P27 Kip1 Research Articles

ChemInform Abstract: Role of AMP‐Activated Protein Kinase in Cancer Therapy

AbstractReview: 133 refs.

CCN5/WISP-2 promotes growth arrest of triple-negative breast cancer cells through accumulation and trafficking of p27(Kip1) via Skp2 and FOXO3a regulation.

The matricellular protein CCN5/WISP-2 represents a promising target in triple-negative breast cancer (TNBC) because treatment or induced activation of CCN5 in TNBC cells promotes cell growth arrest at the G0/G1 phase, reduces cell proliferation and delays tumor growth in the xenograft model. Our studies found that the p27(Kip1) tumor suppressor protein is upregulated and relocalized to the nucleus from cytoplasm by CCN5 in these cells and that these two events (upregulation and relocalization of p27(Kip1)) are critical for CCN5-induced growth inhibition of TNBC cells. In the absence of CCN5, p27(Kip1) resides mostly in the cytoplasm, which is associated with the aggressive nature of cancer cells. Mechanistically, CCN5 inhibits Skp2 expression, which seems to stabilize the p27(Kip1) protein in these cells. On the other hand, CCN5 also recruits FOXO3a to mediate the transcriptional regulation of p27(Kip1). The recruitment of FOXO3a is achieved by the induction of its expression and activity through shifting from cytoplasm to the nucleus. Our data indicate that CCN5 blocks PI3K/AKT signaling to dephosphorylate at S318, S253 and Thr32 in FOXO3a for nuclear relocalization and activation of FOXO3a. Moreover, inhibition of α6β1 receptors diminishes CCN5 action on p27(Kip1) in TNBC cells. Collectively, these data suggest that CCN5 effectively inhibits TNBC growth through the accumulation and trafficking of p27(Kip1) via Skp2 and FOXO3a regulation, and thus, activation of CCN5 may have the therapeutic potential to kill TNBC.

A selective microRNA-based strategy inhibits restenosis while preserving endothelial function.

Drugs currently approved to coat stents used in percutaneous coronary interventions do not discriminate between proliferating vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). This lack of discrimination delays reendothelialization and vascular healing, increasing the risk of late thrombosis following angioplasty. We developed a microRNA-based (miRNA-based) approach to inhibit proliferative VSMCs, thus preventing restenosis, while selectively promoting reendothelialization and preserving EC function. We used an adenoviral (Ad) vector that encodes cyclin-dependent kinase inhibitor p27(Kip1) (p27) with target sequences for EC-specific miR-126-3p at the 3' end (Ad-p27-126TS). Exogenous p27 overexpression was evaluated in vitro and in a rat arterial balloon injury model following transduction with Ad-p27-126TS, Ad-p27 (without miR-126 target sequences), or Ad-GFP (control). In vitro, Ad-p27-126TS protected the ability of ECs to proliferate, migrate, and form networks. At 2 and 4 weeks after injury, Ad-p27-126TS-treated animals exhibited reduced restenosis, complete reendothelialization, reduced hypercoagulability, and restoration of the vasodilatory response to acetylcholine to levels comparable to those in uninjured vessels. By incorporating miR-126-3p target sequences to leverage endogenous EC-specific miR-126, we overexpressed exogenous p27 in VSMCs, while selectively inhibiting p27 overexpression in ECs. Our proof-of-principle study demonstrates the potential of using a miRNA-based strategy as a therapeutic approach to specifically inhibit vascular restenosis while preserving EC function.

Healing the injured vessel wall using microRNA-facilitated gene delivery.

Drug-eluting stents have emerged as potent weapons in the treatment of patients with symptomatic coronary artery disease by reducing restenosis rates; however, a significant clinical consequence of these stents is delayed reendothelialization, which may increase the risk of late stent thrombosis. In this issue of the JCI, Santulli and colleagues generated an adenovirus that expresses the cyclin-dependent kinase inhibitor p27(Kip1) (p27) and bears four tandem copies of target sequences for the endothelial cell-enriched microRNA (miRNA) miR-126-3p (Ad-p27-126TS) in an attempt to specifically reduce proliferation of vascular smooth muscle cells, but not endothelial cells. Indeed, delivery of Ad-p27-126TS to balloon-injured arteries in rats not only induced faster and more complete reendothelialization, but also effectively improved neointimal hyperplasia, hypercoagulability, and vasoreactivity. Collectively, these findings provide a cogent foundation for the potential therapeutic use of miRNA-facilitated gene delivery strategies to heal vessel wall injury.

