The Effect of GADD45a on Furazolidone‐Induced S‐Phase Cell‐Cycle Arrest in Human Hepatoma G2 Cells

In this study, overexpression of GADD45a induced by furazolidone in HepG2 cells could arouse S‐phase cell cycle arrest, suppress cell proliferation, and increase the activities of cyclin D1, cyclin D3, and cyclin‐dependent kinase 6 (CDK6). To the opposite, GADD45a knockdown cells by RNAi could reduce furazolidone‐induced S‐phase cell cycle arrest, increase the cell viability, decrease the activities of cyclin D1, cyclin D3, and CDK6; however, cyclin‐dependent kinase 4 (CDK4) showed no change. Moreover, data from our current studies show that cyclin D1, cyclin D3, and CDK6 are target genes functioning at the downstream of the GADD45a pathway induced by furazolidone. These results demonstrate that the GADD45a pathway is partially responsible for the furazolidone‐induced S‐phase cell cycle arrest. GADD45a influences furazolidone‐induced S‐phase cell cycle arrest in human hepatoma G2 cells via cyclin D1, cyclin D3, and CDK6, but not CDK4.     

Butylene fipronil induces apoptosis in PC12 murine nervous cells via activation of p16‐CDK4/6‐cyclin D1 and mitochondrial apoptotic pathway

Butylene fipronil (BFPN) is a phenylpyrazole insecticide, acting at the γ‐aminobutyric acid (GABA) receptor. Here, we show that BFPN inducedcytotoxicity in PC12 murinenervous cells, which lacks GABA receptor. Treatment with BFPN for 48 hours significantly enhanced G0/G1 arrest and induced apoptosis. BFPN decreased the expression of cyclin‐dependent kinase (CDK4 and CDK6) and increased P16 and cyclin D1. Simultaneously, Bcl‐2 protein was declined while Bax and cytochrome c were significantly enhanced in BFPN‐treated groups. The apoptotic enzymes caspase‐8, ‐9, and ‐3 were also activated by BFPN. Furthermore, treatment with BFPN significantly stimulated reactive oxygen species (ROS) generation, and pretreatment with antioxidant diphenyleneiodonium, substantially reduced cell death. Overall, these results suggest that BFPN is effective to induce G0/G1‐phase arrest and apoptosis in PC12 murine nervous cell. Stimulating ROS generation and activation of P16‐CDK4/6‐cyclin D1 and mitochondrial apoptotic pathway may participate in the cytotoxicity of BFPN.     

MICAL1 facilitates breast cancer cell proliferation via ROS‐sensitive ERK/cyclin D pathway

Molecule interacting with CasL 1 (MICAL1) is a multidomain flavoprotein mono‐oxygenase that strongly involves in cytoskeleton dynamics and cell oxidoreduction metabolism. Recently, results from our laboratory have shown that MICAL1 modulates reactive oxygen species (ROS) production, and the latter then activates phosphatidyl inositol 3‐kinase (PI3K)/protein kinase B (Akt) signalling pathway which regulates breast cancer cell invasion. Herein, we performed this study to assess the involvement of MICAL1 in breast cancer cell proliferation and to explore the potential molecular mechanism. We noticed that depletion of MICAL1 markedly reduced cell proliferation in breast cancer cell line MCF‐7 and T47D. This effect of MICAL1 on proliferation was independent of wnt/β‐catenin and NF‐κB pathways. Interestingly, depletion of MICAL1 significantly inhibited ROS production, decreased p‐ERK expression and unfavourable for proliferative phenotype of breast cancer cells. Likewise, MICAL1 overexpression increased p‐ERK level as well as p‐ERK nucleus translocation. Moreover, we investigated the effect of MICAL1 on cell cycle‐related proteins. MICAL1 positively regulated CDK4 and cyclin D expression, but not CDK2, CDK6, cyclin A and cyclin E. In addition, more expression of CDK4 and cyclin D by MICAL1 overexpression was blocked by PI3K/Akt inhibitor LY294002. LY294002 treatment also attenuated the increase in the p‐ERK level in MICAL1‐overexpressed breast cancer cells. Together, our results suggest that MICAL1 exhibits its effect on proliferation via maintaining cyclin D expression through ROS‐sensitive PI3K/Akt/ERK signalling in breast cancer cells.     

