PKB/Akt phosphorylates p27, impairs nuclear import of p27 and opposes p27-mediated G1 arrest

Voluntary physical activity abolishes the proliferative tumor growth microenvironment created by adipose tissue in animals fed a high fat diet

The molecular mechanisms behind the obesity-breast cancer association may be regulated via adipokine secretion by white adipose tissue. Specifically, adiponectin and leptin are altered with adiposity and exert antagonistic effects on cancer cell proliferation. We set out to determine whether altering adiposity in vivo via high fat diet (HFD) feeding changed the tumor growth supporting nature of adipose tissue and whether voluntary physical activity (PA) could ameliorate these HFD-dependent effects. We show that conditioned media (CM) created from the adipose tissue of HFD fed animals caused an increase in the proliferation of MCF7 cells compared with cells exposed to CM prepared from the adipose of lean chow diet fed counterparts. This increased proliferation was driven within the MCF7 cells by an HFD-dependent antagonism between AMP-activated protein kinase (AMPK) and protein kinase B (Akt) signaling pathways, decreasing p27 protein levels via reduced phosphorylation at T198 and downregulation of adiponectin receptor 1 (AdipoR1). PA can ameliorate these proliferative effects of HFD-CM on MCF7 cells, increasing p27(T198) by AMPK, reducing pAkt(T308), and increasing AdipoR1, resulting in cell cycle withdrawal in a manner that depends on the PA intensity. High physical activity (>3 km/day) completely abolished the effects of HFD feeding. In addition, AdipoR1 overexpression mimics the effects of exercise, abolishing the proliferative effects of the HFD-CM on MCF7 cells and further enhancing the antiproliferative effects of PA on the HFD-CM. Thus voluntary PA represents a means to counteract the proliferative effects of adipose tissue on breast cancers in obese patients.

p27 Is a Candidate Prognostic Biomarker and Metastatic Promoter in Osteosarcoma

Metastatic progression is the major cause of death in osteosarcoma, the most common bone malignancy in children and young adults. However, prognostic biomarkers and efficacious targeted treatments for metastatic disease remain lacking. Using an immunoproteomic approach, we discovered that autoantibodies against the cell-cycle kinase inhibitor p27 (KIP1, CDKN1B) were elevated in plasma of high-risk osteosarcoma patients. Using a large cohort of serum samples from osteosarcoma patients (n = 233), we validated that a higher level of the p27 autoantibody significantly correlated with poor overall and event-free survival (P < 0.05). Immunohistochemical analysis also showed that p27 was mislocalized to the cytoplasm in the majority of osteosarcoma cases and in highly metastatic osteosarcoma cell lines. We demonstrated that ectopic expression of cytoplasmic p27 promoted migration and invasion of osteosarcoma cells, whereas shRNA-mediated gene silencing suppressed these effects. In addition, mutations at the p27 phosphorylation sites S10 or T198, but not T157, abolished the migratory and invasive phenotypes. Furthermore, the development of pulmonary metastases increased in mice injected with cells expressing cytoplasmic p27 compared with an empty vector control. Collectively, our findings support further investigation of p27 as a potential prognostic biomarker and therapeutic target in osteosarcoma cases exhibiting aberrant p27 subcellular localization. Cancer Res; 76(13); 4002-11. ©2016 AACR.

The non-canonical functions of p27(Kip1) in normal and tumor biology

p27(Kip1) was first discovered as a key regulator of cell proliferation. The canonical function of p27(Kip1) is inhibition of cyclin-dependent kinase (CDK) activity. In addition to its initial identification as a CDK inhibitor, p27(Kip1) has also emerged as an intrinsically unstructured, multifunctional protein with numerous non-canonical, CDK-independent functions that exert influence on key processes such as cell cycle regulation, cytoskeletal dynamics and cellular plasticity, cell migration, and stem-cell proliferation and differentiation. Many of these non-canonical functions, depending on the cell-specific contexts such as oncogenic activation of signaling pathways, have the ability to turn pro-oncogenic in nature and even contribute to tumor-aggressiveness and metastasis. This review discusses the various non-canonical, CDK-independent mechanisms by which p27(Kip1) functions either as a tumor-suppressor or tumor-promoter.

Inhibition of miR301 enhances Akt-mediated cell proliferation by accumulation of PTEN in nucleus and its effects on cell-cycle regulatory proteins

Micro-RNAs (miRs) represent an innovative class of genes that act as regulators of gene expression. Recently, the aberrant expression of several miRs has been associated with different types of cancers. In this study, we show that miR301 inhibition influences PI3K-Akt pathway activity. Akt overexpression in MCF7 and MDAMB468 cells caused downregulation of miR301 expression. This effect was confirmed by co-transfection of miR301-modulators in the presence of Akt. Cells overexpressing miR301-inhibitor and Akt, exhibited increased migration and proliferation. Experimental results also confirmed PI3K, PTEN and FoxF2 as regulatory targets for miR301. Furthermore, Akt expression in conjunction with miR301-inhibitor increased nuclear accumulation of PTEN, thus preventing it from downregulating the PI3K-signalling. In summary, our data emphasize the importance of miR301 inhibition on PI3K-Akt pathway-mediated cellular functions. Hence, it opens new avenues for the development of new anti-cancer agents preferentially targeting PI3K-Akt pathway.

CSN6 deregulation impairs genome integrity in a COP1-dependent pathway

Understanding genome integrity and DNA damage response are critical to cancer treatment. In this study, we identify CSN6's biological function in regulating genome integrity. Constitutive photomorphogenic 1 (COP1), an E3 ubiquitin ligase regulated by CSN6, is downregulated by DNA damage, but the biological consequences of this phenomenon are poorly understood. p27^Kip1 is a critical CDK inhibitor involved in cell cycle regulation, but its response to DNA damage remains unclear. Here, we report that p27^Kip1 levels are elevated after DNA damage, with concurrent reduction of COP1 levels. Mechanistic studies showed that during DNA damage response COP1's function as an E3 ligase of p27 is compromised, thereby reducing the ubiquitin-mediated degradation of p27^Kip1. Also, COP1 overexpression leads to downregulation of p27^Kip1, thereby promoting the expression of mitotic kinase Aurora A. Overexpression of Aurora A correlates with poor survival. These findings provide new insight into CSN6-COP1-p27^Kip1-Aurora A axis in DNA damage repair and tumorigenesis.

Autophagy and Apoptotic Crosstalk: Mechanism of Therapeutic Resistance in HER2-Positive Breast Cancer

While breast cancer patients benefit from the use of HER2 inhibitors, many fail therapy and become resistant to treatment, indicating a critical need to prevent treatment failure. A number of studies have emerged that highlight the catabolic process of autophagy in breast cancer as a mechanism of resistance to chemotherapy and targeted inhibitors. Furthermore, recent research has begun to dissect how autophagy signaling crosstalks with apoptotic signaling. Thus, a possible strategy in fighting resistance is to couple targeting of apoptotic and autophagy signaling pathways. In this review, we discuss how cellular response by autophagy circumvents cell death to promote resistance of breast cancers to HER2 inhibitors, as well as the potential avenues of therapeutic intervention.

AKT signaling in ERBB2-amplified breast cancer

The PI3K/AKT pathway is the focus of several targeted therapeutic agents for a variety of malignancies. In ERBB2-amplified breast cancer, the hyperactivation of this signaling cascade is associated with resistance to ERBB2-targeted therapy. This can occur through gain-of-function alterations or compensatory mechanisms that enter into play upon pharmacological pressure. The strong rationale in combining anti-ERBB2 agents with PI3K/AKT inhibitors, together with the identification of genomic alterations conferring sensitivity to targeted inhibition, are guiding the design of clinical studies aimed at preventing the emergence of drug resistance and achieving more durable response. In the present review, we describe the involvement of this pathway in breast cancer pathogenesis, with an emphasis on AKT kinases, and provide insight into currently available targeted agents for the treatment of ERBB2-amplified breast cancer. Finally, we provide preliminary data on a novel AKT3 mutation detected in the context of resistance to anti-ERBB2 therapy as an example of genomics-based approaches towards uncovering novel actionable targets in this setting.

