P27 Kip1 mRNA Research Articles

Effect on the proliferation of bovine corneal endothelial cells by small hairpin RNA interference targeting p27Kip1

To clarify the proliferation of bovine corneal endothelial cells (bCEC) by interference with the recombinant plasmid of short hairpin RNA (shRNA) against p27Kip1, a kind of cyclin-dependent kinase inhibitor (CKI). It was an experimental study. Three p27Kip1-shRNA template DNA sequences containing small hairpin structure were designed and synthesized as experimental groups. Plasmid expressing irrelevant shRNA with a random combination was used as negative shRNA. The products were inserted into the Pgensil-1 plasmid and the recombinant plasmid of Pgenesil-P1, Pgenesil-P2, Pgenesil-P3 and Pgenesil-HK were constructed. The recombinant plasmids were transfected into bCEC cells with liposome and a blank group. The expression of mRNA and protein of p27Kip1 was detected by RT-PCR and Western blot after stable transfection, and the plasmid with the best inhibitory effect was selected. The growth of the experimental group, Pgenesil-HK group and blank group were assessed by MTT. The influence of shRNA-p27Kip1 on bCEC cell cycle was deteceted by flow cytometry (FCM). All statistical analyses were performed using one-way ANOVA. Restrictive enzyme digestion and sequence analysis showed that four recombinant plamids were constructed successfully and the aim sequence was obtained. The expression of p27Kip1 mRNA and p27Kip1 protein of Pgenesil-P1 group, Pgenesil-P2 group and Pgenesil-P3 group were all lower than that in the control group, including blank group and negative siRNA group. The inhibitive rate of mRNA reached 32.71%, 67.76% and 80.28% (F = 453.102, P = 0.000 in each group) and the inhibitive rate of protein reached 29.27%, 64.73% and 76.13% (F = 75.385, P = 0.000 in each group) compared with the blank group. As the lowest expression among the three positive shRNA group, Pgenesil-P3 was selected for the next steps. There was no significant difference between blank group and negative Pgenesil-HK of the expression of p27Kip1 protein (P = 0.356) and the express of p27Kip1 mRNA (P = 0.246). Compared with the control group and the blank group, the growth of the bCEC transfected by Pgenesil-P3 was significantly promoted with increased cell percent of S-phrase (F = 334.957, P = 0.000) and decreased cell percent of G1-phrase (F = 134.224, P = 0.000). shRNA-p27Kip1 can down-regulate the expression of bCEC effectively and increase the growth of bCEC. shRNA-p27Kip1 RNA interference may be an effective method to promote the proliferation of CEC.

Effects of the combined blockade of EGFR and ErbB-2 on signal transduction and regulation of cell cycle regulatory proteins in breast cancer cells.

Abstract Abstract #2130 Co-expression of EGFR and ErbB-2 occurs in a subset of primary breast carcinoma, and it is associated with worse prognosis. We previously demonstrated that treatment of breast cancer cells that express both receptors with a combination of the EGFR tyrosine kinase inhibitor gefitinib (G) and the anti-ErbB-2 monoclonal antibody herceptin (H) results in a synergistic anti-tumor effect. Such combination failed to show significant activity in a phase I/II clinical trial. However, patients enrolled in this trial were not selected for expression of EGFR. We explored the molecular mechanisms involved in the synergism of G and H in breast cancer cells. Treatment of both SK-BR-3 and BT-474 cells with a combination of G+H produced a more significant reduction of AKT and p42/p44-MAPK (MAPK) activation as compared with treatment with a single agent. The combination also produced a more prolonged blockade of both signalling pathways. In agreement with these findings, treatment with G+H induced a more pronounced accumulation of cells in the G0/G1 phase of the cell cycle as compared with treatment with a single drug. A sub-G0/G1 peak, suggestive of apoptosis, was evident in cells treated with the combination but not with G or H. The combination of G+H produced a more significant increase in the levels of p27kip1 and of hypophosphorylated forms of pRb2, and a more significant decrease in the levels of Cyclin D1 and survivin as compared with a single agent. Analysis of p27kip1 protein stability, in presence of the protein synthesis inhibitor cycloheximide, revealed that both G and the combination of G+H significantly increased the stability of p27kip1, with the combination showing higher effects. Furthermore, breast cancer cells treated with the combination expressed higher levels of p27kip1 mRNA as compared with cells treated with a single drug. The combination also induced a significant increase in the nuclear levels of the FKHRL-1 transcription factor that was not observed in cells treated with G or H alone. Treatment of breast cancer cells with the dual EGFR/ErbB-2 inhibitor lapatinib produced an increase in the levels of p27kip1 and of hypophosphorylated pRb2, and a decrease in the levels of Cyclin D1 and survivin comparable to that observed following treatment with the combination of G+H. In addition, an increase in p27kip1 mRNA and in the nuclear levels of FKHRL-1 was induced in breast cancer cells by treatment with lapatinib. These findings suggest that the synergistic anti-tumor effects deriving from EGFR and ErbB-2 blockade are mediated by significant alterations in the expression of cell cycle regulatory proteins, including transcriptional and post-transcriptional regulation of p27kip1 expression. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2130.

