G1 phase arrest by the phosphatidylinositol 3-kinase inhibitor LY 294002 is correlated to up-regulation of p27Kip1 and inhibition of G1 CDKs in choroidal melanoma cells

New insights into the prognosis of intraocular malignancy: Interventions for association mechanisms between cancer and diabetes

The intraocular malignancies, which mostly originate from the retina and uvea, exhibit a high incidence of blindness and even death. Uveal melanoma (UM) and retinoblastoma (RB) are the most common intraocular malignancies in adults and children, respectively. The high risks of distant metastases lead to an extremely poor prognosis. Nowadays, various epidemiological studies have demonstrated that diabetes is associated with the high incidence and mortality of cancers, such as liver cancer, pancreatic cancer, and bladder cancer. However, the mechanisms and interventions associated with diabetes and intraocular malignancies have not been reviewed. In this review, we have summarized the associated mechanisms between diabetes and intraocular malignancy. Diabetes mellitus is a chronic metabolic disease characterized by prolonged periods of hyperglycemia. Recent studies have reported that the abnormal glucose metabolism, insulin resistance, and the activation of the IGF/insulin-like growth factor-1 receptor (IGF-1R) signaling axis in diabetes contribute to the genesis, growth, proliferation, and metastases of intraocular malignancy. In addition, diabetic patients are more prone to suffer severe complications and poor prognosis after radiotherapy for intraocular malignancy. Based on the common pathogenesis shared by diabetes and intraocular malignancy, they may be related to interventions and treatments. Therefore, interventions targeting the abnormal glucose metabolism, insulin resistance, and IGF-1/IGF-1R signaling axis show therapeutic potentials to treat intraocular malignancy.

Regulation of Cell Cycle Progression by Growth Factor-Induced Cell Signaling

The cell cycle is the series of events that take place in a cell, which drives it to divide and produce two new daughter cells. The typical cell cycle in eukaryotes is composed of the following phases: G1, S, G2, and M phase. Cell cycle progression is mediated by cyclin-dependent kinases (Cdks) and their regulatory cyclin subunits. However, the driving force of cell cycle progression is growth factor-initiated signaling pathways that control the activity of various Cdk–cyclin complexes. While the mechanism underlying the role of growth factor signaling in G1 phase of cell cycle progression has been largely revealed due to early extensive research, little is known regarding the function and mechanism of growth factor signaling in regulating other phases of the cell cycle, including S, G2, and M phase. In this review, we briefly discuss the process of cell cycle progression through various phases, and we focus on the role of signaling pathways activated by growth factors and their receptor (mostly receptor tyrosine kinases) in regulating cell cycle progression through various phases.

Plk1-Mediated Phosphorylation of TSC1 Enhances the Efficacy of Rapamycin

The AKT/TSC/mTOR axis is an important pathway controlling cell growth, survival, and proliferation in response to extracellular cues. Recently, it was reported that AKT activity fluctuates across the cell cycle. However, it remains unclear whether downstream targets of AKT are also regulated by the cell cycle. Here, we report that mTORC1 activity inversely correlates with AKT activity during the cell cycle. Mechanistically, Plk1 phosphorylation of TSC1 at S467 and S578 interfered with TSC1/TSC2 binding, destabilized TSC1, promoted dissociation of the TSC complex from the lysosome, and eventually led to mTORC1 activation. Tumors derived from cancer cells expressing the TSC1-S467E/S578E mutant exhibited greater sensitivity to rapamycin than those expressing WT TSC1. Collectively, our data support a model in which Plk1, instead of AKT, regulates the TSC/mTORC1 pathway during mitosis, eventually regulating the efficacy of rapamycin.Significance: This seminal report shows that activation of mTORC1 can be independent of AKT during mitosis. Cancer Res; 78(11); 2864-75. ©2018 AACR.

Programmed Death-1 Inhibition of Phosphatidylinositol 3-Kinase/AKT/Mechanistic Target of Rapamycin Signaling Impairs Sarcoidosis CD4+ T Cell Proliferation

Patients with progressive sarcoidosis exhibit increased expression of programmed death-1 (PD-1) receptor on their CD4⁺ T cells. Up-regulation of this marker of T cell exhaustion is associated with a reduction in the proliferative response to T cell receptor (TCR) stimulation, a defect that is reversed by PD-1 pathway blockade. Genome-wide association studies and microarray analyses have correlated signaling downstream from the TCR with sarcoidosis disease severity, but the mechanism is not yet known. Reduced phosphatidylinositol 3-kinase (PI3K)/AKT expression inhibits proliferation by inhibiting cell cycle progression. To test the hypothesis that PD-1 expression attenuates TCR-dependent activation of PI3K/AKT activity in progressive systemic sarcoidosis, we analyzed PI3K/AKT/mechanistic target of rapamycin (mTOR) expression at baseline and after PD-1 pathway blockade in CD4⁺ T cells isolated from patients with sarcoidosis and healthy control subjects. We confirmed an increased percentage of PD-1⁺ CD4⁺ T cells and reduced proliferative capacity in patients with sarcoidosis compared with healthy control subjects (P < 0.001). There was a negative correlation with PD-1 expression and proliferative capacity (r = -0.70, P < 0.001). Expression of key mediators of cell cycle progression, including PI3K and AKT, were significantly decreased. Gene and protein expression levels reverted to healthy control levels after PD-1 pathway blockade. Reduction in sarcoidosis CD4⁺ T cell proliferative capacity is secondary to altered expression of key mediators of cell cycle progression, including the PI3K/AKT/mTOR pathway, via PD-1 up-regulation. This supports the concept that PD-1 up-regulation drives the immunologic deficits associated with sarcoidosis severity by inducing signaling aberrancies in key mediators of cell cycle progression.

Preparation and characterization of (-)-Epigallocatechin-3-gallate (EGCG)-loaded nanoparticles and their inhibitory effects on Human breast cancer MCF-7 cells

We were employing nanotechnology to improve the targeting ability of (−)-Epigallocatechin-3-gallate (EGCG) towards MCF-7 cells, and two kinds of EGCG nanoparticles (FA-NPS-PEG and FA-PEG-NPS) were obtained, besides, their characteristics and effects on MCF-7 cells were studied. The results indicated that (i) both FA-NPS-PEG and FA-PEG-NPS have high stabilities; (ii) their particles sizes were 185.0 ± 13.5 nm and 142.7 ± 7.2 nm, respectively; (iii) their encapsulation efficiencies of EGCG were 90.36 ± 2.20% and 39.79 ± 7.54%, respectively. (iv) there was no cytotoxicity observed in EGCG, FA-NPS-PEG and FA-PEG-NPS toward MCF-7 cells over all concentrations (0~400 μg/mL) tested; (v) EGCG, FA-NPS-PEG and FA-PEG-NPS inhibited MCF-7 cells proliferation in dose-dependent manners, with the average IC₅₀ of 470.5 ± 33.0, 65.9 ± 0.4 and 66.6 ± 0.6 μg/mL; (vi) EGCG, FA-NPS-PEG and FA-PEG-NPS could modulated the expressions of several key regulatory proteins in PI3K-Akt pathway such as up-regulation of PTEN, p21 and Bax, and down-regulation of p-PDK1, p-AKT, CyclinD1 and Bcl-2, which gave an illustration about the mechanism by which EGCG nanoparticles inhibited MCF-7 cells proliferation. In this study, EGCG nanoparticles can significantly enhance the targeting ability and efficacy of EGCG, which is considered to an experimental foundation for further research on its activity, targeting ability and metabolism in vivo.