Interferon-γ-induced p27KIP1 binds to and targets MYC for proteasome-mediated degradation

The Myc oncoprotein is tightly regulated at multiple levels including ubiquitin-mediated protein turnover. We recently demonstrated that inhibition of Cdk2-mediated phosphorylation of Myc at Ser-62 pharmacologically or through interferon (IFN)-γ-induced expression of p27(Kip1) (p27) repressed Myc's activity to suppress cellular senescence and differentiation. In this study we identified an additional activity of p27 to interfere with Myc independent of Ser-62 phosphorylation. p27 is required and sufficient for IFN-γ-induced turnover of Myc. p27 interacted with Myc in the nucleus involving the C-termini of the two proteins, including Myc box 4 of Myc. The C-terminus but not the Cdk2 binding fragment of p27 was sufficient for inducing Myc degradation. Protein expression data of The Cancer Genome Atlas breast invasive carcinoma set revealed significantly lower Myc protein levels in tumors with highly expressed p27 lacking phosphorylation at Thr-157--a marker for active p27 localized in the nucleus. Further, these conditions correlated with favorable tumor stage and patient outcome. This novel regulation of Myc by IFN-γ/p27(KIP1) potentially offers new possibilities for therapeutic intervention in tumors with deregulated Myc.

DC120, a novel AKT inhibitor, preferentially suppresses nasopharyngeal carcinoma cancer stem-like cells by downregulating Sox2

Side population (SP) contains cancer stem-like cells (CSLCs). In this study, we characterized SP cells from nasopharyngeal carcinoma (NPC) cell lines and found that SP cells had a higher self-renewal ability in vitro and greater tumorigenicity in vivo. The AKT pathway was activated in NPC SP cells. DC120, a 2-pyrimidyl-5-amidothiazole inhibitor of the ATP binding site of AKT, inhibited phosphorylation of FKHRL1 and GSK-3β. DC120 inhibited SP fraction, the sphere-forming ability in vitro and growth of primary xenografts as well as secondary xenografts’ tumor recurrence. This inhibition was accompanied by reduced expression of stem-related gene Sox2 due to induction of p27 and miR-30a. A combination of DC120 and CDDP more effectively inhibited NPC cells compared with monotherapy in vitro and in vivo. Clinical evaluation of DC120 is warranted.

The soybean-derived peptide lunasin inhibits non-small cell lung cancer cell proliferation by suppressing phosphorylation of the retinoblastoma protein

Lunasin, a soybean bioactive peptide, has both chemopreventive and chemotherapeutic activities. The aim of this study was to determine the chemotherapeutic potential of lunasin against human lung cancer. Treatment of non-small cell lung cancer (NSCLC) cells with highly purified soybean-derived lunasin caused limited, cell-line specific anti-proliferative effects on anchorage-dependent growth whereas two normal bronchial epithelial cell lines were unaffected. Lunasin's antiproliferative effects were potentiated upon utilization of anchorage-independent conditions. Furthermore, NSCLC cell lines that were unaffected by lunasin in anchorage-dependent assays exhibited a dose-dependent inhibition in colony formation or colony size. Mouse xenograft studies revealed that 30 mg lunasin/kg body weight per day decreased NSCLC H1299 tumor volume by 63.0% at day 32. Mechanistic studies using cultured NSCLC H661 cells showed that lunasin inhibited cell cycle progression at the G1/S phase interface without inducing apoptosis. Immunoblot analyses of key cell-cycle proteins demonstrated that lunasin altered the expression of the G1 specific cyclin-dependent kinase complex components, increased levels of p27Kip1, reduced levels of phosphorylated Akt, and ultimately inhibited the sequential phosphorylation of the retinoblastoma protein (RB). These results establish for the first time that lunasin can inhibit NSCLC proliferation by suppressing cell-cycle dependent phosphorylation of RB.

Investigation of triazole-linked indole and oxindole glycoconjugates as potential anticancer agents: novel Akt/PKB signaling pathway inhibitors

Novel triazole-linked indole and oxindole glycoconjugates as inhibitors of the Akt/PKB signaling pathway.

Mg(++) requirement for MtHK binding, and Mg(++) stabilization of mitochondrial membranes via activation of MtHK & MtCK and promotion of mitochondrial permeability transition pore closure: A hypothesis on mechanisms underlying Mg(++)'s antioxidant and cytoprotective effects

Evidence points to magnesium's antioxidant, anti-necrotic, and anti-apoptotic effects in cardio- and neuroprotection. With magnesium being involved in over 300 biochemical reactions, the mechanisms underlying its cytoprotective and antioxidant effects have remained elusive. The profound anti-apoptotic, anabolic, and antioxidant effects of mitochondrion bound hexokinase (MtHk), and the anti-apoptotic, anti-necrotic, and antioxidant functions of mitochondrial creatine kinase (MtCK) have been established over the past few decades. As powerful regulators of the mitochondrial permeability transition pore (PTP), MtHK and MtCK promote anti-apoptosis and anti-necrosis by stabilizing mitochondrial outer and inner membranes. In this article, it is proposed that magnesium is essentially and directly involved in mitochondrial membrane stabilization via (i) Mg(++) ion requirement for the binding of mitochondrial hexokinase (ii) Mg(++)'s allosteric activation of mitochondrial bound hexokinase, and stimulation of mitochondrial bound creatine kinase activities, and (iii) Mg(++) inhibition of PTP opening by Ca(++) ions. These effects of Mg(++) ions are indirectly supplanted by the stimulatory effect of magnesium on the Akt kinase survival pathway. The "Magnesium/Calcium Yin Yang Hypothesis" proposes here that because of the antagonistic effects of Ca(++) and Mg(++) ions in the presence of high Ca(++) ion concentration at MtHK, MtCK, and PTP, magnesium supplementation may provide cytoprotective effects in the treatment of some degenerative diseases and cytopathies with high intracellular [Ca(++)]/ [Mg(++)] ratio at these sites, whether of genetic, developmental, drug induced, ischemic, immune based, toxic, or infectious etiology.

Nuclear Localization of DNAJB6 Is Associated With Survival of Patients With Esophageal Cancer and Reduces AKT Signaling and Proliferation of Cancer Cells

BACKGROUND & AIMS

The DnaJ (Hsp40) homolog, subfamily B, member 6 (DNAJB6) is part of a family of proteins that regulates chaperone activities. One of its isoforms, DNAJB6a, contains a nuclear localization signal and regulates β-catenin signaling during breast cancer development. We investigated the role of DNAJB6 in the pathogenesis of esophageal squamous cell carcinoma (ESCC).

METHODS

We performed immunohistochemical analyses of primary ESCC samples and lymph node metastases from a cohort of 160 patients who underwent esophagectomy with no preoperative chemoradiotherapy at Hong Kong Queen Mary Hospital. Data were collected on patient outcomes over a median time of 12.1 ± 2.9 months. Retrospective survival association analyses were performed. Wild-type and mutant forms of DNAJB6a were overexpressed in cancer cell lines (KYSE510, KYSE 30TSI, KYSE140, and KYSE70TS), which were analyzed in proliferation and immunoblot assays, or injected subcutaneously into nude mice. Levels of DNAJB6 were knocked down in ESCC cell lines (KYSE450 and T.Tn), immortalized normal esophageal epithelial cell lines (NE3 and NE083), and other cells with short hairpin RNAs, or by genome engineering. Bimolecular fluorescence complementation was used to study interactions between proteins in living cells.

