βTrCP controls the lysosome-mediated degradation of CDK1, whose accumulation correlates with tumor malignancy

Autophagy-related myosins: Critical roles and potential therapeutic effects in malignancies

Myosins, a superfamily of actin-based molecular motor proteins, are important regulators of actin cytoskeleton structure and remodeling. They act as mechano-sensors of the tumor environment, controlling key cellular processes associated with tumorigenesis and mediating various cellular activities, including muscle contraction, cell migration, intracellular transport, membrane protrusion formation, cell adhesion, and cell signaling. In eukaryotic cells, autophagy plays a crucial role in maintaining cellular homeostasis by transporting cytoplasmic cargo to lysosomes for selective degradation. In tumors, recent research has explored the function of the role of myosin-influenced autophagy and tumor microenvironment-associated immune cells. Increasing evidence exists on how myosins and their mediated autophagy-related processes affect cancer development and progression. In this review, we discuss and dissect the functions played by different myosins at various stages of autophagy, and how myosins mediate autophagy involvement in the tumor process, based on the summaries of these findings, we provide new perspectives for possible therapeutic strategies.

The antitumor peptide M1-20 induced the degradation of CDK1 through CUL4-DDB1-DCAF1-involved ubiquitination

CDK1 is an oncogenic serine/threonine kinase known to play an important role in the regulation of the cell cycle. FOXM1, as one of the CDK1 substrates, requires binding of CDK1/CCNB1 complex for phosphorylation-dependent recruitment of p300/CBP coactivators to mediate transcriptional activity. Previous studies from our laboratory found that a novel peptide (M1-20) derived from the C-terminus of FOXM1 exhibited potent inhibitory effects for cancer cells. Based on these proofs and to explore the inhibitory mechanism of M1-20, we designed experiments and found that CDK1 served as an important target of M1-20. M1-20 enhanced the ubiquitination and degradation of CDK1 by CUL4-DDB1-DCAF1 complexes through the proteasome pathway. M1-20 could also affect the formation of CDK1/CCNB1 complexes. In addition, compared to RO3306, a CDK1 inhibitor, M1-20 exhibited excellent inhibitory effects in FVB/N MMTV-PyVT murine model of spontaneous breast cancer. These results suggested that M1-20 was a potential CDK1 inhibitor for the treatment of cancer.

Dysregulation of deubiquitination in breast cancer

Breast cancer (BC) is a highly frequent malignant tumor that poses a serious threat to women's health and has different molecular subtypes, histological subtypes, and biological features, which act by activating oncogenic factors and suppressing cancer inhibitors. The ubiquitin-proteasome system (UPS) is the main process contributing to protein degradation, and deubiquitinases (DUBs) are reverse enzymes that counteract this process. There is growing evidence that dysregulation of DUBs is involved in the occurrence of BC. Herein, we review recent research findings in BC-associated DUBs, describe their nature, classification, and functions, and discuss the potential mechanisms of DUB-related dysregulation in BC. Furthermore, we present the successful treatment of malignant cancer with DUB inhibitors, as well as analyzing the status of targeting aberrant DUBs in BC.

Molecules inducing specific cyclin-dependent kinase degradation and their possible use in cancer therapy

Cyclin-dependent kinases (CDKs) play an important role in the regulation of cell proliferation, and many CDK inhibitors were developed. However, pan-CDK inhibitors failed to be approved due to intolerant toxicity or low efficacy and the use of selective CDK4/6 inhibitors is limited by resistance. Protein degraders have the potential to increase selectivity, efficacy and overcome resistance, which provides a novel strategy for regulating CDKs. In this review, we summarized the function of CDKs in regulating the cell cycle and transcription, and introduced the representative CDK inhibitors. Then we made a detailed introduction about four types of CDKs degraders, including their action mechanisms, research status and application prospects, which could help the development of novel CDKs degraders.

