty acid synthase; GSK3β, glycogen synthase-3β; HAT, histone acetyltransferase; HDAC, histone deacetylase; HK2, hexokinase 2; HNF4α, and hepatocyte nuclear factor 4α; HR, homologous recombination; IR, ionizing radiation; KIP, kinase inhibitory protein; MCL, mantle cell lymphoma; NHEJ, non-homologous end-joining; PCAF, p300/CREB binding-associated protein; PGC1α, PPARγ co-activator 1α; PEST, proline-glutamic acid-serine-threonine, PK, pyruvate kinase; PPAR, peroxisome proliferator-activated receptor; RB1, retinoblastoma protein; ROS, reactive oxygen species; SRC, steroid receptor coactivator; STAT, signal transducer and activator of transcription; TGFβ, transforming growth factor β; UPS, ubiquitin-proteasome system; USP22, ubiquitin-specific peptidase 22; XPO1 (or CRM1) exportin 1.

Multiple effects of CDK4/6 inhibition in cancer: From cell cycle arrest to immunomodulation

Dysregulation of the cell cycle is a hallmark of cancer that leads to aberrant cellular proliferation. CDK4/6 are cyclin-dependent kinases activated in response to proliferative signaling, which induce RB hyper-phosphorylation and hence activation of E2F transcription factors, thus promoting cell cycle progression through the S phase. Pharmacologic inhibition of CDK4/6 by palbociclib, ribociclib, or abemaciclib has been showing promising activity in multiple cancers with the best results achieved in combination with other agents. Indeed, CDK4/6 inhibitors are currently approved in combination with endocrine therapy for the treatment of estrogen receptor-positive, human epidermal growth factor receptor 2-negative advanced or metastatic breast cancer. Moreover, a number of clinical trials are currently underway to test the efficacy of combining CDK4/6 inhibitors with different drugs not only in breast but also in other types of cancer. Beyond the inhibition of cell proliferation, CDK4/6 inhibitors have recently revealed new effects on cancer cells and on tumor microenvironment. In particular, it has been reported that these agents induce a senescent-like phenotype, impact on cell metabolism and exert both immunomodulatory and immunogenic effects. Here we describe recent data on the anti-tumor effects of CDK4/6 inhibitors as single agents or in combined therapies, focusing in particular on their metabolic and immunomodulatory activities.

Glucose Drives Growth Factor-Independent Esophageal Cancer Proliferation via Phosphohistidine-Focal Adhesion Kinase Signaling

BACKGROUND & AIMS

Most targeted therapies against cancer are designed to block growth factor-stimulated oncogenic growth. However, response rates are low, and resistance to therapy is high. One mechanism might relate to the ability of tumor cells to induce growth factor-independent proliferation (GFIP). This project aims to understand how (1) cancer cells preferentially derive a major growth advantage by using critical metabolic products of glucose, such as phosphoenolpyruvate (PEP), to drive proliferation and (2) esophageal squamous cell carcinoma (ESCC) cells, but not esophageal adenocarcinoma cells, can induce GFIP by using glycolysis to activate phosphohistidine (poHis)-mediated signaling through focal adhesion kinase (FAK).

METHODS

The hypothesis to be tested is that ESCC GFIP induced by glucose is facilitated by PEP-mediated histidine phosphorylation (poHis) of FAK, leading to the possibility that ESCC progression can be targeted by blocking poHis signaling. Biochemical, molecular biological, and in vivo experiments including bromodeoxyuridine/5-ethynyl-2'-deoxyuridine labeling, radioisotope tracing, CRISPR gene editing, and analysis of signaling gene sets in human cancer tissues and xenograft models were performed to define the mechanisms underlying ESCC GFIP.

RESULTS

Glucose promotes growth factor-independent DNA replication and accumulation of PEP in ESCC cells. PEP is the direct phospho-donor to poHis58-FAK within a known "HG" motif for histidine phosphorylation. Glucose-induced poHis58 promotes growth factor-independent FAK-mediated proliferation. Furthermore, glucose activates phosphatidylinositol-3'-kinase/AKT via poHis58-FAK signaling. Non-phosphorylatable His58A-FAK reduces xenograft growth.

