Cdk2 and Cdk4 regulate the centrosome cycle and are critical mediators of centrosome amplification in p53-null cells

Mitotic kinases are emerging therapeutic targets against metastatic breast cancer

This review aims to outline mitotic kinase inhibitors' roles as potential therapeutic targets and assess their suitability as a stand-alone clinical therapy or in combination with standard treatments for advanced-stage solid tumors, including triple-negative breast cancer (TNBC). Breast cancer poses a significant global health risk, with TNBC standing out as the most aggressive subtype. Comprehending the role of mitosis is crucial for understanding how TNBC advances from a solid tumor to metastasis. Chemotherapy is the primary treatment used to treat TNBC. Some types of chemotherapeutic agents target cells in mitosis, thus highlighting the need to comprehend the molecular mechanisms governing mitosis in cancer. This understanding is essential for devising targeted therapies to disrupt these mitotic processes, prevent or treat metastasis, and improve patient outcomes. Mitotic kinases like Aurora kinase A, Aurora Kinase B, never in mitosis gene A-related kinase 2, Threonine-Tyrosine kinase, and Polo-kinase 1 significantly impact cell cycle progression by contributing to chromosome separation and centrosome homeostasis. When these kinases go awry, they can trigger chromosome instability, increase cell proliferation, and activate different molecular pathways that culminate in a transition from epithelial to mesenchymal cells. Ongoing clinical trials investigate various mitotic kinase inhibitors as potential biological treatments against advanced solid tumors. While clinical trials against mitotic kinases have shown some promise in the clinic, more investigation is necessary, since they induce severe adverse effects, particularly affecting the hematopoietic system.

The centrosome: a critical hub for cell cycle regulation

Cyclins and cyclin-dependent kinases (CDKs) localize to the centrosome, but their significance in the cell cycle is unclear. Recently, Roberts et al. revealed that centrosomal cyclin B-CDK is required for mitotic entry and phosphorylation of substrates. This suggests that the centrosome acts as a signaling hub controlling the cell cycle.

Centrosome amplification-related signature correlated with immune microenvironment and treatment response predicts prognosis and improves diagnosis of hepatocellular carcinoma by integrating machine learning and single-cell analyses

BACKGROUND

Centrosome amplification is a well-recognized oncogenic driver of tumor initiation and progression across a variety of malignancies and has been linked with tumor aggressiveness, metastasis, and adverse prognosis. Nevertheless, the significance of centrosome amplification in HCC is not well understood.

METHODS

The TCGA dataset was downloaded for centrosome amplification-related signature construction using the LASSO-penalized Cox regression algorithm, while the ICGC dataset was obtained for signature validation. Single-cell RNA sequencing from GSE149614 was analyzed to profile gene expression and the liver tumor niche.

RESULTS

A total of 134 centrosome amplification-related prognostic genes in HCC were detected and 6 key prognostic genes (SSX2IP, SPAG4, SAC3D1, NPM1, CSNK1D, and CEP55) among them were screened out to construct a signature with both high sensitivity and specificity in diagnosis and prognosis of HCC patients. The signature, as an independent factor, was associated with frequent recurrences, high mortality rates, advanced clinicopathologic features, and high vascular invasions. Moreover, the signature was intimately associated with cell cycle-related pathways and TP53 mutation profile, suggesting its underlying role in accelerating cell cycle progression and leading to liver cancer development. Meanwhile, the signature was also closely correlated with immunosuppressive cell infiltration and immune checkpoint expression, making it a vital immunosuppressive factor in the tumor microenvironment. Upon single-cell RNA sequencing, SSX2IP and SAC3D1 were found to be specially expressed in liver cancer stem-like cells, where they promoted cell cycle progression and hypoxia.

CONCLUSIONS

This study provided a direct molecular link of centrosome amplification with clinical characteristics, tumor microenvironment, and clinical drug-response, highlighting the critical role of centrosome amplification in liver cancer development and therapy resistance, thereby providing valuable insights into prognostic prediction and therapeutic response of HCC.

CDK2 inhibition disorders centrosome stoichiometry and alters cellular outcomes in aneuploid cancer cells

Cyclin-dependent Kinase 2 (CDK2) inhibition prevents supernumerary centrosome clustering. This causes multipolarity, anaphase catastrophe and apoptotic death of aneuploid cancers. This study elucidated how CDK2 antagonism affected centrosome stoichiometry. Focused ion beam scanning electron microscopy (FIB-SEM) and immunofluorescent imaging were used. Studies interrogated multipolar mitosis after pharmacologic or genetic repression of CDK2. CDK2/9 antagonism with CYC065 (Fadraciclib)-treatment disordered centrosome stoichiometry in aneuploid cancer cells, preventing centrosome clustering. This caused ring-like chromosomes or multipolar cancer cells to form before onset of cell death. Intriguingly, CDK2 inhibition caused a statistically significant increase in single centrioles rather than intact centrosomes with two centrioles in cancer cells having chromosome rings or multipolarity. Statistically significant alterations in centrosome stoichiometry were undetected in other mitotic cancer cells. To confirm this pharmacodynamic effect, CDK2 but not CDK9 siRNA-mediated knockdown augmented cancer cells with chromosome ring or multipolarity formation. Notably, engineered gain of CDK2, but not CDK9 expression, reversed emergence of cancer cells with chromosome rings or multipolarity, despite CYC065-treatment. In marked contrast, CDK2 inhibition of primary human alveolar epithelial cells did not confer statistically significant increases of cells with ring-like chromosomes or multipolarity. Hence, CDK2 antagonism caused differential effects in malignant versus normal alveolar epithelial cells. Translational relevance was confirmed by CYC065-treatment of syngeneic lung cancers in mice. Mitotic figures in tumors exhibited chromosome rings or multipolarity. Thus, CDK2 inhibition preferentially disorders centrosome stoichiometry in cancer cells. Engaging this disruption is a strategy to explore against aneuploid cancers in future clinical trials.

Nucleolar phosphoprotein modifications as a marker of apoptosis induced by RITA treatment

Reactivating p53 and Inducing Tumor Apoptosis (RITA) has been reported to increase the p53 activity and to trigger p53-dependent apoptosis in cancer cells with wild-type p53. Tumor suppressor p53 interacts with nucleolar phosphoproteins nucleophosmin (NPM) and nucleolin (NCL), which have crucial role in many cellular processes. Specific NPM mutations associated with acute myeloid leukemia (AML) cause aberrant localization of NPM and p53 in the cytoplasm with possible impact on the p53 function. We tested an effect of RITA on primary cells, and we found significant RITA-induced changes in NPM and NCL phosphorylation associated with apoptosis in cells of AML patients, but not that of healthy donors. Subsequent screening of several AML cell lines revealed heterogeneous response to RITA, and confirmed an association of the specific phosphorylation with apoptosis. While decreased NCL phosphorylation at Threonines T76 and T84 could be attributed to RITA-induced cell cycle arrest, enhanced NPM phosphorylation at Threonine T199 was not accompanied by the cell cycle changes and it correlated with sensitivity to RITA. Simultaneously, inverse changes occurred at Serine S4 of the NPM. These new findings of RITA mechanism of action could establish the NPM pT199/pS4 ratio as a marker for suitability of RITA treatment of AML cells.

Cigarette smoke condensate induces centrosome clustering in normal lung epithelial cells

BACKGROUND

Unlike normal cells, cancer cells frequently have multiple centrosomes that can cluster to form bipolar mitotic spindles and allow for successful cell division. Inhibiting centrosome clustering, therefore, holds therapeutic promise to promote cancer cell-specific cell death.

METHODS

We used confocal microscopy, real-time PCR, siRNA knockdown, and western blot to analyze centrosome clustering and declustering using normal lung bronchial epithelial and nonsmall-cell lung cancer (NSCLC) cell lines. Also, we used Ingenuity Pathway Analysis software to identify novel pathways associated with centrosome clustering.

RESULTS

In this study, we found that exposure to cigarette smoke condensate induces centrosome amplification and clustering in human lung epithelial cells. We observed a similar increase in centrosome amplification and clustering in unexposed NSCLC cell lines which may suggest a common underlying mechanism for lung carcinogenesis. We identified a cyclin D2-mediated centrosome clustering pathway that involves a sonic hedgehog-forkhead box protein M1 axis which is critical for mitosis. We also observed that cyclin D2 knockdown induced multipolar mitotic spindles that could eventually lead to cell death.

