RSK1 drives p27Kip1 phosphorylation at T198 to promote RhoA inhibition and increase cell motility

C-terminally phosphorylated p27 activates self-renewal driver genes to program cancer stem cell expansion, mammary hyperplasia and cancer

In many cancers, a stem-like cell subpopulation mediates tumor initiation, dissemination and drug resistance. Here, we report that cancer stem cell (CSC) abundance is transcriptionally regulated by C-terminally phosphorylated p27 (p27pT157pT198). Mechanistically, this arises through p27 co-recruitment with STAT3/CBP to gene regulators of CSC self-renewal including MYC, the Notch ligand JAG1, and ANGPTL4. p27pTpT/STAT3 also recruits a SIN3A/HDAC1 complex to co-repress the Pyk2 inhibitor, PTPN12. Pyk2, in turn, activates STAT3, creating a feed-forward loop increasing stem-like properties in vitro and tumor-initiating stem cells in vivo. The p27-activated gene profile is over-represented in STAT3 activated human breast cancers. Furthermore, mammary transgenic expression of phosphomimetic, cyclin-CDK-binding defective p27 (p27CK-DD) increases mammary duct branching morphogenesis, yielding hyperplasia and microinvasive cancers that can metastasize to liver, further supporting a role for p27pTpT in CSC expansion. Thus, p27pTpT interacts with STAT3, driving transcriptional programs governing stem cell expansion or maintenance in normal and cancer tissues.

The Role of p90 Ribosomal S6 Kinase (RSK) in Tyrosine Kinase Inhibitor (TKI)-Induced Cardiotoxicity

Targeted therapy, such as tyrosine kinase inhibitors (TKIs), has been approved to manage various cancer types. However, TKI-induced cardiotoxicity is a limiting factor for their use. This issue has raised the need for investigating potential cardioprotective techniques to be combined with TKIs. Ribosomal S6-kinases (RSKs) are a downstream effector of the mitogen-activated-protein-kinase (MAPK) pathway; specific RSK isoforms, such as RSK1 and RSK2, have been expressed in cancer cells, in which they increase tumour proliferation. Selective targeting of those isoforms would result in tumour suppression. Moreover, activation of RSKs expressed in the heart has resulted in cardiac hypertrophy and arrhythmia; thus, inhibiting RSKs would result in cardio-protection. This review article presents an overview of the usefulness of RSK inhibitors that can be novel agents to be assessed in future research for their effect in reducing cancer proliferation, as well as protecting the heart from cardiotoxicity induced by TKIs.

RSK1 and RSK2 serine/threonine kinases regulate different transcription programs in cancer

The 90 kDa ribosomal S6 kinases (RSKs) are serine threonine kinases comprising four isoforms. The isoforms can have overlapping functions in regulation of migration, invasion, proliferation, survival, and transcription in various cancer types. However, isoform specific differences in RSK1 versus RSK2 functions in gene regulation are not yet defined. Here, we delineate ribosomal S6 kinases isoform-specific transcriptional gene regulation by comparing transcription programs in RSK1 and RSK2 knockout cells using microarray analysis. Microarray analysis revealed significantly different mRNA expression patterns between RSK1 knockout and RSK2 knockout cell lines. Importantly some of these functions have not been previously recognized. Our analysis revealed RSK1 has specific roles in cell adhesion, cell cycle regulation and DNA replication and repair pathways, while RSK2 has specific roles in the immune response and interferon signaling pathways. We further validated that the identified gene sets significantly correlated with mRNA datasets from cancer patients. We examined the functional significance of the identified transcriptional programs using cell assays. In alignment with the microarray analysis, we found that RSK1 modulates the mRNA and protein expression of Fibronectin1, affecting cell adhesion and CDK2, affecting S-phase arrest in the cell cycle, and impairing DNA replication and repair. Under similar conditions, RSK2 showed increased ISG15 transcriptional expression, affecting the immune response pathway and cytokine expression. Collectively, our findings revealed the occurrence of RSK1 and RSK2 specific transcriptional regulation, defining separate functions of these closely related isoforms.

Estrone, the major postmenopausal estrogen, binds ERa to induce SNAI2, epithelial-to-mesenchymal transition, and ER+ breast cancer metastasis

Recent work showed that the dominant post-menopausal estrogen, estrone, cooperates with nuclear factor κB (NF-κB) to stimulate inflammation, while pre-menopausal 17β-estradiol opposes NF-κB. Here, we show that post-menopausal estrone, but not 17β-estradiol, activates epithelial-to-mesenchymal transition (EMT) genes to stimulate breast cancer metastasis. HSD17B14, which converts 17β-estradiol to estrone, is higher in cancer than normal breast tissue and in metastatic than primary cancers and associates with earlier metastasis. Treatment with estrone, but not 17β-estradiol, and HSD17B14 overexpression both stimulate an EMT, matrigel invasion, and lung, bone, and liver metastasis in estrogen-receptor-positive (ER+) breast cancer models, while HSD17B14 knockdown reverses the EMT. Estrone:ERα recruits CBP/p300 to the SNAI2 promoter to induce SNAI2 and stimulate an EMT, while 17β-estradiol:ERα recruits co-repressors HDAC1 and NCOR1 to this site. Present work reveals novel differences in gene regulation by these estrogens and the importance of estrone to ER+ breast cancer progression. Upon loss of 17β-estradiol at menopause, estrone-liganded ERα would promote ER+ breast cancer invasion and metastasis.

ERK2 signaling regulates cell-cell adhesion of epithelial cells and enhances growth factor-induced cell scattering

The ERK signaling pathway, consisting of core protein kinases Raf, MEK and effector kinases ERK1/2, regulates various biological outcomes such as cell proliferation, differentiation, apoptosis, or cell migration. Signal transduction through the ERK signaling pathway is tightly controlled at all levels of the pathway. However, it is not well understood whether ERK pathway signaling can be modulated by the abundance of ERK pathway core kinases. In this study, we investigated the effects of low-level overexpression of the ERK2 isoform on the phenotype and scattering of cuboidal MDCK epithelial cells growing in discrete multicellular clusters. We show that ERK2 overexpression reduced the vertical size of lateral membranes that contain cell-cell adhesion complexes. Consequently, ERK2 overexpressing cells were unable to develop cuboidal shape, remained flat with increased spread area and intercellular adhesive contacts were present only on the basal side. Interestingly, ERK2 overexpression was not sufficient to increase phosphorylation of multiple downstream targets including transcription factors and induce global changes in gene expression, namely to increase the expression of pro-migratory transcription factor Fra1. However, ERK2 overexpression enhanced HGF/SF-induced cell scattering as these cells scattered more rapidly and to a greater extent than parental cells. Our results suggest that an increase in ERK2 expression primarily reduces cell-cell cohesion and that weakened intercellular adhesion synergizes with upstream signaling in the conversion of the multicellular epithelium into single migrating cells. This mechanism may be clinically relevant as the analysis of clinical data revealed that in one type of cancer, pancreatic adenocarcinoma, ERK2 overexpression correlates with a worse prognosis.

p27, The Cell Cycle and Alzheimer´s Disease

The cell cycle consists of successive events that lead to the generation of new cells. The cell cycle is regulated by different cyclins, cyclin-dependent kinases (CDKs) and their inhibitors, such as p27^Kip1. At the nuclear level, p27^Kip1 has the ability to control the evolution of different phases of the cell cycle and oppose cell cycle progression by binding to CDKs. In the cytoplasm, diverse functions have been described for p27^Kip1, including microtubule remodeling, axonal transport and phagocytosis. In Alzheimer’s disease (AD), alterations to cycle events and a purported increase in neurogenesis have been described in the early disease process before significant pathological changes could be detected. However, most neurons cannot progress to complete their cell division and undergo apoptotic cell death. Increased levels of both the p27^Kip1 levels and phosphorylation status have been described in AD. Increased levels of Aβ42, tau hyperphosphorylation or even altered insulin signals could lead to alterations in p27^Kip1 post-transcriptional modifications, causing a disbalance between the levels and functions of p27^Kip1 in the cytoplasm and nucleus, thus inducing an aberrant cell cycle re-entry and alteration of extra cell cycle functions. Further studies are needed to completely understand the role of p27^Kip1 in AD and the therapeutic opportunities associated with the modulation of this target.