Phosphatidylinositol 3-Kinase (PI3K) and phosphatidylinositol 3-kinase-related kinase (PIKK) inhibitors: importance of the morpholine ring

Phosphatidylinositol 3-kinases (PI3Ks) and phosphatidylinositol 3-kinase-related protein kinases (PIKKs) are two related families of kinases that play key roles in regulation of cell proliferation, metabolism, migration, survival, and responses to diverse stresses including DNA damage. To design novel efficient strategies for treatment of cancer and other diseases, these kinases have been extensively studied. Despite their different nature, these two kinase families have related origin and share very similar kinase domains. Therefore, chemical inhibitors of these kinases usually carry analogous structural motifs. The most common feature of these inhibitors is a critical hydrogen bond to morpholine oxygen, initially present in the early nonspecific PI3K and PIKK inhibitor 3 (LY294002), which served as a valuable chemical tool for development of many additional PI3K and PIKK inhibitors. While several PI3K pathway inhibitors have recently shown promising clinical responses, inhibitors of the DNA damage-related PIKKs remain thus far largely in preclinical development.

Alternol induces an S-phase arrest of melanoma B16F0 cells

Alternol is a novel compound purified from the fermentation products of a microorganism in the yew tree bark. This study looks at the effects of alternol on the proliferation and cell cycle distribution of mouse melanoma cells. The inhibition of cell proliferation and changes in cell cycle distribution were analysed by sulforhodamine B and flow cytometry assays, respectively. mRNA expression of cyclin A, cyclin-dependent kinase 2 (CDK2), proliferating cell nuclear antigen (PCNA) and CDK inhibitor1A (p21) were measured by real-time reverse transcription PCR (RT-PCR). The protein levels of cyclin A, CDK2 and PCNA were analysed by Western blot analysis. p21 was measured by ELISA. Alternol treatment caused a significant decrease in the proliferation rate of B16F0 and B16F10 cells, which were significantly arrested in S phase, but this treatment had less effect on normal human embryonic kidney 293T cells. The mechanism by which alternol inhibits B16F0 proliferation in vitro may be associated with the inhibition of CDK2 and PCNA, and the activation of p21.

Proteomic profiling identified multiple short-lived members of the central proteome as the direct targets of the addicted oncogenes in cancer cells

"Oncogene addiction" is an unexplained phenomenon in the area of cancer targeted therapy. In this study, we have tested a hypothesis that rapid apoptotic response of cancer cells following acute inhibition of the addicted oncogenes is because of loss of multiple short-lived proteins whose activity normally maintain cell survival by blocking caspase activation directly or indirectly. It was shown that rapid apoptotic response or acute apoptosis could be induced in both A431 and MiaPaCa-2 cells, and quick down-regulation of 17 proteins, which were all members of the central proteome of human cells, was found to be associated with the onset of acute apoptosis. Knockdown of PSMD11 could partially promote the occurrence of acute apoptosis in both MiaPaCa-2 and PANC-1 pancreatic cancer cells. These findings indicate that maintaining the stability of central proteome may be a primary mechanism for addicted oncogenes to maintain the survival of cancer cells through various signaling pathways, and quick loss of some of the short-lived members of the central proteome may be the direct reason for the rapid apoptotic response or acute apoptosis following acute inhibition of the addicted oncogenes in cancer cells. These findings we have presented can help us better understand the phenomenon of oncogene-addiction and may have important implications for the targeted therapy of cancer.

Phosphatidylinositol 3-kinases inhibitor LY294002 potentiates the cytotoxic effects of doxorubicin, vincristine, and etoposide in a panel of cancer cell lines

Many novel therapeutic approaches to overcome chemoresistance have involved targeting specific signaling pathways such as the phosphatidylinositol 3-kinase (PI3K) pathway. PI3K is a known stress response pathway which is involved in the regulation of cell survival, apoptosis, and growth. Inhibition of this pathway may possibly restore or augment the effectiveness of chemotherapy. Using three human malignant cell lines, we examined the effects of LY294002 (PI3K inhibitor) on chemotherapeutic agent-induced apoptosis and cytotoxicity. An antimicrotubule agent vincristine, a topoisomerase II inhibitor etoposide, and a DNA cross-linking agent doxorubicin were used accompanied with LY294002. Cell viability was determined by MTT assay, and the induction of apoptosis was assessed by immunoblotting of caspase-3. Blocking the PI3K/Akt cascade with a PI3K inhibitor LY294002 (10 μM) increased the cytotoxic effect of vincristine and doxorubicin on SK-OV-3 cell line. Furthermore, LY294002 showed a greater promoting effect in etoposide- and doxorubicin-induced cytotoxicity on MDA-MB-468 and A549 cells. The quantity of cleaved caspase-3 in cancer cells that had combination therapy was increased compared with that in the cells treated with each drug alone. We suggest that inhibitors of the PI3K/Akt pathway in combination with chemotherapeutic agents may induce cell death effectively and be a potent modality to treat various types of cancer. The effectiveness of such combination therapy is depending to the used cell line and class of anticancer drug.

Characterization of Torin2, an ATP-competitive inhibitor of mTOR, ATM, and ATR

mTOR is a highly conserved serine/threonine protein kinase that serves as a central regulator of cell growth, survival, and autophagy. Deregulation of the PI3K/Akt/mTOR signaling pathway occurs commonly in cancer and numerous inhibitors targeting the ATP-binding site of these kinases are currently undergoing clinical evaluation. Here, we report the characterization of Torin2, a second-generation ATP-competitive inhibitor that is potent and selective for mTOR with a superior pharmacokinetic profile to previous inhibitors. Torin2 inhibited mTORC1-dependent T389 phosphorylation on S6K (RPS6KB1) with an EC(50) of 250 pmol/L with approximately 800-fold selectivity for cellular mTOR versus phosphoinositide 3-kinase (PI3K). Torin2 also exhibited potent biochemical and cellular activity against phosphatidylinositol-3 kinase-like kinase (PIKK) family kinases including ATM (EC(50), 28 nmol/L), ATR (EC(50), 35 nmol/L), and DNA-PK (EC(50), 118 nmol/L; PRKDC), the inhibition of which sensitized cells to Irradiation. Similar to the earlier generation compound Torin1 and in contrast to other reported mTOR inhibitors, Torin2 inhibited mTOR kinase and mTORC1 signaling activities in a sustained manner suggestive of a slow dissociation from the kinase. Cancer cell treatment with Torin2 for 24 hours resulted in a prolonged block in negative feedback and consequent T308 phosphorylation on Akt. These effects were associated with strong growth inhibition in vitro. Single-agent treatment with Torin2 in vivo did not yield significant efficacy against KRAS-driven lung tumors, but the combination of Torin2 with mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitor AZD6244 yielded a significant growth inhibition. Taken together, our findings establish Torin2 as a strong candidate for clinical evaluation in a broad number of oncologic settings where mTOR signaling has a pathogenic role.

Thy-1-mediated cell-cell contact induces astrocyte migration through the engagement of αVβ3 integrin and syndecan-4

Cell adhesion to the extracellular matrix proteins occurs through interactions with integrins that bind to Arg-Gly-Asp (RGD) tripeptides, and syndecan-4, which recognizes the heparin-binding domain of other proteins. Both receptors trigger signaling pathways, including those that activate RhoGTPases such as RhoA and Rac1. This sequence of events modulates cell adhesion to the ECM and cell migration. Using a neuron-astrocyte model, we have reported that the neuronal protein Thy-1 engages αVβ3 integrin and syndecan-4 to induce RhoA activation and strong astrocyte adhesion to their underlying substrate. Thus, because cell-cell interactions and strong cell attachment to the matrix are considered antagonistic to cell migration, we hypothesized that Thy-1 stimulation of astrocytes should preclude cell migration. Here, we studied the effect of Thy-1 expressing neurons on astrocyte polarization and migration using a wound-healing assay and immunofluorescence analysis. Signaling molecules involved were studied by affinity precipitation, western blotting and the usage of specific antibodies. Intriguingly, Thy-1 interaction with its two receptors was found to increase astrocyte polarization and migration. The latter events required interactions of these receptors with both the RGD-like sequence and the heparin-binding domain of Thy-1. Additionally, prolonged Thy-1-receptor interactions inhibited RhoA activation while activating FAK, PI3K and Rac1. Therefore, sustained engagement of integrin and syndecan-4 with the neuronal surface protein Thy-1 induces astrocyte migration. Interestingly we identify here, a cell-cell interaction that despite initially inducing strong cell attachment, favors cell migration upon persistent stimulation by engaging the same signaling receptors and molecules as those utilized by the extracellular matrix proteins to stimulate cell movement.