Targeting CDK1 in cancer: mechanisms and implications

Cyclin dependent kinases (CDKs) are serine/threonine kinases that are proposed as promising candidate targets for cancer treatment. These proteins complexed with cyclins play a critical role in cell cycle progression. Most CDKs demonstrate substantially higher expression in cancer tissues compared with normal tissues and, according to the TCGA database, correlate with survival rate in multiple cancer types. Deregulation of CDK1 has been shown to be closely associated with tumorigenesis. CDK1 activation plays a critical role in a wide range of cancer types; and CDK1 phosphorylation of its many substrates greatly influences their function in tumorigenesis. Enrichment of CDK1 interacting proteins with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted to demonstrate that the associated proteins participate in multiple oncogenic pathways. This abundance of evidence clearly supports CDK1 as a promising target for cancer therapy. A number of small molecules targeting CDK1 or multiple CDKs have been developed and evaluated in preclinical studies. Notably, some of these small molecules have also been subjected to human clinical trials. This review evaluates the mechanisms and implications of targeting CDK1 in tumorigenesis and cancer therapy.

An autonomous mathematical model for the mammalian cell cycle

A mathematical model for the mammalian cell cycle is developed as a system of 13 coupled nonlinear ordinary differential equations. The variables and interactions included in the model are based on detailed consideration of available experimental data. A novel feature of the model is inclusion of cycle tasks such as origin licensing and initiation, nuclear envelope breakdown and kinetochore attachment, and their interactions with controllers (molecular complexes involved in cycle control). Other key features are that the model is autonomous, except for a dependence on external growth factors; the variables are continuous in time, without instantaneous resets at phase boundaries; mechanisms to prevent rereplication are included; and cycle progression is independent of cell size. Eight variables represent cell cycle controllers: the Cyclin D1-Cdk4/6 complex, APC^Cdh1, SCF^βTrCP, Cdc25A, MPF, NuMA, the securin-separase complex, and separase. Five variables represent task completion, with four for the status of origins and one for kinetochore attachment. The model predicts distinct behaviors corresponding to the main phases of the cell cycle, showing that the principal features of the mammalian cell cycle, including restriction point behavior, can be accounted for in a quantitative mechanistic way based on known interactions among cycle controllers and their coupling to tasks. The model is robust to parameter changes, in that cycling is maintained over at least a five-fold range of each parameter when varied individually. The model is suitable for exploring how extracellular factors affect cell cycle progression, including responses to metabolic conditions and to anti-cancer therapies.

USP14 regulates cell cycle progression through deubiquitinating CDK1 in breast cancer

Abnormal proliferation and cell cycle perturbation are the main hallmarks of breast cancer. Cyclin-dependent kinase 1 (CDK1) is one of the key kinases for cell transition from the G2 phase to M phase during the cell cycle progression. However, little is known about the degradation mechanisms of CDK1. USP14 (ubiquitin-specific processing protease 14) is an important proteasome-associated deubiquitinase that is critical for proteome homeostasis and plays a crucial role in the initiation and development of cancer. In this study, we find that USP14 shows high expression in breast cancer cells and results in the abnormal proliferation of cancer cells. Furthermore, we examine cell cycle distribution by flow cytometry and find that inhibition of USP14 causes cell cycle arrest in G2/M phase. As CDK1 is the key kinase in G2/M phase, we detect the interaction between USP14 and CDK1 and the effect of USP14 on the deubiquitination of CDK1. The results reveal that USP14 interacts with CDK1 and stabilizes CDK1 by deubiquitinating K48-linked ubiquitination. In conclusion, our findings reveal an indispensable role of USP14 in regulating cell cycle progression by stabilizing CDK1 in breast cancer, suggesting that USP14 may be used as a potential therapeutic target in breast cancer therapy.

Inhibition of the CDK2 and Cyclin A complex leads to autophagic degradation of CDK2 in cancer cells

Cyclin-dependent kinase 2 (CDK2) complex is significantly over-activated in many cancers. While it makes CDK2 an attractive target for cancer therapy, most inhibitors against CDK2 are ATP competitors that are either nonspecific or highly toxic, and typically fail clinical trials. One alternative approach is to develop non-ATP competitive inhibitors; they disrupt interactions between CDK2 and either its partners or substrates, resulting in specific inhibition of CDK2 activities. In this report, we identify two potential druggable pockets located in the protein-protein interaction interface (PPI) between CDK2 and Cyclin A. To target the potential druggable pockets, we perform a LIVS in silico screening of a library containing 1925 FDA approved drugs. Using this approach, homoharringtonine (HHT) shows high affinity to the PPI and strongly disrupts the interaction between CDK2 and cyclins. Further, we demonstrate that HHT induces autophagic degradation of the CDK2 protein via tripartite motif 21 (Trim21) in cancer cells, which is confirmed in a leukemia mouse model and in human primary leukemia cells. These results thus identify an autophagic degradation mechanism of CDK2 protein and provide a potential avenue towards treating CDK2-dependent cancers.