From neural stem cells to glioblastoma: A natural history of GBM recapitulated in vitro

Due to its aggressive and invasive nature glioblastoma (GBM), the most common and aggressive primary brain tumour in adults, remains almost invariably lethal. Significant advances in the last several years have elucidated much of the molecular and genetic complexities of GBM. However, GBM exhibits a vast genetic variation and a wide diversity of phenotypes that have complicated the development of effective therapeutic strategies. This complex pathogenesis makes necessary the development of experimental models that could be used to further understand the disease, and also to provide a more realistic testing ground for potential therapies. In this report, we describe the process of transformation of primary mouse embryo astrocytes into immortalized cultures with neural stem cell characteristics, that are able to generate GBM when injected into the brain of C57BL/6 mice, or heterotopic tumours when injected IV. Overall, our results show that oncogenic transformation is the fate of NSC if cultured for long periods in vitro. In addition, as no additional hit is necessary to induce the oncogenic transformation, our model may be used to investigate the pathogenesis of gliomagenesis and to test the effectiveness of different drugs throughout the natural history of GBM.

Discovery, Optimization, and Structure-Activity Relationship Study of Novel and Potent RSK4 Inhibitors as Promising Agents for the Treatment of Esophageal Squamous Cell Carcinoma

Ribosomal S6 protein kinase 4 (RSK4) was identified to be a promising target for the treatment of esophageal squamous cell carcinoma (ESCC) in our previous research, whose current treatments are primarily chemotherapy and radiotherapy due to the lack of targeted therapy. However, few potent and specific RSK4 inhibitors are reported. In this study, a series of 1,4-dihydro-2H-pyrimido[4,5-d][1,3]oxazin-2-ones derivatives were designed and synthesized as novel and potent RSK4 inhibitors. Compound 14f was identified with potent RSK4 inhibitory activity both in vitro and in vivo. 14f significantly inhibited the proliferation and invasion of ESCC cells in vitro with IC50 values of 0.57 and 0.98 μM, respectively. It dose dependently inhibited the phosphorylation of RSK4 downstream substrates while exerting little effect on the substrates of RSK1-3 in ESCC cells. The markedly suppressed tumor growth and no observed toxicity to main organs in the ESCC xenograft mouse model suggested 14f to be a promising RSK4-targeting agent for ESCC treatment.

p27Kip1, an Intrinsically Unstructured Protein with Scaffold Properties

The Cyclin-dependent kinase (CDK) regulator p27^Kip1 is a gatekeeper of G1/S transition. It also regulates G2/M progression and cytokinesis completion, via CDK-dependent or -independent mechanisms. Recently, other important p27^Kip1 functions have been described, including the regulation of cell motility and migration, the control of cell differentiation program and the activation of apoptosis/autophagy. Several factors modulate p27^Kip1 activities, including its level, cellular localization and post-translational modifications. As a matter of fact, the protein is phosphorylated, ubiquitinated, SUMOylated, O-linked N-acetylglicosylated and acetylated on different residues. p27^Kip1 belongs to the family of the intrinsically unstructured proteins and thus it is endowed with a large flexibility and numerous interactors, only partially identified. In this review, we look at p27^Kip1 properties and ascribe part of its heterogeneous functions to the ability to act as an anchor or scaffold capable to participate in the construction of different platforms for modulating cell response to extracellular signals and allowing adaptation to environmental changes.

RSK Isoforms in Acute Myeloid Leukemia

Ribosomal S6 Kinases (RSKs) are a group of serine/threonine kinases that function downstream of the Ras/Raf/MEK/ERK signaling pathway. Four RSK isoforms are directly activated by ERK1/2 in response to extracellular stimuli including growth factors, hormones, and chemokines. RSKs phosphorylate many cytosolic and nuclear targets resulting in the regulation of diverse cellular processes such as cell proliferation, survival, and motility. In hematological malignancies such as acute myeloid leukemia (AML), RSK isoforms are highly expressed and aberrantly activated resulting in poor outcomes and resistance to chemotherapy. Therefore, understanding RSK function in leukemia could lead to promising therapeutic strategies. This review summarizes the current information on human RSK isoforms and discusses their potential roles in the pathogenesis of AML and mechanism of pharmacological inhibitors.

Lupus susceptibility region containing CDKN1B rs34330 mechanistically influences expression and function of multiple target genes, also linked to proliferation and apoptosis

OBJECTIVE

A recent genome-wide association study (GWAS) reported a significant genetic association between rs34330 of cyclin-dependent kinase inhibitor 1B (CDKN1B) and risk of systemic lupus erythematosus (SLE) in Han Chinese. This study aims to validate the reported association and elucidate the biochemical mechanisms underlying the variant's effect.

METHODS

We performed allelic association with SLE followed by meta-analysis across 11 independent cohorts (n=28,872). We applied in silico bioinformatics and experimental validation in SLE-relevant cell lines to determine the functional consequences of rs34330.

RESULTS

We replicated genetic association between SLE and rs34330 (P_meta =5.29x10^-22 , OR (95% CI)=0.84 (0.81-0.87)). Follow-up bioinformatics and eQTL analysis suggest that rs34330 is located in active chromatin and potentially regulates several target genes. Using luciferase and ChIP-qPCR, we demonstrated substantial allele-specific promoter and enhancer activity, and allele-specific binding of three histone marks (H3K27ac, H3K4me3, H3K4me1), RNA pol II, CTCF, and a critical immune transcription factor (IRF-1). Chromosome conformation capture (3C) detected long-range chromatin interactions between rs34330 and the promoters of neighboring genes APOLD1 and DDX47, and effects on CDKN1B and the other target genes were directly validated by CRISPR-based genome editing. Finally, CRISPR-dCas9-based epigenetic activation/silencing confirmed these results. Gene-edited cell lines also showed higher levels of proliferation and apoptosis.

CONCLUSION

Collectively, these findings suggest a mechanism whereby the rs34330 risk allele (C) influences the presence of histone marks, RNA pol II, and the IRF-1 transcription factor to regulate expression of several target genes linked to proliferation and apoptosis, which potentially underlie the association of rs34330 with SLE.

A cancer-associated CDKN1B mutation induces p27 phosphorylation on a novel residue: a new mechanism for tumor suppressor loss-of-function

CDKN1B haploinsufficiency promotes the development of several human cancers. The gene encodes p27^Kip1, a protein playing pivotal roles in the control of growth, differentiation, cytoskeleton dynamics, and cytokinesis. CDKN1B haploinsufficiency has been associated with chromosomal or gene aberrations. However, very few data exist on the mechanisms by which CDKN1B missense mutations facilitate carcinogenesis. Here, we report a functional study on a cancer‐associated germinal p27^Kip1 variant, namely glycine9‐>arginine‐p27^Kip1 (G9R‐p27^Kip1) identified in a parathyroid adenoma. We unexpectedly found that G9R‐p27^Kip1 lacks the major tumor suppressor activities of p27^Kip1 including its antiproliferative and pro‐apoptotic functions. In addition, G9R‐p27^Kip1 transfection in cell lines induces the formation of more numerous and larger spheres when compared to wild‐type p27^Kip1‐transfected cells. We demonstrated that the mutation creates a consensus sequence for basophilic kinases causing a massive phosphorylation of G9R‐p27^Kip1 on S12, a residue normally never found modified in p27^Kip1. The novel S12 phosphorylation appears responsible for the loss of function of G9R‐p27^Kip1 since S12AG9R‐p27^Kip1 recovers most of the p27^Kip1 tumor suppressor activities. In addition, the expression of the phosphomimetic S12D‐p27^Kip1 recapitulates G9R‐p27^Kip1 properties. Mechanistically, S12 phosphorylation enhances the nuclear localization of the mutant protein and also reduces its cyclin‐dependent kinase (CDK)2/CDK1 inhibition activity. To our knowledge, this is the first reported case of quantitative phosphorylation of a p27^Kip1 variant on a physiologically unmodified residue associated with the loss of several tumor suppressor activities. In addition, our findings demonstrate that haploinsufficiency might be due to unpredictable post‐translational modifications due to generation of novel consensus sequences by cancer‐associated missense mutations.

