Genome-wide survey of protein kinases required for cell cycle progression

Cyclin-dependent protein kinases and cell cycle regulation in biology and disease

Cyclin Dependent Kinases (CDKs) are closely connected to the regulation of cell cycle progression, having been first identified as the kinases able to drive cell division. In reality, the human genome contains 20 different CDKs, which can be divided in at least three different sub-family with different functions, mechanisms of regulation, expression patterns and subcellular localization. Most of these kinases play fundamental roles the normal physiology of eucaryotic cells; therefore, their deregulation is associated with the onset and/or progression of multiple human disease including but not limited to neoplastic and neurodegenerative conditions. Here, we describe the functions of CDKs, categorized into the three main functional groups in which they are classified, highlighting the most relevant pathways that drive their expression and functions. We then discuss the potential roles and deregulation of CDKs in human pathologies, with a particular focus on cancer, the human disease in which CDKs have been most extensively studied and explored as therapeutic targets. Finally, we discuss how CDKs inhibitors have become standard therapies in selected human cancers and propose novel ways of investigation to export their targeting from cancer to other relevant chronic diseases. We hope that the effort we made in collecting all available information on both the prominent and lesser-known CDK family members will help in identify and develop novel areas of research to improve the lives of patients affected by debilitating chronic diseases.

Sugar signals pedal the cell cycle!

Cell cycle involves the sequential and reiterative progression of important events leading to cell division. Progression through a specific phase of the cell cycle is under the control of various factors. Since the cell cycle in multicellular eukaryotes responds to multiple extracellular mitogenic cues, its study in higher forms of life becomes all the more important. One such factor regulating cell cycle progression in plants is sugar signalling. Because the growth of organs depends on both cell growth and proliferation, sugars sensing and signalling are key control points linking sugar perception to regulation of downstream factors which facilitate these key developmental transitions. However, the basis of cell cycle control via sugars is intricate and demands exploration. This review deals with the information on sugar and TOR-SnRK1 signalling and how they manoeuvre various events of the cell cycle to ensure proper growth and development.

Deficiency of mastl, a mitotic regulator, results in cell detachment from developing tissues of zebrafish embryos

To form tissues with unique functions and structures, it is important that the cells that comprise them maintain physical contact. On the other hand, with each mitosis, drastic changes in cell shapes, cell adhesion, and cytoskeletal architecture may cause such contacts to be temporarily weakened, risking improper development and maintenance of tissues. Despite such risks, tissues form properly during normal development. However, it is not well understood whether mitotic abnormalities affect tissue formation. Here, analysis of zebrafish embryos with aberrant mitosis shows that proper progression of mitosis is important to maintain cell contact in developing tissues. By screening mutants with abnormal trunk and tail development, we obtained a mutant with perturbed expression of some tissue-specific genes in embryonic caudal regions. The responsible gene is mastl/gwl, which is involved in progression of mitosis. Analysis focusing on the chordo-neural hinge (CNH), the primordium of axial tissues, shows that cell detachment from the CNH is increased in mastl mutant embryos. Time-lapse imaging reveals that this cell detachment occurs during mitosis. These results suggest that cells are unable to maintain contact due to abnormalities in progression of mitosis in mastl mutants.

Ana1/CEP295 is an essential player in the centrosome maintenance program regulated by Polo kinase and the PCM

Centrioles are part of centrosomes and cilia, which are microtubule organising centres (MTOC) with diverse functions. Despite their stability, centrioles can disappear during differentiation, such as in oocytes, but little is known about the regulation of their structural integrity. Our previous research revealed that the pericentriolar material (PCM) that surrounds centrioles and its recruiter, Polo kinase, are downregulated in oogenesis and sufficient for maintaining both centrosome structural integrity and MTOC activity. We now show that the expression of specific components of the centriole cartwheel and wall, including ANA1/CEP295, is essential for maintaining centrosome integrity. We find that Polo kinase requires ANA1 to promote centriole stability in cultured cells and eggs. In addition, ANA1 expression prevents the loss of centrioles observed upon PCM-downregulation. However, the centrioles maintained by overexpressing and tethering ANA1 are inactive, unlike the MTOCs observed upon tethering Polo kinase. These findings demonstrate that several centriole components are needed to maintain centrosome structure. Our study also highlights that centrioles are more dynamic than previously believed, with their structural stability relying on the continuous expression of multiple components.

PFTK1 kinase regulates axogenesis during development via RhoA activation

BACKGROUND

PFTK1/Eip63E is a member of the cyclin-dependent kinases (CDKs) family and plays an important role in normal cell cycle progression. Eip63E expresses primarily in postnatal and adult nervous system in Drosophila melanogaster but its role in CNS development remains unknown. We sought to understand the function of Eip63E in the CNS by studying the fly ventral nerve cord during development.

RESULTS

Our results demonstrate that Eip63E regulates axogenesis in neurons and its deficiency leads to neuronal defects. Functional interaction studies performed using the same system identify an interaction between Eip63E and the small GTPase Rho1. Furthermore, deficiency of Eip63E homolog in mice, PFTK1, in a newly generated PFTK1 knockout mice results in increased axonal outgrowth confirming that the developmental defects observed in the fly model are due to defects in axogenesis. Importantly, RhoA phosphorylation and activity are affected by PFTK1 in primary neuronal cultures. We report that GDP-bound inactive RhoA is a substrate of PFTK1 and PFTK1 phosphorylation is required for RhoA activity.

CONCLUSIONS

In conclusion, our work establishes an unreported neuronal role of PFTK1 in axon development mediated by phosphorylation and activation of GDP-bound RhoA. The results presented add to our understanding of the role of Cdks in the maintenance of RhoA-mediated axon growth and its impact on CNS development and axonal regeneration.

Computational analysis of regulatory regions in human protein kinases

Eukaryotic proteins often feature modular domain structures comprising globular domains that are connected by linker regions and intrinsically disordered regions that may contain important functional motifs. The intramolecular interactions of globular domains and nonglobular regions can play critical roles in different aspects of protein function. However, studying these interactions and their regulatory roles can be challenging due to the flexibility of nonglobular regions, the long insertions separating interacting modules, and the transient nature of some interactions. Obtaining the experimental structures of multiple domains and functional regions is more difficult than determining the structures of individual globular domains. High-quality structural models generated by AlphaFold offer a unique opportunity to study intramolecular interactions in eukaryotic proteins. In this study, we systematically explored intramolecular interactions between human protein kinase domains (KDs) and potential regulatory regions, including globular domains, N- and C-terminal tails, long insertions, and distal nonglobular regions. Our analysis identified intramolecular interactions between human KDs and 35 different types of globular domains, exhibiting a variety of interaction modes that could contribute to orthosteric or allosteric regulation of kinase activity. We also identified prevalent interactions between human KDs and their flanking regions (N- and C-terminal tails). These interactions exhibit group-specific characteristics and can vary within each specific kinase group. Although long-range interactions between KDs and nonglobular regions are relatively rare, structural details of these interactions offer new insights into the regulation mechanisms of several kinases, such as HASPIN, MAPK7, MAPK15, and SIK1B.