Natural Pesticide Dihydrorotenone Arrests Human Plasma Cancer Cells at the G0/G1 Phase of the Cell Cycle

Dihydrorotenone (DHR) is a natural pesticide used for farming including organic produces. We recently found that DHR induces human plasma cell apoptosis by provoking endoplasmic reticulum stress. In the present study, we found that DHR arrested human plasma cancer cells at the G0/G1 phase of the cell cycle. Mechanistical studies demonstrated that cell cycle arrest was associated with downregulated cell cycle promotors including cyclin D2, cyclin D3, cyclin‐dependent kinases (CDK4, CKD6), and phosphorylated‐Rb. DHR inhibited cyclin D2 transactivation, thus inhibiting its mRNA expression. In addition, DHR upregulated the cell cycle repressors p21 and p53. DHR also increased the phosphorylation level of p53, suggesting the upregulated transactivation function of p53, which was confirmed by the induction of p21, a substrate of activated p53. Moreover, DHR downregulated AKT and ERK phosphorylation, an incentive of cell cycle progression. Therefore, these results collectively demonstrated that DHR disrupts the cell cycle progress, which suggests that DHR is toxic to human plasma cells. Caution is thus suggested when handling with this agent.     

MiR‐34b‐3p represses cell proliferation,cell cycle progression and cell apoptosis in non‐small‐cell lung cancer (NSCLC) by targeting CDK4

Lung cancer is the most common incident cancer, with a high mortality worldwide, and non‐small‐cell lung cancer (NSCLC) accounts for approximately 85% of cases. Numerous studies have shown that the aberrant expression of microRNAs (miRNAs) is associated with the development and progression of cancers. However, the clinical significance and biological roles of most miRNAs in NSCLC remain elusive. In this study, we identified a novel miRNA, miR‐34b‐3p, that suppressed NSCLC cell growth and investigated the underlying mechanism. miR‐34b‐3p was down‐regulated in both NSCLC tumour tissues and lung cancer cell lines (H1299 and A549). The overexpression of miR‐34b‐3p suppressed lung cancer cell (H1299 and A549) growth, including proliferation inhibition, cell cycle arrest and increased apoptosis. Furthermore, luciferase reporter assays confirmed that miR‐34b‐3p could bind to the cyclin‐dependent kinase 4 (CDK4) mRNA 3′‐untranslated region (3′‐UTR) to suppress the expression of CDK4 in NSCLC cells. H1299 and A549 cell proliferation inhibition is mediated by cell cycle arrest and apoptosis with CDK4 interference. Moreover, CDK4 overexpression effectively reversed miR‐34‐3p‐repressed NSCLC cell growth. In conclusion, our findings reveal that miR‐34b‐3p might function as a tumour suppressor in NSCLC by targeting CDK4 and that miR‐34b‐3p may, therefore, serve as a biomarker for the diagnosis and treatment of NSCLC.     

2-Methoxy-4-vinylphenol can induce cell cycle arrest by blocking the hyper-phosphorylation of retinoblastoma protein in benzo[a]pyrene-treated NIH3T3 cells

Benzo[a]pyrene (BaP) is an environment carcinogen that can enhance cell proliferation by disturbing the signal transduction pathways in cell cycle regulation. In this study, the effects of 2M4VP on cell proliferation, cell cycle and cell cycle regulatory proteins were studied in BaP-treated NIH 3T3 cells to establish the molecular mechanisms of 2M4VP as anti-proliferative agents. 2M4VP exerted a dose-dependent inhibitory effect on cell growth correlated with a G1 arrest. Analysis of G1 cell cycle regulators expression revealed 2M4VP increased expression of CDK inhibitor, p21Waf1/Cip1 and p15 INK4b, decreased expression of cyclin D1 and cyclin E, and inhibited kinase activities of CDK4 and CDK2. However, 2M4VP did not affect the expression of CDK4 and CDK2. Also, 2M4VP inhibited the hyper-phosphorylation of Rb induced by BaP. Our results suggest that 2M4VP induce growth arrest of BaP-treated NIH 3T3 cells by blocking the hyper-phosphorylation of Rb via regulating the expression of cell cycle-related proteins.     