Regulation of p27Kip1 and p57Kip2 Functions by Natural Polyphenols

In numerous instances, the fate of a single cell not only represents its peculiar outcome but also contributes to the overall status of an organism. In turn, the cell division cycle and its control strongly influence cell destiny, playing a critical role in targeting it towards a specific phenotype. Several factors participate in the control of growth, and among them, p27^Kip1 and p57^Kip2, two proteins modulating various transitions of the cell cycle, appear to play key functions. In this review, the major features of p27 and p57 will be described, focusing, in particular, on their recently identified roles not directly correlated with cell cycle modulation. Then, their possible roles as molecular effectors of polyphenols’ activities will be discussed. Polyphenols represent a large family of natural bioactive molecules that have been demonstrated to exhibit promising protective activities against several human diseases. Their use has also been proposed in association with classical therapies for improving their clinical effects and for diminishing their negative side activities. The importance of p27^Kip1 and p57^Kip2 in polyphenols’ cellular effects will be discussed with the aim of identifying novel therapeutic strategies for the treatment of important human diseases, such as cancers, characterized by an altered control of growth.

p27 as a Transcriptional Regulator: New Roles in Development and Cancer

p27 binds and inhibits cyclin-CDK to arrest the cell cycle. p27 also regulates other processes including cell migration and development independent of its cyclin-dependent kinase (CDK) inhibitory action. p27 is an atypical tumor suppressor-deletion or mutational inactivation of the gene encoding p27, CDKN1B, is rare in human cancers. p27 is rarely fully lost in cancers because it can play both tumor suppressive and oncogenic roles. Until recently, the paradigm was that oncogenic deregulation results from either loss of growth restraint due to excess p27 proteolysis or from an oncogenic gain of function through PI3K-mediated C-terminal p27 phosphorylation, which disrupts the cytoskeleton to increase cell motility and metastasis. In cancers, C-terminal phosphorylation alters p27 protein-protein interactions and shifts p27 from CDK inhibitor to oncogene. Recent data indicate p27 regulates transcription and acts as a transcriptional coregulator of cJun. C-terminal p27 phosphorylation increases p27-cJun recruitment to and action on target genes to drive oncogenic pathways and repress differentiation programs. This review focuses on noncanonical, CDK-independent functions of p27 in migration, invasion, development, and gene expression, with emphasis on how transcriptional regulation by p27 illuminates its actions in cancer. A better understanding of how p27-associated transcriptional complexes are regulated might identify new therapeutic targets at the interface between differentiation and growth control.

Absence of Nuclear p16 Is a Diagnostic and Independent Prognostic Biomarker in Squamous Cell Carcinoma of the Cervix

The tumor-suppressor protein p16 is paradoxically overexpressed in cervical cancer (CC). Despite its potential as a biomarker, its clinical value and the reasons for its failure in tumor suppression remain unclear. Our purpose was to determine p16 clinical and biological significance in CC. p16 expression pattern was examined by immunohistochemistry in 78 CC cases (high-grade squamous intraepithelial lesions (HSILs) and squamous cell carcinomas of the cervix –SCCCs). CC cell proliferation and invasion were monitored by real-time cell analysis and Transwell^® invasion assay, respectively. Cytoplasmic p16 interactors were identified from immunoprecipitated extracts by liquid chromatography-tandem mass spectrometry, and colocalization was confirmed by double-immunofluorescence. We observed that SCCCs showed significantly more cytoplasmic than nuclear p16 expression than HSILs. Importantly, nuclear p16 absence significantly predicted poor outcome in SCCC patients irrespective of other clinical parameters. Moreover, we demonstrated that cytoplasmic p16 interacted with CDK4 and other unreported proteins, such as BANF1, AKAP8 and AGTRAP, which could sequester p16 to avoid nuclear translocation, and then, impair its anti-tumor function. Our results suggest that the absence of nuclear p16 could be a diagnostic biomarker between HSIL and SCCC, and an independent prognostic biomarker in SCCC; and explain why p16 overexpression fails to stop CC growth.

The affinity of RSK for cylitol analogues of SL0101 is critically dependent on the B-ring C-4'-hydroxy

Five cyclitol analogues of SL0101 with variable substitution at the C-4' position (i.e., OH, Cl, F, H, OMe) were synthesized. The series of analogues were evaluated for their ability to inhibit p90 ribosomal S6 kinase (RSK) activity. The study demonstrated the importance of the B-ring C-4' hydroxy group for RSK1/2 inhibition.

Regulatory Role of Hexokinase 2 in Modulating Head and Neck Tumorigenesis

To support great demand of cell growth, cancer cells preferentially obtain energy and biomacromolecules by glycolysis over mitochondrial oxidative phosphorylation (OxPhos). Among all glycolytic enzymes, hexokinase (HK), a rate-limiting enzyme at the first step of glycolysis to catalyze cellular glucose into glucose-6-phosphate, is herein emphasized. Four HK isoforms, HK1-HK4, were discovered in nature. It was shown that HK2 expression is enriched in many tumor cells and correlated with poorer survival rates in most neoplastic cells. HK2-mediated regulations for cell malignancy and mechanistic cues in regulating head and neck tumorigenesis, however, are not fully elucidated. Cellular malignancy index, such as cell growth, cellular motility, and treatment sensitivity, and molecular alterations were determined in HK2-deficient head and neck squamous cell carcinoma (HNSCC) cells. By using various cancer databases, HK2, but not HK1, positively correlates with HNSCC progression in a stage-dependent manner. A high HK2 expression was detected in head and neck cancerous tissues compared with their normal counterparts, both in mouse and human subjects. Loss of HK2 in HNSCC cells resulted in reduced cell (in vitro) and tumor (in vivo) growth, as well as decreased epithelial-mesenchymal transition–mediated cell movement; in contrast, HK2-deficient HNSCC cells exhibited greater sensitivity to chemotherapeutic drugs cisplatin and 5-fluorouracil but are more resistant to photodynamic therapy, indicating that HK2 expression could selectively define treatment sensitivity in HNSCC cells. At the molecular level, it was found that HK2 alteration drove metabolic reprogramming toward OxPhos and modulated oncogenic Akt and mutant TP53-mediated signals in HNSCC cells. In summary, the present study showed that HK2 suppression could lessen HNSCC oncogenicity and modulate therapeutic sensitivity, thereby being an ideal therapeutic target for HNSCCs.

Mislocalized cytoplasmic p27 activates PAK1-mediated metastasis and is a prognostic factor in osteosarcoma

The development of pulmonary metastasis is the leading cause of death in osteosarcoma (OS), which is the most common malignant bone tumor in children. We have previously reported that the tumor suppressor p27 (KIP1, CDKN1B) is frequently mislocalized to the cytoplasm of OS. However, its prognostic significance and metastatic mechanism are still elusive. Here, we show that cytoplasmic p27 significantly correlated with a higher metastatic status and poorer survival of OS patients (n = 136, P < 0.05), highlighting the clinical significance of p27 mislocalization in OS. Mechanistically, cytoplasmic p27 is co‐immunoprecipitated with p21‐activated kinase 1 (PAK1), which resulted in higher PAK1 phosphorylations, actin polymerization, and cell motility in p27‐mislocalized OS cells. Silencing PAK1 expression in different p27‐mislocalized OS cell lines decreased the migratory and adhesion abilities in vitro, as well as the development of pulmonary metastases in vivo. Similar PAK1‐dependent motility was also observed in other p27‐mislocalized cancer cell lines. In summary, our study suggests that cytoplasmic p27‐mediated PAK1 activation is crucial for OS metastasis. A biomarker‐guided targeted therapeutic approach for metastatic OS and other cancers harboring p27 mislocalization can be developed, where cytoplasmic p27 is used for risk stratification and PAK1 can be exploited as a potential therapeutic target.

Rho-ROCK Signaling in Normal Physiology and as a Key Player in Shaping the Tumor Microenvironment

The Rho-ROCK signaling network has a range of specialized functions of key biological importance, including control of essential developmental processes such as morphogenesis and physiological processes including homeostasis, immunity, and wound healing. Deregulation of Rho-ROCK signaling actively contributes to multiple pathological conditions, and plays a major role in cancer development and progression. This dynamic network is critical in modulating the intricate communication between tumor cells, surrounding diverse stromal cells and the matrix, shaping the ever-changing microenvironment of aggressive tumors. In this chapter, we overview the complex regulation of the Rho-ROCK signaling axis, its role in health and disease, and analyze progress made with key approaches targeting the Rho-ROCK pathway for therapeutic benefit. Finally, we conclude by outlining likely future trends and key questions in the field of Rho-ROCK research, in particular surrounding Rho-ROCK signaling within the tumor microenvironment.