Regulation of intestinal stem cell activity by a mitotic cell cycle regulator Polo in Drosophila

Maintaining a definite and stable pool of dividing stem cells plays an important role in organ development. This process requires an appropriate progression of mitosis for proper spindle orientation and polarity to ensure the ability of stem cells to proliferate and differentiate correctly. Polo-like kinases (Plks)/Polo are the highly conserved serine/threonine kinases involved in the initiation of mitosis as well as in the progression of the cell cycle. Although numerous studies have investigated the mitotic defects upon loss of Plks/Polo in cells, little is known about the in vivo consequences of stem cells with abnormal Polo activity in the context of tissue and organism development. The current study aimed to investigate this question using the Drosophila intestine, an organ dynamically maintained by the intestinal stem cells (ISCs). The results indicated that the polo depletion caused a reduction in the gut size due to a gradual decrease in the number of functional ISCs. Interestingly, the polo-deficient ISCs showed an extended G2/M phase and aneuploidy and were subsequently eliminated by premature differentiation into enterocytes (ECs). In contrast, the constitutively active Polo (poloT182D) suppressed ISC proliferation, induced abnormal accumulation of β-tubulin in cells, and drove ISC loss via apoptosis. Therefore, Polo activity should be properly maintained for optimal stem cell function. Further analysis suggested that polo was a direct target gene of Sox21a, a Sox transcription factor that critically regulates stem cell activity. Together, this study provided a novel perspective on the correlation between the progression of mitosis and the ISC function in Drosophila.

m6 A promotes planarian regeneration

Regeneration is the regrowth of damaged tissues or organs, a vital process in response to damages from primitive organisms to higher mammals. Planarian possesses active whole-body regenerative capability owing to its vast reservoir of adult stem cells, neoblasts, providing an ideal model to delineate the underlying mechanisms for regeneration. RNA N⁶ -methyladenosine (m⁶ A) modification participates in many biological processes, including stem cell self-renewal and differentiation, in particular the regeneration of haematopoietic stem cells and axons. However, how m⁶ A controls regeneration at the whole-organism level remains largely unknown. Here, we demonstrate that the depletion of m⁶ A methyltransferase regulatory subunit wtap abolishes planarian regeneration, potentially through regulating genes related to cell-cell communication and cell cycle. Single-cell RNA-seq (scRNA-seq) analysis unveils that the wtap knockdown induces a unique type of neural progenitor-like cells (NP-like cells), characterized by specific expression of the cell-cell communication ligand grn. Intriguingly, the depletion of m⁶ A-modified transcripts grn, cdk9 or cdk7 partially rescues the defective regeneration of planarian caused by wtap knockdown. Overall, our study reveals an indispensable role of m⁶ A modification in regulating whole-organism regeneration.

Mapping the Protein Kinome: Current Strategy and Future Direction

The kinome includes over 500 different protein kinases, which form an integrated kinase network that regulates cellular phosphorylation signals. The kinome plays a central role in almost every cellular process and has strong linkages with many diseases. Thus, the evaluation of the cellular kinome in the physiological environment is essential to understand biological processes, disease development, and to target therapy. Currently, a number of strategies for kinome analysis have been developed, which are based on monitoring the phosphorylation of kinases or substrates. They have enabled researchers to tackle increasingly complex biological problems and pathological processes, and have promoted the development of kinase inhibitors. Additionally, with the increasing interest in how kinases participate in biological processes at spatial scales, it has become urgent to develop tools to estimate spatial kinome activity. With multidisciplinary efforts, a growing number of novel approaches have the potential to be applied to spatial kinome analysis. In this paper, we review the widely used methods used for kinome analysis and the challenges encountered in their applications. Meanwhile, potential approaches that may be of benefit to spatial kinome study are explored.

Nuak kinase signaling in development and disease of the central nervous system

Protein kinases represent important signaling hubs for a variety of biological functions. Many kinases are traditionally studied for their roles in cancer cell biology, but recent advances in neuroscience research show repurposed kinase function to be important for nervous system development and function. Two members of the AMP-activated protein kinase (AMPK) related family, NUAK1 and NUAK2, have drawn attention in neuroscience due to their mutations in autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), schizophrenia, and intellectual disability (ID). Furthermore, Nuak kinases have also been implicated in tauopathy and other disorders of aging. This review highlights what is known about the Nuak kinases in nervous system development and disease and explores the possibility of Nuak kinases as targets for therapeutic innovation.

The Green Valley of Drosophila melanogaster Constitutive Heterochromatin: Protein-Coding Genes Involved in Cell Division Control

Constitutive heterochromatin represents a significant fraction of eukaryotic genomes (10% in Arabidopsis, 20% in humans, 30% in D. melanogaster, and up to 85% in certain nematodes) and shares similar genetic and molecular properties in animal and plant species. Studies conducted over the last few years on D. melanogaster and other organisms led to the discovery of several functions associated with constitutive heterochromatin. This made it possible to revise the concept that this ubiquitous genomic territory is incompatible with gene expression. The aim of this review is to focus the attention on a group of protein-coding genes resident in D. melanogaster constitutive of heterochromatin, which are implicated in different steps of cell division.

Localized efficacy of environmental RNAi in Tetranychus urticae

Environmental RNAi has been developed as a tool for reverse genetics studies and is an emerging pest control strategy. The ability of environmental RNAi to efficiently down-regulate the expression of endogenous gene targets assumes efficient uptake of dsRNA and its processing. In addition, its efficiency can be augmented by the systemic spread of RNAi signals. Environmental RNAi is now a well-established tool for the manipulation of gene expression in the chelicerate acari, including the two-spotted spider mite, Tetranychus urticae. Here, we focused on eight single and ubiquitously-expressed genes encoding proteins with essential cellular functions. Application of dsRNAs that specifically target these genes led to whole mite body phenotypes—dark or spotless. These phenotypes were associated with a significant reduction of target gene expression, ranging from 20 to 50%, when assessed at the whole mite level. Histological analysis of mites treated with orally-delivered dsRNAs was used to investigate the spatial range of the effectiveness of environmental RNAi. Although macroscopic changes led to two groups of body phenotypes, silencing of target genes was associated with the distinct cellular phenotypes. We show that regardless of the target gene tested, cells that displayed histological changes were those that are in direct contact with the dsRNA-containing gut lumen, suggesting that the greatest efficiency of the orally-delivered dsRNAs is localized to gut tissues in T. urticae.

Discovery of Small-Molecule Degraders of the CDK9-Cyclin T1 Complex for Targeting Transcriptional Addiction in Prostate Cancer

Aberrant hyperactivation of cyclins results in carcinogenesis and therapy resistance in cancers. Direct degradation of the specific cyclin or cyclin-dependent kinase (CDK)-cyclin complex by small-molecule degraders remains a great challenge. Here, we applied the first application of hydrophobic tagging to induce degradation of CDK9-cyclin T1 heterodimer, which is required to keep productive transcription of oncogenes in cancers. LL-K9-3 was identified as a potent small-molecule degrader of CDK9-cyclin T1. Quantitative and time-resolved proteome profiling exhibited LL-K9-3 induced selective and synchronous degradation of CDK9 and cyclin T1. The expressions of androgen receptor (AR) and cMyc were reduced by LL-K9-3 in 22RV1 cells. LL-K9-3 exhibited enhanced anti-proliferative and pro-apoptotic effects compared with its parental CDK9 inhibitor SNS032 and suppressed downstream signaling of CDK9 and AR more effectively than SNS032. Moreover, LL-K9-3 inhibited AR and Myc-driven oncogenic transcriptional programs and exerted stronger inhibitory effects on several intrinsic target genes of AR than the monomeric CDK9 PROTAC (Thal-SNS032).