The antitumorgenic actions of estrogen receptor beta in breast cancer cells.

Abstract Abstract #3056 Recent studies have suggested that ERβ may oppose actions of ERα in breast cancer cells and clinical studies indicate that loss of ERβ expression in ERα positive tumors is associated with a poor prognosis and perhaps resistance to tamoxifen therapy. Clinical evidence indicates that in post menopausal women hormone replacement therapy significantly decreased incidence of colon cancer, suggesting that estrogens have a protective role . We have recently found that in SW 480 colon cancer cells, (ER negative) stable expression of ERβ decreased SKP2, c-myc but not p27kip1 mRNA measured by real time PCR. These results were confirmed for c-myc and SKP2 at the protein level. However, ERβ expression increased only p27 protein levels. Addition of E2 did not regulate effects of ERβ expression.
 Similar results have been observed with T47D (ER positive breast cancer cells) stably over expressing ERβ. In the latter cells and MCF7 (ER alpha positive) cells over expressing ERβ, E2 induced β catenin protein expression was blocked by ERβ. The latter also blocked AKT and ERK activation by E2 and induced apoptosis, in an E2 independent fashion. ERβ expression also blocked E2 induced growth in MCF 7 cells. Antibody array analysis showed that ERβ regulated >100 proteins at or above the 2 fold level in T47D breast cancer cells,where as 2D PAGE/MS showed that over 60 proteins changed significantly, both types of analysis and Western blots indicate that ERβ regulates Sp1,HSP70,β catenin, c-Jun, JNK,c-Jun ,BAD among other proteins. Antibody arrays and MS have therefore revealed unsuspected targets of ERβ action. Thus, ERβ appears to oppose several actions of ERα in breast cancer cells and block colon cancer cell growth, independently of E2. Design of selective ERβ activating agents or delivery of ERβ using gene therapy may be of substantial utility in the treatment of breast and colon cancer. Category27. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3056.

Inhibition of p27Kip1 gene transcription by mitogens

How mitogens reduce the abundance of the cell cycle inhibitor p27Kip1 is an important question, and regulation of p27Kip1 translation and turnover has been described. Here we show that platelet-derived growth factor (PDGF) reduces the activity of the p27Kip1 promoter and the abundance of the p27Kip1 transcript in density-arrested mouse fibroblasts. Inhibition of p27Kip1 gene expression by PDGF required protein synthesis and histone deacetylase activity but not Akt or ERK activity. PDGF increased the expression of c-Myc in the absence but not presence of a histone deacetylase inhibitor, and c-Myc inhibited p27Kip1 promoter activity when ectopically expressed in fibroblasts. c-Myc targeted the same region of the p27Kip1 promoter as did PDGF (deletion analysis) and interacted with this region in vivo (chromatin immunoprecipitation assay). Collectively, these findings suggest that c-Myc mediates the inhibitory effects of PDGF on the p27Kip1 promoter. We also demonstrate reductions in p27Kip1 mRNA abundance in primary splenocytes exposed to concanavalin A and in T cells exposed to interleukin-2 (IL-2). In contrast to PDGF in fibroblasts, IL-2 required Akt activity for maximal reductions in p27Kip1 promoter activity and mRNA abundance in T cells. Thus, mitogens repress p27Kip1 gene transcription in multiple systems and by multiple mechanisms.