Regioselective Synthesis of a C-4'' Carbamate,C-6'' n-Pr Substituted Cyclitol Analogue of SL0101

An asymmetric synthesis of two analogues of SL0101 (1) has been achieved. The effort is aimed at the discovery of inhibitors of the p90 ribosomal S6 kinase (RSK) with improved bioavailability. The route relies upon the use of the Taylor catalyst to regioselectively install C-3″ acetyl or carbamate functionality. This study led to the identification of a third-generation analogue of SL0101 with a C-4″ n-Pr-carbamate and a C-3″ acetate with improved RSK inhibitory activity.

p90 ribosomal S6 kinase (RSK) phosphorylates myosin phosphatase and thereby controls edge dynamics during cell migration

Cell migration is essential to embryonic development, wound healing, and cancer cell dissemination. Cells move via leading-edge protrusion, substrate adhesion, and retraction of the cell's rear. The molecular mechanisms by which extracellular cues signal to the actomyosin cytoskeleton to control these motility mechanics are poorly understood. The growth factor-responsive and oncogenically activated protein extracellular signal-regulated kinase (ERK) promotes motility by signaling in actin polymerization-mediated edge protrusion. Using a combination of immunoblotting, co-immunoprecipitation, and myosin-binding experiments and cell migration assays, we show here that ERK also signals to the contractile machinery through its substrate, p90 ribosomal S6 kinase (RSK). We probed the signaling and migration dynamics of multiple mammalian cell lines and found that RSK phosphorylates myosin phosphatase–targeting subunit 1 (MYPT1) at Ser-507, which promotes an interaction of Rho kinase (ROCK) with MYPT1 and inhibits myosin targeting. We find that by inhibiting the myosin phosphatase, ERK and RSK promote myosin II–mediated tension for lamella expansion and optimal edge dynamics for cell migration. These findings suggest that ERK activity can coordinately amplify both protrusive and contractile forces for optimal cell motility.

Growth Arrest Triggers Extra-Cell Cycle Regulatory Function in Neurons: Possible Involvement of p27kip1 in Membrane Trafficking as Well as Cytoskeletal Regulation

Cell cycle regulation is essential for the development of multicellular organisms, but many cells in adulthood, including neurons, exit from cell cycle. Although cell cycle-related proteins are suppressed after cell cycle exit in general, recent studies have revealed that growth arrest triggers extra-cell cycle regulatory function (EXCERF) in some cell cycle proteins, such as p27(kip1), p57(kip2), anaphase-promoting complex/cyclosome (APC/C), and cyclin E. While p27 is known to control G1 length and cell cycle exit via inhibition of cyclin-dependent kinase (CDK) activities, p27 acquires additional cytoplasmic functions in growth-arrested neurons. Here, we introduce the EXCERFs of p27 in post-mitotic neurons, mainly focusing on its actin and microtubule regulatory functions. We also show that a small amount of p27 is associated with the Golgi apparatus positive for Rab6, p115, and GM130, but not endosomes positive for Rab5, Rab7, Rab8, Rab11, SNX6, or LAMTOR1. p27 is also colocalized with Dcx, a microtubule-associated protein. Based on these results, we discuss here the possible role of p27 in membrane trafficking and microtubule-dependent transport in post-mitotic cortical neurons. Collectively, we propose that growth arrest leads to two different fates in cell cycle proteins; either suppressing their expression or activating their EXCERFs. The latter group of proteins, including p27, play various roles in neuronal migration, morphological changes and axonal transport, whereas the re-activation of the former group of proteins in post-mitotic neurons primes for cell death.

p27kip1 at the crossroad between actin and microtubule dynamics

The p27^kip1 protein, mainly known as a negative regulator of cell proliferation, has also been involved in the control of other cellular processes, including the regulation of cytoskeleton dynamics. Notably, these two functions involve distinct protein domains, residing in the N- and C-terminal halves, respectively. In the last two decades, p27^kip1 has been reported to interact with microtubule and acto-myosin cytoskeletons, both in direct and indirect ways, overall drawing a picture in which several factors play their role either in synergy or in contrast one with another. As a result, the role of p27^kip1 in cytoskeleton dynamics has been implicated in cell migration, both in physiologic and in neoplastic contexts, modulating cytokinesis, lipid raft trafficking, and neuronal development. Recently, two distinct papers have further reported a central role for p27^kip1 in the control of microtubule stability and post-translational modifications, dissecting the interaction between p27^kip1 and α-tubulin-acetyl-transferase (α-TAT), an enzyme involved in the stability of microtubules, and protein-regulator of cytokinesis 1 (PRC1), a nuclear regulator of the central spindle during mitosis. In light of these recent evidences, we will comment on the role of p27^kip1 on cytoskeleton regulation and its implication for cancer progression.

Rewiring of RSK-PDZ Interactome by Linear Motif Phosphorylation

Phosphorylation of short linear peptide motifs is a widespread process for the dynamic regulation of protein-protein interactions. However, the global impact of phosphorylation events on the protein-protein interactome is rarely addressed. The disordered C-terminal tail of ribosomal S6 kinase 1 (RSK1) binds to PDZ domain-containing scaffold proteins, and it harbors a phosphorylatable PDZ-binding motif (PBM) responsive to epidermal growth factor stimulation. Here, we examined binding of two versions of the RSK1 PBM, either phosphorylated or unphosphorylated at position -3, to almost all (95%) of the 266 PDZ domains of the human proteome. PBM phosphorylation dramatically altered the PDZ domain-binding landscape of RSK1, by strengthening or weakening numerous interactions to various degrees. The RSK-PDZome interactome analyzed in this study reveals how linear motif-based phospho-switches convey stimulus-dependent changes in the context of related network components.

p27 transcriptionally coregulates cJun to drive programs of tumor progression

PI3K is activated in over 60% of human cancers, mediating C-terminal p27 phosphorylation. This work reveals cooperation between PI3K and cJun pathways: p27 phosphorylation by PI3K-activated kinases stimulates p27/cJun corecruitment to chromatin and activation of transcription programs of cell adhesion, motility, TGFB2, and epithelial–mesenchymal transformation to drive tumor progression. Prior analysis showed that high p27pT157 strongly associates with activated AKTpS273 and p90^RSKpT359 in human breast cancers. These cancers also differentially express p27/cJun target genes and identify a poor prognostic group. In cancers, the cell cycle-restraining effects of p27 are lost through increased proteolysis and decreased translation. We reveal a previously unknown oncogenic action of p27, in which p27 acts as a cJun coactivator to drive oncogenic gene expression programs.

p27 shifts from CDK inhibitor to oncogene when phosphorylated by PI3K effector kinases. Here, we show that p27 is a cJun coregulator, whose assembly and chromatin association is governed by p27 phosphorylation. In breast and bladder cancer cells with high p27pT157pT198 or expressing a CDK-binding defective p27pT157pT198 phosphomimetic (p27CK−DD), cJun is activated and interacts with p27, and p27/cJun complexes localize to the nucleus. p27/cJun up-regulates TGFB2 to drive metastasis in vivo. Global analysis of p27 and cJun chromatin binding and gene expression shows that cJun recruitment to many target genes is p27 dependent, increased by p27 phosphorylation, and activates programs of epithelial–mesenchymal transformation and metastasis. Finally, human breast cancers with high p27pT157 differentially express p27/cJun-regulated genes of prognostic relevance, supporting the biological significance of the work.

Nuclear co-expression of p21 and p27 induced effective cell-cycle arrest in T24 cells treated with BCG

A proposed mechanism underlying the effect of bacillus Calmette-Guérin (BCG) treatment for bladder cancer cells is as follows: BCG-induced crosslinking of cell-surface receptors results in the activation of signaling cascades, including cell-cycle regulators. However, the clinical significance of cell-cycle regulators such as p21 and p27 is controversial. Here we investigated the relationship between BCG exposure and p21 and p27. We used confocal laser microscopy to examine the expression levels of pKi67, p21 and p27 in T24 cells (derived from human urothelial carcinoma) exposed six times to BCG. We performed dual immunofluorescence staining methods for p21 and p27 and observed the localization of nuclear and cytoplasm expressions. We investigated the priority of p27 over p21 regarding nuclear expression by using p27 Stealth RNAi™ (p27-siRNA). With 2-h BCG exposure, the nuclear-expression level of p21 and p27 was highest, while pKi67 was lowest. The percentage of double nuclear-expression of p21 and p27 in BCG cells was significantly higher than that in control cells during the 1st to 6th exposure (P < 0.05), and the expression of pKi67 showed the opposite of this pattern. Approximately 10% of the nuclear p21 was independent of p27, whereas the cytoplasmic p21 was dependent on p27. Our results suggested that the nuclear co-expression of p21 and p27 caused effective cell-cycle arrest, and thus the evaluation of the nuclear co-expression of p21 and p27 might help determine the effectiveness of BCG treatment.