T-type Ca2+ channel blocker, KYS05047 induces G1 phase cell cycle arrest by decreasing intracellular Ca2+ levels in human lung adenocarcinoma A549 cells

In a previous study, we found that the 3,4-dihydroquinazoline derivative, 4-(Benzylcarbamoylmethyl)-2-(biphenyl-4-ylamino)-3-(5-tert-butyloxycarbamoyl-1-pentyl)-3,4-dihydroquinazoline (KYS05047), was a selective T-type Ca(2+) channel blocker with anti-proliferative effects against various cancer cells. However, the mechanism responsible for its effects has not been studied. In this study, we investigated the effect of KYS05047 on cell cycle arrest and the mechanisms involved in human lung adenocarcinoma A549 cells. Among the G(1) phase cell cycle-related proteins examined, the levels of cyclin-dependent protein kinase (Cdk2) and Cdk4 were reduced by KYS05047 (7 μM), whereas the steady-state levels of cyclin D1 and E were unaffected. In addition, KYS05047 increased the protein level of p27(KIP1) and suppressed the kinase activities of Cdk2 and Cdk4. In addition, pretreatment with KCl, which increases intracellular Ca(2+) levels, prevented KYS05047-induced intracellular Ca(2+) decreases and cell cycle arrest. Furthermore, the administration of KYS05047 (2 or 10 mg/kg, po) for 21 days was also found to significantly inhibit tumor growth in an A549 xenograft nude mice model. In conclusion, our results suggested that KYS05047 induced G(1) phase cell cycle arrest in A549 cells associated with a decrease in intracellular Ca(2+) concentrations and inhibited the in vivo tumor growth of A549 xenograft mice.

Alteronol inhibits proliferation in HeLa cells through inducing a G1-phase arrest

Objectives

Alteronol is a novel compound purified from fermentation products of a microorganism in the bark of the yew tree. The study was designed to evaluate the anticancer effects of alteronol.

Methods

Human cervical carcinoma cell line HeLa was cultured in vitro. The cell viability was evaluated by using sulforhodamine B assay. The cell cycle distribution was analysed by flow cytometry. The level of cyclin D1 protein was evaluated using Western blot analysis. The changes in cyclinD1, CDK4 and p21 were detected by ELISA assay and the changes in G1-related regulators were detected by RT-PCR assay.

Key findings

Our data showed that alteronol inhibited the proliferation of HeLa cells and induced G1 phase arrest. Downregulation of the mRNA levels of CDK2, CDK4 and cyclin D1 and upregulation of p21 in alteronol-treated cells were observed.

Conclusions

Downregulation of the mRNA levels of CDK2, CDK4 and cyclin D1 and upregulation of p21 might be a possible mechanism for the inhibition of proliferation induced by alteronol in HeLa cells.

Therapeutic implications of the emerging molecular biology of uveal melanoma

Uveal melanoma represents the most common primary intraocular malignancy in adults. Although uveal and cutaneous melanomas both arise from melanocytes, uveal melanoma is clinically and biologically distinct from its more common cutaneous counterpart. Metastasis occurs frequently in this disease, and once distant spread occurs, outcomes are poor. No effective systemic therapies are currently available; however, recent advances in our understanding of the biology of this rare and devastating disease, combined with the growing availability of targeted agents, which can be used to rationally exploit these findings, hold the promise for novel and effective therapies in the foreseeable future. Herein, we review our rapidly growing understanding of the molecular biology of uveal melanoma, including the pathogenic roles of GNAQ (guanine nucleotide binding protein q polypeptide)/11, PTEN (phosphatase and tensin homolog), IGF (insulin-like growth factor)/IGF-1 receptor, MET (hepatocyte growth factor), BAP1 [breast cancer 1, early onset (BRCA1)-associated protein-1], and other key molecules, potential therapeutic strategies derived from this emerging biology, and the next generation of recently initiated clinical trials for the treatment of advanced uveal melanoma.

Preclinical pharmacology, antitumor activity, and development of pharmacodynamic markers for the novel, potent AKT inhibitor CCT128930

AKT is frequently deregulated in cancer, making it an attractive anticancer drug target. CCT128930 is a novel ATP-competitive AKT inhibitor discovered using fragment- and structure-based approaches. It is a potent, advanced lead pyrrolopyrimidine compound exhibiting selectivity for AKT over PKA, achieved by targeting a single amino acid difference. CCT128930 exhibited marked antiproliferative activity and inhibited the phosphorylation of a range of AKT substrates in multiple tumor cell lines in vitro, consistent with AKT inhibition. CCT128930 caused a G(1) arrest in PTEN-null U87MG human glioblastoma cells, consistent with AKT pathway blockade. Pharmacokinetic studies established that potentially active concentrations of CCT128930 could be achieved in human tumor xenografts. Furthermore, CCT128930 also blocked the phosphorylation of several downstream AKT biomarkers in U87MG tumor xenografts, indicating AKT inhibition in vivo. Antitumor activity was observed with CCT128930 in U87MG and HER2-positive, PIK3CA-mutant BT474 human breast cancer xenografts, consistent with its pharmacokinetic and pharmacodynamic properties. A quantitative immunofluorescence assay to measure the phosphorylation and total protein expression of the AKT substrate PRAS40 in hair follicles is presented. Significant decreases in pThr246 PRAS40 occurred in CCT128930-treated mouse whisker follicles in vivo and human hair follicles treated ex vivo, with minimal changes in total PRAS40. In conclusion, CCT128930 is a novel, selective, and potent AKT inhibitor that blocks AKT activity in vitro and in vivo and induces marked antitumor responses. We have also developed a novel biomarker assay for the inhibition of AKT in human hair follicles, which is currently being used in clinical trials.

Phosphatidylinositol 3-kinase inhibitor(LY294002) induces apoptosis of human nasopharyngeal carcinoma in vitro and in vivo

Background

To evaluate whether PI3K/Akt pathway could effect on apoptosis and its mechanism in nasopharyngeal carcinoma cells.

Methods

The activation of the PI3K/Akt and its effect on CNE-2Z cells in vivo and in vitro was investigated by MTT assay, flow cytometry, western blot, ELISA, terminal deoxyribonucleotide transferase-mediated nick-end labeling assays (TUNEL), and immunohistochemical analyses, using PI3K inhibitor, LY294002.

Results

The results showed that LY294002 inhibited the phosphorylating of Akt (S473), cell proliferation, and induced apoptosis in CNE-2Z cells. However, our experiment results also demonstrated that apoptosis-induced LY294002 was directly regulated by caspase-9 activation pathway.

Conclusion

These data suggested that PI3K inhibitor, LY294002, induced apoptosis by caspase-9 activation pathway and might be as a potentially useful target for therapeutic intervention in nasopharyngeal carcinoma patients.

Liver X receptors interfere with cytokine-induced proliferation and cell survival in normal and leukemic lymphocytes

Liver X receptors (LXRs) are nuclear receptors regulating lipid and cholesterol metabolism. Recent data indicate an additional role of LXR in immunity by controlling dendritic cell and T-cell function and in breast and prostate cancer cells. Here, we show that LXR activation interferes with IL-2 and IL-7-induced proliferation and cell cycle progression of human T-cell blasts mainly through inhibited phosphorylation of the retinoblastoma protein and decreased expression of the cell cycle protein cyclin B. Comparable results were obtained with IL-2-dependent chronic lymphoblastic leukemia (CLL) T cells. Furthermore, we show for B-CLL cells that LXR are functionally active and inhibit expression of survival genes bcl-2 and MMP-9, and significantly reduce cell viability, suggesting an interference of LXR with cytokine-dependent CLL cell survival. In conclusion, our data reveal LXR as a potent modulator of cytokine-dependent proliferation and survival of normal and malignant T and B lymphocytes. This novel LXR action could find clinical application in immunosuppressive and antileukemic therapies.