SILAC kinase screen identifies potential MASTL substrates

Microtubule-associated serine/threonine kinase-like (MASTL) has emerged as a critical regulator of mitosis and as a potential oncogene in a variety of cancer types. To date, Arpp-19/ENSA are the only known substrates of MASTL. However, with the roles of MASTL expanding and increased interest in development of MASTL inhibitors, it has become critical to determine if there are additional substrates and what the optimal consensus motif for MASTL is. Here we utilized a whole cell lysate in vitro kinase screen combined with stable isotope labelling of amino acids in cell culture (SILAC) to identify potential substrates and the residue preference of MASTL. Using the related AGC kinase family members AKT1/2, the kinase screen identified several known and new substrates highly enriched for the validated consensus motif of AKT. Applying this method to MASTL identified 59 phospho-sites on 67 proteins that increased in the presence of active MASTL. Subsequent in vitro kinase assays suggested that MASTL may phosphorylate hnRNPM, YB1 and TUBA1C under certain in vitro conditions. Taken together, these data suggest that MASTL may phosphorylate several additional substrates, providing insight into the ever-increasing biological functions and roles MASTL plays in driving cancer progression and therapy resistance.

Mitotic protein kinase-driven crosstalk of machineries for mitosis and metastasis

Accumulating evidence indicates that mitotic protein kinases are involved in metastatic migration as well as tumorigenesis. Protein kinases and cytoskeletal proteins play a role in the efficient release of metastatic cells from a tumor mass in the tumor microenvironment, in addition to playing roles in mitosis. Mitotic protein kinases, including Polo-like kinase 1 (PLK1) and Aurora kinases, have been shown to be involved in metastasis in addition to cell proliferation and tumorigenesis, depending on the phosphorylation status and cellular context. Although the genetic programs underlying mitosis and metastasis are different, the same protein kinases and cytoskeletal proteins can participate in both mitosis and cell migration/invasion, resulting in migratory tumors. Cytoskeletal remodeling supports several cellular events, including cell division, movement, and migration. Thus, understanding the contributions of cytoskeletal proteins to the processes of cell division and metastatic motility is crucial for developing efficient therapeutic tools to treat cancer metastases. Here, we identify mitotic kinases that function in cancer metastasis as well as tumorigenesis. Several mitotic kinases, namely, PLK1, Aurora kinases, Rho-associated protein kinase 1, and integrin-linked kinase, are considered in this review, as an understanding of the shared machineries between mitosis and metastasis could be helpful for developing new strategies to treat cancer.

Improving understanding of the mechanisms linking cell division and cancer spread (metastasis) could provide novel strategies for treatment. A group of enzymes involved in cell division (mitosis) are also thought to play critical roles in the spread of cancers. Hyungshin Yim at Hanyang University in Ansan, South Korea, and co-workers in Korea and the USA reviewed the roles of several mitotic enzymes that are connected with metastasis as well as tumorigenesis. They discussed how these enzymes modify cytoskeletal proteins and other substrates during cancer progression. Some regulatory control of cell cytoskeletal structures is required for cancer cells to metastasize. Recent research has uncovered crosstalk between mitotic enzymes and metastatic cytoskeletal molecules in various cancers. Targeting mitotic enzymes and the ways they influence cytoskeletal mechanisms could provide valuable therapeutic strategies for suppressing metastasis.

TEM Imaging of Membrane Choreography During Mitosis of Drosophila Tissue Culture Cells

Schneider 2 (S2) cells are one of the most widely used Drosophila cell lines, and are specifically suitable for genetic dissection of biological processes by RNA interference. We have recently developed a method that allows an easy preparation of samples for transmission electron microscopy (TEM) analysis of S2 cells. This method is based on the collection and pelleting of the cells in test tubes, followed by fixation and staining of pellets in the same tubes. Pellets are then embedded in resin and used to prepare ultrathin sections for TEM observation. Our Method allows clear visualization of the complex membrane transformations that characterize mitosis in S2 cells. It also allows precise analysis of microtubule behavior during the different mitotic phases. Although the method was specifically developed for S2 cells, our preliminary results indicate that it can be successfully applied to other types of Drosophila tissue culture cells.

The Hippo Signaling Pathway in Cancer: A Cell Cycle Perspective

Simple Summary

Cancer is increasingly viewed as a cell cycle disease in that the dysregulation of the cell cycle machinery is a common feature in cancer. The Hippo signaling pathway consists of a core kinase cascade as well as extended regulators, which together control organ size and tissue homeostasis. The aberrant expression of cell cycle regulators and/or Hippo pathway components contributes to cancer development, and for this reason, we specifically focus on delineating the roles of the Hippo pathway in the cell cycle. Improving our understanding of the Hippo pathway from a cell cycle perspective could be used as a powerful weapon in the cancer battlefield.

Abstract

Cell cycle progression is an elaborate process that requires stringent control for normal cellular function. Defects in cell cycle control, however, contribute to genomic instability and have become a characteristic phenomenon in cancers. Over the years, advancement in the understanding of disrupted cell cycle regulation in tumors has led to the development of powerful anti-cancer drugs. Therefore, an in-depth exploration of cell cycle dysregulation in cancers could provide therapeutic avenues for cancer treatment. The Hippo pathway is an evolutionarily conserved regulator network that controls organ size, and its dysregulation is implicated in various types of cancers. Although the role of the Hippo pathway in oncogenesis has been widely investigated, its role in cell cycle regulation has not been comprehensively scrutinized. Here, we specifically focus on delineating the involvement of the Hippo pathway in cell cycle regulation. To that end, we first compare the structural as well as functional conservation of the core Hippo pathway in yeasts, flies, and mammals. Then, we detail the multi-faceted aspects in which the core components of the mammalian Hippo pathway and their regulators affect the cell cycle, particularly with regard to the regulation of E2F activity, the G1 tetraploidy checkpoint, DNA synthesis, DNA damage checkpoint, centrosome dynamics, and mitosis. Finally, we briefly discuss how a collective understanding of cell cycle regulation and the Hippo pathway could be weaponized in combating cancer.

Functional requirements of protein kinases and phosphatases in the development of the Drosophila melanogaster wing

Protein kinases and phosphatases constitute a large family of conserved enzymes that control a variety of biological processes by regulating the phosphorylation state of target proteins. They play fundamental regulatory roles during cell cycle progression and signaling, among other key aspects of multicellular development. The complement of protein kinases and phosphatases includes approximately 326 members in Drosophila, and they have been the subject of several functional screens searching for novel components of signaling pathways and regulators of cell division and survival. These approaches have been carried out mostly in cell cultures using RNA interference to evaluate the contribution of each protein in different functional assays, and have contributed significantly to assign specific roles to the corresponding genes. In this work we describe the results of an evaluation of the Drosophila complement of kinases and phosphatases using the wing as a system to identify their functional requirements in vivo. We also describe the results of several modifying screens aiming to identify among the set of protein kinases and phosphatases additional components or regulators of the activities of the Epidermal Growth Factor and Insulin receptors signaling pathways.