Cytoplasmic p27Kip1 promotes tumorigenesis via suppression of RhoB activity

The cell cycle inhibitor p27^Kip1 is a tumor suppressor via the inhibition of CDK complexes in the nucleus. However, p27 also plays other functions in the cell and may acquire oncogenic roles when located in the cytoplasm. Activation of oncogenic pathways such as Ras or PI3K/AKT causes the relocalization of p27 in the cytoplasm, where it can promote tumorigenesis by unclear mechanisms. Here, we investigated how cytoplasmic p27 participates in the development of non-small cell lung carcinomas. We provide molecular and genetic evidence that the oncogenic role of p27 is mediated, at least in part, by binding to and inhibiting the GTPase RhoB, which normally acts as a tumor suppressor in the lung. Genetically modified mice revealed that RhoB expression is preferentially lost in tumors in which p27 is absent and maintained in tumors expressing wild-type p27 or p27^CK- , a mutant that cannot inhibit CDKs. Moreover, although the absence of RhoB promoted tumorigenesis in p27^-/- animals, it had no effect in p27^CK- knock-in mice, suggesting that cytoplasmic p27 may act as an oncogene, at least in part, by inhibiting the activity of RhoB. Finally, in a cohort of lung cancer patients, we identified a subset of tumors harboring cytoplasmic p27 in which RhoB expression is maintained and these characteristics were strongly associated with decreased patient survival. Thus, monitoring p27 localization and RhoB levels in non-small cell lung carcinoma patients appears to be a powerful prognostic marker for these tumors. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Molecular mechanisms underlying progesterone-induced cytoplasmic retention of p27 in breast cancer cells

It has been reported that progesterone (P4) can contribute to the aggressiveness of human breast cancers through promoting cytoplasmic localization of p27 and stimulating proliferation. However, the molecular mechanisms underlying P4-induced cytoplasmic retention of p27 are still unclear. Here, we demonstrated that P4 (12.5-100 nM) concentration-dependently increased the number of T47D and MCF-7 cells. P4 (50 nM) also time-dependently increased the levels of p27 protein. Knock-down of p27 using the small interfering RNA (siRNA) technique abolished the P4-increased cell number of T47D and MCF-7. The signaling pathway involved in the P4-promoted breast cancer cell proliferation was further investigated. Our results suggest that P4 activated the PI3K/AKT-mediated signaling, subsequently increasing phophorylation of p27 at pT198 and T157, and thereby caused cytoplasmic retention of p27 protein. In addition, P4 activated kinase-interacting stathmin (KIS), subsequently increasing phosphorylation of nuclear p27 at serine 10 (S10), and thereby caused cytoplasmic translocation of p27pS10 from the nucleus. P4 also increased the level of nuclear CDK2pT160, thereby inducing p27 phosphorylation at T187, and hence caused cytosolic translocation of p27pT187 from the nucleus. In the cytosol, both p27pS10 and p27pT187 were degraded via the ubiquitin-proteasome pathway. Taken together, our data suggest that P4 promoted breast cancer cell proliferation through cytoplasmic retention of p27pT157 and p27pT198 and nuclear export of p27pS10 and p27pT187.

p27Kip1 regulates the microtubule bundling activity of PRC1

Cytokinesis begins in anaphase with the formation of the central spindle. PRC1 is a microtubule associated protein that plays an essential role in central spindle formation by crosslinking antiparallel microtubules. We have identified PRC1 as a novel binding partner for p27^Kip1 (p27). p27 is a cyclin-CDK inhibitor that causes cell cycle arrest in G1. However, p27 has also been involved in the regulation of G2/M progression and cytokinesis, as well as of other cellular processes, including actin and microtubule cytoskeleton dynamics. We found that p27 interferes with the ability of PRC1 to bind to microtubules, without affecting PRC1 dimerization or its capacity to interact with other partners such as KIF4. In this way, p27 inhibited microtubule bundling by PRC1 in vitro and prevented the extensive microtubule bundling phenotype caused by PRC1 overexpression in cells in culture. Finally, co-expression of p27 or a p27 mutant that does not bind cyclin-CDKs inhibited multinucleation induced by PRC1 overexpression. Together, our results suggest that p27 may participate in the regulation of mitotic progression in a CDK-independent manner by modulating PRC1 activity.

Caveolin-1 promotes Ewing sarcoma metastasis regulating MMP-9 expression through MAPK/ERK pathway

Ewing sarcoma (ES) is a bone and soft tissue sarcoma affecting mostly children and young adults. Caveolin-1 (CAV1) is a well-known target of EWS/FLI1, the main driver of ES, with an oncogenic role in ES. We have previously described how CAV1 is able to induce metastasis in ES via matrix metalloproteinase-9 (MMP-9). In the present study we showed how CAV1 silencing in ES reduced MEK1/2 and ERK1/2 phosphorylation. Accordingly, chemical inhibition of MEK1/2 resulted in reduction in MMP-9 expression and activity that correlated with reduced migration and invasion. IQ Motif Containing GTPase Activating Protein 1 (IQGAP1) silencing reduced MEK1/2 and ERK1/2 phosphorylation and MMP-9 expression. Furthermore, IQGAP1 silenced cells showed a marked decrease in their migratory and invasive capacity. We demonstrated that CAV1 and IQGAP1 localize in close proximity at the cellular edge, thus IQGAP1 could be the connecting node between CAV1 and MEK/ERK in ES metastatic phenotype. Analysis of the phosphorylation profile of CAV1-silenced cells showed a decrease of p-ribosomal protein S6 (RPS6). RPS6 can be phosphorylated by p90 ribosomal S6 kinases (RSK) proteins. CAV1-silenced cells showed reduced levels of p-RSK1 and treatment with U0126 provoked the same effect. Despite not affecting ERK1/2 and RPS6 phosphorylation status neither MMP-9 expression nor activity, RSK1 silencing resulted in a reduced migratory and invasive capacity in vitro and reduced incidence of metastases in vivo in a novel orthotopic model. The present work provides new insights into CAV1-driven metastatic process in ES unveiling novel key nodes.

Mapping Interactions between p27 and RhoA that Stimulate Cell Migration

p27 mediates cell cycle arrest by binding to and inhibiting cyclin-dependent kinase/cyclin complexes, but p27 can also contribute to pro-oncogenic signaling upon mislocalization to the cytoplasm. Cytoplasmic p27 stimulates cell migration by associating with RhoA and interfering with the exchange of GDP from RhoA stimulated by guanine nucleotide exchange factors. We used biophysical methods to show that the N-terminus of p27 directly interacts with RhoA in vitro. The affinity of p27 for RhoA is low, with an equilibrium dissociation constant of hundreds of micromolar; however, at high concentrations, p27 interfered with guanine nucleotide exchange factor-mediated nucleotide exchange from RhoA. We also show that promotion of cell migration in scratch wound cell healing assays requires full-length p27 despite the C-terminus being dispensable for the direct interaction between p27 and RhoA in vitro. These results suggest that there may be an unidentified factor(s) that associates with the C-terminus of p27 to enhance its interactions with RhoA and promote cell migration.

Gastrin-induced miR-222 promotes gastric tumor development by suppressing p27kip1

Background and Aims

Elevated circulating concentrations of the hormone gastrin contribute to the development of gastric adenocarcinoma and types-1 and 2 gastric neuroendocrine tumors (NETs). MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate proteins which in turn influence various biological processes. We hypothesised that gastrin induces the expression of specific gastric miRNAs within CCK2 receptor (CCK2R) expressing cells and that these mediate functionally important actions of gastrin.

Results

Gastrin increased miR-222 expression in AGS_GR cells, with maximum changes observed at 10 nM G17 for 24 h. Signalling occurred via CCK2R and the PKC and PI3K pathways. miR-222 expression was increased in the serum and gastric corpus mucosa of hypergastrinemic INS-GAS mice and hypergastrinemic patients with autoimmune atrophic gastritis and type 1 gastric NETs; it decreased in patients following treatment with the CCK2R antagonist netazepide (YF476). Gastrin-induced miR-222 overexpression resulted in reduced expression and cytoplasmic mislocalisation of p27^kip1, which in turn caused actin remodelling and increased migration in AGS_GR cells.

Materials and Methods

miRNA PCR arrays were used to identify changes in miRNA expression following G17 treatment of human gastric adenocarcinoma cells stably transfected with CCK2R (AGS_GR). miR-222 was further investigated using primer assays and samples from hypergastrinemic mice and humans. Chemically synthesised mimics and inhibitors were used to assess cellular phenotypical changes associated with miR-222 dysregulation.