Blocking phosphoinositide 3-kinase activity in colorectal cancer cells reduces proliferation but does not increase apoptosis alone or in combination with cytotoxic drugs

In response to growth factors, class IA phosphoinositide 3-kinases (PI3K) phosphorylate phosphatidylinositol-4,5-bisphosphate, converting it to phosphatidylinositol-3,4,5-trisphosphate to activate protein kinase B/Akt. This is widely reported to promote tumorigenesis via increased cell survival, proliferation, migration, and invasion, and many tumor types, including colorectal cancer, exhibit increased PI3K signaling. To investigate the effect of inhibiting PI3K and as an alternative to the use of small molecular inhibitors of PI3K with varying degrees of selectivity, HT29 and HCT116 colorectal cancer cells bearing mutant PIK3CA were generated that could be induced with doxycycline to express synchronously a dominant negative subunit of PI3K, Deltap85alpha. On induction, decreased levels of phosphorylated protein kinase B were detected, confirming PI3K signaling impairment. Induction of Deltap85alpha in vitro reduced cell number via accumulation in G(0)-G(1) phase of the cell cycle in the absence of increased apoptosis. These effects were recapitulated in vivo. HT29 cells expressing Deltap85alpha and grown as tumor xenografts had a significantly slower growth rate on administration of doxycycline with reduced Ki67 staining without increased levels of apoptotic tissue biomarkers. Furthermore, in vitro Deltap85alpha expression did not sensitize HT29 cells to oxaliplatin- or etoposide-induced apoptosis, irrespective of drug treatment schedule. Further analysis comparing isogenic HCT116 cells with and without mutation in PIK3CA showed no effect of the mutation in either proliferative or apoptotic response to PI3K inhibition. These data show in colorectal cancer cells that PI3K inhibition does not provoke apoptosis per se nor enhance oxaliplatin- or etoposide-induced cell death.

Targeting melanoma with dual phosphoinositide 3-kinase/mammalian target of rapamycin inhibitors

Phosphoinositide 3-kinase (PI3K)/protein kinase B/Akt and Ras/mitogen-activated protein kinase pathways are often constitutively activated in melanoma and have thus been considered as promising drug targets. Exposure of melanoma cells to NVP-BAG956, NVP-BBD130, and NVP-BEZ235, a series of novel, potent, and stable dual PI3K/mammalian target of rapamycin (mTOR) inhibitors, resulted in complete G1 growth arrest, reduction of cyclin D1, and increased levels of p27(KIP1), but negligible apoptosis. In contrast, treatment of melanoma with the pan-class I PI3K inhibitor ZSTK474 or the mTORC1 inhibitor rapamycin resulted only in minor reduction of cell proliferation. In a syngeneic B16 mouse melanoma tumor model, orally administered NVP-BBD130 and NVP-BEZ235 efficiently attenuated tumor growth at primary and lymph node metastatic sites with no obvious toxicity. Metastatic melanoma in inhibitor-treated mice displayed reduced numbers of proliferating and significantly smaller tumor cells. In addition, neovascularization was blocked and tumoral necrosis increased when compared with vehicle-treated mice. In conclusion, compounds targeting PI3K and mTOR simultaneously were advantageous to attenuate melanoma growth and they develop their potential by targeting tumor growth directly, and indirectly via their interference with angiogenesis. Based on the above results, NVP-BEZ235, which has entered phase I/II clinical trials in patients with advanced solid tumors, has a potential in metastatic melanoma therapy.

Simultaneous blockade of AP-1 and phosphatidylinositol 3-kinase pathway in non-small cell lung cancer cells

c-Jun is a major constituent of AP-1 transcription factor that transduces multiple mitogen growth signals, and it is frequently overexpressed in non-small cell lung cancers (NSCLCs). Earlier, we showed that blocking AP-1 by the overexpression of a c-Jun dominant-negative mutant, TAM67, inhibited NSCLC cell growth. The phosphatidylinositol 3-kinase (PI3K)/Akt signal transduction pathway is important in transformation, proliferation, survival and metastasis of NSCLC cells. In this study, we used NCI-H1299 Tet-on clone cells that express TAM67 under the control of inducible promoter to determine the effects of inhibition of AP-1 and PI3K on cell growth. The PI3K inhibitor, LY294002, produced a dose-dependent inhibition of growth in H1299 cells and that inhibition was enhanced by TAM67. TAM67 increased dephosphorylation of Akt induced by LY294002 and reduced the TPA response element DNA-binding of phosphorylated c-Jun. TAM67 increased G1 cell cycle blockade induced by LY294002, which was partially associated with cyclin A decrease and p27^Kip1 accumulation. Furthermore, TAM67 and LY294002 act, at least additively, to inhibit anchorage-independent growth of the H1299 cells. These results suggest that AP-1 and PI3K/Akt pathways play an essential role in the growth of some NSCLC cells.

High glucose increase cell cycle regulatory proteins level of mouse embryonic stem cells via PI3-K/Akt and MAPKs signal pathways

This study examined the effects of high glucose on cell proliferation and its related signal pathways using mouse embryonic stem (ES) cells. Here, we showed that high glucose level significantly increased [3H]thymidine incorporation, BrdU incorporation, the number of cells, [3H]leucine, and [3H]proline incorporation in a time-( >3 hr) and dose-(> 25 mM) dependent manner. Moreover, high glucose level increased the cellular reactive oxygen species (ROS), Akt, and mitogen-activated protein kinases (MAPKs) phosphorylation. Subsequently, these signaling molecules involved in high glucose-induced increase of [3H]thymidine incorporation. High glucose level also increased cyclin D1, cyclin E, cyclin-dependent kinase (CDK) 2, and CDK 4 protein levels, which is cell cycle regulatory proteins acting in G1-S phase of cell cycle. Inhibition of phosphatidylinositol 3-kinase (PI3-K) (LY 294002: PI3-kinase inhibitor, 10(-6) M), Akt (Akt inhibitor, 10(-5) M), and p44/42 MAPKs (PD 98059: MEK inhibitor, 10(-5) M) decreased these proteins. High glucose level phosphorylated the RB protein, which was decreased by inhibition of PI3-K and Akt. In conclusion, high glucose level stimulates mouse ES cell proliferation via the PI3-K/Akt and MAPKs pathways.

The priming/completion paradigm to explain growth factor-dependent cell cycle progression

Approximately 50 years ago, researchers established conditions to maintain cells in tissue culture: Likely et al. (1952), Scherer et al. (1953), Eagle (1955). This simple model system set the stage for discovery of growth factors and the signaling systems that they engage to mediate cellular responses such as proliferation. The purpose of this review is to present the original view of how growth factors regulate cell cycle progression and an updated (priming/completion) version of how growth factors advance resting cells through the cell cycle.

Phosphoinositide 3-kinase in disease: timing, location, and scaffolding

When PI3Ks are deregulated by aberrant surface receptors or modulators, accumulation of PtdIns(3,4,5)P3 leads to increased cell growth, proliferation and contact-independent survival. The PI3K/PKB/TOR axis controls protein synthesis and growth, while PtdIns(3,4,5)P3-mediated activation of Rho GTPases directs cell motility. PI3K activity has been linked to the formation of tumors, metastasis, chronic inflammation, allergy and cardiovascular disease. Although increased PtdIns(3,4,5)P3 is a well-established cause of disease, it is seldom known which PI3K isoform is implied. Recent work has demonstrated that PI3Kgamma contributes to the control of cAMP levels in the cardiac system, where the protein acts as a scaffold, but not as a lipid kinase.