Simultaneous CK2/TNIK/DYRK1 inhibition by 108600 suppresses triple negative breast cancer stem cells and chemotherapy-resistant disease

Triple negative breast cancer (TNBC) remains challenging because of heterogeneous responses to chemotherapy. Incomplete response is associated with a greater risk of metastatic progression. Therefore, treatments that target chemotherapy-resistant TNBC and enhance chemosensitivity would improve outcomes for these high-risk patients. Breast cancer stem cell-like cells (BCSCs) have been proposed to represent a chemotherapy-resistant subpopulation responsible for tumor initiation, progression and metastases. Targeting this population could lead to improved TNBC disease control. Here, we describe a novel multi-kinase inhibitor, 108600, that targets the TNBC BCSC population. 108600 treatment suppresses growth, colony and mammosphere forming capacity of BCSCs and induces G2M arrest and apoptosis of TNBC cells. In vivo, 108600 treatment of mice bearing triple negative tumors results in the induction of apoptosis and overcomes chemotherapy resistance. Finally, treatment with 108600 and chemotherapy suppresses growth of pre-established TNBC metastases, providing additional support for the clinical translation of this agent to clinical trials.

CDK9: A Comprehensive Review of Its Biology, and Its Role as a Potential Target for Anti-Cancer Agents

Cyclin-dependent kinases (CDKs) are proteins pivotal to a wide range of cellular functions, most importantly cell division and transcription, and their dysregulations have been implicated as prominent drivers of tumorigenesis. Besides the well-established role of cell cycle CDKs in cancer, the involvement of transcriptional CDKs has been confirmed more recently. Most cancers overtly employ CDKs that serve as key regulators of transcription (e.g., CDK9) for a continuous production of short-lived gene products that maintain their survival. As such, dysregulation of the CDK9 pathway has been observed in various hematological and solid malignancies, making it a valuable anticancer target. This therapeutic potential has been utilized for the discovery of CDK9 inhibitors, some of which have entered human clinical trials. This review provides a comprehensive discussion on the structure and biology of CDK9, its role in solid and hematological cancers, and an updated review of the available inhibitors currently being investigated in preclinical and clinical settings.

Integrin-Linked-Kinase Overexpression Is Implicated in Mechanisms of Genomic Instability in Human Colorectal Cancer

BACKGROUND

Genomic instability is a hallmark of cancer cells contributing to tumor development and progression. Integrin-linked kinase (ILK) is a focal adhesion protein with well-established role in carcinogenesis. We have previously shown that ILK overexpression is critically implicated in human colorectal cancer (CRC) progression. In light of the recent findings that ILK regulates centrosomes and mitotic spindle formation, we aimed to determine its implication in mechanisms of genomic instability in human CRC.

METHODS

Association of ILK expression with markers of genomic instability (micronuclei formation, nucleus size, and intensity) was investigated in diploid human colon cancer cells HCT116 upon ectopic ILK overexpression, by immunofluorescence and in human CRC samples by Feulgen staining. We also evaluated the role of ILK in mitotic spindle formation, by immunofluorescence, in HCT116 cells upon inhibition and overexpression of ILK. Finally, we evaluated association of ILK overexpression with markers of DNA damage (p-H2AX, p-ATM/ATR) in human CRC tissue samples by immunohistochemistry and in ILK-overexpressing cells by immunofluorescence.

RESULTS

We showed that ILK overexpression is associated with genomic instability markers in human colon cancer cells and tissues samples. Aberrant mitotic spindles were observed in cells treated with specific ILK inhibitor (QLT0267), while ILK-overexpressing cells failed to undergo nocodazole-induced mitotic arrest. ILK overexpression was also associated with markers of DNA damage in HCT116 cells and human CRC tissue samples.

CONCLUSIONS

The above findings indicate that overexpression of ILK is implicated in mechanisms of genomic instability in CRC suggesting a novel role of this protein in cancer.

Regulation of PCTAIRE1 protein stability by AKT1, LKB1 and BRCA1

PCTAIRE1, also known as CDK16, is a cyclin-dependent kinase that is regulated by cyclin Y. It is a member of the serine-threonine family of kinases and its functions have primarily been implicated in cellular processes like vesicular transport, neuronal growth and development, myogenesis, spermatogenesis and cell proliferation. However, as extensive studies on PCTAIRE1 have not yet been conducted, the signaling pathways for this kinase involved in governing many cellular processes are yet to be elucidated in detail. Here, we report the association of PCTAIRE1 with important cellular proteins involved in major cell signaling pathways, especially cell proliferation. In particular, here we show that PCTAIRE1 interacts with AKT1, a key player of the PI3K signaling pathway that is responsible for promoting cell survival and proliferation. Our studies show that PCTAIRE1 is a substrate of AKT1 that gets stabilized by it. Further, we show that PCTAIRE1 also interacts with and is degraded by LKB1, a kinase that is known to suppress cellular proliferation and also regulate cellular energy metabolism. Moreover, our results show that PCTAIRE1 is also degraded by BRCA1, a well-known tumor suppressor. Together, our studies highlight the regulation of PCTAIRE1 by key players of the major cell signaling pathways involved in regulating cell proliferation, and therefore, provide crucial links that could be explored further to elucidate the mechanistic role of PCTAIRE1 in cell proliferation and tumorigenesis.

Phosphoproteome Profiling Revealed the Importance of mTOR Inhibition on CDK1 Activation to Further Regulate Cell Cycle Progression

The mammalian target of rapamycin (mTOR) functions as a critical regulator of cell cycle progression. However, the underlying mechanism by which mTOR regulates cell cycle progression remains elusive. In this study, we used stable isotope labeling of amino acids in cell culture with a two-step strategy for phosphopeptide enrichment and high-throughput quantitative mass spectrometry to perform a global phosphoproteome analysis of mTOR inhibition by rapamycin. By monitoring the phosphoproteome alterations upon rapamycin treatment, downregulation of mTOR signaling pathway was detected and enriched. Further functional analysis of phosphoproteome revealed the involvement of cell cycle events. Specifically, the elevated profile of cell cycle-related substrates was observed, and the activation of CDK1, MAPK1, and MAPK3 kinases was determined. Second, pathway interrogation using kinase inhibitor treatment confirmed that CDK1 activation operated downstream from mTOR inhibition to further regulate cell cycle progression. Third, we found that the activation of CDK1 following 4-12 h of mTOR inhibition was accompanied by the activation of the Greatwall-endosulfine complex. In conclusion, we presented a high-confidence phosphoproteome map inside the cells upon mTOR inhibition by rapamycin. Our data implied that mTOR inhibition could contribute to CDK1 activation for further regulating cell cycle progression, which was mediated by the Greatwall-endosulfine complex.

PINK1/Parkin Influences Cell Cycle by Sequestering TBK1 at Damaged Mitochondria, Inhibiting Mitosis

PINK1 and Parkin are established mediators of mitophagy, the selective removal of damaged mitochondria by autophagy. PINK1 and Parkin have been proposed to act as tumor suppressors, as loss-of-function mutations are correlated with enhanced tumorigenesis. However, it is unclear how PINK1 and Parkin act in coordination during mitophagy to influence the cell cycle. Here we show that PINK1 and Parkin genetically interact with proteins involved in cell cycle regulation, and loss of PINK1 and Parkin accelerates cell growth. PINK1- and Parkin-mediated activation of TBK1 at the mitochondria during mitophagy leads to a block in mitosis due to the sequestration of TBK1 from its physiological role at centrosomes during mitosis. Our study supports a diverse role for the far-reaching, regulatory effects of mitochondrial quality control in cellular homeostasis and demonstrates that the PINK1/Parkin pathway genetically interacts with the cell cycle, providing a framework for understanding the molecular basis linking PINK1 and Parkin to mitosis.