RESULTS

In primary ESCC samples, patients whose tumors had high nuclear levels of DNAJB6 had longer overall survival times (19.2 ± 1.8 months; 95% confidence interval [CI], 15.6-22.8 mo) than patients whose tumors had low nuclear levels of DNAJB6 (12.6 ± 1.4 mo; 95% CI, 9.8-15.4 mo; P = .004, log-rank test). Based on Cox regression analysis, patients whose tumors had high nuclear levels of DNAJB6 had a lower risk of death than patients with low levels (hazard ratio, 0.562; 95% CI, 0.379-0.834; P = .004). Based on log-rank analysis and Cox regression analysis, the combination of the nuclear level of DNAJB6 and the presence of lymph node metastases at diagnosis could be used to stratify patients into groups with good or bad outcomes (P < .0005 for both analyses). There was a negative association between the nuclear level of DNAJB6 and the presence of lymph node metastases (P = .022; Pearson χ(2) test). Cancer cell lines that overexpressed DNAJB6a formed tumors more slowly in nude mice than control cells or cells that expressed a mutant form of DNAJB6a that did not localize to the nucleus. DNAJB6 knockdown in cancer cell lines promoted their growth as xenograft tumors in mice. A motif of histidine, proline, and aspartic acid in the J domain of DNAJB6a was required for its tumor-suppressive effects and signaling via AKT1. Loss of DNAJB6a resulted in up-regulation of AKT signaling in cancer cell lines and immortalized esophageal epithelial cells. Expression of a constitutively active form of AKT1 restored proliferation to tumor cells that overexpressed DNAJB6a, and DNAJB6a formed a complex with AKT1 in living cells. The expression of DNAJB6a reduced the sensitivity of ESCC to AKT inhibitors; the expression level of DNAJB6a affected AKT signaling in multiple cancer cell lines.

CONCLUSIONS

Nuclear localization of DNAJB6 is associated with longer survival times of patients with ESCC. DNAJB6a reduces AKT signaling, and DNAJB6 expression in cancer cells reduces their proliferation and growth of xenograft tumors in mice. DNAJB6a might be developed as a biomarker for progression of ESCC.

Mislocalization of p27 to the cytoplasm of breast cancer cells confers resistance to anti-HER2 targeted therapy

As a cell cycle inhibitor and tumor suppressor, p27 is frequently misregulated in human cancers. Increased degradation is the most common mechanism of misregulation, however in some cancers, p27 is mislocalized from its cell cycle inhibitory location in the nucleus, to the cytoplasm. In normal cells cytoplasmic p27 has functions that are distinct from its cell cycle-regulatory nuclear functions. Therefore, an important question is whether localization of p27 to the cytoplasm in tumor cells is primarily a mechanism for cancelling its inhibitory effect on cell proliferation, or whether cytoplasmic p27 has more direct oncogenic actions. To study p27 mislocalization in human cancers we screened a panel of common breast cancer cell lines. We observed that p27 accumulated in the cytoplasm exclusively in cell lines that are Her2+. To address the significance of p27 mislocalization in Her2+ breast cancer cells we interrogated the cellular response to the dual-Her2/EGFR kinase inhibitor, lapatinib. Knockdown of p27 using shRNA sensitized Her2+ cells to lapatinib-induced apoptosis. Moreover, expression of a constitutively cytoplasmic form of p27 (p27ΔNLS) reversed the lapatinib-induced apoptosis, suggesting that cytoplasmic p27 contributed to lapatinib resistance in Her2+ breast cancer cells by suppressing apoptosis. Our results suggest that p27 localization may be useful as a predictive biomarker of therapeutic response in patients with Her2+ breast cancers.

Discovery of Small Molecules that Inhibit the Disordered Protein, p27(Kip1)

Disordered proteins are highly prevalent in biological systems, they control myriad signaling and regulatory processes, and their levels and/or cellular localization are often altered in human disease. In contrast to folded proteins, disordered proteins, due to conformational heterogeneity and dynamics, are not considered viable drug targets. We challenged this paradigm by identifying through NMR-based screening small molecules that bound specifically, albeit weakly, to the disordered cell cycle regulator, p27^Kip1 (p27). Two groups of molecules bound to sites created by transient clusters of aromatic residues within p27. Conserved chemical features within these two groups of small molecules exhibited complementarity to their binding sites within p27, establishing structure-activity relationships for small molecule:disordered protein interactions. Finally, one compound counteracted the Cdk2/cyclin A inhibitory function of p27 in vitro, providing proof-of-principle that small molecules can inhibit the function of a disordered protein (p27) through sequestration in a conformation incapable of folding and binding to a natural regulatory target (Cdk2/cyclin A).

Association of cytoplasmic p27 expression with an unfavorable response to cisplatin-based chemotherapy and poor outcomes in non-small cell lung cancer

Reduced nuclear p27 expression is associated with a poor outcome in various cancers, including non-small cell lung cancer (NSCLC). Cytoplasmic p27 expression was shown to be associated with an unfavorable response to chemotherapy and poor outcomes in some carcinomas, but it has not been well studied in NSCLC. Herein, p27 expression in 219 tumors surgically resected from NSCLC patients was evaluated by immunohistochemistry (IHC). The most common of p27 immunostaining in lung tumors was observed in the cytoplasm (N-/C+, 32 %), followed by negative (N-/C-, 29 %), nucleus (N+/C-, 24 %), and nucleus plus cytoplasm (N+/C+, 15 %). Kaplan-Meier and Cox regression models showed that p27 N-/C+ tumors exhibited the worst overall survival (OS) and relapse-free survival (RFS) among the four categories of tumors. Among 135 of 219 patients who received cisplatin-based chemotherapy, p27 N-/C+ tumors most commonly showed an unfavorable response to cisplatin-based chemotherapy, followed by p27 N-/C- tumors when p27 N+/C- tumors were used as a reference. IHC analysis for phosphorylated extracellular signal-regulated kinase (p-ERK) and Bcl-2 expression in the lung tumors was performed to test whether ERK activation could enhance p27 nuclear export and the expression of Bcl-2 to test whether ERK activation could enhance p27 nuclear export and Bcl-2 expression. The data showed that p-ERK expression was positively correlated with cytoplasmic p27 (N-/C+) and Bcl-2 expression in the lung tumors. Patients with high Bcl-2-expressing tumors treated with cisplatin-based chemotherapy showed unfavorable predictive values in a subset of this study population. Therefore, we suggest that cytoplasmic p27 (N-/C+) via ERK-activated Bcl-2 expression may predict an unfavorable response to cisplatin-based chemotherapy and poor outcomes in NSCLC.

SUMOylation regulates p27Kip1 stability and localization in response to TGFβ

Exposure of normal and tumor-derived cells to TGFβ results in different outcomes, depending on the regulation of key targets. The CDK inhibitor p27(Kip1) is one of these TGFβ targets and is essential for the TGFβ-induced cell cycle arrest. TGFβ treatment inhibits p27(Kip1) degradation and induces its nuclear translocation, through mechanisms that are still unknown. Recent evidences suggest that SUMOylation, a post-translational modification able to modulate the stability and subcellular localization of target proteins, critically modifies members of the TGFβ signaling pathway. Here, we demonstrate that p27(Kip1) is SUMOylated in response to TGFβ treatment. Using different p27(Kip1) point mutants, we identified lysine 134 (K134) as the residue modified by small ubiquitin-like modifier 1 (SUMO1) in response to TGFβ treatment. TGFβ-induced K134 SUMOylation increased protein stability and nuclear localization of both endogenous and exogenously expressed p27(Kip1). We observed that SUMOylation regulated p27(Kip1) binding to CDK2, thereby governing its nuclear proteasomal degradation through the phosphorylation of threonine 187. Importantly, p27(Kip1) SUMOylation was necessary for proper cell cycle exit following TGFβ treatment. These data indicate that SUMOylation is a novel regulatory mechanism that modulates p27(Kip1) function in response to TGFβ stimulation. Given the involvement of TGFβ signaling in cancer cell proliferation and invasion, our data may shed light on an important aspect of this pathway during tumor progression.