CDK2 can drive the proliferation of cancer cells. Here, the authors screened for a non-ATP competitive inhibitor of the CDK2/cylinA complex and find that Homoharringtonine can disrupt the complex and promote the degradation of CDK2.

The Intricate Interplay between Cell Cycle Regulators and Autophagy in Cancer

Simple Summary

Autophagy is an intracellular catabolic program regulated by multiple external and internal cues. A large amount of evidence unraveled that cell-cycle regulators are crucial in its control. This review highlights the interplay between cell-cycle regulators, including cyclin-dependent kinase inhibitors, cyclin-dependent kinases, and E2F factors, in the control of autophagy all along the cell cycle. Beyond the intimate link between cell cycle and autophagy, this review opens therapeutic perspectives in modulating together these two aspects to block cancer progression.

Abstract

In the past decade, cell cycle regulators have extended their canonical role in cell cycle progression to the regulation of various cellular processes, including cellular metabolism. The regulation of metabolism is intimately connected with the function of autophagy, a catabolic process that promotes the efficient recycling of endogenous components from both extrinsic stress, e.g., nutrient deprivation, and intrinsic sub-lethal damage. Mediating cellular homeostasis and cytoprotection, autophagy is found to be dysregulated in numerous pathophysiological contexts, such as cancer. As an adaptative advantage, the upregulation of autophagy allows tumor cells to integrate stress signals, escaping multiple cell death mechanisms. Nevertheless, the precise role of autophagy during tumor development and progression remains highly context-dependent. Recently, multiple articles has suggested the importance of various cell cycle regulators in the modulation of autophagic processes. Here, we review the current clues indicating that cell-cycle regulators, including cyclin-dependent kinase inhibitors (CKIs), cyclin-dependent kinases (CDKs), and E2F transcription factors, are intrinsically linked to the regulation of autophagy. As an increasing number of studies highlight the importance of autophagy in cancer progression, we finally evoke new perspectives in therapeutic avenues that may include both cell cycle inhibitors and autophagy modulators to synergize antitumor efficacy.

Synthesis, Antiproliferative Activity, Apoptotic Profiling, and In‐silico ADME of New Thienylbenzamidine Derivatives

Twelve new thienylbenzamidines and their analogues 4 a–i, 7, and 12 a, b were synthesized and their anti‐proliferative activity was evaluated against 60 cancer cell lines. The tested compounds showed potent anticancer activity against most cancer cell lines with median growth inhibition (GI50)<2 μM. Leukemia and renal cancer cell lines were the most responsive. Compound 12 a was the most active exhibiting GI50, total growth inhibition (TGI), and median lethal concentration (LC50) at 1.65, 3.71, and 9.3 μM, respectively. The benzamidine derivatives exerted their anti‐proliferative activity without causing any toxicity in normal human lung fibroblast (WI‐38) cells. The selectivity index (SI) ranged from 5.6 to 59.0 fold. Compound 4 h was the most selective compound (SI=59), and it was the least cytotoxic to WI‐38 cells. The cationic compounds 4 c, 4 h, 4 i, 7, and 12 b with high SI were selected for further mechanistic studies. Compounds 4 c, 4 h, and 4 i exerted their antiproliferative activity by inducing the cell cycle arrest (elevated p53 and downregulated cyclin‐dependent kinase 1 (cdk1)) and inducing apoptosis (elevated caspase 3). Compounds 7 and 12 b exerted their activity by inhibiting the growth and proliferation of cancer cells through inhibiting both topoisomerase II (topoII) and thioredoxin reductase1 (txnrd1). Finally, in silico predictions of the physicochemical, pharmacokinetic and drug‐likeness profiles of these new derivatives proved the oral availability and the inability to cross the blood‐brain barrier.