Sarraf et al. use mouse and fly genetics to discover that PINK1 and Parkin influence cell cycle progression. Mitophagy and mitosis independently activate TBK1 at damaged mitochondria and centrosomes, respectively, influencing whether the cell will address mitochondrial quality control or progress with proliferation.

Quantitative kinase and phosphatase profiling reveal that CDK1 phosphorylates PP2Ac to promote mitotic entry

The reciprocal regulation of phosphoprotein phosphatases (PPPs) by protein kinases is essential to cell cycle progression and control, particularly during mitosis for which the role of kinases has been extensively studied. PPPs perform much of the serine/threonine dephosphorylation in eukaryotic cells and achieve substrate selectivity and specificity through the interaction of distinct regulatory subunits with conserved catalytic subunits in holoenzyme complexes. Using a mass spectrometry-based chemical proteomics approach to enrich, identify, and quantify endogenous PPP holoenzyme complexes combined with kinase profiling, we investigated the phosphorylation-dependent regulation of PPP holoenzymes in mitotic cells. We found that cyclin-dependent kinase 1 (CDK1) phosphorylated a threonine residue on the catalytic subunit of the phosphatase PP2A, which disrupted its holoenzyme formation with the regulatory subunit B55. The consequent decrease in the dephosphorylation of PP2A-B55 substrates promoted mitotic entry. This direct phosphorylation by CDK1 was in addition to a previously reported indirect mechanism, thus adding a layer to the interaction between CDK1 and PP2A in regulating mitotic entry.

Insight on Transcriptional Regulation of the Energy Sensing AMPK and Biosynthetic mTOR Pathway Genes

The Adenosine Monophosphate-activated Protein Kinase (AMPK) and the Mechanistic Target of Rapamycin (mTOR) are two evolutionarily conserved kinases that together regulate nearly every aspect of cellular and systemic metabolism. These two kinases sense cellular energy and nutrient levels that in turn are determined by environmental nutrient availability. Because AMPK and mTOR are kinases, the large majority of studies remained focused on downstream substrate phosphorylation by these two proteins, and how AMPK and mTOR regulate signaling and metabolism in normal and disease physiology through phosphorylation of their substrates. Compared to the wealth of information known about the signaling and metabolic pathways modulated by these two kinases, much less is known about how the transcription of AMPK and mTOR pathway genes themselves are regulated, and the extent to which AMPK and mTOR regulate gene expression to cause durable changes in phenotype. Acute modification of cellular systems can be achieved through phosphorylation, however, induction of chronic changes requires modulation of gene expression. In this review we will assemble evidence from published studies on transcriptional regulation by AMPK and mTOR and discuss about the putative transcription factors that regulate expression of AMPK and mTOR complex genes.

MASTL: A novel therapeutic target for Cancer Malignancy

Targeting mitotic kinases is an emerging anticancer approach with promising preclinical outcomes. Microtubule‐associated serine/threonine kinase like (MASTL), also known as Greatwall (Gwl), is an important mitotic kinase that regulates mitotic progression of normal or transformed cells by blocking the activity of tumor suppressor protein phosphatase 2A (PP2A). MASTL upregulation has now been detected in multiple cancer types and associated with aggressive clinicopathological features. Apart, an aberrant MASTL activity has been implicated in oncogenic transformation through the development of chromosomal instability and alteration of key oncogenic signaling pathways. In this regard, recent publications have revealed potential role of MASTL in the regulation of AKT/mTOR and Wnt/β‐catenin signaling pathways, which may be independent of its regulation of PP2A‐B55 (PP2A holoenzyme containing a B55‐family regulatory subunit). Taken together, MASTL kinase has emerged as a novel target for cancer therapeutics, and hence development of small molecule inhibitors of MASTL may significantly improve the clinical outcomes of cancer patients. In this article, we review the role of MASTL in cancer progression and the current gaps in this knowledge. We also discuss potential efficacy of MASTL expression for cancer diagnosis and therapy.

LKB1 inactivation leads to centromere defects and genome instability via p53-dependent upregulation of survivin

Inactivating mutations in the liver kinase B1 (LKB1) tumor suppressor gene underlie Peutz-Jeghers syndrome (PJS) and occur frequently in various human cancers. We previously showed that LKB1 regulates centrosome duplication via PLK1. Here, we report that LKB1 further helps to maintain genomic stability through negative regulation of survivin, a member of the chromosomal passenger complex (CPC) that mediates CPC targeting to the centromere. We found that loss of LKB1 led to accumulation of misaligned and lagging chromosomes at metaphase and anaphase and increased the appearance of multi- and micro-nucleated cells. Ectopic LKB1 expression reduced these features and improved mitotic fidelity in LKB1-deficient cells. Through pharmacological and genetic manipulations, we showed that LKB1-mediated repression of survivin is independent of AMPK, but requires p53. Consistent with the key influence of LKB1 on survivin expression, immunohistochemical analysis indicated that survivin is highly expressed in intestinal polyps from a PJS patient. Lastly, we reaffirm a potential therapeutic avenue to treat LKB1-mutated tumors by demonstrating the increased sensitivity to survivin inhibitors of LKB1-deficient cells.

The Unusual Suspects in Cytokinesis: Fitting the Pieces Together

Cytokinesis is the step of the cell cycle in which the cell must faithfully separate the chromosomes and cytoplasm, yielding two daughter cells. The assembly and contraction of the contractile network is spatially and temporally coupled with the formation of the mitotic spindle to ensure the successful completion of cytokinesis. While decades of studies have elucidated the components of this machinery, the so-called usual suspects, and their functions, many lines of evidence are pointing to other unexpected proteins and sub-cellular systems as also being involved in cytokinesis. These we term the unusual suspects. In this review, we introduce recent discoveries on some of these new unusual suspects and begin to consider how these subcellular systems snap together to help complete the puzzle of cytokinesis.

AKT Regulates Mitotic Progression of Mammalian Cells by Phosphorylating MASTL, Leading to Protein Phosphatase 2A Inactivation

Microtubule-associated serine/threonine kinase like (MASTL), also known as Greatwall (Gwl) kinase, has an important role in the regulation of mitosis. By inhibiting protein phosphatase 2A (PP2A), it plays a crucial role in activating one of the most important mitotic kinases, known as cyclin-dependent kinase 1 (CDK1). MASTL has been seen to be upregulated in various types of cancers and is also involved in tumor recurrence. It is activated by CDK1 through phosphorylations in the activation/T-loop, but the complete mechanism of its activation is still unclear. Here, we report that AKT phosphorylates MASTL at residue T299, which plays a critical role in its activation. Our results suggest that AKT increases CDK1-mediated phosphorylation and hence the activity of MASTL, which, in turn, promotes mitotic progression through PP2A inhibition. We also show that the oncogenic potential of AKT is augmented by MASTL activation, since AKT-mediated proliferation in colorectal cell lines can be attenuated by inhibiting and/or silencing MASTL. In brief, we report that AKT plays an important role in the progression of mitosis in mammalian cells and that it does so through the phosphorylation and activation of MASTL.