Akt-induced promotion of cell-cycle progression at G2/M phase involves upregulation of NF-Y binding activity in PC12 cells

Akt is a key downstream effector of the PI3K signaling pathway and plays a role in cell growth and survival. Expression of a myristoylated constitutively active form of Akt (myr-Akt) in PC12 cells could override cell-growth arrest at G2/M phase and apoptosis that were induced by etoposide treatment. On the other hand, inactivation of Akt by expression of its dominant negative mutant form (km-Akt) inhibited cell proliferation by arresting the cells at G2/M phase. Expression of myr-Akt also led to an increase in the protein and mRNA levels of CDK1 and cyclin B1. Furthermore, EMSA data revealed that expression of myr-Akt promoted the binding of NF-Y to the consensus CCAAT promoter sequence, whereas expression of km-Akt almost completely abolished it. Moreover, the Akt activity was minimal in the cells that were arrested at G2/M phase by nocodazole treatment, but reached to a maximal level as the cells progressed to mitosis and G1 phase upon removal of the drug. Treatment with Akt inhibitors, but not with those of MEK or p70S6K, blocked the release of the cells from the nocodazole-induced G2/M arrest, further revealing that the Akt activity is required for G2/M phase transition. These results suggest that Akt facilitate cell-cycle progression at G2/M phase in PC12 cells and this Akt activity is correlated with upregulation of NF-Y DNA-binding activity and cyclin B1/CDK1 gene expression.

P27 expression is regulated by separate signaling pathways, downstream of Ras, in each cell cycle phase

The cyclin inhibitory protein p27Kip1 (p27) plays a vital role in regulating cell proliferation in response to the extracellular growth environment. Active proliferation requires the suppression of p27 levels throughout the cell cycle. Late in the cell cycle, p27 degradation requires phosphorylation of Thr 187 by cyclin dependent kinase 2, leading to recognition by the SCF ubiquitin ligase containing the Skp2 F-box protein. Suppression of p27 is also essential for cell proliferation early in the cell cycle, but this occurs independently of Skp2, whose expression is suppressed during G1 phase. In this study, we use a time lapse and quantitative imaging approach to study the connection between proliferative signaling and the degradation of p27 during each cell cycle period in actively cycling cells. Ras activity was required for the suppression of p27 levels throughout the cell cycle, but separate pathways downstream of Ras signaling were required in different cell cycle periods. For example, inhibitors of MEK and phosphatidylinositol-3-kinase induced p27 expression primarily in G1 phase, while inhibitors of AKT activity stimulated these levels primarily in S phase. Skp2 was expressed in a Ras-dependent manner at higher levels late in the cell cycle. Its ablation resulted in higher p27 levels primarily in G2 phase as expected. The fact that separate signaling pathways downstream of Ras function in each cell cycle phase to suppress p27 levels helps explain the vital connection between proliferative signaling, cell cycle control, and p27 expression.

Identification of nonsteroidal anti-inflammatory drug-activated gene (NAG-1) as a novel downstream target of phosphatidylinositol 3-kinase/AKT/GSK-3beta pathway

The signaling pathway of phosphatidylinositol 3-kinase (PI3K)/AKT, which is involved in cell survival, proliferation, and growth, has become a major focus in targeting cancer therapeutics. Nonsteroidal anti-inflammatory drug-activated gene (NAG-1) was previously identified as a gene induced by several anti-tumorigenic compounds including nonsteroidal anti-inflammatory drugs, peroxisome proliferator-activated receptor gamma ligands, and dietary compounds. NAG-1 has been shown to exhibit anti-tumorigenic and/or pro-apoptotic activities in vivo and in vitro. In this report, we showed a PI3K/AKT/glycogen synthase kinase-3beta (GSK-3beta) pathway regulates NAG-1 expression in human colorectal cancer cells as assessed by the inhibition of PI3K, AKT, and GSK-3beta. PI3K inhibition by LY294002 showed an increase in NAG-1 protein and mRNA expression, and 1l-6-hydroxymethyl-chiro-inositol 2(R)-2-O-methyl-3-O-octadecylcarbonate (AKT inhibitor) also induced NAG-1 expression. LY294002 caused increased apoptosis, cell cycle, and cell growth arrest in HCT-116 cells. Inhibition of GSK-3beta, which is negatively regulated by AKT, using AR-A014418 and lithium chloride completely abolished LY294002-induced NAG-1 expression as well as the NAG-1 promoter activity. Furthermore, the down-regulation of GSK-3 gene using small interference RNA resulted in a decline of the NAG-1 expression in the presence of LY294002. These data suggest that expression of NAG-1 is regulated by PI3K/AKT/GSK-3beta pathway in HCT-116 cells and may provide a further understanding of the important role of PI3K/AKT/GSK-3beta pathway in tumorigenesis.

A late, prolonged activation of the phosphatidylinositol 3-kinase pathway is required for T cell proliferation

Activation of the phosphatidylinositol-3 kinase (PI 3-K) pathway is associated with the proliferation of many cell types, including T lymphocytes. However, recent studies in cell lines stably expressing deletion mutants of IL-2R that fail to activate PI 3-K have questioned the requirement for this pathway in cell cycle regulation. In this study with IL-2 and IL-7, we show in primary T cells that, unlike IL-2, IL-7 fails to induce the early activation of PI 3-K seen within minutes and normally associated with cytokine signaling. However, kinetic experiments showed that both of these T cell growth factors induce a distinct and sustained phase of PI 3-K activity several hours after stimulation. This delayed activation correlates with cell cycle induction and from studies using inhibitors of PI 3-K signaling, we show that this later phase, unlike the early activation within minutes, is required for cell cycle induction. The data presented here will have major implications for our understanding of the mechanism of T cell proliferation as well as the regulation of PI 3-K activity.

PI3K/Akt signalling pathway and cancer

Phosphatidylinositol-3 kinases, PI3Ks, constitute a lipid kinase family characterized by their ability to phosphorylate inositol ring 3'-OH group in inositol phospholipids to generate the second messenger phosphatidylinositol-3,4,5-trisphosphate (PI-3,4,5-P(3)). RPTK activation results in PI(3,4,5)P(3) and PI(3,4)P(2) production by PI3K at the inner side of the plasma membrane. Akt interacts with these phospholipids, causing its translocation to the inner membrane, where it is phosphorylated and activated by PDK1 and PDK2. Activated Akt modulates the function of numerous substrates involved in the regulation of cell survival, cell cycle progression and cellular growth. In recent years, it has been shown that PI3K/Akt signalling pathway components are frequently altered in human cancers. Cancer treatment by chemotherapy and gamma-irradiation kills target cells primarily by the induction of apoptosis. However, the development of resistance to therapy is an important clinical problem. Failure to activate the apoptotic programme represents an important mode of drug resistance in tumor cells. Survival signals induced by several receptors are mediated mainly by PI3K/Akt, hence this pathway may decisively contribute to the resistant phenotype. Many of the signalling pathways involved in cellular transformation have been elucidated and efforts are underway to develop treatment strategies that target these specific signalling molecules or their downstream effectors. The PI3K/Akt pathway is involved in many of the mechanisms targeted by these new drugs, thus a better understanding of this crossroad can help to fully exploit the potential benefits of these new agents.

G1 cell cycle progression and the expression of G1 cyclins are regulated by PI3K/AKT/mTOR/p70S6K1 signaling in human ovarian cancer cells

Ovarian cancer is one of the most common cancers among women. Recent studies demonstrated that the gene encoding the p110alpha catalytic subunit of phosphatidylinositol 3-kinase (PI3K) is frequently amplified in ovarian cancer cells. PI3K is involved in multiple cellular functions, including proliferation, differentiation, antiapoptosis, tumorigenesis, and angiogenesis. In this study, we demonstrate that the inhibition of PI3K activity by LY-294002 inhibited ovarian cancer cell proliferation and induced G(1) cell cycle arrest. This effect was accompanied by the decreased expression of G(1)-associated proteins, including cyclin D1, cyclin-dependent kinase (CDK) 4, CDC25A, and retinoblastoma phosphorylation at Ser(780), Ser(795), and Ser(807/811). Expression of CDK6 and beta-actin was not affected by LY-294002. Expression of the cyclin kinase inhibitor p16(INK4a) was induced by the PI3K inhibitor, whereas steady-state levels of p21(CIP1/WAF1) were decreased in the same experiment. The inhibition of PI3K activity also inhibited the phosphorylation of AKT and p70S6K1, but not extracellular regulated kinase 1/2. The G(1) cell cycle arrest induced by LY-294002 was restored by the expression of active forms of AKT and p70S6K1 in the cells. Our study shows that PI3K transmits a mitogenic signal through AKT and mammalian target of rapamycin (mTOR) to p70S6K1. The mTOR inhibitor rapamycin had similar inhibitory effects on G(1) cell cycle progression and on the expression of cyclin D1, CDK4, CDC25A, and retinoblastoma phosphorylation. These results indicate that PI3K mediates G(1) progression and cyclin expression through activation of an AKT/mTOR/p70S6K1 signaling pathway in the ovarian cancer cells.