CONCLUSIONS

Here we report a novel role of cyclin D2 in the regulation of centrosome clustering, which could allow the identification of tumors sensitive to cyclin D2 inhibitors. Our data reveal a pathway that can be targeted to inhibit centrosome clustering by interfering with the expression of cyclin D2-associated genes.

Ethnic and racial-specific differences in levels of centrosome-associated mitotic kinases, proliferative and epithelial-to-mesenchymal markers in breast cancers

Molecular epidemiology evidence indicates racial and ethnic differences in the aggressiveness and survival of breast cancer. Hispanics/Latinas (H/Ls) and non-Hispanic Black women (NHB) are at higher risk of breast cancer (BC)-related death relative to non-Hispanic white (NHW) women in part because they are diagnosed with hormone receptor-negative (HR) subtype and at higher stages. Since the cell cycle is one of the most commonly deregulated cellular processes in cancer, we propose that the mitotic kinases TTK (or Mps1), TBK1, and Nek2 could be novel targets to prevent breast cancer progression among NHBs and H/Ls. In this study, we calculated levels of TTK, p-TBK1, epithelial (E-cadherin), mesenchymal (Vimentin), and proliferation (Ki67) markers through immunohistochemical (IHC) staining of breast cancer tissue microarrays (TMAs) that includes samples from 6 regions in the Southeast of the United States and Puerto Rico -regions enriched with NHB and H/L breast cancer patients. IHC analysis showed that TTK, Ki67, and Vimentin were significantly expressed in triple-negative (TNBC) tumors relative to other subtypes, while E-cadherin showed decreased expression. TTK correlated with all of the clinical variables but p-TBK1 did not correlate with any of them. TCGA analysis revealed that the mRNA levels of multiple mitotic kinases, including TTK, Nek2, Plk1, Bub1, and Aurora kinases A and B, and transcription factors that are known to control the expression of these kinases (e.g. FoxM1 and E2F1-3) were upregulated in NHBs versus NHWs and correlated with higher aneuploidy indexes in NHB, suggesting that these mitotic kinases may be future novel targets for breast cancer treatment in NHB women.

Keep Calm and Carry on with Extra Centrosomes

Simple Summary

Precise chromosome segregation during mitosis is a vital event orchestrated by formation of bipolar spindle poles. Supernumerary centrosomes, caused by centrosome amplification, deteriorates mitotic processes, resulting in segregation defects leading to chromosomal instability (CIN). Centrosome amplification is frequently observed in various types of cancer and considered as a significant contributor to destabilization of chromosomes. This review provides a comprehensive overview of causes and consequences of centrosome amplification thoroughly describing molecular mechanisms.

Abstract

Aberrations in the centrosome number and structure can readily be detected at all stages of tumor progression and are considered hallmarks of cancer. Centrosome anomalies are closely linked to chromosome instability and, therefore, are proposed to be one of the driving events of tumor formation and progression. This concept, first posited by Boveri over 100 years ago, has been an area of interest to cancer researchers. We have now begun to understand the processes by which these numerical and structural anomalies may lead to cancer, and vice-versa: how key events that occur during carcinogenesis could lead to amplification of centrosomes. Despite the proliferative advantages that having extra centrosomes may confer, their presence can also lead to loss of essential genetic material as a result of segregational errors and cancer cells must deal with these deadly consequences. Here, we review recent advances in the current literature describing the mechanisms by which cancer cells amplify their centrosomes and the methods they employ to tolerate the presence of these anomalies, focusing particularly on centrosomal clustering.

CDK4 has the ability to regulate Aurora B and Cenpp expression in mouse keratinocytes

Cyclin-dependent kinase 4 (CDK4) is a critical molecule that regulates key aspects of cell proliferation through phosphorylation of the retinoblastoma (Rb) family of proteins. In the last few years, it has been suggested that CDK4 plays alternative roles in cell proliferation and tumorigenesis. The main aim of the present study was to define a novel CDK4 function as a transcriptional regulator of genes involved in chromosome segregation, contributing to the G2/M phase transition. Herein, chromatin-immunoprecipitation reverse transcription-quantitative PCR assays were performed to demonstrate that CDK4 could occupy the promoter region of genes associated with chromosomal segregation, such as Aurora-B (Aurkb) and Centromere Protein P (CENP-P). Moreover, gain- and loss-of-function experiments showed that CDK4 participated in the transcriptional regulation of Aurkb and CENP-P. The finding that Aurkb may have a crucial role in chromosome bi-orientation and the spindle assembly checkpoint, and that CENP-P could be required for proper kinetochore function suggests that dysregulation of CDK4 expression induces chromosomal instability and, in some cases, cancer development.

Expression of lncRNA TINCR in the placenta of patients with pre-eclampsia and its effect on the biological behaviours of trophoblasts

To explore the effect of lncRNA TINCR on the biological behaviours of trophoblasts, we detected and analyzed the expression of terminal differentiation-induced non-protein coding RNA (TINCR) in the placenta tissues of pre-eclamptic and non-pre-eclamptic pregnant women. The gain- and loss-of-function of TINCR was performed to examine the proliferation, migration and invasion abilities of Htr-8/Svneo cells. The levels of epithelial-mesenchymal transition (EMT)-related proteins, cyclin and Wnt/β-catenin pathway were detected. High expression of lncRNA TINCR appeared in placental tissues of patients with pre-eclampsia. The proliferation, invasion and migration of Htr-8/Svneo cells were promoted by TINCR downregulation; the cells were transited from G0/G1 to S phase; and EMT was promoted and the Wnt/β-catenin pathway was activated. In summary, the downregulation of lncRNA TINCR activated the Wnt/β-catenin pathway and promoted the proliferation, invasion and migration of Htr-8/Svneo cells. This study may provide a theoretical basis for treatment of patients with pre-eclampsia.

The Nek2 centrosome-mitotic kinase contributes to the mesenchymal state, cell invasion, and migration of triple-negative breast cancer cells

Nek2 (NIMA-related kinase 2) is a serine/threonine-protein kinase that localizes to centrosomes and kinetochores, controlling centrosome separation, chromosome attachments to kinetochores, and the spindle assembly checkpoint. These processes prevent centrosome amplification (CA), mitotic dysfunction, and chromosome instability (CIN). Our group and others have suggested that Nek2 maintains high levels of CA/CIN, tumor growth, and drug resistance. We identified that Nek2 overexpression correlates with poor survival of breast cancer. However, the mechanisms driving these phenotypes are unknown. We now report that overexpression of Nek2 in MCF10A cells drives CA/CIN and aneuploidy. Besides, enhanced levels of Nek2 results in larger 3D acinar structures, but could not initiate tumors in a p53+/+ or a p53-/- xenograft model. Nek2 overexpression induced the epithelial-to-mesenchymal transition (EMT) while its downregulation reduced the expression of the mesenchymal marker vimentin. Furthermore, either siRNA-mediated downregulation or INH6's chemical inhibition of Nek2 in MDA-MB-231 and Hs578t cells showed important EMT changes and decreased invasion and migration. We also showed that Slug and Zeb1 are involved in Nek2 mediated EMT, invasion, and migration. Besides its role in CA/CIN, Nek2 contributes to breast cancer progression through a novel EMT mediated mechanism.

14-3-3γ prevents centrosome duplication by inhibiting NPM1 function

14-3-3 proteins bind to ligands via phospho-serine containing consensus motifs. However, the molecular mechanisms underlying complex formation and dissociation between 14-3-3 proteins and their ligands remain unclear. We identified two conserved acidic residues in the 14-3-3 peptide-binding pocket (D129 and E136) that potentially regulate complex formation and dissociation. Altering these residues to alanine led to opposing effects on centrosome duplication. D129A inhibited centrosome duplication, whereas E136A stimulated centrosome amplification. These results were due to the differing abilities of these mutant proteins to form a complex with NPM1. Inhibiting complex formation between NPM1 and 14-3-3γ led to an increase in centrosome duplication and over-rode the ability of D129A to inhibit centrosome duplication. We identify a novel role of 14-3-3γ in regulating centrosome licensing and a novel mechanism underlying the formation and dissociation of 14-3-3 ligand complexes dictated by conserved residues in the 14-3-3 family.