Synthesis of new thienylpicolinamidine derivatives and possible mechanisms of antiproliferative activity

Three thienylpicolinamidine derivatives 4a-c were prepared from their corresponding picolinonitriles 3a-c on treatment with lithium trimethylsilylamide, LiN(TMS)2, followed by a de-protection step using ethanol/HCl (gas). DFT calculations were used to optimize the geometric structure of the newly synthesized picolinamidines. The comparison of DFT calculated spectral data with the experimental data (1H-NMR and 13C-NMR) showed a good agreement. The in vitro antiproliferative activity of the cationic compounds 4a-c was determined against 60 cancer cell lines representing nine types of cancer. The tested picolinamidines were highly active with compounds 4a and 4b eliciting mainly cytotoxic activity with GI values ranging from -7.17 to -86.03. Leukemia (SR and K-562), colon (SW-620 and HT29), and non-small cell lung cancer (NCI-H460) cell lines were the most responsive to the investigated picolinamidines. In particular, 4-methoxyphenyl derivative 4a showed a profound growth deterring power with GI50 of 0.34 μM against SR, 0.43 μM against SW-620, and 0.52 μM against NCI-H460. The three tested picolinamidines elicited potent GI50 values against all tested cell lines at low micromolar to sub-micromolar level. The new picolinamidines were selective and did not affect normal human fibroblasts. The selectivity index ranged from 13-21 μM. The novel picolinamidines downregulated the expression of key genes in the cell cycle, cdk1 and topoII, but did not affect p53 or txnrd1. Compounds 4b and 4c caused a significant reduction in the concentrations of TopoII and MAPK proteins but were devoid of any effect on the activity of caspase 3. Taken together, these promising anticancer candidates are effective at very low concentrations and safe to normal cells, and most probably work through arresting the cell cycle, and therefore, they deserve further investigations.

Proteomic Analysis of Protein Ubiquitination Events in Human Primary and Metastatic Colon Adenocarcinoma Tissues

Protein ubiquitination is essential for multiple physiological processes through regulating the stability or function of target proteins and has been found to play critical roles in human cancers. However, the protein ubiquitination profile of human metastatic colon adenocarcinoma tissue has not been elucidated yet. In this study, a proprietary ubiquitin branch (K-ε-GG) antibody-based label-free quantitative proteomics and bioinformatics were performed to identify the global protein ubiquitination profile between human primary (Colon) and metastatic colon adenocarcinoma (Meta) tissues. A total of 375 ubiquitination sites from 341 proteins were identified as differentially modificated (| Fold change| > 1.5, p < 0.05) in Meta group compared with the Colon group. Among them, 132 ubiquitination sites from 127 proteins were upregulated and 243 ubiquitination sites from 214 proteins were downregulated in Meta group. Fifteen ubiquitination motifs were found. Furthermore, GO and KEGG pathway analysis indicated that proteins with altered ubiquitination in Meta group were enriched in pathways highly related to cancer metastasis, such as RNA transport and cell cycle. We speculate that the altered ubiquitination of CDK1 may be a pro-metastatic factor in colon adenocarcinoma. This study provides novel scientific evidences to elucidate the biological functions of protein ubiquitination in human colon adenocarcinoma and insights into its potential mechanisms of colon cancer metastasis, which would be helpful to discover novel biomarkers and therapeutic targets for effective treatment of colon cancer.

Secreted breast tumor interstitial fluid microRNAs and their target genes are associated with triple-negative breast cancer, tumor grade, and immune infiltration

Background

Studies on tumor-secreted microRNAs point to a functional role of these in cellular communication and reprogramming of the tumor microenvironment. Uptake of tumor-secreted microRNAs by neighboring cells may result in the silencing of mRNA targets and, in turn, modulation of the transcriptome. Studying miRNAs externalized from tumors could improve cancer patient diagnosis and disease monitoring and help to pinpoint which miRNA-gene interactions are central for tumor properties such as invasiveness and metastasis.

Methods

Using a bioinformatics approach, we analyzed the profiles of secreted tumor and normal interstitial fluid (IF) microRNAs, from women with breast cancer (BC). We carried out differential abundance analysis (DAA), to obtain miRNAs, which were enriched or depleted in IFs, from patients with different clinical traits. Subsequently, miRNA family enrichment analysis was performed to assess whether any families were over-represented in the specific sets. We identified dysregulated genes in tumor tissues from the same cohort of patients and constructed weighted gene co-expression networks, to extract sets of co-expressed genes and co-abundant miRNAs. Lastly, we integrated miRNAs and mRNAs to obtain interaction networks and supported our findings using prediction tools and cancer gene databases.