CONCLUSIONS

Glucose induces ESCC, but not esophageal adenocarcinoma GFIP via PEP-His58-FAK-AKT signaling. ESCC progression is controlled by actionable growth factor-independent, glucose-induced pathways that regulate proliferation through novel histidine phosphorylation of FAK.

Cyclin B1/CDK1-regulated mitochondrial bioenergetics in cell cycle progression and tumor resistance

A mammalian cell houses two genomes located separately in the nucleus and mitochondria. During evolution, communications and adaptations between these two genomes occur extensively to achieve and sustain homeostasis for cellular functions and regeneration. Mitochondria provide the major cellular energy and contribute to gene regulation in the nucleus, whereas more than 98% of mitochondrial proteins are encoded by the nuclear genome. Such two-way signaling traffic presents an orchestrated dynamic between energy metabolism and consumption in cells. Recent reports have elucidated the way how mitochondrial bioenergetics synchronizes with the energy consumption for cell cycle progression mediated by cyclin B1/CDK1 as the communicator. This review is to recapitulate cyclin B1/CDK1 mediated mitochondrial activities in cell cycle progression and stress response as well as its potential link to reprogram energy metabolism in tumor adaptive resistance. Cyclin B1/CDK1-mediated mitochondrial bioenergetics is applied as an example to show how mitochondria could timely sense the cellular fuel demand and then coordinate ATP output. Such nucleus-mitochondria oscillation may play key roles in the flexible bioenergetics required for tumor cell survival and compromising the efficacy of anti-cancer therapy. Further deciphering the cyclin B1/CDK1-controlled mitochondrial metabolism may invent effect targets to treat resistant cancers.

Unraveling Interfaces between Energy Metabolism and Cell Cycle in Plants

Oscillation in energy levels is widely variable in dividing and differentiated cells. To synchronize cell proliferation and energy fluctuations, cell cycle-related proteins have been implicated in the regulation of mitochondrial energy-generating pathways in yeasts and animals. Plants have chloroplasts and mitochondria, coordinating the cell energy flow. Recent findings suggest an integrated regulation of these organelles and the nuclear cell cycle. Furthermore, reports indicate a set of interactions between the cell cycle and energy metabolism, coordinating the turnover of proteins in plants. Here, we discuss how cell cycle-related proteins directly interact with energy metabolism-related proteins to modulate energy homeostasis and cell cycle progression. We provide interfaces between cell cycle and energy metabolism-related proteins that could be explored to maximize plant yield.

Cyclin D1 unbalances the redox status controlling cell adhesion, migration, and drug resistance in myeloma cells

The interactions of multiple myeloma (MM) cells with their microenvironment are crucial for pathogenesis. MM cells could interact differentially with their microenvironment depending on the type of cyclin D they express. We established several clones that constitutively express cyclin D1 from the parental RPMI8226 MM cell line and analyzed the impact of cyclin D1 expression on cell behavior. We performed a gene expression profiling study on cyclin D1-expressing vs. control cells and validated the results by semi-quantitative RT-PCR. The expression of cyclin D1 altered the transcription of genes that control adhesion and migration. We confirmed that cyclin D1 increases cell adhesion to stromal cells and fibronectin, stabilizes F-actin fibers, and enhances chemotaxis and inflammatory chemokine secretion. Both control and cyclin D1-expressing cells were more resistant to acute carfilzomib treatment when cultured on stromal cells than in suspension. However, this resistance was specifically reduced in cyclin D1-expressing cells after pomalidomide pre-treatment that modifies tumor cell/microenvironment interactions. Transcriptomic analysis revealed that cyclin D1 expression was also associated with changes in the expression of genes controlling metabolism. We also found that cyclin D1 expression disrupted the redox balance by producing reactive oxygen species. The resulting oxidative stress activated the p44/42 mitogen-activated protein kinase (or ERK1/2) signaling pathway, increased cell adhesion to fibronectin or stromal cells, and controlled drug sensitivity.

Our results have uncovered a new function for cyclin D1 in the control of redox metabolism and interactions of cyclin D1-expressing MM cells with their bone marrow microenvironment.