P27 kip1 haplo-insufficiency improves cardiac function in early-stages of myocardial infarction by protecting myocardium and increasing angiogenesis by promoting IKK activation.

p27kip1 (p27) is widely known as a potent cell cycle inhibitor in several organs, especially in the heart. However, its role has not been fully defined during the early phase of myocardial infarction (MI). In this study, we investigated the relationships between p27, vascular endothelial growth factor/hepatocyte growth factor (VEGF/HGF) and NF-κB in post-MI cardiac function repair both in vivo and in the hypoxia/ischemia-induced rat myocardiocyte model. In vivo, haplo-insufficiency of p27 improved cardiac function, diminished the infarct zone, protected myocardiocytes and increased angiogenesis by enhancing the production of VEGF/HGF. In vitro, the presence of conditioned medium from hypoxia/ischemia-induced p27 knockdown myocardiocytes reduced the injury caused by hypoxia/ischemia in myocardiocytes, and this effect was reversed by VEGF/HGF neutralizing antibodies, consistent with the cardioprotection being due to VEGF/HGF secretion. We also observed that p27 bound to IKK and that p27 haplo-insufficiency promoted IKK/p65 activation both in vivo and in vitro, thereby inducing the NF-κB downstream regulator, VEGF/HGF. Furthermore, IKKi and IKK inhibitor negated the effect of VEGF/HGF. Therefore, we conclude that p27 haplo-insufficiency protects against heart injury by VEGF/HGF mediated cardioprotection and increased angiogenesis through promoting IKK activation.

Overexpression or silencing of FOXO3a affects proliferation of endothelial progenitor cells and expression of cell cycle regulatory proteins.

Endothelial dysfunction is involved in the pathogenesis of many cardiovascular diseases such as atherosclerosis. Endothelial progenitor cells (EPCs) have been considered to be of great significance in therapeutic angiogenesis. Furthermore, the Forkhead box O (FOXO) transcription factors are known to be important regulators of cell cycle. Therefore, we investigated the effects of changes in FOXO3a activity on cell proliferation and cell cycle regulatory proteins in EPCs. The constructed recombinant adenovirus vectors Ad-TM (triple mutant)-FOXO3a, Ad-shRNA-FOXO3a and the control Ad-GFP were transfected into EPCs derived from human umbilical cord blood. Assessment of transfection efficiency using an inverted fluorescence microscope and flow cytometry indicated a successful transfection. Additionally, the expression of FOXO3a was markedly increased in the Ad-TM-FOXO3a group but was inhibited in the Ad-shRNA-FOXO3a group as seen by western blotting. Overexpression of FOXO3a suppressed EPC proliferation and modulated expression of the cell cycle regulatory proteins including upregulation of the cell cycle inhibitor p27kip1 and downregulation of cyclin-dependent kinase 2 (CDK2), cyclin D1 and proliferating cell nuclear antigen (PCNA). In the Ad-shRNA-FOXO3a group, the results were counter-productive. Furthermore, flow cytometry for cell cycle analysis suggested that the active mutant of FOXO3a caused a noticeable increase in G1- and S-phase frequencies, while a decrease was observed after FOXO3a silencing. In conclusion, these data demonstrated that FOXO3a could possibly inhibit EPC proliferation via cell cycle arrest involving upregulation of p27kip1 and downregulation of CDK2, cyclin D1 and PCNA.

A mechanistic role for the chromatin modulator, NAP1L1, in pancreatic neuroendocrine neoplasm proliferation and metastases.