Targeting Pin1 for Modulation of Cell Motility and Cancer Therapy

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) specifically binds and isomerizes the phosphorylated serine/threonine-proline (pSer/Thr-Pro) motif, which leads to changes in protein conformation and function. Pin1 is widely overexpressed in cancers and plays an important role in tumorigenesis. Mounting evidence has revealed that targeting Pin1 is a potential therapeutic approach for various cancers by inhibiting cell proliferation, reducing metastasis, and maintaining genome stability. In this review, we summarize the underlying mechanisms of Pin1-mediated upregulation of oncogenes and downregulation of tumor suppressors in cancer development. Furthermore, we also discuss the multiple roles of Pin1 in cancer hallmarks and examine Pin1 as a desirable pharmaceutical target for cancer therapy. We also summarize the recent progress of Pin1-targeted small-molecule compounds for anticancer activity.

Centrosome amplification: a quantifiable cancer cell trait with prognostic value in solid malignancies

Numerical and/or structural centrosome amplification (CA) is a hallmark of cancers that is often associated with the aberrant tumor karyotypes and poor clinical outcomes. Mechanistically, CA compromises mitotic fidelity and leads to chromosome instability (CIN), which underlies tumor initiation and progression. Recent technological advances in microscopy and image analysis platforms have enabled better-than-ever detection and quantification of centrosomal aberrancies in cancer. Numerous studies have thenceforth correlated the presence and the degree of CA with indicators of poor prognosis such as higher tumor grade and ability to recur and metastasize. We have pioneered a novel semi-automated pipeline that integrates immunofluorescence confocal microscopy with digital image analysis to yield a quantitative centrosome amplification score (CAS), which is a summation of the severity and frequency of structural and numerical centrosome aberrations in tumor samples. Recent studies in breast cancer show that CA increases across the disease progression continuum, while normal breast tissue exhibited the lowest CA, followed by cancer-adjacent apparently normal, ductal carcinoma in situ and invasive tumors, which showed the highest CA. This finding strengthens the notion that CA could be evolutionarily favored and can promote tumor progression and metastasis. In this review, we discuss the prevalence, extent, and severity of CA in various solid cancer types, the utility of quantifying amplified centrosomes as an independent prognostic marker. We also highlight the clinical feasibility of a CA-based risk score for predicting recurrence, metastasis, and overall prognosis in patients with solid cancers.

Loss of Both CDKN2A and CDKN2B Allows for Centrosome Overduplication in Melanoma

Centrosomes duplicate only once in coordination with the DNA replication cycle and have an important role in segregating genetic material. In contrast, most cancer cells have centrosome aberrations, including supernumerary centrosomes, and this correlates with aneuploidy and genetic instability. The tumor suppressors p16 (CDKN2A) and p15 (CDKN2B) (encoded by the familial melanoma CDKN2 locus) inhibit CDK4/6 activity and have important roles in cellular senescence. p16 is also associated with suppressing centrosomal aberrations in breast cancer; however, the role of p15 in centrosome amplification is unknown. Here, we investigated the relationship between p15 and p16 expression, centrosome number abnormalities, and melanoma progression in cell lines derived from various stages of melanoma progression. We found that normal human melanocyte lines did not exhibit centrosome number abnormalities, whereas those from later stages of melanoma did. Additionally, under conditions of S-phase block, p15 and p16 status determined whether centrosome overduplication would occur. Indeed, removal of p15 from p16-negative cell lines derived from various stages of melanoma progression changed cells that previously would not overduplicate their centrosomes into cells that did. Although this study used cell lines in vitro, it suggests that, during clinical melanoma progression, sequential loss of p15 and p16 provides conditions for centrosome duplication to become deregulated with consequences for genome instability.

Targeting centrosome amplification, an Achilles' heel of cancer

Due to cell-cycle dysregulation, many cancer cells contain more than the normal compliment of centrosomes, a state referred to as centrosome amplification (CA). CA can drive oncogenic phenotypes and indeed can cause cancer in flies and mammals. However, cells have to actively manage CA, often by centrosome clustering, in order to divide. Thus, CA is also an Achilles' Heel of cancer cells. In recent years, there have been many important studies identifying proteins required for the management of CA and it has been demonstrated that disruption of some of these proteins can cause cancer-specific inhibition of cell growth. For certain targets therapeutically relevant interventions are being investigated, for example, small molecule inhibitors, although none are yet in clinical trials. As the field is now poised to move towards clinically relevant interventions, it is opportune to summarise the key work in targeting CA thus far, with particular emphasis on recent developments where small molecule or other strategies have been proposed. We also highlight the relatively unexplored paradigm of reversing CA, and thus its oncogenic effects, for therapeutic gain.

Targeting CDK2 in cancer: challenges and opportunities for therapy

Cyclin-dependent kinase 2 (CDK2) plays a pivotal part in cell cycle regulation and is involved in a range of biological processes. CDK2 interacts with and phosphorylates proteins in pathways such as DNA damage, intracellular transport, protein degradation, signal transduction, DNA and RNA metabolism and translation. CDK2 and its regulatory subunits are deregulated in many human cancers and there is emerging evidence suggesting CDK2 inhibition elicits antitumor activity in a subset of tumors with defined genetic features. Previous CDK2 inhibitors were nonspecific and limited by off-target effects. The development of new-generation CDK2 inhibitors represents a therapeutic opportunity for CDK2-dependent cancers.

Role of E2Fs and mitotic regulators controlled by E2Fs in the epithelial to mesenchymal transition

The epithelial-to-mesenchymal transition (EMT) is a complex cellular process in which epithelial cells acquire mesenchymal properties. EMT occurs in three biological settings: development, wound healing and fibrosis, and tumor progression. Despite occurring in three independent biological settings, EMT signaling shares some molecular mechanisms that allow epithelial cells to de-differentiate and acquire mesenchymal characteristics that confer cells invasive and migratory capacity to distant sites. Here we summarize the molecular mechanism that delineates EMT and we will focus on the role of E2 promoter binding factors (E2Fs) in EMT during tumor progression. Since the E2Fs are presently undruggable due to their control in numerous pivotal cellular functions and due to the lack of selectivity against individual E2Fs, we will also discuss the role of three mitotic regulators and/or mitotic kinases controlled by the E2Fs (NEK2, Mps1/TTK, and SGO1) in EMT that can be useful as drug targets.

Impact statement

The study of the epithelial to mesenchymal transition (EMT) is an active area of research since it is one of the early intermediates to invasion and metastasis—a state of the cancer cells that ultimately kills many cancer patients. We will present in this review that besides their canonical roles as regulators of proliferation, unregulated expression of the E2F transcription factors may contribute to cancer initiation and progression to metastasis by signaling centrosome amplification, chromosome instability, and EMT. Since our discovery that the E2F activators control centrosome amplification and mitosis in cancer cells, we have identified centrosome and mitotic regulators that may represent actionable targets against EMT and metastasis in cancer cells. This is impactful to all of the cancer patients in which the Cdk/Rb/E2F pathway is deregulated, which has been estimated to be most cancer patients with solid tumors.

Palbociclib Promotes Dephosphorylation of NPM/B23 at Threonine 199 and Inhibits Endometrial Cancer Cell Growth

Endometrial cancer incidence rates are growing, especially in countries with rapid socioeconomic transitions. Despite recent advances in chemotherapy, hormone therapy, and targeted therapy, advanced/recurrent disease remains a clinical challenge. Palbociclib—a selective inhibitor of cyclin-dependent kinases (CDK) 4/6—has therapeutic potential against estrogen receptor (ER)-positive and HER2-negative breast cancer. However, the question as to whether it can be clinically useful in endometrial cancer remains open. Here, we show that combined treatment with palbociclib and megesterol acetate exerts synergistic antiproliferative effects against endometrial cancer cells. Treatment of cancer cells with palbociclib suppressed NPM/B23 phosphorylation at threonine 199 (Thr199). We further demonstrated that CDK6 acts as a NPM/B23 kinase. Palbociclib-induced NPM/B23 dephosphorylation sensitized endometrial cancer cells to megesterol acetate through the upregulation of ERα expression. Immunohistochemistry revealed an overexpression of phospho-NPM/B23 (Thr199) in human endometrial cancer, and phospho-NPM/B23 (Thr199) expression levels were inversely associated with Erα in clinical specimen. In a xenograft tumor model, the combination of palbociclib and megesterol acetate successfully inhibited tumor growth. Taken together, our data indicate that palbociclib promoted NPM/B23 dephosphorylation at Thr199—an effect mediated by disruption of CDK6 kinase activity. We conclude that palbociclib holds promise for the treatment of endometrial cancer when used in combination with megesterol acetate.