Cyclin d1 depletion interferes with cancer oxidative balance and sensitizes cancer cells to senescence

Expression of cyclin D1 is required for cancer cell survival and proliferation. This is presumably due to the role of cyclin D1 in RB inactivation. Here we investigated the prosurvival function of cyclin D1 in a number of cancer cell lines. We found that cyclin D1 depletion facilitated cellular senescence in several cancer cell lines tested. Senescence triggered by cyclin D1 depletion was more extensive than that caused by the prolonged CDK4 inhibition. Intriguingly, the senescence caused by cyclin D1 depletion was independent of RB status of the cancer cell. We identified a buildup of intracellular reactive oxygen species, in the cancer cells that underwent senescence upon cyclin D1 depletion, but not in CDK4 inhibition, and that ROS buildup was responsible for the senescence. Lastly, the senescence was found to be instigated by the p38/JNK-FOXO3a-p27 pathway. Therefore, expression of cyclin D1 prevents cancer cells from undergoing senescence, at least partially, by keeping the level of intracellular oxidative stress at a tolerable sub-lethal level. Depletion of cyclin D1 promotes the RB-independent pro-senescence pathway, and cancer cell succumbing to the endogenous oxidative stress.

Cytoplasmic cyclin D1 controls the migration and invasiveness of mantle lymphoma cells

Mantle cell lymphoma (MCL) is a hematologic neoplasm characterised by the t(11;14)(q13;q32) translocation leading to aberrant cyclin D1 expression. The cell functions of cyclin D1 depend on its partners and/or subcellular distribution, resulting in different oncogenic properties. We observed the accumulation of cyclin D1 in the cytoplasm of a subset of MCL cell lines and primary cells. In primary cells, this cytoplasmic distribution was correlated with a more frequent blastoid phenotype. We performed immunoprecipitation assays and mass spectrometry on enriched cytosolic fractions from two cell lines. The cyclin D1 interactome was found to include several factors involved in adhesion, migration and invasion. We found that the accumulation of cyclin D1 in the cytoplasm was associated with higher levels of migration and invasiveness. We also showed that MCL cells with high cytoplasmic levels of cyclin D1 engrafted more rapidly into the bone marrow, spleen, and brain in immunodeficient mice. Both migration and invasion processes, both in vivo and in vitro, were counteracted by the exportin 1 inhibitor KPT-330, which retains cyclin D1 in the nucleus. Our data reveal a role of cytoplasmic cyclin D1 in the control of MCL cell migration and invasion, and as a true operator of MCL pathogenesis.

A lowered 26S proteasome activity correlates with mantle lymphoma cell lines resistance to genotoxic stress

Background

Mantle cell lymphoma (MCL) is a B-cell hemopathy characterized by the t(11;14) translocation and the aberrant overexpression of cyclin D1. This results in an unrestrained cell proliferation. Other genetic alterations are common in MCL cells such as SOX11 expression, mutations of ATM and/or TP53 genes, activation of the NF-κB signaling pathway and NOTCH receptors. These alterations lead to the deregulation of the apoptotic machinery and resistance to drugs. We observed that among a panel of MCL cell lines, REC1 cells were resistant towards genotoxic stress. We studied the molecular basis of this resistance.

Methods

We analyzed the cell response regarding apoptosis, senescence, cell cycle arrest, DNA damage response and finally the 26S proteasome activity following a genotoxic treatment that causes double strand DNA breaks.

Results

MCL cell lines displayed various sensitivity/resistance towards genotoxic stress and, in particular, REC1 cells did not enter apoptosis or senescence after an etoposide treatment. Moreover, the G2/M cell cycle checkpoint was deficient in REC1 cells. We observed that three main actors of apoptosis, senescence and cell cycle regulation (cyclin D1, MCL1 and CDC25A) failed to be degraded by the proteasome machinery in REC1 cells. We ruled out a default of the βTrCP E3-ubiquitine ligase but detected a lowered 26S proteasome activity in REC1 cells compared to other cell lines.

Conclusion

The resistance of MCL cells to genotoxic stress correlates with a low 26S proteasome activity. This could represent a relevant biomarker for a subtype of MCL patients with a poor response to therapies and a high risk of relapse.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3530-z) contains supplementary material, which is available to authorized users.