BackgroundThe chromatin remodeler NAP1L1, which is upregulated in small intestinal neuroendocrine neoplasms (NENs), has been implicated in cell cycle progression. As p57Kip2 (CDKN1C), a negative regulator of proliferation and a tumor suppressor, is controlled by members of the NAP1 family, we tested the hypothesis that NAP1L1 may have a mechanistic role in regulating pancreatic NEN proliferation through regulation of p57Kip2.ResultsNAP1L1 silencing (siRNA and shRNA/lipofectamine approach) decreased proliferation through inhibition of mechanistic (mammalian) target of rapamycin pathway proteins and their phosphorylation (p < 0.05) in the pancreatic neuroendocrine neoplasm cell line BON in vitro (p < 0.0001) and resulted in significantly smaller (p < 0.05) and lighter (p < 0.05) tumors in the orthotopic pancreatic NEN mouse model. Methylation of the p57 Kip2 promoter was decreased by NAP1L1 silencing (p < 0.05), and expression of p57Kip2 (transcript and protein) was upregulated. For methylation of the p57 Kip2 promoter, NAP1L1 bound directly to the promoter (−164 to +21, chromatin immunoprecipitation). In 43 pancreatic NEN samples (38 primaries and 5 metastasis), NAP1L1 was over-expressed in metastasis (p < 0.001), expression which was inversely correlated with p57Kip2 (p < 0.01) on mRNA and protein levels. Menin was not differentially expressed.ConclusionNAP1L1 is over-expressed in pancreatic neuroendocrine neoplasm metastases and epigenetically promotes cell proliferation through regulation of p57 Kip2 promoter methylation.

Extracellular signal-regulated kinases 1/2 and Akt contribute to triclosan-stimulated proliferation of JB6 Cl 41-5a cells.

Triclosan is a broad spectrum anti-bacterial agent widely used in many personal care products, household items, medical devices, and clinical settings. Human exposure to triclosan is mainly through oral and dermal routes. In previous studies, we found that sub-chronic dermal exposure of B6C3F1 mice to triclosan induced epidermal hyperplasia and focal necrosis; however, the mechanisms for these responses remain elusive. In this study, using mouse epidermis-derived JB6 Cl 41-5a cells, we found that triclosan stimulated cell growth in a concentration- and time-dependent manner. Enhanced cell proliferation was demonstrated by a substantial increase in the percentage of BrdU-positive cells, an elevation in the protein levels of cyclin D1 and cyclin A, and a reduction in the protein level of p27(Kip1). Western blotting analysis revealed that triclosan induced the activation of extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), p38, and Akt. Pre-treatment of the cells with PD184352, an inhibitor of the upstream kinase MEK1/2, or with wortmannin, an inhibitor of phosphoinositide 3-kinase, blocked triclosan-mediated phosphorylation of ERK1/2 and Akt, respectively, and substantially suppressed triclosan-stimulated cell proliferation, whereas the JNK inhibitor SP600125 or the p38 inhibitor SB203580 had little to no effect on triclosan-stimulated cell proliferation. The phosphorylation activation of ERK1/2 and Akt was further confirmed on the skin of mice dermally administered triclosan. These data suggest that the activation of ERK1/2 and Akt is involved in triclosan-stimulated proliferation of JB6 Cl 41-5a cells.

Secreted protein acidic and rich in cysteine inhibits the growth of human pancreatic cancer cells with G1 arrest induction.

Aberrant secreted protein acidic and rich in cysteine (SPARC) expression has been reported to play an important role in the tumor development. However, the pattern and the role of SPARC in pancreatic cancer remain largely unknown. Therefore, we further deciphered the role of SPARC played in pancreatic cancer. We first evaluated the SPARC expression in human pancreatic cancer tissues and pancreatic cancer cells. Then we forced expression and silenced SPARC expression in pancreatic cancer cell lines MIA PaCa2 and PANC-1, respectively, using lentivirus vectors. We characterized the stable cells in vitro. In this study, we found that SPARC expression was weak in cancer cells in specimens which negatively correlated with the expression level of phosphorylated pRB and poorer outcome. Moreover, our results demonstrated that SPARC negatively regulated pancreatic cell growth in vitro. Furthermore, we disclosed that the activation of p53 and p27(Kip1) may involve in the effect of SPARC on pancreatic cancer cells. SPARC is downregulated in pancreatic cancer cells and retards the growth of pancreatic cancer cell. Taken together, these results indicate SPARC may be a potential target for pancreatic cancer therapy.