Ampelopsin inhibits human glioma through inducing apoptosis and autophagy dependent on ROS generation and JNK pathway

Glioma is the most common form of malignant brain cancer with high mortality rate in human. Therefore, finding effective therapeutic strategy and revealing the underlying molecular mechanism is necessary. Ampelopsin (Amp), an effective component of the traditional Chinese herb of Ampelopsis grossedentata, is reported to have important biological properties, including anti-inflammatory, anti-cancer, and anti-oxidant activity; however, its effects on human glioma are poorly understood. Here, the in vitro and in vivo study was performed to investigate the anti-glioma ability of Ampelopsin. Human glioma cell lines of U251 and A172 were treated with Ampelopsin (0, 25, 50, and 100 uM) for 24 h, followed by various analysis. And human glioma xenograft models were established by injecting U251, accompanied with administration of Ampelopsin at 50 and 100 mg/kg to confirm the anti-cancer role of Ampelopsin. We found that Ampelopsin could suppress the glioma cell proliferation by modulating G1 and S phase arrest. Incubation with Ampelopsin led to the activity of Caspase-8, Caspase-9, Caspase-3 and poly (ADP-ribose) polymerases (PARP), indicating that Ampelopsin induced apoptotic response via both intrinsic and extrinsic signaling pathways. Additionally, autophagy was also observed in Ampelopsin-treated cancer cells, which is evidenced by autophagosome formation and LC3B-II accumulation. Ampelopsin-caused cancer cell death was obviously regained by apoptosis inhibitors. Further, Ampelopsin activated c-Jun N-terminal protein kinase (JNK) expression and enhanced reactive oxygen species (ROS) generation. Suppressing JNK markedly ameliorated Ampelopsin-induced apoptosis and autophagy, and ROS scavenger exhibited similar results. In vivo, Ampelopsin inhibited tumor growth and progression in mouse xenograft models. In conclusion, our findings indicated that Ampelopsin led to G1 and S phase arrest, triggered apoptosis and autophagy through potentiating ROS generation and JNK activation in human glioma cells. Thus, Ampelopsin might be a promising candidate against human glioma.

MYCN is amplified during S phase, and c‑myb is involved in controlling MYCN expression and amplification in MYCN‑amplified neuroblastoma cell lines

Neuroblastoma derived from primitive sympathetic neural precursors is a common type of solid tumor in infants. MYCN proto-oncogene bHLH transcription factor (MYCN) amplification and 1p36 deletion are important factors associated with the poor prognosis of neuroblastoma. Expression levels of MYCN and c-MYB proto-oncogene transcription factor (c-myb) decline during the differentiation of neuroblastoma cells; E2F transcription factor 1 (E2F1) activates the MYCN promoter. However, the underlying mechanism of MYCN overexpression and amplification requires further investigation. In the present study, potential c-Myb target genes, and the effect of c-myb RNA interference (RNAi) on MYCN expression and amplification were investigated in MYCN-amplified neuroblastoma cell lines. The mRNA expression levels and MYCN gene copy number in five neuroblastoma cell lines were determined by quantitative polymerase chain reaction. In addition, variations in potential target gene expression and MYCN gene copy number between pre- and post-c-myb RNAi treatment groups in MYCN-amplified Kelly, IMR32, SIMA and MHH-NB-11 cell lines, normalized to those of non-MYCN-amplified SH-SY5Y, were examined. To determine the associations between gene expression levels and chromosomal aberrations, MYCN amplification and 1p36 alterations in interphases/metaphases were analyzed using fluorescence in situ hybridization. Statistical analyses revealed correlations between 1p36 alterations and the expression of c-myb, MYB proto-oncogene like 2 (B-myb) and cyclin dependent kinase inhibitor 1A (p21). Additionally, the results of the present study also demonstrated that c-myb may be associated with E2F1 and L3MBTL1 histone methyl-lysine binding protein (L3MBTL1) expression, and that E2F1 may contribute to MYCN, B-myb, p21 and chromatin licensing and DNA replication factor 1 (hCdt1) expression, but to the repression of geminin (GMNN). On c-myb RNAi treatment, L3MBTL1 expression was silenced, while GMNN was upregulated, indicating G₂/M arrest. In addition, MYCN gene copy number increased following treatment with c-myb RNAi. Notably, the present study also reported a 43.545% sequence identity between upstream of MYCN and Drosophila melanogaster amplification control element 3, suggesting that expression and/or amplification mechanisms of developmentally-regulated genes may be evolutionarily conserved. In conclusion, c-myb may be associated with regulating MYCN expression and amplification. c-myb, B-myb and p21 may also serve a role against chromosome 1p aberrations. Together, it was concluded that MYCN gene is amplified during S phase, potentially via a replication-based mechanism.

Centrosome aberrations and chromosome instability contribute to tumorigenesis and intra-tumor heterogeneity

Centrosomes serve as the major microtubule organizing centers in cells and thereby contribute to cell shape, polarity, and motility. Also, centrosomes ensure equal chromosome segregation during mitosis. Centrosome aberrations arise when the centrosome cycle is deregulated, or as a result of cytokinesis failure. A long-standing postulate is that centrosome aberrations are involved in the initiation and progression of cancer. However, this notion has been a subject of controversy because until recently the relationship has been correlative. Recently, it was shown that numerical or structural centrosome aberrations can initiate tumors in certain tissues in mice, as well as invasion. Particularly, we will focus on centrosome amplification and chromosome instability as drivers of intra-tumor heterogeneity and their consequences in cancer. We will also discuss briefly the controversies surrounding this theory to highlight the fact that the role of both centrosome amplification and chromosome instability in cancer is highly context-dependent. Further, we will discuss single-cell sequencing as a novel technique to understand intra-tumor heterogeneity and some therapeutic approaches to target chromosome instability.

Cytokinesis arrest and multiple centrosomes in B cell chronic lymphocytic leukaemia

Cytokinesis failure leads to the emergence of tetraploid cells and multiple centrosomes. Chronic lymphocytic leukaemia (CLL) is the most common haematological malignancy in adults and is characterized by clonal B cell expansion. Here, we show that a significant number of peripheral blood CLL cells are arrested in cytokinesis and that this event occurred after nuclear envelope reformation and before cytoplasmic abscission. mRNA expression data showed that several genes known to be crucial for cell cycle regulation, checkpoint and centromere function, such as ING4, ING5, CDKN1A and CDK4, were significantly dysregulated in CLL samples. Our results demonstrate that CLL cells exhibit difficulties in completing mitosis, which is different from but may, at least in part, explain the previously reported accumulation of CLL cells in G0/1.

Alteronol induces cell cycle arrest and apoptosis via increased reactive oxygen species production in human breast cancer T47D cells

Objective

Emerging evidence showed that alteronol has a potential antitumour effect in several tumour cells. However, the antitumour effect of alteronol on breast cancer has not been reported. This study investigated the mechanisms of alteronol-induced cell proliferation inhibition in human breast cancer T47D cells.

Methods

After treatment with alteronol, T47D cell proliferation was examined by MTT assay. The cell cycle distribution, cell apoptosis, reactive oxygen species level and mitochondrial membrane potential were evaluated via flow cytometry. Next, the protein levels of cyclin B1, cdc2, p21, p-cyclin B1, p-cdc2, p53, Bax, Bcl-2 and cytochrome c were analysed using Western blot analysis. Meanwhile, the mRNA levels of cyclin B1, cdc2, p21 and p53 were examined by qRT-PCR.

Key findings

Our data showed that alteronol inhibited the proliferation of T47D cells via inducing G2-phase arrest and cell apoptosis. Compared with control group, alteronol significantly increased ROS level and triggered mitochondrial dysfunction in alteronol-treated T47D cells. Further studies showed that the mRNA and protein levels of cdc2 and cyclin B1 were downregulated, while the mRNA and protein levels of p21, p53, p-cyclin B1, p-cdc2 and cytochrome c were upregulated. In addition, the expression level of Bax was increased, and the expression level of Bcl-2 was decreased.