Macrophage migration inhibitory factor regulatesproliferation of gastric cancer cellsvia the PI3K/Akt pathway

To investigate the effects of macrophage migration inhibitory factor (MIF) on proliferation of human gastric cancer MGC-803 cells and expression of cyclin D1 and p27(Kip1) in them, and further determine whether the effects are related to the PI3K/Akt signal transduction pathway. Gastric cancer MGC-803 cells were cultured and then treated with 50 microg/L recombinant human MIF (rhMIF) with and without a PI3K inhibitor, LY294002 (25 micromol/L). MTT assay was used to detect the proliferation of MGC-803 cells. Cell cycle was detected by flow cytometry. Expression of cyclin D1 and p27(Kip1) mRNA was by reverse transcription-polymerase chain reaction. Protein expression of phosphorylated Akt (p-Akt), Akt, cyclin D1 and p27(Kip1) was examined by immunocytochemistry and Western blotting. rhMIF significantly stimulated the proliferation of MGC-803 cells and cell cycle progression from G1 phase to S phase in a concentration- and time-dependent manner. After the MGC-803 cells were treated with rhMIF for 24 h, the expression of cyclin D1 was significantly up-regulated compared with the cells not treated with rhMIF at both mRNA and protein levels (0.97 +/- 0.02 vs 0.74 +/- 0.01, P = 0.002; 0.98 +/- 0.05 vs 0.69 +/- 0.04, P = 0.003). The p27(Kip1) was down-regulated but only statistically significant at the protein level. rhMIF significantly increased the expression of p-Akt, which reached the peak at 30 min, but did not affect the expression of Akt. However, LY294002 inhibited all the effects of rhMIF. Macrophage MIF increases the proliferation of gastric cancer cells, induces the expression of cyclin D1 at the transcriptional level and inhibits the expression of p27(Kip1) at the post-transcriptional level via the PI3K/Akt pathway.

Structure and activity of the internal ribosome entry site within the human p27Kip1 5’-untranslated region

The cyclin dependent kinase inhibitor p27Kip1 is a key cell cycle regulatory protein that is often downregulated in cancer cells. The cellular levels of p27Kip1 are regulated, in part, through translational control mechanisms. The 5’-UTR of the p27Kip1 mRNA is known to harbor an IRES that may facilitate expression of p27Kip1 under conditions of stress such as loss of cell adhesion or growth factor and nutrient deprivation. The results presented here further characterize the p27Kip1 5’-UTR and its IRES activity. We confirm that the major transcription start site of the p27Kip1 gene produces an mRNA with a 5’-UTR of ~472 nucleotides. Other minor transcripts are also observed but the 472 nucleotide 5’-UTR displays the highest IRES activity. A structural model for the 472 nucleotide 5’-UTR was derived from nuclease digestion patterns coupled with MFOLD secondary structural prediction software. These results indicate that the 5’-UTR has significant secondary structure but also contains a large single-stranded loop that extends from nucleotides -31 to -66 relative to the start codon. Mapping of the ribosome entry window indicates that the ribosome is recruited to this single-stranded loop. The single-stranded loop also includes a U-rich sequence that has previously been shown to bind several proteins, including HuR. This is significant because HuR has previously been shown to inhibit p27Kip1 IRES activity and cause down regulation of endogenous p27Kip1 protein levels. Thus HuR may inhibit IRES activity by blocking the ribosome entry site.

Advanced glycation end products induce cell cycle arrest and proinflammatory changes in osteoarthritic fibroblast-like synovial cells

IntroductionAdvanced glycation end products (AGEs) have been introduced to be involved in the pathogenesis of osteoarthritis (OA). The influence of AGEs on osteoarthritic fibroblast-like synovial cells (FLS) has been incompletely understood as yet. The present study investigates a potential influence of AGE-modified bovine serum albumin (AGE-BSA) on cell growth, and on the expression of proinflammatory and osteoclastogenic markers in cultured FLS.MethodsFLS were established from OA joints and stimulated with AGE-BSA. The mRNA expression of p27Kip1, RAGE (receptor for AGEs), nuclear factor kappa B subunit p65 (NFκB p65), tumor necrosis factor alpha (TNF-α, interleukin-6 (IL-6), receptor activator of NFκB ligand (RANKL) and osteoprotegerin was measured by real-time PCR. The respective protein expression was evaluated by western blot analysis or ELISA. NFκB activation was investigated by luciferase assay and electrophoretic mobility shift assay (EMSA). Cell cycle analysis, cell proliferation and markers of necrosis and early apoptosis were assessed. The specificity of the response was tested in the presence of an anti-RAGE antibody.ResultsAGE-BSA was actively taken up into the cells as determined by immunohistochemistry and western blots. AGE-induced p27Kip1 mRNA and protein expression was associated with cell cycle arrest and an increase in necrotic, but not apoptotic cells. NFκB activation was confirmed by EMSAs including supershift experiments. Anti-RAGE antibodies attenuated all AGE-BSA induced responses. The increased expression of RAGE, IL-6 and TNF-α together with NFκB activation indicates AGE-mediated inflammation. The decreased expression of RANKL and osteoprotegerin may reflect a diminished osteoclastogenic potential.ConclusionsThe present study demonstrates that AGEs modulate growth and expression of genes involved in the pathophysiological process of OA. This may lead to functional and structural impairment of the joints.