Monoclonal antibody targeting of the cell surface molecule TM4SF5 inhibits the growth of hepatocellular carcinoma.

The cell surface transmembrane receptor TM4SF5 has been implicated in hepatocellular carcinoma (HCC), but its candidacy as a therapeutic target has not been evaluated. Building on findings that immunization with a peptide vaccine targeting human TM4SF5 can exert prophylactic and therapeutic effects in a murine model of HCC, we developed a monoclonal antibody to characterize expression of TM4SF5 in HCC and to target its function there as an anticancer strategy. We found that the antibody modulated cell signaling in HCC cells in vitro, reducing cell motility, modulating E-cadherin expression, altering p27(kip1) localization, and increasing RhoA activity. Using a mouse xenograft model of human HCC, we documented the in vivo efficacy of the antibody, which suppressed tumor growth in either tumor prevention or treatment designs. Our work offers a preclinical proof of concept for TM4SF5 as a promising target for antibody therapeutics to treat HCC. Cancer Res; 74(14); 3844-56. ©2014 AACR.

Antagonistic regulation of p57kip2 by Hes/Hey downstream of Notch signaling and muscle regulatory factors regulates skeletal muscle growth arrest.

A central question in development is to define how the equilibrium between cell proliferation and differentiation is temporally and spatially regulated during tissue formation. Here, we address how interactions between cyclin-dependent kinase inhibitors essential for myogenic growth arrest (p21(cip1) and p57(kip2)), the Notch pathway and myogenic regulatory factors (MRFs) orchestrate the proliferation, specification and differentiation of muscle progenitor cells. We first show that cell cycle exit and myogenic differentiation can be uncoupled. In addition, we establish that skeletal muscle progenitor cells require Notch signaling to maintain their cycling status. Using several mouse models combined with ex vivo studies, we demonstrate that Notch signaling is required to repress p21(cip1) and p57(kip2) expression in muscle progenitor cells. Finally, we identify a muscle-specific regulatory element of p57(kip2) directly activated by MRFs in myoblasts but repressed by the Notch targets Hes1/Hey1 in progenitor cells. We propose a molecular mechanism whereby information provided by Hes/Hey downstream of Notch as well as MRF activities are integrated at the level of the p57(kip2) enhancer to regulate the decision between progenitor cell maintenance and muscle differentiation.

Global Programmed Switch in Neural Daughter Cell Proliferation Mode Triggered by a Temporal Gene Cascade

During central nervous system (CNS) development, progenitors typically divide asymmetrically, renewing themselves while budding off daughter cells with more limited proliferative potential. Variation in daughter cell proliferation has a profound impact on CNS development and evolution, but the underlying mechanisms remain poorly understood. We find that Drosophila embryonic neural progenitors (neuroblasts) undergo a programmed daughter proliferation mode switch, from generating daughters that divide once (type I) to generating neurons directly (type 0). This typeI>0 switch is triggered by activation of Dacapo (mammalian p21(CIP1)/p27(KIP1)/p57(Kip2)) expression in neuroblasts. In the thoracic region, Dacapo expression is activated by the temporal cascade (castor) and the Hox gene Antennapedia. In addition, castor, Antennapedia, and the late temporal gene grainyhead act combinatorially to control the precise timing of neuroblast cell-cycle exit by repressing Cyclin E and E2f. This reveals a logical principle underlying progenitor and daughter cell proliferation control in the Drosophila CNS.

Activation of the receptor for advanced glycation end products induces nuclear inhibitor of protein phosphatase-1 suppression

The activation of the receptor for advanced glycation end products (RAGE) is involved in the development of diabetic nephropathy. Analysis of protein phosphatase-1 indicated that advanced glycation end products did not affect its expression, but increased its phosphatase activity. Using differential display analysis we previously demonstrated that stimulation of RAGE in podocytes modulates the expression of numerous genes, among others nuclear inhibitor of protein phosphatase-1 (NIPP1). Here we found that silencing of NIPP1 induced podocyte hypertrophy, cell cycle arrest, and significantly increased protein phosphatase-1 activity. NIPP1 downregulation was associated with increased p27(Kip1) protein expression. Reporter assays revealed a transcriptional activation of nuclear factor-κB in podocytes after suppression of NIPP1. The protein level of NIPP1 was also significantly reduced in podocytes of diabetic mice. Blocking the RAGE in vivo by a soluble analog elevated the NIPP1 protein in podocytes of diabetic mice. Thus, activation of the RAGE by advanced glycation end products or other ligands suppresses NIPP1 expression in diabetic nephropathy, contributes to podocyte hypertrophy, and glomerular inflammation.