Conclusions

These data indicate a novel mechanism contributing to gastrin-associated gastric tumor development. miR-222 may also be a promising biomarker for monitoring gastrin induced premalignant changes in the stomach.

Analysis of ORP2-knockout hepatocytes uncovers a novel function in actin cytoskeletal regulation

ORP2 is implicated in cholesterol transport, triglyceride metabolism, and adrenocortical steroid hormone production. We addressed ORP2 function in hepatocytes by generating ORP2-knockout (KO) HuH7 cells by CRISPR-Cas9 gene editing, followed by analyses of transcriptome, F-actin morphology, migration, adhesion, and proliferation. RNA sequencing of ORP2-KO cells revealed >2-fold changes in 579 mRNAs. The Ingenuity Pathway Analysis (IPA) uncovered alterations in the following functional categories: cellular movement, cell-cell signaling and interaction, cellular development, cellular function and maintenance, cellular growth and proliferation, and cell morphology. Many pathways in these categories involved actin cytoskeleton, cell migration, adhesion, or proliferation. Analysis of the ORP2 interactome uncovered 109 putative new partners. Their IPA analysis revealed Ras homolog A (RhoA) signaling as the most significant pathway. Interactions of ORP2 with SEPT9, MLC12, and ARHGAP12 were validated by independent assays. ORP2-KO resulted in abnormal F-actin morphology characterized by impaired capacity to form lamellipodia, migration defect, and impaired adhesion and proliferation. Rescue of the migration phenotype and generation of typical cell surface morphology required an intact ORP2 phosphoinositide binding site, suggesting that ORP2 function involves phosphoinositide binding and transport. The results point at a novel function of ORP2 as a lipid-sensing regulator of the actin cytoskeleton, with impacts on hepatocellular migration, adhesion, and proliferation.-Kentala, H., Koponen, A., Kivelä, A. M., Andrews, R., Li, C., Zhou, Y., Olkkonen, V. M. Analysis of ORP2-knockout hepatocytes uncovers a novel function in actin cytoskeletal regulation.

Zinc enhances the cellular energy supply to improve cell motility and restore impaired energetic metabolism in a toxic environment induced by OTA

Exogenous nutrient elements modulate the energetic metabolism responses that are prerequisites for cellular homeostasis and metabolic physiology. Although zinc is important in oxidative stress and cytoprotection processes, its role in the regulation of energetic metabolism remains largely unknown. In this study, we found that zinc stimulated aspect in cell motility and was essential in restoring the Ochratoxin A (OTA)-induced energetic metabolism damage in HEK293 cells. Moreover, using zinc supplementation and zinc deficiency models, we observed that zinc is conducive to mitochondrial pyruvate transport, oxidative phosphorylation, carbohydrate metabolism, lipid metabolism and ultimate energy metabolism in both normal and toxic-induced oxidative stress conditions in vitro, and it plays an important role in restoring impaired energetic metabolism. This zinc-mediated energetic metabolism regulation could also be helpful for DNA maintenance, cytoprotection and hereditary cancer traceability. Therefore, zinc can widely adjust energetic metabolism and is essential in restoring the impaired energetic metabolism of cellular physiology.

Co-targeting PI3K, mTOR, and IGF1R with small molecule inhibitors for treating undifferentiated pleomorphic sarcoma

Undifferentiated pleomorphic sarcomas (UPSs) are aggressive mesenchymal malignancies with no definitive cell of origin or specific recurrent genetic hallmarks. These tumors are largely chemoresistant; thus, identification of potential therapeutic targets is necessary to improve patient outcome. Previous studies demonstrated that high expression of activated protein kinase B (AKT) in patients with UPS corresponds to poor disease-specific survival. Here, we demonstrate that inhibiting phosphatidylinositol-3-kinase/mammalian target of rapamycin (PI3K/mTOR) signaling using a small molecule inhibitor reduced UPS cell proliferation and motility and xenograft growth; however, increased phosphorylation of insulin-like growth factor 1 receptor (IGF1R) indicated the potential for adaptive resistance following treatment through compensatory receptor activation. Co-treatment with a dual PI3K/mTOR inhibitor and an anti-IGF1R kinase inhibitor reduced in vivo tumor growth rates despite a lack of antiproliferative effects in vitro. Moreover, this combination treatment significantly decreased UPS cell migration and invasion, which is linked to changes in p27 subcellular localization. Our results demonstrate that targeted inhibition of multiple components of the IGF1R/PI3K/mTOR pathway was more efficacious than single-agent therapy and suggest that co-targeting this pathway could be a beneficial therapeutic strategy for patients with UPS.

ERK signalling as a regulator of cell motility

Cell motility is regulated by multiple processes, including cell protrusion, cell retraction, cell-matrix adhesion, polarized exocytosis and polarized vesicle trafficking, each of which is spatiotemporally controlled by various intracellular signalling pathways. Dysregulation of cell motility leads to pathological conditions, such as tumour invasion and metastasis. Accumulating evidence has revealed that extracellular signal-regulated kinase (ERK) signalling is one of the critical regulators of cell motility, although it is classically known as an important regulator of cell proliferation, differentiation and survival through regulation of gene expression. ERK and its downstream kinase, p90 ribosomal S6 kinase (RSK), dynamically regulate cell motility mainly through direct phosphorylation of various molecules that are not necessarily involved in the regulation of gene transcription and translation. In this review, we summarize how ERK signalling regulates cell motility by focusing on the components of the cell motility machinery that are directly regulated by ERK or RSK.

VEGFA links self-renewal and metastasis by inducing Sox2 to repress miR-452, driving Slug

Cancer stem cells (CSC) appear to have increased metastatic potential, but mechanisms underlying this are poorly defined. Here we show that VEGFA induction of Sox2 promotes EMT and tumor metastasis. In breast lines and primary cancer culture, VEGFA rapidly upregulates SOX2 expression, leading to SNAI2 induction, EMT, increased invasion and metastasis. We show Sox2 downregulates miR-452, which acts as a novel metastasis suppressor to directly target the SNAI2 3′-untranslated region (3′-UTR). VEGFA stimulates Sox2- and Slug-dependent cell invasion. VEGFA increases lung metastasis in vivo, and this is abrogated by miR-452 overexpression. Furthermore, SNAI2 transduction rescues metastasis suppression by miR-452. Thus, in addition to its angiogenic action, VEGFA upregulates Sox2 to drive stem cell expansion, together with miR-452 loss and Slug upregulation, providing a novel mechanism whereby cancer stem cells acquire metastatic potential. Prior work showed EMT transcription factor overexpression upregulates CSC. Present work indicates that stemness and metastasis are a two-way street: Sox2, a major mediator of CSC self-renewal, also governs the metastatic process.

Defining the role of the RSK isoforms in cancer

The 90kDa ribosomal S6 kinase (RSK) family is a group of Ser/Thr protein kinases (RSK1-4) that function downstream of the Ras/mitogen-activated protein kinase (MAPK) signalling pathway. RSK regulates many substrates involved in cell survival, growth, and proliferation, and as such, deregulated RSK activity has been associated with multiple cancer types. RSK expression and activity are dysregulated in several malignancies, including breast, prostate, and lung cancer, and available evidence suggests that RSK may be a promising cancer therapeutic target. Current limitations include the lack of RSK inhibitors with suitable pharmacokinetics and selectivity toward particular isoforms. This review briefly describes the current knowledge on RSK activation and function, with a particular emphasis on RSK-dependent mechanisms associated with tumorigenesis and pharmacological inhibition.

p27Kip1 promotes invadopodia turnover and invasion through the regulation of the PAK1/Cortactin pathway

p27^Kip1 (p27) is a cyclin-CDK inhibitor and negative regulator of cell proliferation. p27 also controls other cellular processes including migration and cytoplasmic p27 can act as an oncogene. Furthermore, cytoplasmic p27 promotes invasion and metastasis, in part by promoting epithelial to mesenchymal transition. Herein, we find that p27 promotes cell invasion by binding to and regulating the activity of Cortactin, a critical regulator of invadopodia formation. p27 localizes to invadopodia and limits their number and activity. p27 promotes the interaction of Cortactin with PAK1. In turn, PAK1 promotes invadopodia turnover by phosphorylating Cortactin, and expression of Cortactin mutants for PAK-targeted sites abolishes p27’s effect on invadopodia dynamics. Thus, in absence of p27, cells exhibit increased invadopodia stability due to impaired PAK1-Cortactin interaction, but their invasive capacity is reduced compared to wild-type cells. Overall, we find that p27 directly promotes cell invasion by facilitating invadopodia turnover via the Rac1/PAK1/Cortactin pathway.