Results

Network analysis showed co-expressed genes and miRNA regulators, associated with tumor lymphocyte infiltration. All of the genes were involved in immune system processes, and many had previously been associated with cancer immunity. A subset of these, BTLA, CXCL13, IL7R, LAMP3, and LTB, was linked to the presence of tertiary lymphoid structures and high endothelial venules within tumors. Co-abundant tumor interstitial fluid miRNAs within this network, including miR-146a and miR-494, were annotated as negative regulators of immune-stimulatory responses. One co-expression network encompassed differences between BC subtypes. Genes differentially co-expressed between luminal B and triple-negative breast cancer (TNBC) were connected with sphingolipid metabolism and predicted to be co-regulated by miR-23a. Co-expressed genes and TIF miRNAs associated with tumor grade were BTRC, CHST1, miR-10a/b, miR-107, miR-301a, and miR-454.

Conclusion

Integration of IF miRNAs and mRNAs unveiled networks associated with patient clinicopathological traits, and underlined molecular mechanisms, specific to BC sub-groups. Our results highlight the benefits of an integrative approach to biomarker discovery, placing secreted miRNAs within a biological context.

Synthesis of new oxadiazol-phthalazinone derivatives with anti-proliferative activity; molecular docking, pro-apoptotic, and enzyme inhibition profile

Background and aim: The current study reports the synthesis and biological evaluation of two novel series of 4-(5-mercapto-1,3,4-oxadiazol-2-yl)phthalazin-1(2H)-one derivatives. Methods: The synthetic reactions were carried out under both conventional and ultrasonic irradiation conditions. The anti-proliferative activity of the newly synthesized compounds against two human epithelial cell lines; liver (HepG2) and breast (MCF-7) in addition to normal fibroblasts (WI-38) was investigated. In addition to molecular docking studies, the possible mechanism(s) of action were also explored. Results: In general, an improvement in synthetic rates and yields was observed when reactions were carried out under sonication compared with classical conditions. The structures of the products were established based on analytical and spectral data. Derivatives 2e and 7d, in addition to compound 1, had significant and selective anti-proliferative activity against liver and breast cancer cell lines without harming normal fibroblasts. These derivatives arrested the cell cycle progression and/or induced apoptosis. This has been manifested by the elevation in the expression of p53 and caspase 3, down-regulation of cdk1, and a reduction in the concentrations of MAPK and Topo II at submicromolar concentrations. The latter results confirmed the molecular docking study. Conclusions: Compound 1 had the best profile on the gene and protein levels (arresting cell cycle and inducing apoptosis). The ability of compounds 1 and 2e to inhibit both MAPK and Topo II nominates these derivatives as potential candidates for further anticancer and antitumor studies.

Design, molecular modeling and anticancer evaluation of thieno[2,3-d]pyrimidine derivatives as inhibitors of topoisomerase II

Synthesis of 4-(3,5-dimethyl-1H-pyrazol-1-yl)-5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidine 1 and its functionalized reactions as nucleophile with various electrophilic reagents were performed through facile methods to yield different cyclic and acyclic derivatives (2-17). The structures of the newly synthesized compounds were established by their elemental analysis and spectral data. Derivatives 4, 14, 16, and 17 in addition to the parent compound 1 had IC50 at ~4-10 µM against HepG2 and MCF7 and were selected for further investigations. All derivatives had high IC50 values (>60 µM) against normal fibroblasts WI38 indicating selectivity against cancer cell lines. Derivatives 4, 14, and 17 up-regulated the expression of p53 by ~3-4 folds. All derivatives caused a significant ~3-fold increase in the expression of executive caspase 3 and significant elevation in cleaved caspase 3 activity. The elevation in the expression of caspase 3 by compound 1 and derivative 16 was not accompanied by an increase in p53 expression or cleaved caspase 3 activity. These two thienopyrimidines may act directly on caspase 3. Derivative 17 was unique in reducing the expression of Topo II by ~60%. The molecular docking showed that derivatives 4 and 17 with high binding energies could bind and inhibit Topoisomerase II (Topo II). In accordance with the docking modelling, derivatives 4 and 17 reduced the Topo II concentration by 82 and 90%, respectively, compared to the untreated cells. However, the parent compound 1 also caused a significant 34% reduction in the enzyme concentration although it was not predicted as a ligand for the enzyme in the docking study. Taken together, derivatives 4, 14 and 17 showed selective cytotoxicity, could arrest cell cycle, and induce apoptosis. Furthermore, they could serve as cytostatic agents by inhibiting/reducing Topo II.