Maternal diabetes modulates kidney formation in murine progeny: the role of hedgehog interacting protein (HHIP).

We hypothesised that maternal diabetes impairs kidney formation in offspring via augmented expression of hedgehog interacting protein (HHIP). Our gene-array results were performed in neonatal kidneys from our murine model of maternal diabetes and indicated that Hhip expression was significantly modulated by maternal diabetes. We systematically examined the functional role of HHIP in kidney formation in our murine maternal diabetes model and elucidated the potential mechanisms related to dysnephrogenesis in vitro. The kidneys of the offspring of diabetic dams, compared with those of the offspring of control non-diabetic dams, showed retardation of development--small kidneys and less ureteric bud (UB) branching morphogenesis. Augmented HHIP expression was observed in the offspring of diabetic dams, initially localised to differentiated metanephric mesenchyme and UB epithelium and subsequently in maturing glomerular endothelial and tubulointerstitial cells. The heightened HHIP targeting TGF-β1 signalling was associated with dysmorphogenesis. In vitro, HHIP overexpression decreased sonic hedgehog and paired box gene 2 proteins (SHH and PAX2, respectively) and increased transcriptional nuclear factor-kappa B (NFκB, p50/p65), phosphorylation of p53, and TGF-β1 expression. In contrast, overexpression of PAX2 inhibited HHIP and NFκB and activated SHH, N-myc and p27(Kip1) expression. Moreover, high glucose stimulated HHIP expression, and then targeted TGF-β1 signalling. Thus, PAX2, via a negative autocrine feedback mechanism, attenuated the stimulatory effect of high glucose on HHIP expression. Maternal diabetes modulates kidney formation in young progeny mediated, at least in part, via augmented HHIP expression.

Time and flow-dependent changes in the p27kip1 gene network drive maladaptive vascular remodeling

Although clinical studies have identified that a single nucleotide polymorphism in the p27(kip1) gene is associated with success or failure after vein bypass grafting, the underlying mechanisms for this difference are not well defined. Using a high-throughput approach in a flow-dependent vein graft model, we explored the differences in p27(kip1)-related genes that drive the enhanced hyperplastic response under low-flow conditions. Bilateral rabbit carotid artery interposition grafts with jugular vein were placed with a unilateral distal outflow branch ligation to create differential flow states. Grafts were harvested at 2 hours and at 1, 3, 7, 14, and 28 days after implantation, measured for neointimal area, and assayed for cell proliferation. Whole-vessel messenger RNA was isolated and analyzed using an Affymetrix (Santa Clara, Calif) gene array platform. Ingenuity Pathway Analysis (Ingenuity, Redwood City, Calif) was used to identify the gene networks surrounding p27(kip1). This gene set was then analyzed for temporal expression changes after graft placement and for differential expression in the alternate flow conditions. Outflow branch ligation resulted in an eightfold difference in mean flow rates throughout the 28-day perfusion period (P < .001). Flow reduction led to a robust hyperplastic response, resulting in a significant increase in intimal area by 7 days (0.13 ± 0.04 mm(2) vs 0.014 ± 0.006 mm(2); P < .005) and progressive growth to 28 days (1.37 ± 0.05 mm(2) vs 0.39 ± 0.06 mm(2); P < .001). At 7 days, low-flow grafts demonstrated a burst of actively dividing intimal cells (36.4 ± 9.4 cells/mm(2) vs 11.5 ± 1.9 cells/mm(2); P = .04). Sixty-five unique genes within the microarray were identified as components of the p27(kip1) network. At a false discovery rate of 0.05, 26 genes demonstrated significant temporal changes, and two dominant patterns of expression were identified. Class comparison analysis identified differential expression of 11 genes at 2 hours and seven genes and 14 days between the high-flow and low-flow grafts (P < .05). At 2 hours, oncostatin M and cadherin 1 were the most differentially expressed. Cadherin 1 and protein kinase B exhibited the greatest differential expression at 14 days. Alterations in flow and shear stress result in divergent patterns of vein graft remodeling. Associated with the dramatic increase in neointimal expansion observed in low-flow vs high-flow grafts is a subset of differentially expressed p27(kip1)-associated genes that correlate with critical stages in the adaptive response. These represent potential biologic targets whose activity may be altered to augment maladaptive vascular remodeling.