MicroRNA-221–222 Regulate the Cell Cycle in Mast Cells

MicroRNAs (miRNAs) constitute a large family of small noncoding RNAs that have emerged as key posttranscriptional regulators in a wide variety of organisms. Because any one miRNA can potentially regulate expression of a distinct set of genes, differential miRNA expression can shape the repertoire of proteins that are actually expressed during development and differentiation or disease. Here, we have used mast cells as a model to investigate the role of miRNAs in differentiated innate immune cells and found that miR-221-222 are significantly up-regulated upon mast cell activation. Using both bioinformatics and experimental approaches, we identified some signaling pathways, transcription factors, and potential cis-regulatory regions that control miR-221-222 transcription. Overexpression of miR-221-222 in a model mast cell line perturbed cell morphology and cell cycle regulation without altering viability. While in stimulated cells miR-221-222 partially counteracted expression of the cell-cycle inhibitor p27(kip1), we found that in the mouse alternative splicing results in two p27(kip1) mRNA isoforms that differ in their 3' untranslated region, only one of which is subject to miR-221-222 regulation. Additionally, transgenic expression of miR-221-222 from bacterial artificial chromosome clones in embryonic stem cells dramatically reduced cell proliferation and severely impaired their accumulation. Our study provides further insights on miR-221-222 transcriptional regulation as well as evidences that miR-221-222 regulate cell cycle checkpoints in mast cells in response to acute activation stimuli.

Peripheral Nerve Injury Induces Down-Regulation of Foxo3a and p27kip1 in Rat Dorsal Root Ganglia

FOXO3a, as a forkhead transcription factor, can control cell cycle through transcriptionally down-regulating p27(kip1) level, which is a key regulator of the mammalian cell cycle and a good candidate to regulate multiple aspects of neurogenesis. To elucidate their expression and function in nervous system lesion and repair, we performed an acute sciatic nerve crush model and studied differential expressions of Foxo3a and p27(kip1) in lumbar dorsal root ganglia. Temporally, Foxo3a protein level was reduced 1 day after injury, and following Foxo3a down-regulation, p27(kip1) mRNA and protein levels were also decreased after injury. Spatially, decreased levels of Foxo3a and p27(kip1) were predominant in neurons and glial cells, which were regenerating axons and largely proliferated after injury, respectively. Together with previous reports, we hypothesized decreased levels of Foxo3a and p27(kip1) in lumbar dorsal root ganglia were implicated in axonal regeneration and the proliferation of glial cells after sciatic nerve injury.

Enhanced neurogenesis from neural progenitor cells with G1/S‐phase cell cycle arrest is mediated by transforming growth factor β1

We have previously demonstrated that a G1/S-phase cell cycle blocker, deferoxamine (DFO), increased the number of new neurons from rat neurosphere cultures, which correlated with prolonged expression of cyclin-dependent kinase (cdk) inhibitor p27(kip1) [H. J. Kim et al. (2006)Brain Research, 1092, 1-15]. The present study focuses on neuronal differentiation mechanisms following treatment of neural stem/progenitor cells (NPCs) with a G1/S-phase cell cycle blocker. The addition of DFO (0.5 mm) or aphidicolin (Aph) (1.5 microm) to neurospheres for 8 h, followed by 3 days of differentiation, resulted in an increased number of neurons and neurite outgrowth. DFO induced enhanced expression of transforming growth factor (TGF)-beta1 and cdk5 at 24 h after differentiation, whereas Aph only increased TGF-beta1 expression. DFO-induced neurogenesis and neurite outgrowth were attenuated by administration of a cdk5 inhibitor, roscovitine, suggesting that the neurogenic mechanisms differ between DFO and Aph. TGF-beta1 (10 ng/mL) did not increase neurite outgrowth but rather the number of beta-tubulin III-positive cells, which was accompanied by enhanced p27(kip1) mRNA expression. In addition, TGF-beta receptor type II expression was observed in nestin-positive NPCs. Results indicated that DFO-induced TGF-beta1 signaling activated smad3 translocation from the cytoplasm to the nucleus. In contrast, TGF-beta1 signaling inhibition, via a TGF-beta receptor type I inhibitor (SB-505124), resulted in decreased DFO-induced neurogenesis, in conjunction with decreased p27(kip1) protein expression and smad3 translocation to the nucleus. These results suggest that cell cycle arrest during G1/S-phase induces TGF-beta1 expression. This, in turn, prompts enhanced neuronal differentiation via smad3 translocation to the nucleus and subsequent p27(kip1) activation in NPCs.