Cyclin F-dependent degradation of E2F7 is critical for DNA repair and G2-phase progression

E2F7 and E2F8 act as tumor suppressors via transcriptional repression of genes involved in S-phase entry and progression. Previously, we demonstrated that these atypical E2Fs are degraded by APC/CCdh1 during G1 phase of the cell cycle. However, the mechanism driving the downregulation of atypical E2Fs during G2 phase is unknown. Here, we show that E2F7 is targeted for degradation by the E3 ubiquitin ligase SCFcyclin F during G2. Cyclin F binds via its cyclin domain to a conserved C-terminal CY motif on E2F7. An E2F7 mutant unable to interact with SCFcyclin F remains stable during G2. Furthermore, SCFcyclin F can also interact and induce degradation of E2F8. However, this does not require the cyclin domain of SCFcyclin F nor the CY motifs in the C-terminus of E2F8, implying a different regulatory mechanism than for E2F7. Importantly, depletion of cyclin F causes an atypical-E2F-dependent delay of the G2/M transition, accompanied by reduced expression of E2F target genes involved in DNA repair. Live cell imaging of DNA damage revealed that cyclin F-dependent regulation of atypical E2Fs is critical for efficient DNA repair and cell cycle progression.

Identification of key modules and prognostic markers in adrenocortical carcinoma by weighted gene co-expression network analysis

Adrenocortical carcinoma (ACC) is a rare and aggressive cancer with a high relapse rate and limited treatment options. Therefore, the identification of potential prognostic markers in patients with ACC may improve early detection, survival rates and may additionally provide novel insights into the early detection of recurrence. In the present study, clinical traits and RNA-seq data of 79 patients with ACC were obtained from The Cancer Genome Atlas (TCGA). Weighted gene co-expression network analysis was carried out and 17 distinct co-expression modules were built to examine the association between the modules and the clinical traits. Of the 17 modules, two co-expression modules, which contained 214 and 168 genes, were significantly correlated with two clinical traits, tumor stage and vital status. Functional enrichment analysis was performed on the selected modules. The results showed that one of the modules was primarily enriched in cell division and the other module was enriched in metabolic pathways, suggesting their involvement in tumor progression. Furthermore, cyclin dependent kinase 1 (CDK1) and ubiquitin C (UBC) were identified as hub genes in both modules. Survival analysis revealed that the high expression of the hub genes significantly correlated with the poor survival rate of patients, suggesting that CDK1 and UBC have vital roles in the progression of ACC. In the present study, a co-expression gene module of ACC was provided and the prognostic genes that may serve as new diagnostic markers in the future were defined.

Selective Autophagy Regulates Cell Cycle in Cancer Therapy

Aberrant function of cell cycle regulators results in uncontrolled cell proliferation, making them attractive therapeutic targets in cancer treatment. Indeed, survival of many cancers exclusively relies on these proteins, and several specific inhibitors are in clinical use. Although the ubiquitin-proteasome system is responsible for the periodic quality control of cell cycle proteins during cell cycle progression, increasing evidence clearly demonstrates the intimate interaction between cell cycle regulation and selective autophagy, important homeostasis maintenance machinery. However, these studies have often led to divergent rather than unifying explanations due to complexity of the autophagy signaling network, the inconsistent functions between general autophagy and selective autophagy, and the different characteristics of autophagic substrates. In this review, we highlight current data illustrating the contradictory and important role of cell cycle proteins in regulating autophagy. We also focus on how selective autophagy acts as a central mechanism to maintain orderly DNA repair and genome integrity by degrading specific cell cycle proteins, regulating cell division, and promoting DNA damage repair. We further discuss the ways in which selective autophagy may impact the cell cycle regulators, since failure to appropriately remove these can interfere with cell death-related processes, including senescence and autophagy-related cell death. Imbalanced cell proliferation is typically utilized by cancer cells to acquire resistance. Finally, we discuss the possibility of a potent anticancer therapeutic strategy that targets selective autophagy or autophagy and cell cycle together.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