Androgen actions via androgen receptor promote PTEN inactivation induced uterine cancer

Haploinsufficient inactivating phosphatase and tensin homolog (Pten) mutations cause Cowden syndrome, an autosomal dominant risk genotype for hormone dependent reproductive cancers. As androgen actions mediated via the androgen receptor (AR) supports uterine growth and may modify uterine cancer risk, we hypothesized that a functional AR may increase PTEN inactivation induced uterine cancer. To test the hypothesis, we compared the PTEN knockout (PTENKO) induced uterine pathology in heterozygous PTENKO and combined heterozygous PTEN and complete AR knockout (PTENARKO) female mice. PTENKO induced uterine pathology was significantly reduced by AR inactivation with severe macroscopic uterine pathology present in 21% of PTENARKO vs 46% of PTENKO at a median age of 45 weeks. This could be due to reduced stroma ERα expression in PTENARKO compared to PTENKO uterus, while AR inactivation did not modify PTEN or P-AKT levels. Unexpectedly, while progesterone (P4) is assumed protective in uterine cancers, serum P4 was significantly higher in PTENKO females compared to WT, ARKO, and PTENARKO females consistent with more corpora lutea in PTENKO ovaries. Serum testosterone and ovarian estradiol were similar between all females. Hence, our results demonstrated AR inactivation mediated protection against PTENKO induced uterine pathology and suggests a potential role for antiandrogens in uterine cancer prevention and treatment.

Increasing cisplatin sensitivity by schedule-dependent inhibition of AKT and Chk1

The effectiveness of DNA damaging chemotherapy drugs can be limited by activation of survival signaling pathways and cell cycle checkpoints that allow DNA repair. Targeting survival pathways and inhibiting cell cycle checkpoints may increase chemotherapy-induced cancer cell killing. AKT and Chk1 are survival and cell cycle checkpoint kinases, respectively, that can be activated by DNA damage. Cisplatin (CP) is a standard chemotherapy agent for osteosarcoma (OS). CP induced apoptosis to varying extents and activated AKT and Chk1 in multiple p53 wild-type and p53-null OS cell lines. A Chk1 inhibitor increased CP-induced apoptosis in all OS cell lines regardless of p53 status. In contrast, an AKT inhibitor increased CP-induced apoptosis only in p53 wild-type OS cells, but not p53 nulll cells. The increased apoptosis in p53 wild-type cells was coincident with decreased p53 protein levels, but increased expression of p53-responsive apoptotic genes Noxa and PUMA. Further studies revealed the inability of AKT inhibitor to CP-sensitize p53-null OS cells resulted from 2 things: 1) AKT inhibition stabilized/maintained p27 levels in CP-treated cells, which then mediated a protective G1-phase cell cycle arrest, 2) AKT inhibition increased the levels of activated Chk1. Finally, schedule dependent inhibition of AKT and Chk1 evaded the protective G1 arrest mediated by p27 and maximized CP-induced OS cell killing. These data demonstrate AKT and Chk1 activation promote survival in CP-treated OS cells, and that strategic, scheduled targeting of AKT and Chk1 can maximize OS cell killing by CP.

P27Kip1 serine 10 phosphorylation determines its metabolism and interaction with cyclin-dependent kinases

p27Kip1 is a critical modulator of cell proliferation by controlling assembly, localization and activity of cyclin-dependent kinase (CDK). p27Kip1 also plays important roles in malignant transformation, modulating cell movement and interaction with the extracellular matrix. A critical p27Kip1 feature is the lack of a stable tertiary structure that enhances its "adaptability" to different interactors and explains the heterogeneity of its function. The absence of a well-defined folding underlines the importance of p27Kip1 post-translational modifications that might highly impact the protein functions. Here, we characterize the metabolism and CDK interaction of phosphoserine10-p27Kip1 (pS10- p27Kip1), the major phosphoisoform of p27Kip1. By an experimental strategy based on specific immunoprecipitation and bidimensional electrophoresis, we established that pS10-p27Kip1 is mainly bound to cyclin E/CDK2 rather than to cyclin A/CDK2. pS10- p27Kip1 is more stable than non-modified p27Kip1, since it is not (or scarcely) phosphorylated on T187, the post-translational modification required for p27Kip1 removal in the nucleus. pS10-p27Kip1 does not bind CDK1. The lack of this interaction might represent a mechanism for facilitating CDK1 activation and allowing mitosis completion. In conclusion, we suggest that nuclear p27Kip1 follows 2 almost independent pathways operating at different rates. One pathway involves threonine-187 and tyrosine phosphorylations and drives the protein toward its Skp2-dependent removal. The other involves serine-10 phosphorylation and results in the elongation of p27Kip1 half-life and specific CDK interactions. Thus, pS10-p27Kip1, due to its stability, might be thought as a major responsible for the p27Kip1-dependent arrest of cells in G1/G0 phase.

N-acetyl cysteine protects human oral keratinocytes from Bis-GMA-induced apoptosis and cell cycle arrest by inhibiting reactive oxygen species-mediated mitochondrial dysfunction and the PI3K/Akt pathway

Bisphenol-A-glycidyl methacrylate (Bis-GMA) released from dental resin materials causes various toxic effects on gingival epithelium. Thus the underlying mechanisms of its cytotoxicity should be elucidated for safety use. One potential cause of cell damage is the generation of reactive oxygen species (ROS) beyond the capacity of a balanced redox regulation. In this study, we found that exposure of human oral keratinocytes (HOKs) to Bis-GMA caused apoptosis and G1/S cell cycle arrest in parallel with an increased ROS level. Moreover, Bis-GMA induced a depletion of mitochondrial membrane potential, an increase in the Bax/Bcl-2 ratio, an activation of caspase-3 and altered expressions of cell cycle-related proteins (p21, PCNA, cyclinD1). Furthermore, the co-treatment of the ROS scavenger N-acetyl cysteine (NAC) obviously attenuated Bis-GMA-induced toxicity. Here we also evaluated the effects of Bis-GMA on the ROS-related PI3k/Akt pathway. We found that Bis-GMA inhibited the phosphorylation of Akt, whereas the amount of phosphorylated Akt was reverted to the control level in the presence of NAC. Our findings suggested that the toxic effects of Bis-GMA were related to ROS production and the antioxidant NAC effectively reduced Bis-GMA-mediated cytotoxicity.