Mammalian target of rapamycin pathway inhibition enhances the effects of 5-aza-dC on suppressing cell proliferation in human gastric cancer cell lines

The present study aimed to evaluate the relationship between mTOR signaling pathway and DNA methylation in cell survival, cell cycle, gene expression and protein level on human gastric cancer cells. Human gastric cancer cell lines, MKN45 and SGC7901 were treated with 5-aza-dC, rapamycin and/or LY294002. Cell viability was analyzed by MTT. Cell cycle distribution was evaluated by flow cytometry (FCM). The transcription level of PTEN and p27 ( Kip1 ) genes was detected by using real-time PCR. Protein expressions were detected by Western blotting. We found that cell viability was moderately reduced when treated with 5-aza-dC alone, but remarkably reduced when mTOR pathway was inhibited together (P<0.01). mTOR inhibition enhances the effects of 5-aza-dC on arresting cell cycle at G2 phase in human gastric cancer cell lines. The expression of PTEN and p27 ( Kip1 ) mRNA was remarkably increased in the gastric cancer cells treated with combind drugs (P<0.01). Phosphorylation of Akt, p70S6K and 4E-BP1 were significantly reduced in the cells treated with LY294002 or RAPA (P<0.01), but we failed to find that 5-aza-dC enhance these effects. We suggested that mTOR inhibition could enhance the effects of 5-aza-dC on suppressing cell proliferation and arresting cell cycle in human gastric cancer cell lines, which might be a potential target for tumor therapy.

Advanced glycation end-products induce cell cycle arrest and hypertrophy in podocytes

Podocyte injury with loss of cells into the urine seems to be an early factor in diabetic nephropathy. Advanced glycation end-products (AGEs) are important mediators of structural and functional renal abnormalities in diabetic nephropathy. We and others have previously described that mice with a deletion in the gene for the cell cycle regulatory p27(Kip1) are protected from some features of diabetic nephropathy. The present study investigates a potential influence of AGE-modified bovine serum albumin (AGE-BSA) on podocyte growth and p27(Kip1) expression in culture. The p27(Kip1) expression was measured by western blots and real-time PCR. Cell cycle analysis, cell hypertrophy, proliferation and various markers of apoptosis and necrosis were assessed. The p27(Kip) expression was inhibited by siRNA or was overexpressed in podocytes with an inducible expression system. AGE-BSA was actively taken up into the cell as determined by immunohistochemistry, western blots and HPLC. Incubation with AGE-BSA induced in differentiated podocytes, but not in tubular cells, p27(Kip1) mRNA and protein expression. This induction was associated with cell cycle arrest of podocytes, cell hypertrophy (as measured by increases in cell size and protein/cell number ratios) and an increase in necrotic, but not apoptotic cells. Inhibition of p27(Kip1) expression with siRNA halted the AGE-BSA-mediated cell cycle arrest and hypertrophy, but did not interfere with AGE uptake into podocytes. In contrast, overexpression of p27(Kip1) using an inducible expression system stimulated hypertrophy and cell cycle arrest of podocytes. Our data demonstrate that AGE-BSA-induced hypertrophy and damage of cultured podocytes occurs by a mechanism involving p27(Kip1). This effect can contribute to the loss of podocytes in diabetic nephropathy.