Molecular pathways: turning proteasomal protein degradation into a unique treatment approach.

Cancer treatment regimens have evolved from single cytotoxic substances affecting all proliferative tissues toward antibodies and kinase inhibitors targeting tumor-specific pathways. Treatment efficacy and cancer survival have improved overall, and side effects have become less frequent. The ubiquitin-proteasome system-mediated proteasomal protein degradation is the most critical pathway to regulate the quantity of signal proteins involved in carcinogenesis and tumor progression. These processes are, as well as protein recycling, highly regulated and offer targets for biomarker and drug development. Unspecific proteasome inhibitors such as bortezomib and carfilzomib have shown clinical efficacy and are approved for clinical use. Inhibitors of more substrate-specific enzymes of degradation processes are being developed and are now in early clinical trials. The novel compounds focus on the degradation of key regulatory proteins such as p53, p27(Kip1), and ß-catenin, and inhibitors specific for growth factor receptor kinase turnover are in preclinical testing.

P27 Protein Protects Metabolically Stressed Cardiomyocytes from Apoptosis by Promoting Autophagy

p27(Kip1) (p27), a key regulator of cell division, has been implicated in autophagy of cancer cells. However, its role in autophagy, the evolutionarily conserved catabolic process that enables cells to remove unwanted proteins and damaged organelles, had not been examined in the heart. Here we report that ectopic delivery of a p27 fusion protein (TAT-p27) was sufficient to induce autophagy in neonatal rat ventricular cardiomyocytes in vitro, under basal conditions and after glucose deprivation. Conversely, lentivirus-delivered shRNA against p27 successfully reduced p27 levels and suppressed basal and glucose-deprived levels of autophagy in cardiomyocytes in vitro. Glucose deprivation mimics myocardial ischemia and induces apoptosis in cardiomyocytes. During glucose deprivation, TAT-p27 inhibited apoptosis, whereas down-regulation of p27 decreased survival of cardiomyocytes. However, inhibition of autophagy by pharmacological (3-methyladenine, chloroquine, or bafilomycin A1) or genetic approaches (siRNA-mediated knockdown of Atg5) sensitized cardiomyocytes to glucose deprivation-induced apoptosis, even in the presence of TAT-p27. TAT-p27 was also able to provoke greater levels of autophagy in resting and fasting cardiomyocytes in vivo. Further, TAT-p27 enhanced autophagy and repressed cardiomyocytes apoptosis, improved cardiac function, and reduced infarct size following myocardial infarction. Again, these effects were lost when cardiac autophagy in vivo was blocked by chloroquine. Taken together, these data show that p27 positively regulates cardiac autophagy in vitro and in vivo, at rest and after metabolic stress, and that TAT-p27 inhibits apoptosis by promoting autophagy in glucose-deprived cardiomyocytes in vitro and in post-myocardial infarction hearts in vivo.

Synemin: an evolving role in tumor growth and progression.