Haspin-dependent and independent effects of the kinase inhibitor 5-Iodotubercidin on self-renewal and differentiation

The kinase Haspin phosphorylates histone H3 at threonine-3 (H3T3ph), creating a docking site for the Chromosomal Passenger Complex (CPC). CPC plays a pivotal role in preventing chromosome misalignment. Here, we have examined the effects of 5-Iodotubercidin (5-ITu), a commonly used Haspin inhibitor, on self-renewal and differentiation of mouse embryonic stem cells (ESCs). Treatment with low concentrations of 5-ITu eliminates the H3T3ph mark during mitosis, but does not affect the mode or the outcome of self-renewal divisions. Interestingly, 5-ITu causes sustained accumulation of p53, increases markedly the expression of histone genes and results in reversible upregulation of the pluripotency factor Klf4. However, the properties of 5-ITu treated cells are distinct from those observed in Haspin-knockout cells generated by CRISPR/Cas9 genome editing, suggesting “off-target” effects. Continuous exposure to 5-ITu allows modest expansion of the ESC population and growth of embryoid bodies, but release from the drug after an initial treatment aborts embryoid body or teratoma formation. The data reveal an unusual robustness of ESCs against mitotic perturbants and suggest that the lack of H3T3ph and the “off-target” effects of 5-ITu can be partially compensated by changes in expression program or accumulation of suppressor mutations.

STK11 is required for the normal program of ciliated cell differentiation in airways

The functional properties of mucosal surfaces are dependent on establishing the correct proportions of specialized epithelial cell types. Multiciliated cells (also known as ciliated cells) are evolutionarily conserved and functionally indispensable epithelial cells, as suggested by the link between ciliated cell dysfunction and chronic human disease. Ciliated cell differentiation is an ordered process that involves initial cell fate determination and multiciliogenesis. STK11, a serine/threonine kinase, has been reported to be downregulated in human diseases associated with ciliopathies and functions as a tumor suppressor. Here, we show that STK11 is a physiological factor for the normal program of ciliated cell differentiation by phosphorylating MARK3, which directly suppresses ERK1/2 mediated pRB inactivation. Loss of Stk11 in airway progenitors impairs the differentiation of ciliated cells in both embryonic and adult airways. Our study establishes that STK11/MARK3/ERK1/2 signaling cascade is a key regulator to integrate ciliated cell fate commitment and the subsequent process of multiciliogenesis.

THANATOS: an integrative data resource of proteins and post-translational modifications in the regulation of autophagy

Macroautophagy/autophagy is a highly conserved process for degrading cytoplasmic contents, determines cell survival or death, and regulates the cellular homeostasis. Besides ATG proteins, numerous regulators together with various post-translational modifications (PTMs) are also involved in autophagy. In this work, we collected 4,237 experimentally identified proteins regulated in autophagy and cell death pathways from the literature. Then we computationally identified potential orthologs of known proteins, and developed a comprehensive database of The Autophagy, Necrosis, ApopTosis OrchestratorS (THANATOS, http://thanatos.biocuckoo.org ), containing 191,543 proteins potentially associated with autophagy and cell death pathways in 164 eukaryotes. We performed an evolutionary analysis of ATG genes, and observed that ATGs required for the autophagosome formation are highly conserved across eukaryotes. Further analyses revealed that known cancer genes and drug targets were overrepresented in human autophagy proteins, which were significantly associated in a number of signaling pathways and human diseases. By reconstructing a human kinase-substrate phosphorylation network for ATG proteins, our results confirmed that phosphorylation play a critical role in regulating autophagy. In total, we mapped 65,015 known sites of 11 types of PTMs to collected proteins, and revealed that all types of PTM substrates were enriched in human autophagy. In addition, we observed multiple types of PTM regulators such as protein kinases and ubiquitin E3 ligases or adaptors were significantly associated with human autophagy, and again the results emphasized the importance of PTM regulations in autophagy. We anticipated THANATOS can be a useful resource for further studies.

Light-Induced Protein Clustering for Optogenetic Interference and Protein Interaction Analysis in Drosophila S2 Cells

Drosophila Schneider 2 (S2) cells are a simple and powerful system commonly used in cell biology because they are well suited for high resolution microscopy and RNAi-mediated depletion. However, understanding dynamic processes, such as cell division, also requires methodology to interfere with protein function with high spatiotemporal control. In this research study, we report the adaptation of an optogenetic tool to Drosophila S2 cells. Light-activated reversible inhibition by assembled trap (LARIAT) relies on the rapid light-dependent heterodimerization between cryptochrome 2 (CRY2) and cryptochrome-interacting bHLH 1 (CIB1) to form large protein clusters. An anti-green fluorescent protein (GFP) nanobody fused with CRY2 allows this method to quickly trap any GFP-tagged protein in these light-induced protein clusters. We evaluated clustering kinetics in response to light for different LARIAT modules, and showed the ability of GFP-LARIAT to inactivate the mitotic protein Mps1 and to disrupt the membrane localization of the polarity regulator Lethal Giant Larvae (Lgl). Moreover, we validated light-induced co-clustering assays to assess protein-protein interactions in S2 cells. In conclusion, GFP-based LARIAT is a versatile tool to answer different biological questions, since it enables probing of dynamic processes and protein-protein interactions with high spatiotemporal resolution in Drosophila S2 cells.

BmHpo mutation induces smaller body size and late stage larval lethality in the silkworm, Bombyx mori

As a core member of the Hippo signaling pathway, Hpo plays a critical role in regulating growth and development. Previous studies reported that loss of function of Hpo results in increased proliferation, reduced apoptosis and induction of tissue overgrowth in Drosophila. In this study, we used CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/Cas9) to study Hpo gene (BmHpo) function in the lepidopteran insect Bombyx mori, known commonly as the silkworm. Sequence analysis of BmHpo revealed an array of deletions in mutants. We found that BmHpo knockout resulted in defects in body size regulation, in developmental defects and pigment accumulation and early death. Our data show that BmHpo is essential for regulation of insect growth and development and that CRISPR/Cas9 technology can serve as a basis for functional analysis of target genes in lepidopteran insects.

Genome editing reveals the function of Yorkie during the embryonic and early larval development in silkworm, Bombyx mori

As a transcriptional coactivator, Yorkie (Yki) is a major downstream target of the Hippo signalling pathway to regulate the organ size during animal development and regeneration. Previous microarray analysis in the silkworm, Bombyx mori, has shown that genes associated with the Hippo pathway were primarily expressed in gonads and imaginal discs. The RNA-interference-mediated silencing of Yki at the early wandering stage delayed B. mori development and ovary maturation, whereas baculovirus-mediated overexpression at the late larval instar facilitated organ growth and accelerated metamorphosis. Here, we employed CRISPR/Cas9-mediated mutagenesis to investigate the function of Yki in B. mori (BmYki) at the embryonic and early larval stages. Knocking out of BmYki led to reduced body size, moulting defects and, eventually, larval lethality. Sequence analysis of CRISPR/Cas9 mutants exhibited an array of deletions in BmYki. As a critical downstream effector of the Hippo kinase cassette, silencing of BmYki at the embryonic stage is indispensable and the consequence is lethal. Given that the Hippo signalling pathway is evolutionarily conserved, Yki has the potential to be a novel molecular target for genetic-based pest management practices.