Effect of p27Kip1 inhibition on proliferation of bovine corneal endothelial cells by RNA interference

Three plasmids (pGenesil-P1, pGenesil-P2, pGenesil-P3) with different p27Kip1-shRNA sequences were designed and synthesized. Their effects on the proliferation of bovine corneal endothelial cells (bCEC) were investigated. Plasmid expressing irrelevant shRNA with a random combination was used as negative control (pGenesil-HK). The recombination of four plamids was confirmed by restrictive enzyme digestion and sequence analysis. The expression of mRNA and protein of p27Kip1 was detected by RT-PCR and Western blotting after stable transfection. The expressions of p27Kip1 mRNA and p27Kip1 protein of pGenesil-P1 group, pGenesil-P2 group and pGenesil-P3 group were all lower than those in the pGenesil-HK group and the blank group (non-transfected group). pGenesil-P3 had the strongest inhibitory effect and was selected for the next steps. The proliferation rates of the pGenesil-P3 group, the pGenesil-HK group and the blank group were assessed by MTT. The influence of shRNA-p27Kip1 on bCEC cell cycle was detected by flow cytometry (FCM). Compared with the control groups, the proliferation rate of the pGenesil-P3 group was increased significantly, and the ratio of S-phase also increased. It is concluded that shRNA-p27Kip1 could down-regulate the expression of p27Kip1 effectively and increase the proliferation of bCEC. RNA interference (RNAi) may be an effective means to promote the proliferation of CEC.

Effect of hypoxia and Beraprost sodium on human pulmonary arterial smooth muscle cell proliferation: the role of p27kip1

BackgroundHypoxia induces the proliferation of pulmonary arterial smooth muscle cell (PASMC) in vivo and in vitro, and prostacyclin analogues are thought to inhibit the growth of PASMC. Previous studies suggest that p27kip1, a kind of cyclin-dependent kinase inhibitor, play an important role in the smooth muscle cell proliferation. However, the mechanism of hypoxia and the subcellular interactions between p27kip1 and prostacyclin analogues in human pulmonary arterial smooth muscle cell (HPASMC) are not fully understood.MethodsWe investigated the role of p27kip1 in the ability of Beraprost sodium (BPS; a stable prostacyclin analogue) to inhibit the proliferation of HPASMC during hypoxia. To clarify the biological effects of hypoxic air exposure and BPS on HPASMC, the cells were cultured in a hypoxic chamber under various oxygen concentrations (0.1–21%). Thereafter, DNA synthesis was measured as bromodeoxyuridine (BrdU) incorporation, the cell cycle was analyzed by flow cytometry with propidium iodide staining. The p27kip1 mRNA and protein expression and it's stability was measured by real-time RT-PCR and Western blotting. Further, we assessed the role of p27kip1 in HPASMC proliferation using p27kip1 gene knockdown using small interfering RNA (siRNA) transfection.ResultsAlthough severe hypoxia (0.1% oxygen) suppressed the proliferation of serum-stimulated HPASMC, moderate hypoxia (2% oxygen) enhanced proliferation in accordance with enhanced p27kip1 protein degradation, whereas BPS suppressed HPASMC proliferation under both hypoxic and normoxic conditions by suppressing p27kip1 degradation with intracellular cAMP-elevation. The 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP), a cAMP analogue, had similar action as BPS in the regulation of p27kip1. Moderate hypoxia did not affect the stability of p27kip1 protein expression, but PDGF, known as major hypoxia-induced growth factors, significantly decreased p27kip1 protein stability. We also demonstrated that BPS and 8-Br-cAMP suppressed HPASMC proliferation under both hypoxic and normoxic conditions by blocking p27kip1 mRNA degradation. Furthermore, p27kip1 gene silencing partially attenuated the effects of BPS and partially restored hypoxia-induced proliferation.ConclusionOur study suggests that moderate hypoxia induces HPASMC proliferation, which is partially dependent of p27kip1 down-regulation probably via the induction of growth factors such as PDGF, and BPS inhibits both the cell proliferation and p27kip1 mRNA degradation through cAMP pathway.