LncRNA ABHD11‐AS1 promotes the development of endometrial carcinoma by targeting cyclin D1

To investigate the expression, role and mechanism of action of long non‐coding RNA (lncRNA) ABHD11‐AS1 in endometrial carcinoma. The expression of lncRNA ABHD11‐AS1 was quantified by qRT‐PCR in human endometrial carcinoma (n = 89) and normal endometrial tissues (n = 27). LncRNA ABHD11‐AS1 was stably overexpressed or knocked‐down in endometrial carcinoma cell lines to examine the cellular phenotype and expression of related molecules. Compared to normal endometrial tissue, lncRNA ABHD11‐AS1 was significantly overexpressed in endometrial carcinoma. Overexpression of lncRNA ABHD11‐AS1 promoted the proliferation, G1‐S progression, invasion and migration of endometrial cancer cells; inhibited apoptosis; up‐regulated cyclin D1, CDK1, CDK2, CDK4, Bcl‐xl and VEGFA; and down‐regulated p16, while ABHD11‐AS1 down‐regulation has the opposite effect. RNA pull down demonstrated that lncRNA ABHD11‐AS1 binds directly to cyclin D1. Knockdown of cyclin D1 can reverse the effect of ABHD11‐AS1. Overexpression of lncRNA ABHD11‐AS1 increased the tumorigenicity and up‐regulated cyclin D1 in an in vivo model of endometrial cancer in nude mice. LncRNA ABHD11‐AS1 functions as an oncogene to promote cell proliferation and invasion in endometrial carcinoma by positively targeting cyclin D1.     

Cyclin D1 downregulation is important for permanent cell cycle exit and initiation of differentiation induced by anchorage‐deprivation in human keratinocytes

To understand the relationship between permanent cell cycle exit and differentiation the immortalized keratinocyte cell line, SIK and the squamous cell carcinoma, SCC9 were compared during differentiation induced by anchorage‐deprivation. The SIK cells when placed in suspension culture promptly lost almost all ability to reinitiate growth by 2 days concomitantly expressing the differentiation specific proteins, transglutaminase (TGK) and involucrin. These cells rapidly underwent G1 cell cycle arrest with complete disappearance of phosphorylated RB. In contrast SCC9 cells neither showed TGK expression nor increase in involucrin. They decreased their colony‐forming ability much more slowly, which coordinated well with a gradual decrease in phosphorylated RB, demonstrating the significant resistance to loss of colony‐forming ability and cell cycle exit. In accordance, cyclin D1, a positive regulator of cyclin‐dependent kinase (CDK) 4/6 which phosphorylates RB decreased drastically in anchorage deprived SIK but not in SCC9 cells. Endogenous cyclin D1 knockdown in SCC9 cells by siRNA enhanced loss of the colony‐forming ability during anchorage‐deprivation. Conversely enforced expression of cyclin D1 in SIK cells and in another immortalized keratinocyte cell line, HaCaT, partly prevented loss of their colony‐forming abilities. Cyclin D1 overexpression antagonized Keratin 10 expression in suspended HaCaT cells. The result demonstrates the importance of cyclin D1 down regulation for proper initiation of keratinocyte differentiation. J. Cell. Biochem. 106: 63–72, 2009. © 2008 Wiley‐Liss, Inc.     

Inhibition of benzo(a)pyrene-induced cell cycle progression by all-trans retinoic acid partly through cyclin D1/E2F-1 pathway in human embryo lung fibroblasts

Benzo(a)pyrene [B(a)P] is a potent environmental carcinogen, which induces cell cycle changes. All-trans retinoic acid (ATRA) is a promising agent in prevention and treatment of human cancers. In the present study, we investigated the inhibition of B(a)P-induced cell cycle progression by ATRA in human embryo lung fibroblast (HELF). Our results showed that after treatment with B(a)P, the expression of cyclin D1 and E2F-1 were both increased significantly in HELF. There were almost no changes of CDK4 and E2F-4 expression by treatment with B(a)P. As expected, pretreatment with ATRA could efficiently decrease B(a)P-induced overexpression of cyclin D1 and E2F-1. In a further study, we stably transfected antisense cyclin D1 and antisense CDK4 plasmid into HELF. The inhibition of cyclin D1 expression and the inhibition of CDK4 expression significantly impaired the B(a)P-induced overexpression of E2F-1 respectively. Pretreatment with ATRA, cells expressing antisense cyclinD1 or antisense CDK4 showed a lesser decrease of B(a)P-induced overexpression of E2F-1 compared with similarly treated HELF. Furthermore, flow cytometry analysis showed that B(a)P promoted cell cycle progression from G(1) phase to S phase, while pretreatment with ATRA could inhibit B(a)P-induced cell cycle progression by an accumulation of cells in the G(1) phase. It was suggested that ATRA could block B(a)P-induced cell cycle promotion partly through the cyclin D1/E2F-1 pathway in HELF.     

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.     