Conclusions

Alteronol induced T47D cell cycle arrest and cell apoptosis through increasing ROS production and triggering mitochondrial dysfunction, and subsequently inhibiting T47D cell proliferation.

Building the right centriole for each cell type

Loncarek and Bettencourt-Dias review molecular mechanisms of centriole biogenesis amongst different organisms and cell types.

The centriole is a multifunctional structure that organizes centrosomes and cilia and is important for cell signaling, cell cycle progression, polarity, and motility. Defects in centriole number and structure are associated with human diseases including cancer and ciliopathies. Discovery of the centriole dates back to the 19th century. However, recent advances in genetic and biochemical tools, development of high-resolution microscopy, and identification of centriole components have accelerated our understanding of its assembly, function, evolution, and its role in human disease. The centriole is an evolutionarily conserved structure built from highly conserved proteins and is present in all branches of the eukaryotic tree of life. However, centriole number, size, and organization varies among different organisms and even cell types within a single organism, reflecting its cell type–specialized functions. In this review, we provide an overview of our current understanding of centriole biogenesis and how variations around the same theme generate alternatives for centriole formation and function.

The E2F activators control multiple mitotic regulators and maintain genomic integrity through Sgo1 and BubR1

The E2F1, E2F2, and E2F3a transcriptional activators control proliferation. However, how the E2F activators regulate mitosis to maintain genomic integrity is unclear. Centrosome amplification (CA) and unregulated spindle assembly checkpoint (SAC) are major generators of aneuploidy and chromosome instability (CIN) in cancer. Previously, we showed that overexpression of single E2F activators induced CA and CIN in mammary epithelial cells, and here we show that combined overexpression of E2F activators did not enhance CA. Instead, the E2F activators elevated expression of multiple mitotic regulators, including Sgo1, Nek2, Hec1, BubR1, and Mps1/TTK. cBioPortal analyses of the TCGA database showed that E2F overexpression in lobular invasive breast tumors correlates with overexpression of multiple regulators of chromosome segregation, centrosome homeostasis, and the SAC. Kaplan-Meier plots identified correlations between individual or combined overexpression of E2F1, E2F3a, Mps1/TTK, Nek2, BubR1, or Hec1 and poor overall and relapse-free survival of breast cancer patients. In MCF10A normal mammary epithelial cells co-overexpressing E2Fs, transient Sgo1 knockdown induced CA, high percentages of premature sister chromatid separation, chromosome losses, increased apoptosis, and decreased cell clonogenicity. BubR1 silencing resulted in chromosome losses without CA, demonstrating that Sgo1 and BubR1 maintain genomic integrity through two distinct mechanisms. Our results suggest that deregulated activation of the E2Fs in mammary epithelial cells is counteracted by activation of a Sgo1-dependent mitotic checkpoint.

Ikk2 regulates cytokinesis during vertebrate development

NFκB signaling has a pivotal role in regulation of development, innate immunity, and inflammation. Ikk2 is one of the two critical kinases that regulate the NFκB signaling pathway. While the role of Ikk2 in immunity, inflammation and oncogenesis has received attention, an understanding of the role of Ikk2 in vertebrate development has been compounded by the embryonic lethality seen in mice lacking Ikk2. We find that despite abnormal angiogenesis in IKK2 zygotic mutants of zebrafish, the maternal activity of Ikk2 supports embryogenesis and maturation of fertile animals and allows to study the role of IKK2 in development. Maternal-zygotic ikk2 mutants represent the first vertebrates globally devoid of maternal and zygotic Ikk2 activity. They are defective in cell proliferation as evidenced by abnormal cytokinesis, nuclear enlargement and syncytialisation of a significant portion of blastoderm. We further document that reduced phosphorylation of Aurora A by Ikk2 could underlie the basis of these defects in cell division.

AIRE is a critical spindle-associated protein in embryonic stem cells

Embryonic stem (ES) cells go though embryo-like cell cycles regulated by specialized molecular mechanisms. However, it is not known whether there are ES cell-specific mechanisms regulating mitotic fidelity. Here we showed that Autoimmune Regulator (Aire), a transcription coordinator involved in immune tolerance processes, is a critical spindle-associated protein in mouse ES(mES) cells. BioID analysis showed that AIRE associates with spindle-associated proteins in mES cells. Loss of function analysis revealed that Aire was important for centrosome number regulation and spindle pole integrity specifically in mES cells. We also identified the c-terminal LESLL motif as a critical motif for AIRE's mitotic function. Combined maternal and zygotic knockout further revealed Aire's critical functions for spindle assembly in preimplantation embryos. These results uncovered a previously unappreciated function for Aire and provide new insights into the biology of stem cell proliferation and potential new angles to understand fertility defects in humans carrying Aire mutations.

Isoliquiritigenin induces apoptosis of human bladder cancer T24 cells via a cyclin-dependent kinase-independent mechanism

The aim of the present study was to investigate whether an increase in cyclin-dependent kinase 2 (CDK2) activity is involved in apoptosis of human bladder cancer T24 cells induced by isoliquiritigenin (ISL). The viability of T24 cells was estimated using a sulforhodamine B assay. Cell morphological changes were examined using Hoechst 33258 staining. The apoptotic rate was determined by staining cells with Annexin V-fluorescein isothiocyanate and propidium iodide labeling. The mitochondrial membrane potential (ΔΨm) was measured using 5,5,6,6-tetrachloro-1,1, 3,3-tetraethyl benzimidazole carbocyanine iodide. Alterations in the apoptosis-related regulators B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), Bcl-2-interacting mediator of cell death (Bim), apoptotic protease-activating facter-1 (Apaf-1), caspase-9 and caspase-3 were determined using reverse transcription-polymerase chain reaction (PCR) and quantitative PCR methods. Western blot analysis was used to detect the expression of Bcl-2, Bax and caspase-3. CDK2 activity was measured using a spectrometric assay. Following treatment with ISL (between 30 and 70 µg/ml) for 24 h, typical apoptotic morphological changes were observed in T24 cells, exhibiting an edge set of chromosomes, nuclear condensation, nuclear fragmentation and other morphological features. Treatment with ISL increased the apoptotic ratio of T24 cells in a concentration-dependent manner and induced a decrease in the ΔΨm in a time-dependent manner. Treatment with ISL upregulated the expression of Bax, Bim, Apaf-1, caspase-9 and caspase-3, downregulated the expression of Bcl-2, and increased CDK2 activity. MK-8776 (an inhibitor of CDK2) antagonized the apoptosis induced by ISL, and, compared with treatment with ISL alone, pretreatment with MK-8776 inhibited the decrease in ΔΨm, downregulated the mRNA expression of Bax, Bim, Apaf-1, caspase-9 and caspase-3, and upregulated Bcl-2 mRNA expression. Western blot analysis demonstrated that, with increasing ISL concentration, the Bcl-2 expression level was significantly decreased (P<0.05), whereas caspase-3 and Bax expression levels were significantly increased (P<0.01). These results indicated that ISL treatment caused a significant decrease in the proliferation rate and increase in apoptosis of T24 cells. The mechanism by which ISL induces T24 cell apoptosis in vitro may be associated with an increase in CDK2 activity, downregulation of the ΔΨm and activation of caspase-3/caspase-9-mediated mitochondrial apoptotic signaling pathways.

USP9X regulates centrosome duplication and promotes breast carcinogenesis

Defective centrosome duplication is implicated in microcephaly and primordial dwarfism as well as various ciliopathies and cancers. Yet, how the centrosome biogenesis is regulated remains poorly understood. Here we report that the X-linked deubiquitinase USP9X is physically associated with centriolar satellite protein CEP131, thereby stabilizing CEP131 through its deubiquitinase activity. We demonstrate that USP9X is an integral component of centrosome and is required for centrosome biogenesis. Loss-of-function of USP9X impairs centrosome duplication and gain-of-function of USP9X promotes centrosome amplification and chromosome instability. Significantly, USP9X is overexpressed in breast carcinomas, and its level of expression is correlated with that of CEP131 and higher histologic grades of breast cancer. Indeed, USP9X, through regulation of CEP131 abundance, promotes breast carcinogenesis. Our experiments identify USP9X as an important regulator of centrosome biogenesis and uncover a critical role for USP9X/CEP131 in breast carcinogenesis, supporting the pursuit of USP9X/CEP131 as potential targets for breast cancer intervention.