The novel protective role of P27 in MLN4924-treated gastric cancer cells

The tumor-suppressor gene cyclin-dependent kinase inhibitor 1B (P27) is downregulated in gastric cancer cells mainly through proteolytic degradation mediated by the SKP-Cullin1-F-Box (SCF) complex. But the correlation between its downregulation and gastric cancer prognosis still remains indefinite. MLN4924, an anti-tumor agent, which suppresses the SCF complex by inhibiting Cullin1 neddylation, emerges as a promising tool to elucidate its functions in gastric cancer cells. In this study, MLN4924 induced significant growth inhibition of gastric cancer cells in a dose-dependent manner, along with the simultaneous accumulation of P27 and cell cycle abnormalities such as G2/M arrest. Importantly, we found that P27 silencing in MLN4924-treated cells resulted in an enhancement of growth inhibition both in vitro and in vivo. Mechanism analysis revealed the antagonism effects of antioxidants to this excess apoptosis, suggesting reactive oxygen species (ROS) overproduction especially in the mitochondria was the principal cause of the augmentation. Moreover, the robust ROS attacked the mitochondria to initiate collapse of the mitochondrial membrane permeability and the exportation of apoptosis-inducing factor (AIF), IAP-binding mitochondrial protein (SMAC/DIABLO) and cytochrome c. Finally, we also found that P27 knockdown affected the expression profile of several critical BH3 family members to amplify the mitochondrial dysfunction and apoptosis. In summary, our findings unveiled a protective role of P27 by maintaining mitochondrial membrane permeability in MLN4924-treated gastric cancer cells, and therefore highlighted the potential combination of MLN4924 with P27 inhibition to improve its therapeutic efficacy.

Nrdp1-mediated ErbB3 degradation inhibits glioma cell migration and invasion by reducing cytoplasmic localization of p27(Kip1)

We previously reported that loss of Nrdp1 contributes to human glioma progression by reducing apoptosis. However, the role of Nrdp1 in glioma migration and invasion has not been investigated. Here, we report that ErbB3, a substrate of Nrdp1, is undetectable in normal brain tissues and grade II/III glioma tissues, but is abundant in a certain percentage of grade IV glioma tissues and is associated with the loss of Nrdp1. This suggests that Nrdp1 may be involved in glioma migration and invasion by regulating ErbB3. Thus, the role of Nrdp1/ErbB3 signaling in glioma cell migration and invasion was investigated using Nrdp1 loss- and gain-of-function. The results show that down-regulation of Nrdp1 by use of short hairpin RNA promoted glioma cell migration and invasion. In contrast, overexpression of Nrdp1 significantly inhibited glioma cell migration and invasion. Further investigation on molecular targets revealed that Nrdp1 decreased the level of ErbB3, which resulted in decreasing p-AKT thereby reducing cytoplasmic p27(Kip1). Taken together, these findings suggest that Nrdp1-mediated ErbB3 degradation suppresses glioma migration and invasion and that loss of Nrdp1 may amplify ErbB3 signaling to contribute to glioma migration and invasion. These findings suggest that Nrdp1 may be a target for glioma therapy.

PI3K-AKT Signaling via Nrf2 Protects against Hyperoxia-Induced Acute Lung Injury, but Promotes Inflammation Post-Injury Independent of Nrf2 in Mice

Lung epithelial and endothelial cell death accompanied by inflammation contributes to hyperoxia-induced acute lung injury (ALI). Impaired resolution of ALI can promote and/or perpetuate lung pathogenesis, including fibrosis. Previously, we have shown that the transcription factor Nrf2 induces cytoprotective gene expression and confers protection against hyperoxic lung injury, and that Nrf2-mediated signaling is also crucial for the restoration of lung homeostasis post-injury. Although we have reported that PI3K/AKT signaling is required for Nrf2 activation in lung epithelial cells, significance of the PI3K/AKT-Nrf2 crosstalk during hyperoxic lung injury and repair remains unclear. Thus, we evaluated this aspect using Nrf2 knockout (Nrf2^–/–) and wild-type (Nrf2^+/+) mouse models. Here, we show that pharmacologic inhibition of PI3K/AKT signaling increased lung inflammation and alveolar permeability in Nrf2^+/+ mice, accompanied by decreased expression of Nrf2-target genes such as Nqo1 and Hmox1. PI3K/AKT inhibition dampened hyperoxia-stimulated Nqo1 and Hmox1 expression in lung epithelial cells and alveolar macrophages. Contrasting with its protective effects, PI3K/AKT inhibition suppressed lung inflammation in Nrf2^+/+ mice during post-injury. In Nrf2^–/– mice exposed to room-air, PI3K/AKT inhibition caused lung injury and inflammation, but it did not exaggerate hyperoxia-induced ALI. During post-injury, PI3K/AKT inhibition did not augment, but rather attenuated, lung inflammation in Nrf2^–/– mice. These results suggest that PI3K/AKT-Nrf2 signaling is required to dampen hyperoxia-induced lung injury and inflammation. Paradoxically, the PI3K/AKT pathway promotes lung inflammation, independent of Nrf2, during post-injury.

Nuclear localized Akt enhances breast cancer stem-like cells through counter-regulation of p21(Waf1/Cip1) and p27(kip1)

Cancer stem-like cells (CSCs) are a rare subpopulation of cancer cells capable of propagating the disease and causing cancer recurrence. In this study, we found that the cellular localization of PKB/Akt kinase affects the maintenance of CSCs. When Akt tagged with nuclear localization signal (Akt-NLS) was overexpressed in SKBR3 and MDA-MB468 cells, these cells showed a 10-15% increase in the number of cells with CSCs enhanced ALDH activity and demonstrated a CD44(+High)/CD24(-Low) phenotype. This effect was completely reversed in the presence of Akt-specific inhibitor, triciribine. Furthermore, cells overexpressing Akt or Akt-NLS were less likely to be in G0/G1 phase of the cell cycle by inactivating p21(Waf1/Cip1) and exhibited increased clonogenicity and proliferation as assayed by colony-forming assay (mammosphere formation). Thus, our data emphasize the importance the intracellular localization of Akt has on stemness in human breast cancer cells. It also indicates a new robust way for improving the enrichment and culture of CSCs for experimental purposes. Hence, it allows for the development of simpler protocols to study stemness, clonogenic potency, and screening of new chemotherapeutic agents that preferentially target cancer stem cells.

SUMMARY

The presented data, (i) shows new, stemness-promoting role of nuclear Akt/PKB kinase, (ii) it underlines the effects of nuclear Akt on cell cycle regulation, and finally (iii) it suggests new ways to study cancer stem-like cells.

The Akt isoforms, their unique functions and potential as anticancer therapeutic targets

Akt (also known as protein kinase B or PKB) is the major downstream nodal point of the PI3K signaling pathway. This pathway is a promising anticancer therapeutic target, because constitutive activation of the PI3K-Akt pathway is correlated with tumor development, progression, poor prognosis, and resistance to cancer therapies. The Akt serine/threonine kinase regulates diverse cellular functions including cell growth, proliferation, glucose metabolism, and survival. Although all three known Akt isoforms (Akt1-3) are encoded by separate genes, their amino acid sequences show a high degree of similarity. For this and other reasons, it has long been assumed that all three Akt isoforms are activated in the same way, and their functions largely overlap. However, accumulating lines of evidence now suggest that the three Akt isoforms might have unique modes of activation and many distinct functions. In particular, it has recently been found that the Akt isoforms are localized at different subcellular compartments in both adipocytes and cancer cells. In this review, we highlight the unique roles of each Akt isoform by introducing published data obtained from both in vitro and in vivo studies. We also discuss the significant potential of the Akt isoforms as effective anticancer therapeutic targets.