Long non‐coding RNA SNHG15 promotes CDK14 expression via miR‐486 to accelerate non‐small cell lung cancer cells progression and metastasis

Long non‐coding RNAs (lncRNAs) have been validated to play important role in multiple cancers, including non‐small cell lung cancer (NSCLC). In present study, our team investigate the biologic role of SNHG15 in the NSCLC tumorigenesis. LncRNA SNHG15 was significantly upregulated in NSCLC tissue samples and cells, and its overexpression was associated with poor prognosis of NSCLC patients. In vitro, loss‐of‐functional cellular experiments showed that SNHG15 silencing significantly inhibited the proliferation, promoted the apoptosis, and induced the cycle arrest at G0//G1 phase. In vivo, xenograft assay showed that SNHG15 silencing suppressed tumor growth of NSCLC cells. Besides, SNHG15 silencing decreased CDK14 protein expression both in vivo and vitro. Bioinformatics tools and luciferase reporter assay confirmed that miR‐486 both targeted the 3′‐UTR of SNHG15 and CDK14 and was negatively correlated with their expression levels. In summary, our study conclude that the ectopic overexpression of SNHG15 contribute to the NSCLC tumorigenesis by regulating CDK14 protein via sponging miR‐486, providing a novel insight for NSCLC pathogenesis and potential therapeutic strategy for NSCLC patients.     

Orai3 Constitutes a Native Store-Operated Calcium Entry That Regulates Non Small Cell Lung Adenocarcinoma Cell Proliferation

Orai channels have been associated with cell proliferation, survival and metastasis in several cancers. The present study investigates the expression and the role of Orai3 in cell proliferation in non-small cell lung cancer (NSCLC). We show that Orai3 is over-expressed in cancer tissues as compared to the non-tumoral ones. Furthermore, Orai3 staining is stronger in high grade tumors. Pharmacological inhibition or knockdown of Orai3 significantly reduced store operated calcium entry (SOCE), inhibited cell proliferation and arrested cells of two NSCLC cell lines in G0/G1 phase. These effects were concomitant with a down-regulation of cyclin D1, cyclin E, CDK4 and CDK2 expression. Moreover, Orai3 silencing decreased Akt phosphorylation levels. In conclusion, Orai3 constitutes a native SOCE pathway in NSCLC that controls cell proliferation and cell cycle progression likely via Akt pathway.     

Cyclic AMP inhibits the proliferation of thyroid carcinoma cell lines through regulation of CDK4 phosphorylation

How cyclic AMP (cAMP) could positively or negatively regulate G1 phase progression in different cell types or in cancer cells versus normal differentiated counterparts has remained an intriguing question for decades. At variance with the cAMP-dependent mitogenesis of normal thyroid epithelial cells, we show here that cAMP and cAMP-dependent protein kinase activation inhibit S-phase entry in four thyroid carcinoma cell lines that harbor a permanent activation of the Raf/ERK pathway by different oncogenes. Only in Ret/PTC1-positive TPC-1 cells did cAMP markedly inhibit the Raf/ERK cascade, leading to mTOR pathway inhibition, repression of cyclin D1 and p21 and p27 accumulation. p27 knockdown did not prevent the DNA synthesis inhibition. In the other cells, cAMP little affected these signaling cascades and levels of cyclins D or CDK inhibitors. However, cAMP differentially inhibited the pRb-kinase activity and T172-phosphorylation of CDK4 complexed to cyclin D1 or cyclin D3, whereas CDK-activating kinase activity remained unaffected. At variance with current conceptions, our studies in thyroid carcinoma cell lines and previously in normal thyrocytes identify the activating phosphorylation of CDK4 as a common target of opposite cell cycle regulations by cAMP, irrespective of its impact on classical mitogenic signaling cascades and expression of CDK4 regulatory partners.     

β‐Carotene Induces Apoptosis in Human Esophageal Squamous Cell Carcinoma Cell Lines via the Cav‐1/AKT/NF‐κB Signaling Pathway

β‐carotene, a type of terpenoid, has many metabolic and physiological functions. In particular, β‐carotene has an antitumor effect. However, the efficacy of β‐carotene against esophageal squamous cell carcinoma (ESCC) remains unclear. In our study, β‐carotene inhibited the growth of ESCC cells and downregulated expression of the Caveolin‐1 (Cav‐1) protein. Cav‐1 protein was expressed only in ESCC cells, not in Het‐1A cells. Moreover, β‐carotene triggered apoptosis, induced cell cycle G0?G1 phase arrest, and inhibited cell migration. To explore the mechanism involved in these processes, we further examined the effect of β‐carotene on the Cav‐1‐mediated AKT/NF‐κB pathway. The results showed that the level of AKT and NF‐κB phosphorylation was dramatically inhibited, which led to an increase in the Bax/Bcl‐2 ratio. Correspondingly, the activity of Caspase‐3 was also enhanced. These data suggest that β‐carotene has an antiproliferative role in ESCC cells and may be a promising chemotherapeutic agent for use against ESCC cells.     