Dear Editor, I read with great interest the recent article by Russ et al. [1]. Synemin plays a major modulatory role in tumor growth and progression in different systemic malignancies. Synemin plays an important role in neurological tumors such as astrocytomas and glioblastomas. For instance, the leading edge of astrocytomas exhibit upregulated synemin levels. This has been confirmed by Pan et al. in a recent study [2]. As a result, simultaneous accentuation of actin and alpha-actin is seen in the leading edge. This further augments tumor cell motility and migration thuds promoting tumor growth. On the other hand, synemin silencing markedly decelerates tumor progression in astrocytomas [3]. In addition, tumor size is significantly attenuated by virtue of decreased rumor proliferation and increased tumoral apoptosis secondary to the silencing of synemin. Tumor cell proliferation in glioblastomas is also significantly augmented by synemin. It mediates this role by forming a complex with “protein phosphatase type-2A” [4]. The formation of this complex results in unhindered and augmented activation of Akt. In addition, synemin attenuates the expression of p21 (Cip1) within the malignant glial tissue [5]. A similar negative impact is seen on p27 (Kip1). The net result is augmented and accelerated G1/S phase transition [6]. In addition, survival of clone stem cells within the glioblastomas is significantly accentuated by synemin. Not surprisingly, synemin silencing results in hypo-phosphorylation of Rb and accentuated G1 phase arrest [7]. Synemin also influences tumor progression in mammary malignancies [8]. For instance, nearly 57 % of breast carcinomas exhibit loss of synemin expression. In 27 % of breast cancers, methylation of the synemin promoter is typically seen [9]. A close relationship exists between loss of synemin expression and synemin promoter methylation. Accentuated synemin promoter methylation is associated with augmented lymph node metastasis. A similar close and direct relationship has been seen between tumor grade, survival rate, and synemin promoter methylation [10]. For instance, the “recurrence free survival” is significantly attenuated following accentuated methylation of the synemin promoter. Synemin also plays an important role in tumor progression in hepatocellular malignancies [11]. For instance, malignant hepatic tissue exhibits attenuated synemin expression in contrast to higher levels noted in adjoining benign hepatic tissue [12]. The above examples clearly illustrate that synemin has a major role to play in the progression of systemic malignancies. Very little research has been done so far regarding its role in neoplastic growth. Further studies are urgently needed to further evaluate its potential significant role in oncology.

Brachyury regulates proliferation of cancer cells via a p27Kip1-dependent pathway.

The T-box transcription factor Brachyury is expressed in a number of tumour types and has been demonstrated to have cancer inducing properties. To date, it has been linked to cancer associated induction of epithelial to mesenchymal transition, tumour metastasis and expression of markers for cancer stem-like cells. Taken together, these findings indicate that Brachyury plays an important role in the progression of cancer, although the mechanism through which it functions is poorly understood. Here we show that Brachyury regulates the potential of Brachyury-positive colorectal cancer cells to proliferate and reduced levels of Brachyury result in inhibition of proliferation, with features consistent with the cells entering a quiescent-like state. This inhibition of proliferation is dependent upon p27Kip1 demonstrating that Brachyury acts to modulate cellular proliferative fate in colorectal cancer cells in a p27Kip1-dependent manner. Analysis of patient derived colorectal tumours reveals a heterogeneous localisation of Brachyury (in the nucleolus, nucleus and cytoplasm) indicating the potential complexity of the regulatory role of Brachyury in solid colorectal tumours.

Cdk5 regulates multiple cellular events in neural development, function and disease.

Cyclin-dependent kinases (CDKs) generally regulate cell proliferation in dividing cells, including neural progenitors. In contrast, an unconventional CDK, Cdk5, is predominantly activated in post-mitotic cells, and involved in various cellular events, such as microtubule and actin cytoskeletal organization, cell-cell and cell-extracellular matrix adhesions, and membrane trafficking. Interestingly, recent studies have indicated that Cdk5 is associated with several cell cycle-related proteins, Cyclin-E and p27(kip1) . Taking advantage of multiple functionality, Cdk5 plays important roles in neuronal migration, layer formation, axon elongation and dendrite arborization in many regions of the developing brain, including cerebral cortex and cerebellum. Cdk5 is also required for neurogenesis at least in the cerebral cortex. Furthermore, Cdk5 is reported to control neurotransmitter release at presynaptic sites, endocytosis of the NMDA receptor at postsynaptic sites and dendritic spine remodeling, and thereby regulate synaptic plasticity and memory formation and extinction. In addition to these physiological roles in brain development and function, Cdk5 is associated with many neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. In this review, I will introduce the physiological and pathological roles of Cdk5 in mammalian brains from the viewpoint of not only in vivo phenotypes but also its molecular and cellular functions.