Regulating the stability and localization of CDK inhibitor p27(Kip1) via CSN6-COP1 axis

The COP9 signalosome subunit 6 (CSN6), which is involved in ubiquitin-mediated protein degradation, is overexpressed in many types of cancer. CSN6 is critical in causing p53 degradation and malignancy, but its target in cell cycle progression is not fully characterized. Constitutive photomorphogenic 1 (COP1) is an E3 ubiquitin ligase associating with COP9 signalosome to regulate important target proteins for cell growth. p27 is a critical G1 CDK inhibitor involved in cell cycle regulation, but its upstream regulators are not fully characterized. Here, we show that the CSN6-COP1 link is regulating p27(Kip1) stability, and that COP1 is a negative regulator of p27(Kip1). Ectopic expression of CSN6 can decrease the expression of p27(Kip1), while CSN6 knockdown leads to p27(Kip1) stabilization. Mechanistic studies show that CSN6 interacts with p27(Kip1) and facilitates ubiquitin-mediated degradation of p27(Kip1). CSN6-mediated p27 degradation depends on the nuclear export of p27(Kip1), which is regulated through COP1 nuclear exporting signal. COP1 overexpression leads to the cytoplasmic distribution of p27, thereby accelerating p27 degradation. Importantly, the negative impact of COP1 on p27 stability contributes to elevating expression of genes that are suppressed through p27 mediation. Kaplan-Meier analysis of tumor samples demonstrates that high COP1 expression was associated with poor overall survival. These data suggest that tumors with CSN6/COP1 deregulation may have growth advantage by regulating p27 degradation and subsequent impact on p27 targeted genes.

PI3K/AKT pathway-mediated regulation of p27(Kip1) is associated with cell cycle arrest and apoptosis in cervical cancer

BACKGROUND

The cyclin-dependent kinase inhibitor p27(Kip1) is known to act as a putative tumor suppressor in several human cancers, including cervical cancer. Down-regulation of p27(Kip1) may occur either through transcription inhibition or through phosphorylation-dependent proteolytic degradation. As yet, the mechanism underlying p27(Kip1) down-regulation and its putative downstream effects on cervical cancer development are poorly understood. Here we assessed the expression and sub-cellular localization of p27(Kip1) and its effects on proliferation, cell cycle progression and (inhibition of) apoptosis in cervical cancer cells.

METHODS

Primary cervical cancer samples (n = 70), normal cervical tissue samples (n = 30) and cervical cancer-derived cell lines (n = 8) were used to assess the expression of p27(Kip1) and AKT1 by RT-PCR, Western blotting and immunohistochemistry, respectively. The effects of the PI3K inhibitor LY294004 and the proteasome inhibitor MG132 on cervical cancer cell proliferation were investigated using a MTT assay. Apoptosis and cell cycle analyses were carried out using flow cytometry, and sub-cellular p27(Kip1) localization analyses were carried out using immunofluorescence assays.

RESULTS

We observed p27(Kip1) down-regulation (p = 0.045) and AKT1 up-regulation (p = 0.046) in both the primary cervical cancer samples and the cervical cancer-derived cell lines, compared to the normal cervical tissue samples tested. Treatment of cervical cancer-derived cell lines with the PI3K inhibitor LY294002 resulted in a reduced AKT1 activity. We also observed a dose-dependent inhibition of cell viability after treatment of these cell lines with the proteasome inhibitor MG132. Treatment of the cells with LY294002 resulted in a G1 cell cycle arrest, a nuclear expression of p27(Kip1), and a cytoplasmic p27(Kip1) accumulation after subsequent treatment with MG132. Additionally, we found that the synergistic effect of MG132 and LY294002 resulted in a sub-G1 cell cycle arrest and apoptosis induction through poly (ADP-ribose) polymerase (PARP) cleavage.

CONCLUSION

Our data suggest that p27(Kip1) down-regulation in cervical cancer cells is primarily regulated through PI3K/AKT-mediated proteasomal degradation. The observed synergistic effect of the MG132 and LY294002 inhibitors may form a basis for the design of novel cervical cancer therapies.

Cytoplasmic p27 promotes epithelial-mesenchymal transition and tumor metastasis via STAT3-mediated Twist1 upregulation

p27 restrains normal cell growth, but PI3K-dependent C-terminal phosphorylation of p27 at threonine 157 (T157) and T198 promotes cancer cell invasion. Here, we describe an oncogenic feedforward loop in which p27pT157pT198 binds Janus kinase 2 (JAK2) promoting STAT3 (signal transducer and activator of transcription 3) recruitment and activation. STAT3 induces TWIST1 to drive a p27-dependent epithelial-mesenchymal transition (EMT) and further activates AKT contributing to acquisition and maintenance of metastatic potential. p27 knockdown in highly metastatic PI3K-activated cells reduces STAT3 binding to the TWIST1 promoter, TWIST1 promoter activity and TWIST1 expression, reverts EMT and impairs metastasis, whereas activated STAT3 rescues p27 knockdown. Cell cycle-defective phosphomimetic p27T157DT198D (p27CK-DD) activates STAT3 to induce a TWIST1-dependent EMT in human mammary epithelial cells and increases breast and bladder cancer invasion and metastasis. Data support a mechanism in which PI3K-deregulated p27 binds JAK2, to drive STAT3 activation and EMT through STAT3-mediated TWIST1 induction. Furthermore, STAT3, once activated, feeds forward to further activate AKT.

The tumor-suppressor gene LZTS1 suppresses colorectal cancer proliferation through inhibition of the AKT-mTOR signaling pathway

The Leucine zipper tumor suppressor gene 1 (LZTS1/FEZ1) gene was originally identified as a potential tumor suppressor. However, the expression pattern and the role of LZTS1 in the progression of colorectal cancer (CRC) have not been well characterized. Herein, we reported that LZTS1 was markedly reduced in CRC tissues compared with matched adjacent normal intestine epithelial tissues. In analysis of 160 CRC specimens, we revealed that decreased expression of LZTS1 was correlated to aggressive characteristics and poor survival of patients with CRC. Moreover, we found that expression of LZTS1 in CRC cells significantly inhibited cell proliferation in vitro and prohibited tumor growth in vitro. On the contrary, silence of LZTS1 promoted cell proliferation and tumor growth in CRC cells. Furthermore, we demonstrated that LZTS1 inhibited cell proliferation and tumor growth in CRC in part via suppression of AMT-mTOR, subsequently down-regulating p27Kip and up-regulating cyclin D1. These findings suggest that LZTS1 plays a potential tumor suppressor role in CRC progression and represents a valuable clinical prognostic marker of this disease.

Akt-mediated phosphorylation of XLF impairs non-homologous end-joining DNA repair

Deficiency in repair of damaged DNA leads to genomic instability and is closely associated with tumorigenesis. Most DNA double-strand-breaks (DSBs) are repaired by two major mechanisms, homologous-recombination (HR) and non-homologous-end-joining (NHEJ). Although Akt has been reported to suppress HR, its role in NHEJ remains elusive. Here, we report that Akt phosphorylates XLF at Thr181 to trigger its dissociation from the DNA ligase IV/XRCC4 complex, and promotes its interaction with 14-3-3β leading to XLF cytoplasmic retention, where cytosolic XLF is subsequently degraded by SCF(β-TRCP) in a CKI-dependent manner. Physiologically, upon DNA damage, XLF-T181E expressing cells display impaired NHEJ and elevated cell death. Whereas a cancer-patient-derived XLF-R178Q mutant, deficient in XLF-T181 phosphorylation, exhibits an elevated tolerance of DNA damage. Together, our results reveal a pivotal role for Akt in suppressing NHEJ and highlight the tight connection between aberrant Akt hyper-activation and deficiency in timely DSB repair, leading to genomic instability and tumorigenesis.