MicroRNA‐206 induces G1 arrest in melanoma by inhibition of CDK4 and Cyclin D

Expression profiling of microRNAs in melanoma lesional skin biopsies compared with normal donor skin biopsies, as well as melanoma cell lines compared with normal melanocytes, revealed that hsa‐miR‐206 was down‐regulated in melanoma (?75.4‐fold, P = 1.7 × 10^?4). MiR‐206 has been implicated in a large number of cancers, including breast, lung, colorectal, ovarian, and prostate cancers; however, its role in tumor development remains largely unknown, its biologic function is poorly characterized, and its targets affecting cancer cells are largely unknown. MiR‐206 reduced growth and migration/invasion of multiple melanoma cell lines. Bioinformatics identified cell cycle genes CDK2, CDK4, Cyclin C, and Cyclin D1 as strong candidate targets. Western blots and 3′UTR reporter gene assays revealed that miR‐206 inhibited translation of CDK4, Cyclin D1, and Cyclin C. Additionally, hsa‐miR‐206 transfection induced G1 arrest in multiple melanoma cell lines. These observations support hsa‐miR‐206 as a tumor suppressor in melanoma and identify Cyclin C, Cyclin D1, and CDK4 as miR‐206 targets.     

DICER1 regulated let‐7 expression levels in p53‐induced cancer repression requires cyclin D1

Let‐7 miRNAs act as tumour suppressors by directly binding to the 3′UTRs of downstream gene products. The regulatory role of let‐7 in downstream gene expression has gained much interest in the cancer research community, as it controls multiple biological functions and determines cell fates. For example, one target of the let‐7 family is cyclin D1, which promotes G0/S cell cycle progression and oncogenesis, was correlated with endoribonuclease DICER1, another target of let‐7. Down‐regulated let‐7 has been identified in many types of tumours, suggesting a feedback loop may exist between let‐7 and cyclin D1. A potential player in the proposed feedback relationship is Dicer, a central regulator of miRNA expression through sequence‐specific silencing. We first identified that DICER1 is the key downstream gene for cyclin D1‐induced let‐7 expression. In addition, we found that let‐7 miRNAs expression decreased because of the p53‐induced cell death response, with deregulated cyclin D1. Our results also showed that cyclin D1 is required for Nutlin‐3 and TAX‐induced let‐7 expression in cancer repression and the cell death response. For the first time, we provide evidence that let‐7 and cyclin D1 form a feedback loop in regulating therapy response of cancer cells and cancer stem cells, and importantly, that alteration of let‐7 expression, mainly caused by cyclin D1, is a sensitive indicator for better chemotherapies response.     

Tumor suppressor gene p16/INK4A/CDKN2A‐dependent regulation into and out of the cell cycle in a spontaneous canine model of breast cancer

p16/INK4A/CDKN2A is an important tumor suppressor gene that arrests cell cycle in G1 phase inhibiting binding of CDK4/6 with cyclin D1, leaving the Rb tumor suppressor protein unphosphorylated and E2F bound and inactive. We hypothesized that p16 has a role in exit from cell cycle that becomes defective in cancer cells. Well characterized p16‐defective canine mammary cancer cell lines (CMT28, CMT27, and CMT12), derived stably p16‐transfected CMT cell clones (CMT27A, CMT27H, CMT28A, and CMT28F), and normal canine fibroblasts (NCF), were used to investigate expression of p16 after serum starvation into quiescence followed by re‐feeding to induce cell cycle re‐entry. The parental CMT cell lines used lack p16 expression either at the mRNA or protein expression levels, while p27 and other p16‐associated proteins, including CDK4, CDK6, cyclin D1, and Rb, were expressed. We have successfully demonstrated cell cycle arrest and relatively synchronous cell cycle re‐entry in parental CMT12, CMT28 and NCF cells as well as p16 transfected CMT27A, CMT27H, CMT28A, and CMT28F cells and confirmed this by ³H‐thymidine incorporation and flow cytometric analysis of cell cycle phase distribution. p16‐transfected CMT27A and CMT27H cells exited cell cycle post‐serum‐starvation in contrast to parental CMT27 cells. NCF, CMT27A, and CMT28F cells expressed upregulated levels of p27 and p16 mRNA, post‐serum starvation, as cells exited cell cycle and entered quiescence. Because quiescence and differentiation are associated with increased levels of p27, our data demonstrating that p16 was upregulated along with p27 during quiescence, suggests a potential role for p16 in maintaining these non‐proliferative states. J. Cell. Biochem. 114: 1355–1363, 2013. © 2012 Wiley Periodicals, Inc.     