DOI:http://dx.doi.org/10.7554/eLife.22207.001

When animals develop from embryos to adults, or try to heal wounds later in life, their cells have to move. Moving means that the cells must invade into their surroundings, a dense network of proteins called the extracellular matrix. The cell first attaches to the extracellular matrix; degrades it; and then moves into the newly opened space. Cells have developed specialized structures called invadosomes to enable all these steps. Invadosomes are never static, they first assemble where cells interact with extracellular matrix, they then release proteins that loosen the matrix, and finally disassemble again to allow cells to move. Invadosomes in cancer cells often become overactive, and can allow the tumor cells to spread throughout the body.

A lot of different proteins are involved in controlling how and when cells move. p27 is a well-known protein usually found in a cell’s nucleus along with the cell’s DNA. Inside the nucleus, p27 suppresses tumor growth by stopping cells from dividing. However, often in cancer cells p27 moves outside of the cell’s nucleus where it contributes to cell movement via an unknown mechanism.

To answer how p27 controls cell invasion, Jeannot et al. used a biochemical technique to uncover which proteins p27 binds to when it is outside of the nucleus. One of its interaction partners was called Cortactin. This protein is known to be an important building block of invadosomes, and is involved in both the assembly and disassembly of these structures. In further experiments, Jeannot studied mouse cells with or without p27 and human cancer cells that can be grown in the laboratory. The experiments revealed that p27 promotes an enzyme called PAK1 to also bind to Cortactin. PAK1 then modified Cortactin, causing whole invadosomes to disassemble, which in turn allowed cells to de-attach from the matrix and move forward. In contrast, cells lacking p27 had more stable invadosomes, attached more strongly to the matrix and were better at degrading it, but could not invade as well as cells with p27.

Overall these experiments showed a new way that p27 promotes cell invasion. The next steps will include finding out exactly how the modification of Cortactin causes the invadosomes to disassemble. Furthermore, it will be important to study whether forcing p27 back into the nucleus can reduce the spread of cancer cells in the body.

DOI:http://dx.doi.org/10.7554/eLife.22207.002

p38α regulates actin cytoskeleton and cytokinesis in hepatocytes during development and aging

Background

Hepatocyte poliploidization is an age-dependent process, being cytokinesis failure the main mechanism of polyploid hepatocyte formation. Our aim was to study the role of p38α MAPK in the regulation of actin cytoskeleton and cytokinesis in hepatocytes during development and aging.

Methods

Wild type and p38α liver-specific knock out mice at different ages (after weaning, adults and old) were used.

Results

We show that p38α MAPK deficiency induces actin disassembly upon aging and also cytokinesis failure leading to enhanced binucleation. Although the steady state levels of cyclin D1 in wild type and p38α knock out old livers remained unaffected, cyclin B1- a marker for G2/M transition- was significantly overexpressed in p38α knock out mice. Our findings suggest that hepatocytes do enter into S phase but they do not complete cell division upon p38α deficiency leading to cytokinesis failure and binucleation. Moreover, old liver-specific p38α MAPK knock out mice exhibited reduced F-actin polymerization and a dramatic loss of actin cytoskeleton. This was associated with abnormal hyperactivation of RhoA and Cdc42 GTPases. Long-term p38α deficiency drives to inactivation of HSP27, which seems to account for the impairment in actin cytoskeleton as Hsp27-silencing decreased the number and length of actin filaments in isolated hepatocytes.

Conclusions

p38α MAPK is essential for actin dynamics with age in hepatocytes.

Cyclin D1, cancer progression, and opportunities in cancer treatment

Mammalian cells encode three D cyclins (D1, D2, and D3) that coordinately function as allosteric regulators of cyclin-dependent kinase 4 (CDK4) and CDK6 to regulate cell cycle transition from G1 to S phase. Cyclin expression, accumulation, and degradation, as well as assembly and activation of CDK4/CDK6 are governed by growth factor stimulation. Cyclin D1 is more frequently dysregulated than cyclin D2 or D3 in human cancers, and as such, it has been more extensively characterized. Overexpression of cyclin D1 results in dysregulated CDK activity, rapid cell growth under conditions of restricted mitogenic signaling, bypass of key cellular checkpoints, and ultimately, neoplastic growth. This review discusses cyclin D1 transcriptional, translational, and post-translational regulations and its biological function with a particular focus on the mechanisms that result in its dysregulation in human cancers.

Development of a RSK Inhibitor as a Novel Therapy for Triple-Negative Breast Cancer

Metastatic breast cancer is an incurable disease and identification of novel therapeutic opportunities is vital. Triple-negative breast cancer (TNBC) frequently metastasizes and high levels of activated p90RSK (RSK), a downstream MEK-ERK1/2 effector, are found in TNBC. We demonstrate, using direct pharmacologic and genetic inhibition of RSK1/2, that these kinases contribute to the TNBC metastatic process in vivo Kinase profiling showed that RSK1 and RSK2 are the predominant kinases targeted by the new inhibitor, which is based on the natural product SL0101. Further evidence for selectivity was provided by the observations that silencing RSK1 and RSK2 eliminated the ability of the analogue to further inhibit survival or proliferation of a TNBC cell line. In vivo, the new derivative was as effective as the FDA-approved MEK inhibitor trametinib in reducing the establishment of metastatic foci. Importantly, inhibition of RSK1/2 did not result in activation of AKT, which is known to limit the efficacy of MEK inhibitors in the clinic. Our results demonstrate that RSK is a major contributor to the TNBC metastatic program and provide preclinical proof-of-concept for the efficacy of the novel SL0101 analogue in vivo Mol Cancer Ther; 15(11); 2598-608. ©2016 AACR.

The B56γ3 regulatory subunit-containing protein phosphatase 2A outcompetes Akt to regulate p27KIP1 subcellular localization by selectively dephosphorylating phospho-Thr157 of p27KIP1

The B56γ-containing protein phosphatase 2A (PP2A-B56γ) has been postulated to have tumor suppressive functions. Here, we report regulation of p27KIP1 subcellular localization by PP2A-B56γ3. B56γ3 overexpression enhanced nuclear localization of p27KIP1, whereas knockdown of B56γ3 decreased p27KIP1 nuclear localization. B56γ3 overexpression decreased phosphorylation at Thr157 (phospho-Thr157), whose phosphorylation promotes cytoplasmic localization of p27KIP1, whereas B56γ3 knockdown significantly increased the level of phospho-Thr157. In vitro, PP2A-B56γ3 catalyzed dephosphorylation of phospho-Thr157 in a dose-dependent and okadaic acid-sensitive manner. B56γ3 did not increase p27KIP1 nuclear localization by down-regulating the upstream kinase Akt activity and outcompeted a myristoylated constitutively active Akt (Aktca) in regulating Thr157 phosphorylation and subcellular localization of p27KIP1. In addition, results of interaction domain mapping revealed that both the N-terminal and C-terminal domains of p27 and a domain at the C-terminus of B56γ3 are required for interaction between p27 and B56γ3. Furthermore, we demonstrated that p27KIP1 levels are positively correlated with B56γ levels in both non-tumor and tumor parts of a set of human colon tissue specimens. However, positive correlation between nuclear p27KIP1 levels and B56γ levels was found only in the non-tumor parts, but not in tumor parts of these tissues, implicating a dysregulation in PP2A-B56γ3-regulated p27KIP1 nuclear localization in these tumor tissues. Altogether, this study provides a new mechanism by which the PP2A-B56γ3 holoenzyme plays its tumor suppressor role.

Loss of p27Kip¹ promotes metaplasia in the pancreas via the regulation of Sox9 expression

p27^Kip1 (p27) is a negative regulator of proliferation and a tumor suppressor via the inhibition of cyclin-CDK activity in the nucleus. p27 is also involved in the regulation of other cellular processes, including transcription by acting as a transcriptional co-repressor. Loss of p27 expression is frequently observed in pancreatic adenocarcinomas in human and is associated with decreased patient survival. Similarly, in a mouse model of K-Ras-driven pancreatic cancer, loss of p27 accelerates tumor development and shortens survival, suggesting an important role for p27 in pancreatic tumorigenesis. Here, we sought to determine how p27 might contribute to early events leading to tumor development in the pancreas. We found that K-Ras activation in the pancreas causes p27 mislocalization at pre-neoplastic stages. Moreover, loss of p27 or expression of a mutant p27 that does not bind cyclin-CDKs causes the mislocalization of several acinar polarity markers associated with metaplasia and induces the nuclear expression of Sox9 and Pdx1 two transcription factors involved in acinar-to-ductal metaplasia. Finally, we found that p27 directly represses transcription of Sox9, but not that of Pdx1. Thus, our results suggest that K-Ras activation, the earliest known event in pancreatic carcinogenesis, may cause loss of nuclear p27 expression which results in derepression of Sox9, triggering reprogrammation of acinar cells and metaplasia.