Opposite long-term regulation of c-Myc and p27Kip1 through overactivation of Raf-1 and the MEK/ERK module in proliferating human choroidal melanoma cells

Although there is no current evidence for ras gene mutation in choroidal melanoma, there is an increasing body of evidence indicating that deregulated intracellular signalling pathways are involved in choroidal melanoma pathogenesis. The various components of the linear Raf/MEK/ERK signalling pathway have been implicated in various tumours. We therefore investigated the role of Raf-1 and the MEK/ERK module in the proliferation of human normal choroidal melanocytes (NCM) and cells from the ocular choroidal melanoma (OCM-1) cell line. OCM-1 cells proliferated four times faster than NCM. High basal activation of the MEK/ERK module was observed in unstimulated OCM-1 cells, whereas rapid and persistent activation was detected after serum stimulation, throughout the 24-h period of culture. In contrast, the activation of MEK/ERK was barely detectable in unstimulated NCM and occurred late (6 h) after the stimulation of cell proliferation. Inhibition of Raf-1 and MEK1/2 activation by pharmacological approaches and of the production of Raf-1 and ERK1/2 by antisense oligonucleotide approaches demonstrated that Raf-1 and the MEK/ERK module controlled proliferation in OCM-1 cells, but not in NCM. OCM-1 cells produced very low levels of p27Kip1, whereas NCM produced constant, high levels of p27Kip1. The inhibition of Raf-1 or MEK1/2 induced a large increase in p27Kip1 in OCM-1 cells, associated with an arrest of cell proliferation. Levels of c-Myc production were high and constant in OCM-1 cells and low in NCM, in contrast to what was observed for p27Kip1. The inhibition of both Raf-1 and MEK1/2 induced a decrease in c-Myc production and downregulated c-Myc activity by preventing c-Myc phosphorylation in OCM-1 cells. We conclude that Raf-1 and the MEK/ERK module control the production of both p27Kip1 and c-Myc, and the activation of c-Myc for OCM-1 cell proliferation.

Role of PI3K/AKT/mTOR signaling in the cell cycle progression of human prostate cancer

Prostate cancer is one of the most common cancers among men. Recent studies demonstrated that PI3K signaling is an important intracellular mediator which is involved in multiple cellular functions including proliferation, differentiation, anti-apoptosis, tumorigenesis, and angiogenesis. In the present study, we demonstrate that the inhibition of PI3K activity by LY294002, inhibited prostate cancer cell proliferation and induced the G(1) cell cycle arrest. This effect was accompanied by the decreased expression of G(1)-associated proteins including cyclin D1, CDK4, and Rb phosphorylation at Ser780, Ser795, and Ser807/811, whereas expression of CDK6 and beta-actin was not affected by LY294002. The expression of cyclin kinase inhibitor, p21(CIP1/WAF1), was induced by LY294002, while levels of p16(INK4) were decreased in the same experiment. The inhibition of PI3K activity also inhibited the phosphorylation and p70(S6K), but not MAPK. PI3K regulates cell cycle through AKT, mTOR to p70(S6K). The mTOR inhibitor rapamycin has similar inhibitory effects on G(1) cell cycle progression and expression of cyclin D1, CDK4, and Rb phosphorylation. These results suggest that PI3K mediates G(1) cell cycle progression and cyclin expression through the activation of AKT/mTOR/p70(S6K) signaling pathway in the prostate cancer cells.

MAP kinase-dependent degradation of p27Kip1 by calpains in choroidal melanoma cells. Requirement of p27Kip1 nuclear export

We investigated the status and the regulation of the cyclin-dependent kinases (CDK) inhibitor p27(Kip1) in a choroidal melanoma tumor-derived cell line (OCM-1). By contrast to normal choroidal melanocytes, the expression level of p27(Kip1) was low in these cells and the mitogen-activated protein (MAP) kinase pathway was constitutively activated. Genetic or chemical inhibition of this pathway induced p27(Kip1) accumulation, whereas MAP kinase reactivation triggered a down-regulation of p27(Kip1) that could be partially reversed by calpain inhibitors. In good accordance, ectopic expression of the cellular calpain inhibitor calpastatin led to an increase of endogenous p27(Kip1) expression. In vitro, p27(Kip1) was degraded by calpains, and OCM-1 cell extracts contained a calcium-dependent p27(Kip1) degradation activity. MAP kinase inhibition partially inhibited both calpain activity and calcium-dependent p27(Kip1) degradation by cellular extracts. Immunofluorescence labeling and subcellular fractionation revealed that p27(Kip1) was in part localized in the cytoplasmic compartment of OCM-1 cells but not of melanocytes, and accumulated into the nucleus upon MAP kinase inhibition. MAP kinase activation triggered a cytoplasmic translocation of the protein, as well as a change in its phosphorylation status. This CRM-1-dependent cytoplasmic translocation was necessary for MAP kinase- and calpain-dependent degradation. Taken together, these data suggest that in tumor-derived cells, p27(Kip1) could be degraded by calpains through a MAP kinase-dependent process, and that abnormal cytoplasmic localization of the protein, probably linked to modifications of its phosphorylation state, could be involved in this alternative mechanism of degradation.

The second phase activation of protein kinase C delta at late G1 is required for DNA synthesis in serum-induced cell cycle progression

BACKGROUND

Cell lines that stably over-express protein kinase C (PKC) delta frequently show a decrease in growth rate and saturation density, leading to the hypothesis that PKC delta has a negative effect on cell proliferation. However, the mode of PKC delta activation, the cell cycle stage requiring PKC delta activity, and the exact role of PKC delta at that stage remains unknown.

RESULTS

Here we show that the treatment of quiescent fibroblasts with serum activates PKC delta at two distinct time points, within 10 min after serum treatment, and for a longer duration between 6 and 10 h. This biphasic activation correlates with the phosphorylation of Thr-505 at the activation loop of PKC delta. Importantly, an inhibitor of PKC delta, rottlerin, suppresses the biphasic activation of PKC delta, and suppression of the second phase of PKC delta activation is sufficient for the suppression of DNA synthesis. Consistent with this, the transient over-expression of PKC delta mutant molecules lacking kinase activity suppresses serum-induced DNA synthesis. These results imply that PKC delta plays a positive role in cell cycle progression. While the over-expression of PKC delta enhances serum-induced DNA synthesis, this was not observed for PKC epsilon. Similar experiments using a series of PKCdelta/ epsilon chimeras showed that the carboxyl-terminal 51 amino acids of PKC delta are responsible for the stimulatory effect. On the other hand, the over-expression of PKC delta suppresses cell entry into M-phase, being consistent with the previous studies based on stable over-expressors.

CONCLUSIONS

We conclude that PKC delta plays a role in the late-G1 phase through the positive regulation of cell-cycle progression, in addition to negative regulation of the entry into M-phase.

Activation of the PI3K/Akt pathway and chemotherapeutic resistance

The resistance of many types of cancer to conventional chemotherapies is a major factor undermining successful cancer treatment. In this review, the role of a signal transduction pathway comprised of the lipid kinase, phosphatidylinositol 3-kinase (PI3K), and the serine/threonine kinase, Akt (or PKB), in chemotherapeutic resistance will be explored. Activation of this pathway plays a pivotal role in essential cellular functions such as survival, proliferation, migration and differentiation that underlie the biology of human cancer. Akt activation also contributes to tumorigenesis and tumor metastasis, and as shown most recently, resistance to chemotherapy. Modulating Akt activity is now a commonly observed endpoint of chemotherapy administration or administration of chemopreventive agents. Studies performed in vitro and in vivo combining small molecule inhibitors of the PI3K/Akt pathway with standard chemotherapy have been successful in attenuating chemotherapeutic resistance. As a result, small molecules designed to specifically target Akt and other components of the pathway are now being developed for clinical use as single agents and in combination with chemotherapy to overcome therapeutic resistance. Specifically inhibiting Akt activity may be a valid approach to treat cancer and increase the efficacy of chemotherapy.