Regulation of IGF-1-dependent cyclin D1 and E expression by hEag1 channels in MCF-7 cells: The critical role of hEag1 channels in G1 phase progression

Insulin-like Growth Factor-1 (IGF-1) plays a key role in breast cancer development and cell cycle regulation. It has been demonstrated that IGF-1 stimulates cyclin expression, thus regulating the G1 to S phase transition of the cell cycle. Potassium (K⁺) channels are involved in the G1 phase progression of the cell cycle induced by growth factors. However, mechanisms that allow growth factors to cooperate with K⁺ channels in order to modulate the G1 phase progression and cyclin expression remain unknown. Here, we focused on hEag1 K⁺ channels which are over-expressed in breast cancer and are involved in the G1 phase progression of breast cancer cells (MCF-7). As expected, IGF-1 increased cyclin D1 and E expression of MCF-7 cells in a cyclic manner, whereas the increase of CDK4 and 2 levels was sustained. IGF-1 stimulated p21^WAF1/Cip1 expression with a kinetic similar to that of cyclin D1, however p27^Kip1 expression was insensitive to IGF-1. Interestingly, astemizole, a blocker of hEag1 channels, but not E4031, a blocker of HERG channels, inhibited the expression of both cyclins after 6-8 h of co-stimulation with IGF-1. However, astemizole failed to modulate CDK4, CDK2, p21^WAF1/Cip1 and p27^Kip1 expression. The down-regulation of hEag1 by siRNA provoked a decrease in cyclin expression. This study is the first to demonstrate that K⁺ channels such as hEag1 are directly involved in the IGF-1-induced up-regulation of cyclin D1 and E expression in MCF-7 cells. By identifying more specifically the temporal position of the arrest site induced by the inhibition of hEag1 channels, we confirmed that hEag1 activity is predominantly upstream of the arrest site induced by serum-deprivation, prior to the up-regulation of both cyclins D1 and E.     

CDK4 coexpression with Ras generates malignant human epidermal tumorigenesis

Ras acts with other proteins to induce neoplasia. By itself, however, strong Ras signaling can suppress proliferation of normal cells. In primary epidermal cells, we found that oncogenic Ras transiently decreases cyclin-dependent kinase (CDK) 4 expression in association with cell cycle arrest in G1 phase. CDK4 co-expression circumvents Ras growth suppression and induces invasive human neoplasia resembling squamous cell carcinoma. Tumorigenesis is dependent on CDK4 kinase function, with cyclin D1 required but not sufficient for this process. In facilitating escape from G1 growth restraints, Ras and CDK4 alter the composition of cyclin D and cyclin E complexes and promote resistance to growth inhibition by INK4 cyclin-dependent kinase inhibitors. These data identify a new role for oncogenic Ras in CDK4 regulation and highlight the functional importance of CDK4 suppression in preventing uncontrolled growth.     

Overexpression of WDR79 in non‐small cell lung cancer is linked to tumour progression

WD‐repeat protein 79 (WDR79), a member of the WD‐repeat protein family, acts as a scaffold protein, participating in telomerase assembly, Cajal body formation and DNA double‐strand break repair. Here, we first report that WDR79 is frequently overexpressed in cell lines and tissues derived from non‐small cell lung cancer (NSCLC). Knockdown of WDR79 significantly inhibited the proliferation of NSCLC cells in vitro and in vivo by inducing cell cycle arrest and apoptosis. WD‐repeat protein 79 ‐induced cell cycle arrest at the G0/G1 phase was associated with the expression of G0/G1‐related cyclins and cyclin‐dependent kinase complexes. We also provide evidence that WDR79 knockdown induces apoptosis via a mitochondrial pathway. Collectively, these results suggest that WDR79 is involved in the tumorigenesis of NSCLC and is a potential novel diagnostic marker and therapeutic target for NSCLC.