MicroRNAs (miR)-221 and miR-222, both overexpressed in human thyroid papillary carcinomas, regulate p27Kip1 protein levels and cell cycle

We have recently reported that MicroRNAs (miR)-221 and miR-222 were up-regulated in human thyroid papillary carcinomas in comparison with the normal thyroid tissue. Bioinformatic analysis proposed the p27(Kip1) protein, a key regulator of cell cycle, as a candidate target for the miR-221/222 cluster. Here, we report that the enforced expression of miR-221 and miR-222 was able to reduce p27(Kip1) protein levels in thyroid carcinoma and HeLa cells in the absence of significant changes in specific p27(Kip1) mRNA levels. This effect is direct as miR-221 and miR-222 negatively regulate the expression of the 3'-untranslated region-based reporter construct from the p27(Kip1) gene, and is dependent on two target sites in this region. Consistent with these results, an enforced expression of the miR-221 and miR-222 induced the thyroid papillary carcinoma cell line (TPC-1) to progress to the S phase of the cell cycle. It is likely that the negative regulation of p27(Kip1) by miR-221 and miR-222 might also have a role in vivo since we report an inverse correlation between miR-221 and miR-222 up-regulation and down-regulation of the p27(Kip1) protein levels in human thyroid papillary carcinomas. Therefore, the data reported here demonstrate that miR-221 and miR-222 are endogenous regulators of p27(Kip1) protein expression, and thereby, the cell cycle.

Regulation of p27Kip1 by miRNA 221/222 in Glioblastoma

Levels of p27Kip1, a key negative regulator of the cell cycle, are often decreased in cancer. In most cancers, levels of p27Kip1 mRNA are unchanged and increased proteolysis of the p27Kip1 protein is thought to be the primary mechanism for its down-regulation. Here we show that p27Kip1 protein levels are also down-regulated by microRNAs in cancer cells. We used RNA interference to reduce Dicer levels in human glioblastoma cell lines and found that this caused an increase in p27Kip1 levels and a decrease in cell proliferation. When the coding sequence for the 3'UTR of the p27Kip1 mRNA was inserted downstream of a luciferase reporter gene, Dicer depletion also enhanced expression of the reporter gene product. The microRNA target site software TargetScan predicts that the 3'UTR of p27Kip1 mRNA contains multiple sites for microRNAs. These include two sites for microRNA 221 and 222, which have been shown to be upregulated in glioblastoma relative to adjacent normal brain tissue. The genes for microRNA 221 and microRNA 222 occupy adjacent sites on the X chromosome; their expression appears to be coregulated and they also appear to have the same target specificity. Antagonism of either microRNA 221 or 222 in glioblastoma cells also caused an increase in p27Kip1 levels and enhanced expression of the luciferase reporter gene fused to the p27Kip1 3'UTR. These data show that p27Kip1 is a direct target for microRNAs 221 and 222, and suggest a role for these microRNAs in promoting the aggressive growth of human glioblastoma.

Rac1-dependent transcriptional up-regulation of p27 Kip1 by homophilic cell–cell contact in vascular endothelial cells

The mechanism for the transcriptional up-regulation of p27 Kip1 due to the formation of the cell–cell contact was investigated in vascular endothelial cells. The induction of the cell–cell contact by adding an extra number of endothelial cells activated Rac1, up-regulated p27 Kip1 mRNA and protein, and also facilitated the cell cycle arrest. Transduction of the Rac1 inhibitor protein using the cell-penetrating peptide or treatment with a Rac1 inhibitor NSC23766 inhibited the p27 Kip1 up-regulation and delayed the cell cycle arrest. Rac1 was therefore suggested to mediate the contact-induced transcriptional up-regulation of p27 Kip1. The role of Rac1 in the regulation of the p27 Kip1 promoter activity was next examined with a luciferase reporter assay. The promoter activity was increased by inducing the cell–cell contact, which was significantly inhibited by the Rac1 inhibitory protein and NSC23766. The evaluation of various truncated promoter regions determined region − 620 to − 573 nucleotides from the initiation codon to be responsible for the contact-induced, Rac1-dependent activation of the p27 Kip1 promoter. The present study thus demonstrated for the first time that the activation of Rac1 due to the cell–cell contact plays a critical role in the transcriptional up-regulation of p27 Kip1 in vascular endothelial cells.

Id3 is a novel regulator of p27kip1 mRNA in early G1 phase and is required for cell-cycle progression