Activation of Akt/protein kinase B overcomes a G(2)/m cell cycle checkpoint induced by DNA damage

Activation of Akt, or protein kinase B, is frequently observed in human cancers. Here we report that Akt activation via overexpression of a constitutively active form or via the loss of PTEN can overcome a G(2)/M cell cycle checkpoint that is induced by DNA damage. Activated Akt also alleviates the reduction in CDC2 activity and mitotic index upon exposure to DNA damage. In addition, we found that PTEN null embryonic stem (ES) cells transit faster from the G(2)/M to the G(1) phase of the cell cycle when compared to wild-type ES cells and that inhibition of phosphoinositol-3-kinase (PI3K) in HEK293 cells elicits G(2) arrest that is alleviated by activated Akt. Furthermore, the transition from the G(2)/M to the G(1) phase of the cell cycle in Akt1 null mouse embryo fibroblasts (MEFs) is attenuated when compared to that of wild-type MEFs. These results indicate that the PI3K/PTEN/Akt pathway plays a role in the regulation of G(2)/M transition. Thus, cells expressing activated Akt continue to divide, without being eliminated by apoptosis, in the presence of continuous exposure to mutagen and accumulate mutations, as measured by inactivation of an exogenously expressed herpes simplex virus thymidine kinase (HSV-tk) gene. This phenotype is independent of p53 status and cannot be reproduced by overexpression of Bcl-2 or Myc and Bcl-2 but seems to counteract a cell cycle checkpoint mediated by DNA mismatch repair (MMR). Accordingly, restoration of the G(2)/M cell cycle checkpoint and apoptosis in MMR-deficient cells, through reintroduction of the missing component of MMR, is alleviated by activated Akt. We suggest that this new activity of Akt in conjunction with its antiapoptotic activity may contribute to genetic instability and could explain its frequent activation in human cancers.

Differentiation of human melanoma cells through p38 MAP kinase is associated with decreased retinoblastoma protein phosphorylation and cell cycle arrest

The retinoblastoma protein (pRB), the product of the retinoblastoma gene, is a key regulator of the cell cycle, affecting apoptosis, proliferation and differentiation. Dysregulation of pRB is implicated in the pathogenesis of many cancers, including malignant melanoma. Recently we demonstrated that alpha-melanocyte-stimulating hormone (alpha-MSH)-induced activation of p38 mitogen-activated protein (MAP) kinase leads to differentiation of B16 murine melanoma cells. The current study assesses the ability of alpha-MSH to activate p38 MAP kinase in COLO 853 human melanoma cells and determines whether this is linked to modulation of pRB activity. Treatment of COLO 853 cells with alpha-MSH induced time- and concentration-dependent increases in the phosphorylation of p38 MAP kinase, which corresponded with its ability to induce melanogenesis and inhibit cell growth. SB 203580, a selective inhibitor of p38 MAP kinase, blocked both the alpha-MSH-induced melanogenic response and inhibition of cell growth. Cell cycle analysis using flow cytometry revealed that treatment of COLO 853 cells with alpha-MSH for 72 h led to an increase in the proportion of cells in the G(1) phase and a marked reduction in the amount of phosphorylated pRB. Both of these effects were reversed by pre-treatment of cells with SB 203580. In summary, we have demonstrated for the first time that the alpha-MSH-induced differentiation of COLO 853 human melanoma cells proceeds via a p38 MAP kinase-mediated pathway and is associated with decreased pRB phosphorylation and accumulation of cells in the G(1) phase.

A discrete cell cycle checkpoint in late G(1) that is cytoskeleton-dependent and MAP kinase (Erk)-independent

Cell spreading on extracellular matrix and associated changes in the actin cytoskeleton (CSK) are necessary for progression through G(1) and entry into S phase of the cell cycle. Pharmacological disruption of CSK integrity inhibits early mitogenic signaling to the extracellular signal-regulated kinase (Erk) subfamily of the mitogen-activated protein kinases (MAPKs) and arrests the cell cycle in G(1). Here we show that this block of G(1) progression is not simply a consequence of inhibition of the MAPK/Erk pathway but instead it reveals the existence of a discrete CSK-sensitive checkpoint. Use of PD98059 to inhibit MAPK/Erk and cytochalasin D (Cyto D) to disrupt the actin CSK at progressive time points in G(1) revealed that the requirement for MAPK/Erk activation lasts only to mid-G(1), while the actin CSK must remain intact up to late G(1) restriction point, R, in order for capillary endothelial cells to enter S phase. Additional analysis using Cyto D pulses defined a narrow time window of 3 h just prior to R in which CSK integrity was shown to be critical for the G(1)/S transition. Cyto D treatment led to down-regulation of cyclin D1 protein and accumulation of the cdk inhibitor, p27(Kip1), independent of cell cycle phase, suggesting that these changes resulted directly from CSK disruption rather than from a general cell cycle block. Together, these data indicate the existence of a distinct time window in late G(1) in which signals elicited by the CSK act independently of early MAPK/Erk signals to drive the cell cycle machinery through the G(1)/S boundary and, hence, promote cell growth.

Baicalein, a novel apoptotic agent for hepatoma cell lines: a potential medicine for hepatoma

This study has demonstrated that baicalein has anticancer effectiveness against human hepatoma cells. The dose response of baicalein in Hep G2 and Hep J2 cells indicates that baicalein decreased viability >90%. In comparison, baicalein had only minimal effects on the viability of control Chang liver cells. Flow cytometric analysis showed that baicalein inhibited the cell cycle of Hep G2 cells in the S phase. In addition, baicalein treatment resulted in a decreased mitochondrial transmembrane potential and damaged the integrity of the cell membrane. The TdT-mediated dUTP-biotin nick end labeling assay results indicated that baicalein elicited a significant increase of DNA fragmentation in Hep G2 cells after incubation for 48 hours. These results indicate that baicalein is an effective antihepatoma agent with minimal influence on noncancer cells. The effects of baicalein on Hep G2 cells include inhibition of the S phase of the cell cycle, dysfunction of mitochondria, and initiation of apoptosis.

ErbB2-overexpressing human mammary carcinoma cells display an increased requirement for the phosphatidylinositol 3-kinase signaling pathway in anchorage-independent growth

The proto-oncogene ErbB2 is known to be amplified and to play an important role in the development of about one-third of human breast cancers. Phosphatidylinositol 3-kinase (PI3K), which is often activated in ErbB2-overexpressing breast cancer cells, is known to regulate cell proliferation and cell survival. Selective inhibitors of the PI3K pathway were used to assess the relevance of PI3K signaling in the anchorage-independent growth of a series of human mammary carcinoma cell lines. Wortmannin, LY294002, and rapamycin at concentrations that did not affect MAPK phosphorylation but substantially inhibited PI3K, Akt, and p70(S6K) significantly suppressed the soft agar growth of tumor cell lines that overexpress ErbB2 but not the growth of tumor lines with low ErbB2 expression. A similar growth inhibition of ErbB2-overexpressing carcinoma lines was observed when a dominant negative p85(PI3K) mutant was introduced into these cells. Forced expression of ErbB2 in breast cancer lines originally expressing low ErbB2 levels augmented receptor expression and sensitized those lines to LY294002- and rapamycin-mediated inhibition of colony formation. Furthermore, treatment with LY294002 resulted in the selective increase of cyclin-dependent kinase inhibitors p21(Cip1) or p27(Kip1) and suppression of cyclin E-associated Cdk2 kinase activity in ErbB2-overexpressing lines, which may account for their hypersensitivity toward inhibitors of the PI3K pathway in anchorage-independent growth. Our results indicate that the PI3K/Akt/p70(S6K) pathway plays an enhanced role in the anchorage-independent growth of ErbB2-overexpressing breast cancer cells, therefore providing a molecular basis for the selective targeting of this signaling pathway in the treatment of ErbB2-related human breast malignancies.