Prenylation inhibition-induced cell death in melanoma: reduced sensitivity in BRAF mutant/PTEN wild-type melanoma cells

While targeted therapy brought a new era in the treatment of BRAF mutant melanoma, therapeutic options for non-BRAF mutant cases are still limited. In order to explore the antitumor activity of prenylation inhibition we investigated the response to zoledronic acid treatment in thirteen human melanoma cell lines with known BRAF, NRAS and PTEN mutational status. Effect of zoledronic acid on proliferation, clonogenic potential, apoptosis and migration of melanoma cells as well as the activation of downstream elements of the RAS/RAF pathway were investigated in vitro with SRB, TUNEL and PARP cleavage assays and videomicroscopy and immunoblot measurements, respectively. Subcutaneous and spleen-to-liver colonization xenograft mouse models were used to evaluate the influence of zoledronic acid treatment on primary and disseminated tumor growth of melanoma cells in vivo. Zoledronic acid more efficiently decreased short-term in vitro viability in NRAS mutant cells when compared to BRAF mutant and BRAF/NRAS wild-type cells. In line with this finding, following treatment decreased activation of ribosomal protein S6 was found in NRAS mutant cells. Zoledronic acid demonstrated no significant synergism in cell viability inhibition or apoptosis induction with cisplatin or DTIC treatment in vitro. Importantly, zoledronic acid could inhibit clonogenic growth in the majority of melanoma cell lines except in the three BRAF mutant but PTEN wild-type melanoma lines. A similar pattern was observed in apoptosis induction experiments. In vivo zoledronic acid did not inhibit the subcutaneous growth or spleen-to-liver colonization of melanoma cells. Altogether our data demonstrates that prenylation inhibition may be a novel therapeutic approach in NRAS mutant melanoma. Nevertheless, we also demonstrated that therapeutic sensitivity might be influenced by the PTEN status of BRAF mutant melanoma cells. However, further investigations are needed to identify drugs that have appropriate pharmacological properties to efficiently target prenylation in melanoma cells.

Chemopreventive Effects of Licorice and Its Components

Cancer is still a major health issue worldwide and identifying novel but safe compounds for prevention and treatment is a high priority. Licorice (Glycyrrhiza) is a perennial plant that is cultivated in many countries and has been reported to exert antioxidant, anti-inflammatory and anticancer effects. However, some components of licorice exert unwanted side effects and therefore identifying safer licorice components would be ideal. The anticancer activities of many of the licorice components appear to include cycle arrest, apoptosis induction, and general antioxidant effects. Commonly reported indirect protein targets important in tumorigenesis include many cell cycle-related proteins, apoptosis-associated proteins, MMP proteins, COX-2, GSK-β, Akt, NF-κB, and MAP kinases. Importantly, several licorice components were reported to directly bind to and inhibit the activities of PI3-K, MKK4, MKK7, JNK1, mTOR, and Cdk2, resulting in decreased carcinogenesis in several cell and mouse models with no obvious toxicity. This review focuses on specific components of licorice for which a direct protein target has been identified.

Contact inhibition modulates intracellular levels of miR-223 in a p27kip1-dependent manner

MicroRNAs (miRs) are a large class of small regulatory RNAs that function as nodes of signaling networks. This implicates that miRs expression has to be finely tuned, as observed during cell cycle progression.

Here, using an expression profiling approach, we provide evidence that the CDK inhibitor p27^Kip1 regulates miRs expression following cell cycle exit. By using wild type and p27KO cells harvested in different phases of the cell cycle we identified several miRs regulated by p27^Kip1 during the G1 to S phase transition. Among these miRs, we identified miR-223 as a miR specifically upregulated by p27^Kip1 in G1 arrested cells. Our data demonstrate that p27^Kip1 regulated the expression of miR-223, via two distinct mechanisms. p27^Kip1 directly stabilized mature miR-223 expression, acting as a RNA binding protein and it controlled E2F1 expression that, in turn, regulated miR-223 promoter activity. The resulting elevated miR-223 levels ultimately participated to arresting cell cycle progression following contact inhibition. Importantly, this mechanism of growth control was conserved in human cells and deranged in breast cancers.

Here, we identify a novel and conserved function of p27^Kip1 that, by modulating miR-223 expression, contributes to proper regulation of cell cycle exit following contact inhibition. Thus we propose a new role for miR-223 in the regulation of breast cancer progression.

Over-Expressed Twist Associates with Markers of Epithelial Mesenchymal Transition and Predicts Poor Prognosis in Breast Cancers via ERK and Akt Activation

Overexpression of Twist, a highly conserved basic helix-loop-helix transcription factor, is associated with epithelial-mesenchymal transition (EMT) and predicts poor prognosis in various kinds of cancers, including breast cancer. In order to further clarify Twist's role in breast cancer, we detected Twist expression in breast cancer tissues by immunohistochemistry. Twist expression was observed in 54% (220/408) of breast cancer patients and was positively associated with tumor size, Ki67, VEGF-C and HER2 expression. Conversely, Twist was negatively associated with estrogen receptor (ER), progesterone receptor (PgR) and E-cadherin expression. Patients with Twist expression had a poorer prognosis for 30-month disease free survival (DFS) (82.9%) than patients with negative Twist (92.3%). Overexpression of Twist led to dramatic changes in cellular morphology, proliferation, migratory/invasive capability, and expression of EMT-related biomarkers in breast cancer cells. Moreover, we show that Twist serves as a driver of tumorigenesis, as well as an inducer of EMT, at least in part, through activation of the Akt and extracellular signal-regulated protein kinase (ERK) pathways which are critical for Twist-mediated EMT. Our results demonstrate that Twist expression is an important prognostic factor in breast cancer patients.

The PI3K/AKT/mTOR interactive pathway

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of the rapamycin (mTOR) signalling pathway is hyperactivated or altered in many cancer types and regulates a broad range of cellular processes including survival, proliferation, growth, metabolism, angiogenesis and metastasis.

Involvement of c-Myc in the proliferation of MCF-7 human breast cancer cells induced by bHLH transcription factor DEC2

Differentiated embryonic chondrocyte expressed gene 1 (DEC1; BHLHE40/Stra13/Sharp2) and differentiated embryonic chondrocyte expressed gene 2 (DEC2; BHLHE41/Sharp1) are basic helix-loop-helix (bHLH) transcriptional factors that are involved in the regulation of cell differentiation, circadian rhythms, response to hypoxia and carcinogenesis. Previous studies have demonstrated that the expression of DECs is induced under hypoxic conditions in various normal and cancer cell lines. In the present study, using RT-qPCR and western blot analysis, we demonstrated that hypoxia induced the expression of DEC1 and DEC2 in MCF-7 human breast cancer cells; their expression levels reached a peak at different time points. In particular, we found that the expression pattern of the hypoxia-inducible factor (HIF)-1α protein was similar to DEC1, and that of the HIF-2α protein was identical to that of DEC2. The knockdown of HIF-2α using siRNA suppressed the phosphorylation of Akt, as well as the expression of DEC2 and c-Myc. Hypoxia failed to affect the expression of DEC2 and c-Myc when the PI3K/Akt signaling pathway was blocked. In addition, the overexpression of DEC1 and DEC2 was induced by transfecting the cells with a pcDNA vector. The overexpression of DEC2, but not that of DEC1, increased the proliferation of the MCF-7 cells under both normoxic and hypoxic conditions. Concomitantly, the expression of c-Myc was upregulated by exposure to hypoxia and by the overexpression of DEC2. In conclusion, DEC2 participates in hypoxia-induced cell proliferation by functioning as a target gene of the PI3K/Akt signaling pathway and regulating the expression of c-Myc.