P27kip is a key inhibitory protein of the cell-cycle progression, which is rapidly downregulated in early G1 phase by a post-translational mechanism involving the proteosomal degradation. In this study, using a wounding model that induces cell-cycle entry of human dermal fibroblasts, we demonstrate that p27mRNA is downregulated when cells progress into the G1 phase, and then it returns to its basal level when cells approach the S phase. By using a quantitative polymerase chain reaction screening we identified inhibitors of differentiation (Id3), a bHLH transcriptional repressor, as a candidate mediator accounting for p27 mRNA decrease. Id3 silencing, using an small interfering RNA approach, reversed the injury mediated p27 downregulation demonstrating that Id3 is involved in the transcriptional repression of p27. Reporter gene experiments and a chromatin immunoprecipitation assay showed that Id3 likely exerts its repressive action through ELK1 inhibition. By inhibiting early p27 downregulation, Id3 depletion blocked (i) the G1-phase progression as assessed by the inhibition of pRb phosphorylation and p130 degradation and (ii) the G1/S transition as observed by the inhibition of cyclin A induction, demonstrating that p27 mRNA decrease is required for cell proliferation. Apart from its effect on the early p27 diminution, Id3 appears also involved in the control of the steady-state level of p27 at the G1/S boundary. In conclusion, this study identifies a novel mechanism of p27 regulation which besides p27 protein degradation also implicates a transcriptional mechanism mediated by Id3.

Potent Inhibition of Serum-Stimulated Responses in Vascular Smooth Muscle Cell Proliferation by 2-Chloro-3-(4-hexylphenyl)-amino-1,4-naphthoquinone, a Newly Synthesized 1,4-Naphthoquinone Derivative

Atherosclerosis, a disease of the large arteries, is the primary cause of heart disease and stroke. The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenetic factor of vascular disorders like atherosclerosis and restenosis after angioplasty. In the present study, the possible anti-proliferative effect of a synthetic 1,4-naphthoquinone derivative, 2-chloro-3-(4-hexylphenyl)-amino-1,4-naphthoquinone (NQ304) was investigated on rat aortic VSMCs. NQ304 was shown to potently inhibit 5% fetal bovine serum (FBS)-induced the growth of VSMCs. Pre-treatment of VSMCs with NQ304 (1-10 microM) for 24 h resulted in significant cell number decreases, i.e., inhibition percentages were 44.75+/-10.77, 73.85+/-6.38 and 89.77+/-6.52% at NQ304 concentrations of 1, 5 and 10 microM, respectively. NQ304 was also found to significantly inhibit 5% FBS-induced DNA synthesis in a concentration-dependent manner. Furthermore, NQ304 elevated p21(cip1) and p27(kip1) mRNA levels and caused G0/G1 phase arrest in cell cycle progression. However, no evidence of NQ304-induced apoptotic or necrotic cell death was obtained, as determined by flow cytometry analysis and DNA fragmentation assays. To investigate the mechanism underlying the anti-proliferative effect of NQ304, we examined the effects of NQ304 on c-fos mRNA expression, activator protein-1 (AP-1) binding activity and extracellular signal-regulated kinase1/2 (ERK1/2) and Akt activation. Pre-treatment of VSMCs with NQ304 (1-10 microM) was found to significantly inhibit the 5% FBS-induced phosphorylations of ERK1/2 and Akt, the activation of AP-1 and the expression of c-fos. These data suggest that the anti-proliferative and cell cycle arresting effects of NQ304 on serum-induced VSMCs may be mediated by AP-1 activation downregulation via the suppression of phosphatidylinositol 3-kinase (PI3K)/Akt and ERK1/2 signaling pathways, and it may contribute to the prevention of atherosclerosis through inhibition of VSMC proliferation.

Skp2 Controls Adipocyte Proliferation during the Development of Obesity

The increase in the mass of adipose tissue during the development of obesity can arise through an increase in cell size, an increase in cell number, or both. Here we show that long term maintenance of C57BL/6 mice on a high fat diet (for approximately 25 weeks) induces an initial increase in adipocyte size followed by an increase in adipocyte number in white adipose tissue. The latter effect was found to be accompanied by up-regulation of expression of the gene for the F-box protein Skp2 as well as by downregulation of the cyclin-dependent kinase inhibitor p27(Kip1), a principal target of the SCF(Skp2) ubiquitin ligase, in white adipose tissue. Ablation of Skp2 protected mice from the development of obesity induced either by a high fat diet or by the lethal yellow agouti (A(y)) mutation, and this protective action was due to inhibition of the increase in adipocyte number without an effect on adipocyte hypertrophy. The reduction in the number of adipocyte caused by Skp2 ablation also inhibited the development of obesity-related insulin resistance in the A(y) mutant mice, although the reduced number of beta cells and reduced level of insulin secretion in Skp2-deficient mice resulted in glucose intolerance. Our observations thus indicate that Skp2 controls adipocyte proliferation during the development of obesity.