The p42/p44 mitogen-activated protein kinase activation triggers p27Kip1 degradation independently of CDK2/cyclin E in NIH 3T3 cells

The p42/p44 mitogen-activated protein (MAP) kinase is stimulated by various mitogenic stimuli, and its sustained activation is necessary for cell cycle G(1) progression and G(1)/S transition. G(1) progression and G(1)/S transition also depend on sequential cyclin-dependent kinase (CDK) activation. Here, we demonstrate that MAP kinase inhibition leads to accumulation of the CDK inhibitor p27(Kip1) in NIH 3T3 cells. Blocking the proteasome-dependent degradation of p27(Kip1) impaired this accumulation, suggesting that MAP kinase does not act on p27(Kip1) protein synthesis. In the absence of extracellular signals (growth factors or cell adhesion), genetic activation of MAP kinase decreased the expression of p27(Kip1) as assessed by cotransfection experiments and by immunofluorescence detection. Importantly, MAP kinase activation also decreased the expression of a p27(Kip1) mutant, which cannot be phosphorylated by CDK2, suggesting that MAP kinase-dependent p27(Kip1) regulation is CDK2-independent. Accordingly, expression of dominant-negative CDK2 did not impair the down-regulation of p27(Kip1) induced by MAP kinase activation. These data demonstrate that the MAP kinase pathway regulates p27(Kip1) expression in fibroblasts essentially through a degradation mechanism, independently of p27(Kip1) phosphorylation by CDK2. This strengthens the role of this CDK inhibitor as a key effector of G(1) growth arrest, whose expression can be controlled by extracellular stimuli-dependent signaling pathways.

Phosphatidylinositol 3-kinase is necessary but not sufficient for thrombopoietin-induced proliferation in engineered Mpl-bearing cell lines as well as in primary megakaryocytic progenitors

Thrombopoietin and its receptor (Mpl) support survival and proliferation in megakaryocyte progenitors and in BaF3 cells engineered to stably express Mpl (BaF3/Mpl). The binding of thrombopoietin to Mpl activates multiple kinase pathways, including the Jak/STAT, Ras/Raf/MAPK, and phosphatidylinositol 3-kinase pathways, but it is not clear how these kinases promote cell cycling. Here, we show that thrombopoietin induces phosphatidylinositol 3-kinase and that phosphatidylinositol 3-kinase is required for thrombopoietin-induced cell cycling in BaF3/Mpl cells and in primary megakaryocyte progenitors. Treatment of BaF3/Mpl cells and megakaryocytes with the phosphatidylinositol 3-kinase inhibitor LY294002 inhibited mitotic and endomitotic cell cycl-ing. BaF3/Mpl cells treated with thrombopoietin and LY294002 were blocked in G(1), whereas megakaryocyte progenitors treated with thrombopoietin and LY294002 showed both a G(1) and a G(2) cell cycle block. Expression of constitutively active Akt in BaF3/Mpl cells restored the ability of thrombopoietin to promote cell cycling in the presence of LY294002. Constitutively active Akt was not sufficient to drive proliferation of BaF3/Mpl cells in the absence of thrombopoietin. We conclude that in BaF3/Mpl cells and megakaryocyte progenitors, thrombopoietin-induced phosphatidylinositol 3-kinase activity is necessary but not sufficient for thrombopoietin-induced cell cycle progression. Phosphatidylinositol 3-kinase activity is likely to be involved in regulating the G(1)/S transition.

Phosphatidylinositol 3-kinase regulates proliferation of RAW 264.7 macrophages

Phosphatidylinositol 3-kinase (P13-kinase) is an enzyme that acts as a direct biochemical link between a novel phosphatidylinositol pathway and a number of proteins containing intrinsic or associated kinase activities. Here we demonstrate that wortmannin, P13-kinase inhibitor, decreases the proliferation of RAW 264.7 macrophages and that another structurally unrelated inhibitor of P13-kinase, LY294002. also inhibits the proliferation. These results indicate a possible involvement of P13-kinase in RAW 264.7 macrophages growth regulation. Wortmannin stimulation of RAW 264.7 macrophages is followed by sustained expression of the mRNA of c-fos and a transient expression of the mRNA of c-jun. We also show that the wortmannin and LY294002 induce a cell cycle arrest in asynchronously growing cells leading to an inhibition of cell proliferation after 12 h of treatment. In addition, wortmannin or LY294002 inhibited the phorbol 12-myristate 13-acetate-induced macrophages proliferation potently. These results suggest that P13-kinase plays an important role in growth regulation of RAW 264.7 macrophages and that protein kinase C is a down stream effector of P13-kinase.

Phosphoinositide 3-kinase-dependent regulation of interleukin-3-induced proliferation: involvement of mitogen-activated protein kinases, SHP2 and Gab2

We have demonstrated previously that class I(A) phosphoinositide 3-kinases play a major role in regulation of interleukin-3 (IL)-3-dependent proliferation. Investigations into the downstream targets involved have identified the MAPK cascade as a target. Expression of Deltap85 and incubation with LY294002 both inhibited IL-3-induced activation of Mek, Erk1, and Erk2. This was most pronounced during the initial phase of Erk activation. The Mek inhibitor, PD98059, blocked IL-3-driven proliferation, an effect enhanced by Deltap85 expression, suggesting that inhibition of Mek and Erks by Deltap85 contributes to the decrease in IL-3-induced proliferation in these cells but that additional pathways may also be involved. To investigate the mechanism leading to decreased activation of Erks, we investigated effects on SHP2 and Gab2, both implicated in IL-3 regulation of Erk activation. Expression of Deltap85 led to a reduction in SHP2 tyrosine phosphorylation and its ability to interact with Grb2 and Gab2 but increased overall tyrosine phosphorylation of Gab2. LY294002 did not perturb SHP2 interactions, potentially related to differences in the effects of these inhibitors on levels of phosphoinositides. These results imply that the regulation of Erks by class I(A) phosphoinositide 3-kinase may contribute to IL-3-driven proliferation and that both SHP2 and Gab2 are possibly involved in this regulation.

Caenorhabditis elegans PIAK, a phospholipid-independent kinase that activates the AKT/PKB survival kinase

Phospholipid-dependent kinase 1 (PDK 1) is a 3'-phospholipid-responsive serine/threonine kinase that plays a critical role in cell survival by phosphorylating and activating the anti-apoptotic AKT/PKB kinase. While PDK 1 is clearly an important component of the cell survival machinery, the potential for phospholipid-independent activation of the AKT/PKB survival pathway has not been extensively examined at the molecular level. We have identified a second form of PDK 1 in the nematode Caenorhabditis elegans that we have termed PIAK (phospholipid-independent AKT/PKB kinase). PIAK is highly homologous to C. elegans and mammalian PDK 1 with the exception that the novel kinase lacks a phospholipid binding pleckstrin homology domain. The domain structure of PIAK suggests that it might be a phospholipid-independent kinase, and PIAK phosphorylates mammalian AKT/PKB at the activating Thr(308) residue in the presence of the phosphatidylinositol (PI) 3-kinase inhibitors as well as in the absence of growth factors. In addition, PIAK is capable of inducing the phospholipid-independent, AKT/PKB-induced phosphorylation of the AFX-type forkhead transcription factor, resulting in its cytoplasmic localization. Because the nuclear localization of this transcription factor induces an apoptotic state, this PIAK-mediated cytoplasmic sequestration allows for cell survival. Finally, PIAK activity appears to be induced by various inhibitors of cell cycle G(1) progression. These data suggest an alternate, phosphatidylinositol 3-kinase-independent mechanism for the activation of the AKT/PKB survival pathway that may be utilized during periods of cellular quiescence.