Fueling the Cell Division Cycle

Cell division is a complex process with high energy demands. However, how cells regulate the generation of energy required for DNA synthesis and chromosome segregation is not well understood. Recent data suggest that changes in mitochondrial dynamics and metabolic pathways such as oxidative phosphorylation (OXPHOS) and glycolysis crosstalk with, and are tightly regulated by, the cell division machinery. Alterations in energy availability trigger cell-cycle checkpoints, suggesting a bidirectional connection between cell division and general metabolism. Some of these connections are altered in human disease, and their manipulation may help in designing therapeutic strategies for specific diseases including cancer. We review here recent studies describing the control of metabolism by the cell-cycle machinery.

Two-way communication between the metabolic and cell cycle machineries: the molecular basis

The relationship between cellular metabolism and the cell cycle machinery is by no means unidirectional. The ability of a cell to enter the cell cycle critically depends on the availability of metabolites. Conversely, the cell cycle machinery commits to regulating metabolic networks in order to support cell survival and proliferation. In this review, we will give an account of how the cell cycle machinery and metabolism are interconnected. Acquiring information on how communication takes place among metabolic signaling networks and the cell cycle controllers is crucial to increase our understanding of the deregulation thereof in disease, including cancer.

Non-canonical functions of cell cycle cyclins and cyclin-dependent kinases

The roles of cyclins and their catalytic partners, the cyclin-dependent kinases (CDKs), as core components of the machinery that drives cell cycle progression are well established. Increasing evidence indicates that mammalian cyclins and CDKs also carry out important functions in other cellular processes, such as transcription, DNA damage repair, control of cell death, differentiation, the immune response and metabolism. Some of these non-canonical functions are performed by cyclins or CDKs, independently of their respective cell cycle partners, suggesting that there was a substantial divergence in the functions of these proteins during evolution.

Intracellular mitochondrial DNA transfers to the nucleus in human cancer cells

Genome instability is a well-known hallmark of cancer cells. With the revolution of high-throughput sequencing technologies, our knowledge of somatically acquired genome structural variation (SV) has greatly improved over the last decade. Remarkably, surveys of thousands of human whole-cancer genomes have shown that chromosomal rearrangements are frequently combined with mitochondrial DNA (mtDNA) fragments somatically transferred to the nucleus. The high transfer rate and features of integration breakpoints provide clues for understanding the potential mechanisms underlying these events and provide insights into the role of mtDNA segments transferred into the nucleus. In this review, I discuss our current understanding of somatic nuclear transfer of mitochondrial DNA into the nuclear genome of human cancer cells.

Pleiotropic signaling evoked by tumor necrosis factor in podocytes

TNF has been implicated in glomerular diseases, but its actions on podocytes are not well understood. Endogenous TNF expression is markedly increased in mouse podocytes exposed to sera from patients with recurrent focal segmental glomerulosclerosis, and TNF is able to increase its own expression in these cells. Exposure of podocytes to TNF increased phosphorylation of NF-κB p65-RelA followed by increased tyrosine phosphorylation of STAT3. STAT3 activation was blocked by the NF-κB inhibitor JSH-23 and by the STAT3 inhibitor stattic, whereas TNF-evoked NF-κB activation was not affected by stattic. TNF treatment increased nuclear accumulation of nuclear factor of activated T cells (NFAT)c1 in podocytes, a process that occurred downstream of STAT3 activation. TNF also increased expression of cyclin D1 but had no effect on cyclin-dependent kinase 4, p27(kip), or podocin. Despite its effects on cyclin D1, TNF treatment for up to 72 h did not cause podocytes to reenter the cell cycle. TNF increased total expression of transient receptor potential (TRP)C6 channels through a pathway dependent on NFATc1 and increased the steady-state expression of TRPC6 subunits on the podocyte cell surface. TNF effects on TRPC6 trafficking required ROS. Consistent with this, La(3+)-sensitive cationic currents activated by a diacylglycerol analog were increased in TNF-treated cells. The effects of TNF on NFATc1 and TRPC6 expression were blocked by cyclosporine A but were not blocked by the pan-TRP inhibitor SKF-96365. TNF therefore influences multiple pathways previously implicated in podocyte pathophysiology and is likely to sensitize these cells to other insults.

Cyclin D1 sensitizes myeloma cells to endoplasmic reticulum stress-mediated apoptosis by activating the unfolded protein response pathway

Background

Cyclin D1 and its kinase partners control cell cycle progression. Cyclin D1 is frequently deregulated in various cancers, including malignant hemopathies, and tumor cells display uncontrolled cell proliferation. Cyclin D1 is not expressed in the B-cell lineage but is found in multiple myeloma (MM) cells in almost 50% of patients with this condition. Paradoxically, cyclin D1 expression is associated with a good prognosis and longer overall survival in MM patients.