Both p62/SQSTM1-HDAC6-dependent autophagy and the aggresome pathway mediate CDK1 degradation in human breast cancer

Cyclin-dependent kinase 1 (CDK1) is the central mammalian regulator of cell proliferation and a promising therapeutic target for breast cancer. In fact, CDK1 inhibition downregulates survival and induces apoptosis. Due to its essential role, CDK1 expression and activity are strictly controlled at various levels. We previously described that CDK1 stability is also regulated and that SCF(βTrCP) ubiquitinates CDK1, which is degraded via the lysosomal pathway. In addition, in breast tumors from patients, we found a negative correlation between CDK1 accumulation and βTrCP levels, and a positive correlation with the degree of tumor malignancy. This prompted us to study the molecular mechanism involved in CDK1 clearance. In this report, we determine that both chemotherapeutic agents and proteolytic stress induce CDK1 degradation in human breast cancer MCF7 cells through p62/HDAC6-mediated selective autophagy. On the one hand, CDK1 binds to p62/SQSTM1-LC3 and, on the other hand, it interacts with HDAC6. Both complexes are dependent on the presence of an intact βTrCP-binding motif on CDK1. Furthermore, we also show that CDK1 is recruited to aggresomes in response to proteasome inhibition for an extended period. We propose CDK1 clearance as a potential predictive biomarker of antitumor treatment efficacy.

Histone deacetylase inhibitors vorinostat and panobinostat induce G1 cell cycle arrest and apoptosis in multidrug resistant sarcoma cell lines

Synovial sarcoma and high grade chondrosarcoma are characterized by their lack of response to conventional cytotoxic chemotherapy, the tendency to develop lung metastases, and low survival rates.

Research within the field prioritizes the development and expansion of new treatment options for dealing with unresectable or metastatic diseases. Numerous clinical trials using histone deacetylases inhibitors (HDACi) have shown specific efficacy as an active antitumor agent for treating a variety of solid tumors. However, as of yet the effect of different HDACi on synovial- and chondrosarcoma cells has not been investigated. In this study, vorinostat (SAHA), panobinostat (LBH-589), and belinostat (PXD101) decreased cell viability of synovial sarcoma (SW-982) and chondrosarcoma (SW-1353) cells in a time- and dose dependent manner and arrested SW-982 cells in the G1/S phase. Western blot analysis determined the responsible cell cycle regulator proteins. In addition, we found apoptotic induction by caspase 3/7 activity, caspase 3 cleavage, and PARP cleavage. In SW-1353 cells only SAHA showed comparable effects. Noteworthy, all HDACi tested had synergistic effects with the topoisomerase II inhibitor doxorubicin in SW-1353 chondrosarcoma cells making the cells more sensitive to the chemotherapeutic drug.

Our results show for the first time that SAHA and LBH-589 reduced viability of sarcoma cells and arrested them at the G1/S checkpoint, while also inducing apoptosis and enhancing chemotherapeutic sensitivity, especially in chondrosarcoma cells. These data demonstrate the exciting potential of HDACi for use in sarcoma treatment.

The role of aberrant proteolysis in lymphomagenesis

PURPOSE OF REVIEW

Deregulated proteolysis is increasingly being implicated in pathogenesis of lymphoma. In this review, we highlight the major cellular processes that are affected by deregulated proteolysis of critical substrates that promote lymphoproliferative disorders.

RECENT FINDINGS

Emerging evidence supports the role of aberrant proteolysis by the ubiquitin proteasome system (UPS) in lymphoproliferative disorders. Several UPS mediators are identified to be altered in lymphomagenesis. However, the precise role of their alteration and comprehensive knowledge of their target substrate critical for lymphomagenesis is far from complete.

SUMMARY

Many E3 ligase and deubiquitinases that contribute to regulated proteolysis of substrates critical for major cellular processes are altered in various lineages of lymphoma. Understanding of the proteolytic regulatory mechanisms of these major cellular pathways may offer novel biomarkers and targets for lymphoma therapy.