The Oncogenic Functions of MASTL Kinase

MASTL kinase is a master regulator of mitosis, essential for ensuring that mitotic substrate phosphorylation is correctly maintained. It achieves this through the phosphorylation of alpha-endosulfine and subsequent inhibition of the tumor suppressor PP2A-B55 phosphatase. In recent years MASTL has also emerged as a novel oncogenic kinase that is upregulated in a number of cancer types, correlating with chromosome instability and poor patient survival. While the chromosome instability is likely directly linked to MASTL's control of mitotic phosphorylation, several new studies indicated that MASTL has additional effects outside of mitosis and beyond regulation of PP2A-B55. These include control of normal DNA replication timing, and regulation of AKT/mTOR and Wnt/β-catenin oncogenic kinase signaling. In this review, we will examine the phenotypes and mechanisms for how MASTL, ENSA, and PP2A-B55 deregulation drives tumor progression and metastasis. Finally, we will explore the rationale for the future development of MASTL inhibitors as new cancer therapeutics.

Ultrastructural analysis of mitotic Drosophila S2 cells identifies distinctive microtubule and intracellular membrane behaviors

BACKGROUND

S2 cells are one of the most widely used Drosophila melanogaster cell lines. A series of studies has shown that they are particularly suitable for RNAi-based screens aimed at the dissection of cellular pathways, including those controlling cell shape and motility, cell metabolism, and host-pathogen interactions. In addition, RNAi in S2 cells has been successfully used to identify many new mitotic genes that are conserved in the higher eukaryotes, and for the analysis of several aspects of the mitotic process. However, no detailed and complete description of S2 cell mitosis at the ultrastructural level has been done. Here, we provide a detailed characterization of all phases of S2 cell mitosis visualized by transmission electron microscopy (TEM).

RESULTS

We analyzed by TEM a random sample of 144 cells undergoing mitosis, focusing on intracellular membrane and microtubule (MT) behaviors. This unbiased approach provided a comprehensive ultrastructural view of the dividing cells, and allowed us to discover that S2 cells exhibit a previously uncharacterized behavior of intracellular membranes, involving the formation of a quadruple nuclear membrane in early prometaphase and its disassembly during late prometaphase. After nuclear envelope disassembly, the mitotic apparatus becomes encased by a discontinuous network of endoplasmic reticulum membranes, which associate with mitochondria, presumably to prevent their diffusion into the spindle area. We also observed a peculiar metaphase spindle organization. We found that kinetochores with attached k-fibers are almost invariably associated with lateral MT bundles that can be either interpolar bundles or k-fibers connected to a different kinetochore. This spindle organization is likely to favor chromosome alignment at metaphase and subsequent segregation during anaphase.

CONCLUSIONS

We discovered several previously unknown features of membrane and MT organization during S2 cell mitosis. The genetic determinants of these mitotic features can now be investigated, for instance by using an RNAi-based approach, which is particularly easy and efficient in S2 cells.

MASTL overexpression promotes chromosome instability and metastasis in breast cancer

MASTL kinase is essential for correct progression through mitosis, with loss of MASTL causing chromosome segregation errors, mitotic collapse and failure of cytokinesis. However, in cancer MASTL is most commonly amplified and overexpressed. This correlates with increased chromosome instability in breast cancer and poor patient survival in breast, ovarian and lung cancer. Global phosphoproteomic analysis of immortalised breast MCF10A cells engineered to overexpressed MASTL revealed disruption to desmosomes, actin cytoskeleton, PI3K/AKT/mTOR and p38 stress kinase signalling pathways. Notably, these pathways were also disrupted in patient samples that overexpress MASTL. In MCF10A cells, these alterations corresponded with a loss of contact inhibition and partial epithelial-mesenchymal transition, which disrupted migration and allowed cells to proliferate uncontrollably in 3D culture. Furthermore, MASTL overexpression increased aberrant mitotic divisions resulting in increased micronuclei formation. Mathematical modelling indicated that this delay was due to continued inhibition of PP2A-B55, which delayed timely mitotic exit. This corresponded with an increase in DNA damage and delayed transit through interphase. There were no significant alterations to replication kinetics upon MASTL overexpression, however, inhibition of p38 kinase rescued the interphase delay, suggesting the delay was a G2 DNA damage checkpoint response. Importantly, knockdown of MASTL, reduced cell proliferation, prevented invasion and metastasis of MDA-MB-231 breast cancer cells both in vitro and in vivo, indicating the potential of future therapies that target MASTL. Taken together, these results suggest that MASTL overexpression contributes to chromosome instability and metastasis, thereby decreasing breast cancer patient survival.

RNA Interference (RNAi) Screening in Drosophila

In the last decade, RNA interference (RNAi), a cellular mechanism that uses RNA-guided degradation of messenger RNA transcripts, has had an important impact on identifying and characterizing gene function. First discovered in Caenorhabditis elegans, RNAi can be used to silence the expression of genes through introduction of exogenous double-stranded RNA into cells. In Drosophila, RNAi has been applied in cultured cells or in vivo to perturb the function of single genes or to systematically probe gene function on a genome-wide scale. In this review, we will describe the use of RNAi to study gene function in Drosophila with a particular focus on high-throughput screening methods applied in cultured cells. We will discuss available reagent libraries and cell lines, methodological approaches for cell-based assays, and computational methods for the analysis of high-throughput screens. Furthermore, we will review the generation and use of genome-scale RNAi libraries for tissue-specific knockdown analysis in vivo and discuss the differences and similarities with the use of genome-engineering methods such as CRISPR/Cas9 for functional analysis.

Part III: Novel checkpoint kinase 2 (Chk2) inhibitors; design, synthesis and biological evaluation of pyrimidine-benzimidazole conjugates

Recently a dramatic development of the cancer drug discovery has been shown in the field of targeted cancer therapy. Checkpoint kinase 2 (Chk2) inhibitors offer a promising approach to enhance the effectiveness of cancer chemotherapy. Accordingly, in this study many pyrimidine-benzimidazole conjugates were designed and twelve feasible derivatives were selected to be synthesized to investigate their activity against Chk2 and subjected to study their antitumor activity alone and in combination with the genotoxic anticancer drugs cisplatin and doxorubicin on breast carcinoma, (ER+) cell line (MCF-7). The results indicated that the studied compounds inhibited Chk2 activity with high potency (IC50 = 5.56 nM - 46.20 nM). The studied candidates exhibited remarkable antitumor activity against MCF-7 (IG50 = 6.6  μM - 24.9 μM). Compounds 10a-c, 14 and 15 significantly potentiated the activity of the studied genotoxic drugs, whereas, compounds 9b and 20-23 antagonized their activity. Moreover, the combination of compound 10b with cisplatin revealed the best apoptotic effect as well as combination of compound 10b with doxorubicin led to complete arrest of the cell cycle at S phase where more than 40% of cells are in the S phase with no cells at G2/M. Structure-activity relationship was discussed on the basis of molecular modeling study using Molecular modeling Environment program (MOE).