Methods

We used two independent MM cell lines (RPMI 8226 and LP1) to generate several clones stably expressing either the green fluorescent protein (GFP) or a GFP-cyclin D1 fusion protein, and we analyzed the properties acquired following cyclin D1 expression.

Results

Whole-genome expression analysis in the cell clones indicated that cyclin D1 profoundly modified several cellular functions, including the regulation of apoptotic cell death. We studied the apoptotic response of GFP- and GFP-cyclin D1-expressing clones to bortezomib-treatment. We found that the apoptotic response occurred faster and was of a greater amplitude in cyclin D1-expressing cells. Cyclin D1 expression enhanced the caspase-dependent apoptosis mediated by the intrinsic mitochondrial pathway. More importantly, cyclin D1 also activated the unfolded protein response (UPR) and induced endoplasmic reticulum (ER) stress-mediated apoptosis.

Conclusion

The ER is well known to be a crucial regulator of plasma cell death and it plays the same role in their malignant counterparts, myeloma cells. This role involves activation of the UPR controlled at least in part by cyclin D1.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1240-y) contains supplementary material, which is available to authorized users.

Metabolic control of the cell cycle

Cell division is a metabolically demanding process, requiring the production of large amounts of energy and biomass. Not surprisingly therefore, a cell's decision to initiate division is co-determined by its metabolic status and the availability of nutrients. Emerging evidence reveals that metabolism is not only undergoing substantial changes during the cell cycle, but it is becoming equally clear that metabolism regulates cell cycle progression. Here, we overview the emerging role of those metabolic pathways that have been best characterized to change during or influence cell cycle progression. We then studied how Notch signaling, a key angiogenic pathway that inhibits endothelial cell (EC) proliferation, controls EC metabolism (glycolysis) during the cell cycle.

Antitumoral activity of lenalidomide in in vitro and in vivo models of mantle cell lymphoma involves the destabilization of cyclin D1/p27KIP1 complexes

PURPOSE

Clinical responses to the immmunomodulatory drug lenalidomide have been observed in patients with relapsed/refractory mantle cell lymphoma (MCL), although its mechanism of action remains partially unknown. We investigated whether the expression and subcellular localization of cyclin D1, a major cell-cycle regulator overexpressed in MCL, and the cyclin-dependent kinase inhibitor p27(KIP1), could identify MCL cases sensitive to lenalidomide, and whether the compound could modulate cyclin D1/p27(KIP1) complexes in MCL cells.

EXPERIMENTAL DESIGN

MCL primary samples and cell lines were analyzed for subcellular levels of cyclin D1/p27(KIP1) complexes by Western blot, immunohistochemistry, immunoprecipitation, and flow cytometry. Activity of lenalidomide in vitro and its effect on cyclin D1/p27(KIP1) complexes were evaluated by real-time PCR, immunoprecipitation, immunofluorescence, and Western blot. In vivo validation was carried out in a mouse xenograft model of human MCL.

RESULTS

We found cyclin D1 and p27(KIP1) to be coordinately expressed in all the MCL samples tested. Immunoprecipitation analyses and siRNA assays suggested a direct role of cyclin D1 in the regulation of p27(KIP1) levels. The nuclear accumulation of both proteins correlated with MCL cell tumorigenicity in vivo, and sensitivity to lenalidomide activity in vitro and in vivo. Lenalidomide mechanism of action relied on cyclin D1 downregulation and disruption of cyclin D1/p27(KIP1) complexes, followed by cytosolic accumulation of p27(KIP1), cell proliferation arrest, apoptosis, and angiogenesis inhibition.

CONCLUSIONS

These results highlight a mechanism of action of lenalidomide in MCL cases with increased tumorigenicity in vivo, which is mediated by the dissociation of cyclin D1/p27(KIP1) complexes, and subsequent proliferation blockade and apoptosis induction.