USP9X is a deubiquitinating enzyme with many known substrates and functions; it has been linked to cancer but the mechanisms remain unclear. Here Li et al. report that USP9X stabilizes the centrosomal protein CEP131 leading to centrosome amplification and breast cancer development.

Targeting NEK2 as a promising therapeutic approach for cancer treatment

Never in Mitosis (NIMA) Related Kinase 2 (NEK2) plays a key role in regulating mitotic processes, including centrosome duplication and separation, microtubule stabilization, kinetochore attachment and spindle assembly checkpoint. NEK2 is aberrantly overexpressed in a wide variety of human cancers and has been implicated in various aspects of malignant transformation, including tumorigenesis, drug resistance and tumor progression. The close relationship between NEK2 and cancer has made it an attractive target for anticancer therapeutic development; however, the mechanisms of how NEK2 coordinates altered signaling to malignant transformation remains unclear. In this paper, we discuss the functional roles of NEK2 in cancer development; highlight some of the significant NEK2 signaling in cancer, and summarize recent advances in the development of NEK2 inhibitors.

Bisphenol A and its analogues disrupt centrosome cycle and microtubule dynamics in prostate cancer

Humans are increasingly exposed to structural analogues of bisphenol A (BPA), as BPA is being replaced by these compounds in BPA-free consumer products. We have previously shown that chronic and developmental exposure to BPA is associated with increased prostate cancer (PCa) risk in human and animal models. Here, we examine whether exposure of PCa cells (LNCaP, C4-2) to low-dose BPA and its structural analogues (BPS, BPF, BPAF, TBBPA, DMBPA and TMBPA) affects centrosome amplification (CA), a hallmark of cancer initiation and progression. We found that exposure to BPA, BPS, DMBPA and TBBPA, in descending order, increased the number of cells with CA, in a non-monotonic dose-response manner. Furthermore, cells treated with BPA and their analogues initiated centrosome duplication at 8 h after release from serum starvation, significantly earlier in G-1 phase than control cells. This response was attended by earlier release of nucleophosmin from unduplicated centrosomes. BPA-exposed cells exhibited increased expression of cyclin-dependent kinase CDK6 and decreased expression of CDK inhibitors (p21^Waf1/CIP1 and p27^KIP1). Using specific antagonists for estrogen/androgen receptors, CA in the presence of BPA or its analogues was likely to be mediated via ESR1 signaling. Change in microtubule dynamics was observed on exposure to these analogues, which, for BPA, was accompanied by increased expression of centrosome-associated protein CEP350 Similar to BPA, chronic treatment of cells with DMBPA, but not other analogues, resulted in the enhancement of anchorage-independent growth. We thus conclude that selected BPA analogues, similar to BPA, disrupt centrosome function and microtubule organization, with DMBPA displaying the broadest spectrum of cancer-promoting effects.

The Role of Aneuploidy in Cancer Evolution

Chromosomal aberrations during cell division represent one of the first recognized features of human cancer cells, and modern detection methods have revealed the pervasiveness of aneuploidy in cancer. The ongoing karyotypic changes brought about by chromosomal instability (CIN) contribute to tumor heterogeneity, drug resistance, and treatment failure. Whole-chromosome and segmental aneuploidies resulting from CIN have been proposed to allow "macroevolutionary" leaps that may contribute to profound phenotypic change. In this review, we will outline evidence indicating that aneuploidy and CIN contribute to cancer evolution.

Centrosome - a promising anti-cancer target

The centrosome, an organelle discovered >100 years ago, is the main microtubule-organizing center in mammalian organisms. The centrosome is composed of a pair of centrioles surrounded by the pericentriolar material (PMC) and plays a major role in the regulation of cell cycle transitions (G1-S, G2-M, and metaphase-anaphase), ensuring the normality of cell division. Hundreds of proteins found in the centrosome exert a variety of roles, including microtubule dynamics, nucleation, and kinetochore–microtubule attachments that allow correct chromosome alignment and segregation. Errors in these processes lead to structural (shape, size, number, position, and composition), functional (abnormal microtubule nucleation and disorganized spindles), and numerical (centrosome amplification [CA]) centrosome aberrations causing aneuploidy and genomic instability. Compelling data demonstrate that centrosomes are implicated in cancer, because there are important oncogenic and tumor suppressor proteins that are localized in this organelle and drive centrosome aberrations. Centrosome defects have been found in pre-neoplasias and tumors from breast, ovaries, prostate, head and neck, lung, liver, and bladder among many others. Several drugs/compounds against centrosomal proteins have shown promising results. Other drugs have higher toxicity with modest or no benefits, and there are more recently developed agents being tested in clinical trials. All of this emerging evidence suggests that targeting centrosome aberrations may be a future avenue for therapeutic intervention in cancer research.

Ubiquitin, the centrosome, and chromosome segregation

For over a century, the abnormal movement or number of centrosomes has been linked with errors of chromosomes distribution in mitosis. While not essential for the formation of the mitotic spindle, the presence and location of centrosomes has a major influence on the manner in which microtubules interact with the kinetochores of replicated sister chromatids and the accuracy with which they migrate to resulting daughter cells. A complex network has evolved to ensure that cells contain the proper number of centrosomes and that their location is optimal for effective attachment of emanating spindle fibers with the kinetochores. The components of this network are regulated through a series of post-translational modifications, including ubiquitin and ubiquitin-like modifiers, which coordinate the timing and strength of signaling events key to the centrosome cycle. In this review, we examine the role of the ubiquitin system in the events relating to centriole duplication and centrosome separation, and discuss how the disruption of these functions impacts chromosome segregation.

Immortalization of human normal and NF1 neurofibroma Schwann cells

Neurofibromas, which are benign Schwann cell tumors, are the hallmark feature in the autosomal dominant condition neurofibromatosis 1 (NF1) and are associated with biallelic loss of NF1 gene function. There is a need for effective therapies for neurofibromas, particularly the larger, plexiform neurofibromas. Tissue culture is an important tool for research. However, it is difficult to derive enriched human Schwann cell cultures, and most enter replicative senescence after 6-10 passages, impeding cell-based research in NF1. Through exogenous expression of human telomerase reverse transcriptase and murine cyclin-dependent kinase (mCdk4), normal (NF1 wild-type), neurofibroma-derived Schwann cells heterozygous for NF1 mutation, and neurofibroma-derived Schwann cells homozygous for NF1 mutation were immortalized, including some matched samples from the same NF1 patient. Initial experiments employed retroviral vectors, while subsequent work utilized lentiviral vectors carrying these genes because of improved efficiency. Expression of both transgenes was required for immortalization. Molecular and immunohistochemical analysis indicated that these cell lines are of Schwann cell lineage and have a range of phenotypes, many of which are consistent with their primary cultures. This is the first report of immortalization and detailed characterization of multiple human NF1 normal nerve and neurofibroma-derived Schwann cell lines, which will be highly useful research tools to study NF1 and other Schwann tumor biology and conditions.

CUEDC2 down-regulation is associated with tumor growth and poor prognosis in lung adenocarcinoma

CUE domain-containing 2 (CUEDC2) is a multi-functional protein, which regulates cell cycle, growth factor signaling and inflammation. We found that CUEDC2 was low in lung adenocarcinoma cell lines and lung adenocarcinoma tissues at both mRNA and protein levels. Low levels of CUEDC2 were correlated with a shorter survival time in patients with lung adenocarcinoma (p = 0.004). CUEDC2 expression was correlated with tumor T classification (P = 0.001) at clinical stage (P = 0.001) and tumor size (P = 0.033). Multivariate analysis suggested that CUEDC2 expression is an independent prognostic indicator for patients with lung adenocarcinoma. Ectopic expression of CUEDC2 decreased cell proliferation in vitro and inhibited tumor growth in nude mice in vivo. Knockdown of endogenous CUEDC2 by short hairpin RNAs (shRNAs) increased tumor growth. Inhibition of proliferation by CUEDC2 was associated with inactivation of the PI3K/Akt pathway, induction of p21 and down-regulation of cyclin D1. Our results suggest that decreased expression of CUEDC2 contributes to tumor growth in lung adenocarcinoma, leading to a poor clinical outcome.