Transcriptome- and proteome-oriented identification of dysregulated eIF4G, STAT3, and Hippo pathways altered by PIK3CA H1047R in HER2/ER-positive breast cancer

PURPOSE

Phosphatidylinositol 3-kinase (PI3K)/AKT pathway aberrations are common in human breast cancer. Furthermore, PIK3CA mutations are commonly associated with resistance to anti-epidermal growth factor receptor 2 (HER2) or anti-estrogen receptor (ER) agents in HER2 or ER positive (HER2⁺/ER⁺) breast cancer. Hence, deciphering the underlying mechanisms of PIK3CA mutations in HER2⁺/ER⁺ breast cancer would provide novel insights into elucidating resistance to anti-HER2/ER therapies.

METHODS

In this study, we systematically investigated the biological consequences of PIK3CA ^H1047R in HER2⁺/ER⁺ breast cancer by uniquely incorporating mRNA transcriptomic data from The Cancer Genome Atlas and proteomic data from reverse-phase protein arrays.

RESULTS

Our integrative bioinformatics analyses revealed that several important pathways such as STAT3 and VEGF/hypoxia were selectively altered by PIK3CA ^H1047R in HER2⁺/ER⁺ breast cancer. Protein differential expression analysis indicated that an elevated eIF4G might promote tumor angiogenesis and growth via regulation of the hypoxia-activated switch in HER2⁺ PIK3CA ^H1047R breast cancer. We observed hypo-phosphorylation of EGFR in HER2⁺ PIK3CA ^H1047R breast cancer versus HER2⁺PIK3CA^wild-type (PIK3CA ^WT). In addition, ER and PIK3CA ^H1047R might cooperate to activate STAT3, MAPK, AKT, and Hippo pathways in ER⁺ PIK3CA ^H1047R breast cancer. A higher YAP_pS127 level was observed in ER⁺ PIK3CA ^H1047R patients than that in an ER⁺ PIK3CA ^WT subgroup. By examining breast cancer cell lines having both microarray gene expression and drug treatment data from the Genomics of Drug Sensitivity in Cancer and the Stand Up to Cancer datasets, we found that the elevated YAP1 mRNA expression was associated with the resistance of BCL-2 family inhibitors, but with the sensitivity to MEK/MAPK inhibitors in breast cancer cells.

CONCLUSIONS

In summary, these findings shed light on the functional consequences of PIK3CA ^H1047R-driven breast tumorigenesis and resistance to the existing therapeutic agents in HER2⁺/ER⁺ breast cancer.

Prognostic Importance of Cell Cycle Regulators Cyclin D1 (CCND1) and Cyclin-Dependent Kinase Inhibitor 1B (CDKN1B/p27) in Sporadic Gastric Cancers

Background. Gastric cancer is known for a notable variety in the course of the disease. Clinical factors, such as tumor stage, grade, and localization, are key in patient survival. It is expected that molecular factors such as somatic mutations and gene amplifications are also underlying tumor biological behavior and may serve as factors for prognosis estimation. Aim. The purpose of this study was to examine gene amplifications from a panel of genes to uncover potential prognostic marker candidates. Methods. A panel of gene amplifications including 71 genes was tested by multiplex ligation-dependent probe amplification (MLPA) technique in 76 gastric cancer samples from a Caucasian population. The correlation of gene amplification status with patient survival was determined by the Kaplan-Meier method. Results. The amplification of two cell cycle regulators, CCND1 and CDKN1B, was identified to have a negative prognostic role. The medial survival of patients with gastric cancer displaying amplification compared to patients without amplification was 192 versus 725 days for CCND1 (P = 0.0012) and 165 versus 611 days for CDKN1B (P = 0.0098). Conclusion. Gene amplifications of CCND1 and CDKN1B are potential candidates to serve as prognostic markers for the stratification of patients based on the estimate of survival in the management of gastric cancer patients.

Regulation of p27Kip1 phosphorylation and G1 cell cycle progression by protein phosphatase PPM1G

The cell cycle, an essential process leading to the cell division, is stringently controlled by the key cell cycle regulators, cyclin-CDK complexes, whose activity is further regulated by a variety of mechanisms. p27^Kip1 is a cyclin-CDK inhibitor that arrests the cell cycle at the G1 phase by blocking the activation of cyclin E-CDK2 complex, preventing the improper entry to the cell cycle. Dysfunction of p27 has been frequently observed in many types of human cancers, resulting from p27 protein degradation and cytoplasmic mislocalization, which are highly regulated by the phosphorylation status of p27. Although the kinases that phosphorylate p27 have been extensively studied, phosphatases that dephosphorylate p27 remain to be elucidated. By using genomic phosphatase screening, we identified a PPM family phosphatase, PPM1G, which could reduce p27 phosphorylation at T198. We further confirmed that PPM1G is a novel p27 phosphatase by demonstrating that PPM1G can interact with and dephosphorylate p27 in cells and in vitro. Functionally, ectopic expression of PPM1G enhanced p27 protein stability and delayed cell cycle progression from G1 to S phase. In accordance, knockdown of PPM1G accelerated p27 degradation during G1 phase and rendered cells resistant to the cell cycle arrest induced by serum deprivation. Mechanistically, PPM1G inhibited the interaction of p27 to 14-3-3θ, a chaperone protein that facilitates p27 nuclear export. Knockdown of PPM1G promoted the cytoplasmic localization of p27. Taken together, our studies identified PPM1G as a novel regulator of p27 that dephosphorylates p27 at T198 site and, together with p27 kinases, PPM1G controls cell cycle progression by maintaining the proper level of p27 protein.

Mutant AKT1-E17K is oncogenic in lung epithelial cells

The hotspot E17K mutation in the pleckstrin homology domain of AKT1 occurs in approximately 0.6–2% of human lung cancers. In this manuscript, we sought to determine whether this AKT1 variant is a bona-fide activating mutation and plays a role in the development of lung cancer. Here we report that in immortalized human bronchial epithelial cells (BEAS-2B cells) mutant AKT1-E17K promotes anchorage-dependent and -independent proliferation, increases the ability to migrate, invade as well as to survive and duplicate in stressful conditions, leading to the emergency of cells endowed with the capability to form aggressive tumours at high efficiency. We provide also evidence that the molecular mechanism whereby AKT1-E17K is oncogenic in lung epithelial cells involves phosphorylation and consequent cytoplasmic delocalization of the cyclin-dependent kinase (cdk) inhibitor p27. In agreement with these results, cytoplasmic p27 is preferentially observed in primary NSCLCs with activated AKT and predicts poor survival.

Molecular mechanisms underlying progesterone-enhanced breast cancer cell migration

Progesterone (P4) was demonstrated to inhibit migration in vascular smooth muscle cells (VSMCs), but to enhance migration in T47D breast cancer cells. To investigate the mechanism responsible for this switch in P4 action, we examined the signaling pathway responsible for the P4-induced migration enhancement in breast cancer cell lines, T47D and MCF-7. Here, we demonstrated that P4 activated the cSrc/AKT signaling pathway, subsequently inducing RSK1 activation, which in turn increased phosphorylation of p27 at T198 and formation of the p27pT198-RhoA complex in the cytosol, thereby preventing RhoA degradation, and eventually enhanced migration in T47D cells. These findings were confirmed in the P4-treated MCF-7. Comparing the P4-induced molecular events in between breast cancer cells and VSMCs, we found that P4 increased p27 phosphorylation at T198 in breast cancer cells through RSK1 activation, while P4 increased p27 phosphorlation at Ser10 in VSMCs through KIS activation. P27pT198 formed the complex with RhoA and prevented RhoA degradation in T47D cells, whereas p-p27Ser10 formed the complex with RhoA and caused RhoA degradation in VSMCs. The results of this study highlight the molecular mechanism underlying P4-enhanced breast cancer cell migration, and suggest that RSK1 activation is responsible for the P4-induced migration enhancement in breast cancer cells.