Link of Zygotic Genome Activation and Cell Cycle Control

The activation of the zygotic genome and onset of transcription in blastula embryos is linked to changes in cell behavior and remodeling of the cell cycle and constitutes a transition from exclusive maternal to zygotic control of development. This step in development is referred to as mid-blastula transition and has served as a paradigm for the link between developmental program and cell behavior and morphology. Here, we discuss the mechanism and functional relationships between the zygotic genome activation and cell cycle control during mid-blastula transition with a focus on Drosophila embryos.

Coupling of Polo kinase activation to nuclear localization by a bifunctional NLS is required during mitotic entry

The Polo kinase is a master regulator of mitosis and cytokinesis conserved from yeasts to humans. Polo is composed of an N-term kinase domain (KD) and a C-term polo-box domain (PBD), which regulates its subcellular localizations. The PBD and KD can interact and inhibit each other, and this reciprocal inhibition is relieved when Polo is phosphorylated at its activation loop. How Polo activation and localization are coupled during mitotic entry is unknown. Here we report that PBD binding to the KD masks a nuclear localization signal (NLS). Activating phosphorylation of the KD leads to exposure of the NLS and entry of Polo into the nucleus before nuclear envelope breakdown. Failures of this mechanism result in misregulation of the Cdk1-activating Cdc25 phosphatase and lead to mitotic and developmental defects in Drosophila. These results uncover spatiotemporal mechanisms linking master regulatory enzymes during mitotic entry.

Drosophila Polo kinase is the founding member of the Polo-Like Kinase (PLK) family and a master regulator of mitosis and cytokinesis. Here the authors uncover a molecular mechanism for the spatiotemporal regulation of Polo kinase during mitotic entry through a phosphorylation event that triggers nuclear import.

Diverse gene expression patterns in response to anticancer drugs between human and mouse cell lines revealed by a comparative transcriptomic analysis

The aim of the present study was to perform comparative genomics using gene expression profile datasets of mice and humans who had been treated with anticancer drugs, to determine the similarities and differences in the antitumor mechanisms in the two mammals. This involved data mining of antitumor gene expression regulation, and screening of genetic loci from experimental mouse models of antitumor targets, to provide a theoretical basis of drug design. Subsequently, 9 overlapping genes with opposite expression patterns were identified across mouse and human cell lines that were treated with a specific cyclin-dependent kinase 4/6 inhibitor, PD0332991. These genes included LIM homeobox 2, adenomedullin, bone marrow stromal cell antigen 1, caveolin 1, histone cluster 1 (HIST1) H2B family member C, HIST1 H3 family member F, low density lipoprotein-receptor related protein 11, prolyl 4-hydroxylase subunit α1 and torsin family 3 member A. In addition, the janus kinase-signal transducer and activator of transcription signaling pathway, Toll-like receptor signaling pathway, T cell receptor signaling pathway and the nucleotide-binding oligomerization domain-like receptor signaling pathway were identified as candidate pathways for explaining antitumor mechanisms.

The Centrioles, Centrosomes, Basal Bodies, and Cilia of Drosophila melanogaster

Centrioles play a key role in the development of the fly. They are needed for the correct formation of centrosomes, the organelles at the poles of the spindle that can persist as microtubule organizing centers (MTOCs) into interphase. The ability to nucleate cytoplasmic microtubules (MTs) is a property of the surrounding pericentriolar material (PCM). The centriole has a dual life, existing not only as the core of the centrosome but also as the basal body, the structure that templates the formation of cilia and flagellae. Thus the structure and functions of the centriole, the centrosome, and the basal body have an impact upon many aspects of development and physiology that can readily be modeled in Drosophila Centrosomes are essential to give organization to the rapidly increasing numbers of nuclei in the syncytial embryo and for the spatially precise execution of cell division in numerous tissues, particularly during male meiosis. Although mitotic cell cycles can take place in the absence of centrosomes, this is an error-prone process that opens up the fly to developmental defects and the potential of tumor formation. Here, we review the structure and functions of the centriole, the centrosome, and the basal body in different tissues and cultured cells of Drosophila melanogaster, highlighting their contributions to different aspects of development and cell division.

Genetic and pharmacological inhibition of TTK impairs pancreatic cancer cell line growth by inducing lethal chromosomal instability

Pancreatic ductal adenocarcinoma, which accounts for the majority of pancreatic cancers, is a lethal disease with few therapeutic options. Genomic profiling of pancreatic ductal adenocarcinoma has identified a complex and heterogeneous landscape. Understanding the molecular characteristics of pancreatic ductal adenocarcinoma will facilitate the identification of potential therapeutic strategies. We analyzed the gene expression profiles of primary tumors from patients compared to normal pancreas and identified high co-overexpression of core components of the spindle assembly checkpoint, including the protein kinase TTK (also known as MPS-1). We found overexpression of TTK protein in a subset of pancreatic ductal adenocarcinoma primary tumors and cell lines. siRNA-mediated depletion or catalytic inhibition of TTK resulted in an aberrant cell cycle profile, multi- and micro-nucleation, induction of apoptosis, and decreased cell proliferation and transformed growth. Selective catalytic inhibition of TTK caused override of the spindle assembly checkpoint-induced cell cycle arrest. Interestingly, we identified ubiquitin specific peptidase 16 (Usp16), an ubiquitin hydrolase, as a phosphorylation substrate of TTK. Usp16 regulates chromosomal condensation and G2/M progression by deubiquitinating histone H2A and polo-like kinase 1. Phosphomimetic mutants of Usp16 show enhanced proteosomal degradation and may prolong the G2/M transition allowing for correction of replication errors. Taken together, our results suggest a critical role for TTK in preventing aneuploidy-induced cell death in pancreatic cancer.

Autophagy and the Cell Cycle: A Complex Landscape

Autophagy is a self-degradation pathway, in which cytoplasmic material is sequestered in double-membrane vesicles and delivered to the lysosome for degradation. Under basal conditions, autophagy plays a homeostatic function. However, in response to various stresses, the pathway can be further induced to mediate cytoprotection. Defective autophagy has been linked to a number of human pathologies, including neoplastic transformation, even though autophagy can also sustain the growth of tumor cells in certain contexts. In recent years, a considerable correlation has emerged between autophagy induction and stress-related cell-cycle responses, as well as unexpected roles for autophagy factors and selective autophagic degradation in the process of cell division. These advances have obvious implications for our understanding of the intricate relationship between autophagy and cancer. In this review, we will discuss our current knowledge of the reciprocal regulation connecting the autophagy pathway and cell-cycle progression. Furthermore, key findings involving nonautophagic functions for autophagy-related factors in cell-cycle regulation will be addressed.

The Hippo Pathway: A Master Regulatory Network Important in Development and Dysregulated in Disease

The Hippo Pathway is a master regulatory network that regulates proliferation, cell growth, stemness, differentiation, and cell death. Coordination of these processes by the Hippo Pathway throughout development and in mature organisms in response to diverse external and internal cues plays a role in morphogenesis, in controlling organ size, and in maintaining organ homeostasis. Given the importance of these processes, the Hippo Pathway also plays an important role in organismal health and has been implicated in a variety of diseases including eye disease, cardiovascular disease, neurodegeneration, and cancer. This review will focus on Drosophila reports that identified the core components of the Hippo Pathway revealing specific downstream biological outputs of this complicated network. A brief description of mammalian reports will complement review of the Drosophila studies. This review will also survey upstream regulation of the core components with a focus on feedback mechanisms.