Cdk2 catalytic activity is essential for meiotic cell division in vivo

Cyclin-dependent kinases (Cdks) control the eukaryotic cell cycle by phosphorylating serine and threonine residues in key regulatory proteins, but some Cdk family members may exert kinase-independent functions that cannot easily be assessed using gene knockout approaches. While Cdk2-deficient mice display near-normal mitotic cell proliferation due to the compensatory activities of Cdk1 and Cdk4, they are unable to undergo meiotic generation of gametes and are consequently sterile. To investigate whether Cdk2 regulates meiosis via protein phosphorylation or by alternative kinase-independent mechanisms, we generated two different knockin mouse strains in which Cdk2 point mutations ablated enzyme activity without altering protein expression levels. Mice homozygous for the mutations Cdk2(D145N/D145N) or Cdk2(T160A/T160A) expressed only 'kinase-dead' variants of Cdk2 under the control of the endogenous promoter, and despite exhibiting normal expression of cell cycle regulatory proteins and complexes, both mutations rendered mice sterile. Mouse cells that expressed only 'kinase-dead' variants of Cdk2 displayed normal mitotic cell cycle progression and proliferation both in vitro and in vivo, indicating that loss of Cdk2 kinase activity exerted little effect on this mode of cell division. In contrast, the reproductive organs of Cdk2 mutant mice exhibited abnormal morphology and impaired function associated with defective meiotic cell division and inability to produce gametes. Cdk2 mutant animals were therefore comparable to gene knockout mice, which completely lack the Cdk2 protein. Together, our data indicate that the essential meiotic functions of Cdk2 depend on its kinase activity, without which the generation of haploid cells is disrupted, resulting in sterility of otherwise healthy animals.

14-3-3γ Prevents Centrosome Amplification and Neoplastic Progression

More than 80% of malignant tumors show centrosome amplification and clustering. Centrosome amplification results from aberrations in the centrosome duplication cycle, which is strictly coordinated with DNA-replication-cycle. However, the relationship between cell-cycle regulators and centrosome duplicating factors is not well understood. This report demonstrates that 14-3-3γ localizes to the centrosome and 14-3-3γ loss leads to centrosome amplification. Loss of 14-3-3γ results in the phosphorylation of NPM1 at Thr-199, causing early centriole disjunction and centrosome hyper-duplication. The centrosome amplification led to aneuploidy and increased tumor formation in mice. Importantly, an increase in passage of the 14-3-3γ-knockdown cells led to an increase in the number of cells containing clustered centrosomes leading to the generation of pseudo-bipolar spindles. The increase in pseudo-bipolar spindles was reversed and an increase in the number of multi-polar spindles was observed upon expression of a constitutively active 14-3-3-binding-defective-mutant of cdc25C (S216A) in the 14-3-3γ knockdown cells. The increase in multi-polar spindle formation was associated with decreased cell viability and a decrease in tumor growth. Our findings uncover the molecular basis of regulation of centrosome duplication by 14-3-3γ and inhibition of tumor growth by premature activation of the mitotic program and the disruption of centrosome clustering.

Genome Stability Requires p53

It is now clear that functional p53 is critical to protect the genome from alterations that lead to tumorigenesis. However, with the myriad of cellular stresses and pathways linked to p53 activation, much remains unknown about how p53 maintains genome stability and the proteins involved. The current understanding of the multiple ways p53 contributes to genome stability and how two of its negative regulators, Mdm2 and Mdmx, induce genome instability will be described.

Opposing post-translational modifications regulate Cep76 function to suppress centriole amplification

Centrioles are critical for many cellular processes including cell division and cilia assembly. The number of centrioles within a cell is under strict control, and deregulation of centriole copy number is a hallmark of cancer. The molecular mechanisms that halt centriole amplification have not been fully elucidated. Here, we found that centrosomal protein of 76 kDa (Cep76), previously shown to restrain centriole amplification, interacts with cyclin-dependent kinase 2 (CDK2) and is a bona fide substrate of this kinase. Cep76 is preferentially phosphorylated by cyclin A/CDK2 at a single site S83, and this event is crucial to suppress centriole amplification in S phase. A novel Cep76 mutation S83C identified in a cancer patient fails to prevent centriole amplification. Mechanistically, Cep76 phosphorylation inhibits activation of polo-like kinase 1 (Plk1), thereby blocking premature centriole disengagement and subsequent amplification. Cep76 can also be acetylated, and enforced acetylation at K279 dampens the protein’s ability to inhibit amplification and precludes S83 phosphorylation. Acetylation of Cep76 normally occurs in G2 phase and correlates with loss of protein function. Our data suggest that temporal changes in posttranslational modifications of Cep76 during the cell cycle regulate its capacity to suppress centriole amplification, and its deregulation may contribute to malignancy.

Aging and Loss of Circulating 17β-Estradiol Alters the Alternative Splicing of ERβ in the Female Rat Brain

Loss of circulating 17β-estradiol (E2) that occurs during menopause can have detrimental effects on cognitive function. The efficacy of hormone replacement therapy declines as women become farther removed from the menopausal transition, yet the molecular mechanisms underlying this age-related switch in E2 efficacy are unknown. We hypothesized that aging and varying lengths of E2 deprivation alters the ratio of alternatively spliced estrogen receptor (ER)β isoforms in the brain of female rats. Further, we tested whether changes in global transcriptional activity and splicing kinetics regulate the alternative splicing of ERβ. Our results revealed brain region-specific changes in ERβ alternative splicing in both aging and E2-deprivation paradigms and showed that ERβ could mediate E2-induced alternative splicing. Global transcriptional activity, as measured by phosphorylated RNA polymerase II, was also regulated by age and E2 in specific brain regions. Finally, we show that inhibition of topoisomerase I resulted in increased ERβ2 splice variant expression.

AP4 is required for mitogen- and c-MYC-induced cell cycle progression

AP4 represents a c-MYC-inducible bHLH-LZ transcription factor, which displays elevated expression in many types of tumors. We found that serum-starved AP4-deficient mouse embryo fibroblasts (MEFs) were unable to resume proliferation and showed a delayed S-phase entry after restimulation. Furthermore, they accumulated as tetraploid cells due to a cytokinesis defect. In addition, AP4 was required for c-MYC-induced cell cycle re-entry. AP4-deficient MEFs displayed decreased expression of CDK2 (cyclin-dependent kinase 2), which we characterized as a conserved and direct AP4 target. Activation of an AP4 estrogen receptor fusion protein (AP4-ER) enhanced proliferation of human diploid fibroblasts in a CDK2-dependent manner. However, in contrast to c-MYC-ER, AP4-ER activation was not sufficient to induce cell cycle re-entry or apoptosis in serum-starved MEFs. AP4-deficiency was accompanied by increased spontaneous and c-MYC-induced DNA damage in MEFs. Furthermore, c-MYC-induced apoptosis was decreased in AP4-deficient MEFs, suggesting that induction of apoptosis by c-MYC is linked to its ability to activate AP4 and thereby cell cycle progression. Taken together, these results indicate that AP4 is a central mediator and coordinator of cell cycle progression in response to mitogenic signals and c-MYC activation. Therefore, inhibition of AP4 function may represent a therapeutic approach to block tumor cell proliferation.

Cytoplasmic nucleophosmin has elevated T199 phosphorylation upon which G2/M phase progression is dependent

The cytoplasmic mutant of nucleophosmin (NPMc) is found approximately in one-third of acute myeloid leukemia (AML) cases and is highly associated with normal karyotype. Whereas previous studies have focused on wtNPM in centrosome duplication, we further elucidate the role of NPM in the cell cycle by utilizing the increased cytoplasmic load of NPMc. Overexpression of NPMc causes increased phosphorylation of NPM on T199 and, to a lesser degree, S4. T199 phosphorylation is dependent on cdk2 but activators of cdk2 were not elevated. Upon inhibition of cdk2, NPMc-overexpressing cells demonstrate a greater G2/M phase arrest than wtNPM or GFP counterparts. However, the number of cells with 2 centrosomes did not increase concordantly. This suggests that the arrest was caused by a delay in centrosome duplication, most likely due to the inhibition of centrosome duplication caused by unphosphorylated NPMc. Overall, these results suggest that the phosphorylation of T199 is important in the mitotic progression of NPMc-expressing cells. This further supports the hypothesis that NPMc is associated with normal karyotypes in AML because the higher cytoplasmic load of NPM can better suppress centrosome overduplication which would otherwise result in unequal segregation of chromosomes during mitosis, leading to aneuploidy and other genomic instabilities.