AS101 prevents diabetic nephropathy progression and mesangial cell dysfunction: regulation of the AKT downstream pathway

Diabetic nephropathy (DN) is characterized by proliferation of mesangial cells, mesangial expansion, hypertrophy and extracellular matrix accumulation. Previous data have cross-linked PKB (AKT) to TGFβ induced matrix modulation. The non-toxic compound AS101 has been previously shown to favorably affect renal pathology in various animal models and inhibits AKT activity in leukemic cells. Here, we studied the pharmacological properties of AS101 against the progression of rat DN and high glucose-induced mesangial dysfunction. In-vivo administration of AS101 to Streptozotocin injected rats didn’t decreased blood glucose levels but ameliorated kidney hypotrophy, proteinuria and albuminuria and downregulated cortical kidney phosphorylation of AKT, GSK3β and SMAD3. AS101 treatment of primary rat glomerular mesangial cells treated with high glucose significantly reduced their elevated proliferative ability, as assessed by XTT assay and cell cycle analysis. This reduction was associated with decreased levels of p-AKT, increased levels of PTEN and decreased p-GSK3β and p-FoxO3a expression. Pharmacological inhibition of PI3K, mTORC1 and SMAD3 decreased HG-induced collagen accumulation, while inhibition of GSK3β did not affect its elevated levels. AS101 also prevented HG-induced cell growth correlated to mTOR and (rp)S6 de-phosphorylation. Thus, pharmacological inhibition of the AKT downstream pathway by AS101 has clinical potential in alleviating the progression of diabetic nephropathy.

Lupeol inhibits proliferation and induces apoptosis of human pancreatic cancer PCNA-1 cells through AKT/ERK pathways

Lupeol, a dietary triterpene, present in many fruits and medicinal plants, has been reported to possess many pharmacological properties including anti-cancer activities both in vitro and in vivo. However, the precise mechanism involved remains largely unknown. The present study is conducted to investigate the anti-cancer activity and the underlying mechanisms of lupeol on human pancreatic cancer proliferating cell nuclear antigen 1 (PCNA-1) cells in vitro and in vivo. Lupeol significantly inhibited the proliferation of the cells in dose- and time-dependent manners and induced apoptosis as well as cell cycle arrest in G0/G1 phase by upregulating P21 and P27 and downregulating cyclin D1. The expression of apoptosis-related proteins in cells was evaluated by western blot analysis, and we found that lupeol induced cell apoptosis by decreasing the levels of p-AKT and p-ERK. In addition, pretreatment with a specific PI3K/AKT activator (IGF-1) significantly neutralized the pro-apoptotic activity of lupeol in PCNA-1 cells, demonstrating the important role of AKT in this process. More importantly, our in vivo studies showed that administration of lupeol decreased tumor growth in a dose-dependent manner. Immunohistochemistry analysis demonstrated the downregulation of p-AKT and p-ERK in tumor tissues following lupeol treatment, consistent with the in vitro results. Therefore, these findings indicate that lupeol can inhibit cell proliferation and induce apoptosis as well as cell cycle arrest of PCNA-1 cells and might offer a therapeutic potential advantage for human pancreatic cancer chemoprevention or chemotherapy.

Progesterone induces RhoA Inactivation in male rat aortic smooth muscle cells through up-regulation of p27(kip1.)

Previously, we showed that progesterone (P4) at physiologic concentrations (5nM-500nM) inhibits proliferation and migration of rat aortic smooth muscle cells (RASMCs). The P4-induced migration inhibition in RASMC was resulted from Rat sacroma homolog gene family, member A (RhoA) inactivation induced by activating the cSrc/AKT/ERK 2/p38 mitogen-activated protein kinase-mediated signaling pathway. We also demonstrated that up-regulation of cyclin-dependent kinase inhibitor 1B (p27(kip1)) is involved in the P4-induced migration inhibition in RASMC. Because P4 can increase formation of the p27(kip1)-RhoA complex in RASMC, this finding led us to hypothesize that the P4-induced inactivation in RhoA might be caused by up-regulation of p27(kip1). Here, we showed that P4 increased phosphorylation of p27(kip1) at Ser10 in the nucleus, which in turn caused p27(kip1) translocation from the nucleus to the cytosol, subsequently increasing formation of the p27(kip1)-RhoA complex. These effects were blocked by knocking-down kinase-interacting stathmin (KIS) using KIS small interfering RNA. Knock-down of p27(kip1) abolished the P4-induced decreases in the level of RhoA protein in RASMC. However, pretreatment of RASMC with the proteasome inhibitor, N-(benzyloxycarbonyl)leucinylleucinylleucinal (MG132), prevented the P4-induced degradation of p27(kip1) and RhoA. Taken together, our investigation of P4-induced migration inhibition in RASMC showed a sequence of associated intracellular events that included 1) increase in formation of the KIS-p27(kip1) complex in the nucleus; 2) phosphorylated nuclear p27(kip1) at Ser10; 3) increased cytosolic translocation of p27(kip1) and formation of the p27(kip1)-RhoA complex in the cytosol; and 4) degradation of p27(kip1) and RhoA through the ubiquitin-proteasome pathway. These findings highlight the molecular mechanisms underlying P4-induced migration inhibition in RASMC.

Cables1 complex couples survival signaling to the cell death machinery

Cables1 is a candidate tumor suppressor that negatively regulates cell growth by inhibiting cyclin-dependent kinases. Cables1 expression is lost frequently in human cancer but little is known about its regulation. Here, we report that Cables1 levels are controlled by a phosphorylation and 14-3-3-dependent mechanism. Mutagenic analyses identified two residues, T44 and T150, that are specifically critical for 14-3-3 binding and that serve as substrates for phosphorylation by the cell survival kinase Akt, which by binding directly to Cables1 recruits 14-3-3 to the complex. In cells, Cables1 overexpression induced apoptosis and inhibited cell growth in part by stabilizing p21 and decreasing Cdk2 kinase activity. Ectopic expression of activated Akt (AKT1) prevented Cables1-induced apoptosis. Clinically, levels of phosphorylated Cables1 and phosphorylated Akt correlated with each other in human lung cancer specimens, consistent with pathophysiologic significance. Together, our results illuminated a dynamic regulatory system through which activated Akt and 14-3-3 work directly together to neutralize a potent tumor suppressor function of Cables1.

Molecular mechanisms underlying the anti-proliferative and anti-migratory effects of folate on homocysteine-challenged rat aortic smooth muscle cells

BACKGROUND AND PURPOSE

Homocysteine is an intermediate product formed during the metabolism of methionine, and is increased in cells with folate deficiency. Patients with hyperhomocysteinemia tend to develop cardiovascular disease. Here, we have examined the molecular mechanisms underlying the anti-proliferative and anti-migratory effects of folate on homocysteine-challenged rat aortic smooth muscle cells (RASMCs).

EXPERIMENTAL APPROACH

Cultures of RASMC were challenged with homocysteine and then incubated with folate added. Changes in p21/p27, AKT and RhoA were followed by RT-PCR, Western blotting and immunocytochemistry. Transfection and anti-sense techniques were also used. Cell viability, growth and migration were measured.

KEY RESULTS

Folate up-regulated p21/p27 through a Src/ERK-dependent mechanism that accounted for its anti-proliferative effects on RASMC. Folate protected RASMC from the effects of homocysteine by reducing AKT1, focal adhesion kinase (FAK), paxillin, and p190RhoGAP activation/phosphorylation, along with cytosolic levels of p21 and p27, and increasing RhoA activation. Overexpression of AKT1, but not of AKT2, induced p21/p27 phosphorylation and increased cytosolic p21/p27 levels, as did homocysteine treatment. By contrast, and similarly to folate treatment, transfection with dominant negative (DN) AKT1 counteracted these effects. Additionally, AKT was shown to be an upstream target of FAK activation. In RASMC overexpressing constitutively active RhoA, activation of RhoA mediated the anti-migratory effects of folate. Addition of Y27632 (a RhoA inhibitor) and DNRhoA counteracted the anti-migratory effects, confirming RhoA involvement.

CONCLUSION AND IMPLICATIONS

Folate was anti-proliferative and anti-migratory in homocysteine-challenged RASMC. Mechanisms underlying folate-mediated protection against the proatherosclerotic effects of homocysteine have been delineated.