New roles of cyclin D1

Cyclins encode regulatory subunits of holoenzymes that phosphorylate a variety of cellular substrates. Although the classic role of cyclins in cell cycle progression and tumorigenesis has been well characterized, new functions have been identified, including the induction of cellular migration and invasion, enhancement of angiogenesis, inhibition of mitochondrial metabolism, regulation of transcription factor signaling via a DNA-bound form, the induction of chromosomal instability, enhancement of DNA damage sensing and DNA damage repair, and feedback governing expression of the noncoding genome. This review describes the mechanisms of these new functions of cyclin D1.

Defective mitochondrial disulfide relay system, altered mitochondrial morphology and function in Huntington's disease

A number of studies have been conducted that link mitochondrial dysfunction (MD) to Huntington's disease (HD); however, contradicting results had resulted in a lack of a clear mechanism that links expression of mutant Huntingtin protein and MD. Mouse homozygous (HM) and heterozygous (HT) mutant striatal cells with two or one allele encoding for a mutant huntingtin protein with 111 polyGln repeats showed a significant impairment of the mitochondrial disulfide relay system (MDRS). This system (consisting of two proteins, Gfer and Mia40) is involved in the mitochondrial import of Cys-rich proteins. The Gfer-to-Mia40 ratio was significantly altered in HM cells compared with controls, along with the expression of mitochondrial proteins considered substrates of the MDRS. In progenitors and differentiated neuron-like HM cells, impairment of MDRS were accompanied by deficient oxidative phosphorylation, Complex I, IV and V activities, decreased mtDNA copy number and transcripts, accumulation of mtDNA deletions and changes in mitochondrial morphology, consistent with other MDRS-deficient biological models, thus providing a framework for the energy deficits observed in this HD model. The majority (>90%) of the mitochondrial outcomes exhibited a gene-dose dependency with the expression of mutant Htt. Finally, decreases in the mtDNA copy number, along with the accumulation of mtDNA deletions, provide a mechanism for the progressive neurodegeneration observed in HD patients.

A defect of the INK4-Cdk4 checkpoint and Myc collaborate in blastoid mantle cell lymphoma-like lymphoma formation in mice

Mantle cell lymphoma (MCL) is a B-cell malignancy characterized by a monoclonal proliferation of lymphocytes with the co-expression of CD5 and CD43, but not of CD23. Typical MCL is associated with overexpression of cyclin D1, and blastoid MCL variants are associated with Myc (alias c-myc) translocations. In this study, we developed a murine model of MCL-like lymphoma by crossing Cdk4(R24C) mice with Myc-3'RR transgenic mice. The Cdk4(R24C) mouse is a knockin strain that expresses a Cdk4 protein that is resistant to inhibition by p16(INK4a) as well as other INK4 family members. Ablation of INK4 control on Cdk4 does not affect lymphomagenesis, B-cell maturation, and functions in Cdk4(R24C) mice. Additionally, B cells were normal in numbers, cell cycle activity, mitogen responsiveness, and Ig synthesis in response to activation. By contrast, breeding Cdk4(R24C) mice with Myc-3'RR transgenic mice prone to develop aggressive Burkitt lymphoma-like lymphoma (CD19(+)IgM(+)IgD(+) cells) leads to the development of clonal blastoid MCL-like lymphoma (CD19(+)IgM(+)CD5(+)CD43(+)CD23(-) cells) in Myc/Cdk4(R24C) mice. Western blot analysis revealed high amounts of Cdk4/cyclin D1 complexes as the main hallmark of these lymphomas. These results indicate that although silent in nonmalignant B cells, a defect in the INK4-Cdk4 checkpoint can participate in lymphomagenesis in conjunction with additional alterations of cell cycle control, a situation that might be reminiscent of the development of human blastoid MCL.

New diagnosis of multiple myeloma in a patient with mantle cell lymphoma: Shared genetic factors or simple coincidence?

Multiple Myeloma and Mantle Cell Lymphoma are well defined hematological malignancies. Understanding of their pathogeneses has led to new therapies and increased survival. We report on a 64-yr-old female who was diagnosed with mantle cell lymphoma in 2003, then multiple myeloma in 2010. We identified only few other cases of concomitant MM and MCL. We also explored the importance of t(11;14)(q13;q32). The development of these two disorders in the same patient may simply be due to chance; however, it may also represent a common genetic hit affecting the B-cell population leading to development of two different malignancies.