Cyclin-Dependent Kinase Inhibitors as Anticancer Therapeutics

Cyclin-dependent kinases (CDKs) have been considered promising drug targets for a number of years, but most CDK inhibitors have failed rigorous clinical testing. Recent studies demonstrating clear anticancer efficacy and reduced toxicity of CDK4/6 inhibitors such as palbociclib and multi-CDK inhibitors such as dinaciclib have rejuvenated the field. Favorable results with palbociclib and its recent U.S. Food and Drug Administration approval demonstrate that CDK inhibitors with narrow selectivity profiles can have clinical utility for therapy based on individual tumor genetics. A brief overview of results obtained with ATP-competitive inhibitors such as palbociclib and dinaciclib is presented, followed by a compilation of new avenues that have been pursued toward the development of novel, non-ATP-competitive CDK inhibitors. These creative ways to develop CDK inhibitors are presented along with crystal structures of these agents complexed with CDK2 to highlight differences in their binding sites and mechanisms of action. The recent successes of CDK inhibitors in the clinic, combined with the potential for structure-based routes to the development of non-ATP-competitive CDK inhibitors, and evidence that CDK inhibitors may have use in suppressing chromosomal instability and in synthetic lethal drug combinations inspire optimism that CDK inhibitors will become important weapons in the fight against cancer.

The centriole duplication cycle

Centrosomes are the main microtubule-organizing centre of animal cells and are important for many critical cellular and developmental processes from cell polarization to cell division. At the core of the centrosome are centrioles, which recruit pericentriolar material to form the centrosome and act as basal bodies to nucleate formation of cilia and flagella. Defects in centriole structure, function and number are associated with a variety of human diseases, including cancer, brain diseases and ciliopathies. In this review, we discuss recent advances in our understanding of how new centrioles are assembled and how centriole number is controlled. We propose a general model for centriole duplication control in which cooperative binding of duplication factors defines a centriole 'origin of duplication' that initiates duplication, and passage through mitosis effects changes that license the centriole for a new round of duplication in the next cell cycle. We also focus on variations on the general theme in which many centrioles are created in a single cell cycle, including the specialized structures associated with these variations, the deuterosome in animal cells and the blepharoplast in lower plant cells.

Interactions of the natural product (+)-avrainvillamide with nucleophosmin and exportin-1 Mediate the cellular localization of nucleophosmin and its AML-associated mutants

Nucleophosmin (NPM1) is a multifunctional phosphoprotein localized predominantly within the nucleoli of eukaryotic cells. Mutations within its C-terminal domain are frequently observed in patients with acute myeloid leukemia (AML), are thought to play a key role in the initiation of the disease, and result in aberrant, cytoplasmic localization of the mutant protein. We have previously shown that the electrophilic antiproliferative natural product (+)-avrainvillamide (1) binds to proteins, including nucleophosmin, by S-alkylation of cysteine residues. Here, we report that avrainvillamide restores nucleolar localization of certain AML-associated mutant forms of NPM1 and provide evidence that this relocalization is mediated by interactions of avrainvillamide with mutant NPM1 and exportin-1 (Crm1). Immunofluorescence and mass spectrometric experiments employing a series of different NPM1 constructs suggest that a specific interaction between avrainvillamide and Cys275 of certain NPM1 mutants mediates the relocalization of these proteins to the nucleolus. Avrainvillamide treatment is also shown to inhibit nuclear export of Crm1 cargo proteins, including AML-associated NPM1 mutants. We also observe that avrainvillamide treatment displaces Thr199-phosphorylated NPM1 from duplicated centrosomes, leads to an accumulation of supernumerary centrosomes, and inhibits dephosphorylation of Thr199-phosphorylated NPM1 by protein phosphatase 1. Avrainvillamide is the first small molecule reported to relocalize specific cytoplasmic AML-associated NPM1 mutants to the nucleolus, providing an important demonstration of principle that small molecule induction of a wild-type NPM1 localization phenotype is feasible in certain human cancer cells.

E2F activators signal and maintain centrosome amplification in breast cancer cells

Centrosomes ensure accurate chromosome segregation by directing spindle bipolarity. Loss of centrosome regulation results in centrosome amplification, multipolar mitosis and aneuploidy. Since centrosome amplification is common in premalignant lesions and breast tumors, it is proposed to play a central role in breast tumorigenesis, a hypothesis that remains to be tested. The coordination between the cell and centrosome cycles is of paramount importance to maintain normal centrosome numbers, and the E2Fs may be responsible for regulating these cycles. However, the role of E2F activators in centrosome amplification is unclear. Because E2Fs are deregulated in Her2(+) cells displaying centrosome amplification, we addressed whether they signal this abnormal process. Knockdown of E2F1 or E2F3 in Her2(+) cells decreased centrosome amplification without significantly affecting cell cycle progression, whereas the overexpression of E2F1, E2F2, or E2F3 increased centrosome amplification in MCF10A mammary epithelial cells. Our results revealed that E2Fs affect the expression of proteins, including Nek2 and Plk4, known to influence the cell/centrosome cycles and mitosis. Downregulation of E2F3 resulted in cell death and delays/blocks in cytokinesis, which was reversed by Nek2 overexpression. Nek2 overexpression enhanced centrosome amplification in Her2(+) breast cancer cells silenced for E2F3, revealing a role for the E2F activators in maintaining centrosome amplification in part through Nek2.

Differential expression of centrosome regulators in Her2+ breast cancer cells versus non-tumorigenic MCF10A cells

Centrosome amplification (CA) amongst particular breast cancer subtypes (Her2+ subtype) is associated with genomic instability and aggressive tumor phenotypes. However, changes in signaling pathways associated with centrosome biology have not been fully explored in subtype specific models. Novel centrosome regulatory genes that are selectively altered in Her2+ breast cancer cells are of interest in discerning why CA is more prevalent in this subtype. To determine centrosome/cell cycle genes that are altered in Her2+ cells that display CA (HCC1954) versus non-tumorigenic cells (MCF10A), we carried out a gene microarray. Expression differences were validated by real-time PCR and Western blotting. After the microarray validation, we pursued a panel of upregulated and downregulated genes based on novelty/relevance to centrosome duplication. Functional experiments measuring CA and BrdU incorporation were completed after genetic manipulation of targets (TTK, SGOL1, MDM2 and SFRP1). Amongst genes that were downregulated in HCC1954 cells, knockdown of MDM2 and SFRP1 in MCF10A cells did not consistently induce CA or impaired BrdU incorporation. Conversely, amongst upregulated genes in HCC1954 cells, knockdown of SGOL1 and TTK decreased CA in breast cancer cells, while BrdU incorporation was only altered by SGOL1 knockdown. We also explored the Kaplan Meier Plot resource and noted that MDM2 and SFRP1 are positively associated with relapse free survival in all breast cancer subtypes, while TTK is negatively correlated with overall survival of Luminal A patients. Based on this functional screen, we conclude that SGOL1 and TTK are important modulators of centrosome function in a breast cancer specific model.

Resveratrol inhibits proliferation in human colorectal carcinoma cells by inducing G1/S‑phase cell cycle arrest and apoptosis through caspase/cyclin‑CDK pathways

The present study compared the effect of resveratrol on HCT116 and Caco-2 human colon cancer cells. Annexin V/propidium iodide staining, MTT assay and western blot analysis revealed that resveratrol induced cycle arrest in the two cell lines, which was evidenced by cell cycle analysis and changes in the expression of the cell cycle proteins cyclin-dependent kinase (CDK) 2, CDK4, cyclin D1, proliferating cell nuclear antigen and P21. Furthermore, resveratrol was found to have a strong apoptosis-inducing effect, which was evidenced through the high percentage of annexin V positive cells and high protein expression of cleaved-caspase-7, cleaved-caspase-9 and cleaved-poly(ADP-ribose) polymerase in the resveratrol-treated cancer cells. In conclusion, these results demonstrated that resveratrol had greater growth inhibitory and cell cycle arrest effects on Caco-2 cells than HCT116 cells, through caspase-dependent and cyclin-CDK pathways.