Decreased level of the cell cycle regulator p27 and increased level of its ubiquitin ligase Skp2 in endometrial carcinoma but not in normal secretory or in hyperstimulated endometrium

Polycystic ovary syndrome and adverse pregnancy outcomes: potential role of decidual function

Polycystic ovary syndrome (PCOS) is a common endocrine disorder affecting fertility and mental health among women of reproductive age. In addition to anovulation and hyperandrogenism, patients also experience metabolic issues, such as insulin resistance, obesity, and dyslipidemia, as well as chronic low-grade inflammation throughout the body. Recent studies have shown that even with assisted reproductive technology to treat anovulatory issues, patients with PCOS still have higher rates of adverse pregnancy outcomes and abortion compared to normal pregnancies. These findings suggest that PCOS may impair the endometrium and disrupt the onset and maintenance of healthy pregnancies. Decidualization is a crucial step in the process of healthy pregnancy, during which endometrial stromal cells (ESCs) differentiate into secretory decidual stromal cells (DSCs) regulated by hormones and local metabolism. This article comprehensively reviews the pathological processes of PCOS and the mechanisms involved in its impaired decidualization. In addition, we explore how PCOS increases the incidence of adverse pregnancy outcomes (APO). By gaining a better understanding of the adverse effects of PCOS on pregnancy and its specific mechanisms, we hope to provide a theoretical basis for reducing APO and improving the live birth rate among women with PCOS.

Targeting the untargetable: RB1-deficient tumours are vulnerable to Skp2 ubiquitin ligase inhibition

Proteins that regulate the cell cycle are accumulated and degraded in a coordinated manner during the transition from one cell cycle phase to the next. The rapid loss of a critical protein, for example, to allow the cell to move from G1/G0 to S phase, is often regulated by its ubiquitination and subsequent proteasomal degradation. Protein ubiquitination is mediated by a series of three ligases, of which the E3 ligases provide the specificity for a particular protein substrate. One such E3 ligase is SCF^Skp1/Cks1, which has a substrate recruiting subunit called S-phase kinase-associated protein 2 (Skp2). Skp2 regulates cell proliferation, apoptosis, and differentiation, can act as an oncogene, and is overexpressed in human cancer. A primary target of Skp2 is the cyclin-dependent kinase inhibitor p27 (CDKN1b) that regulates the cell cycle at several points. The RB1 tumour suppressor gene regulates Skp2 activity by two mechanisms: by controlling its mRNA expression, and by an effect on Skp2's enzymatic activity. For the latter, the RB1 protein (pRb) directly binds to the substrate-binding site on Skp2, preventing protein substrates from being ubiquitinated and degraded. Inactivating mutations in RB1 are common in human cancer, becoming more frequent in aggressive, metastatic, and drug-resistant tumours. Hence, RB1 mutation leads to the loss of pRb, an unrestrained increase in Skp2 activity, the unregulated decrease in p27, and the loss of cell cycle control. Because RB1 mutations lead to the loss of a functional protein, its direct targeting is not possible. This perspective will discuss evidence validating Skp2 as a therapeutic target in RB1-deficient cancer.

Study of the Association of Phosphatase and Tensin Homolog and p27 Expressions in Endometrial Hyperplasia and Carcinoma

Introduction:

Phosphatase and tensin homolog (PTEN) and p27 are commonly mutated gene in endometrial carcinoma (EC) and their association in development of EC has not been fully understood.

The Aim of the Study:

The aim is to clarify the association of PTEN and p27 in EC and their correlation with the histologic grade.

Material and Methods:

Paraffin-embedded 20 and 50 specimens representing EH and EC were collected, cut into 4 mm thick and stained with H&E stain for histopathological examination. All EC cases were graded according to the percentage of nonsquamous solid pattern into 3 grades. Immunohistochemical (IHC) analyses were done using a rabbit polyclonal anti-PTEN antibody and a rabbit monoclonal anti-p27 antibody. Evaluation of reactivity was categorized: 1+ (weak) = less than 10%, 2+ (moderate) = 11 to 50% and 3+ (strong) = more than 50% tumor. t-test, one way ANOVA and chi-square test were used in the statistical analysis.

Results:

Loss of PTEN was seen in 7/20 (35%) and 29/50 (58%) of EH and EC cases with significance (P =0.01824), opposite to 17/20 (85%) and 25/50 (50%) of p27 (P = 0.00334). Both antibodies showed significance in EH cases only (P = 0.00019). No correlation with the histological grade for both antibodies. Four major categories were formulated; PTEN+/p27+ (n = 2, 14, 10%, 28%), PTEN+/p27- (n = 5, 7; 25% and 14%), PTEN-/p27+ (n = 1, 11; 5%, 22%) PTEN-/p27- (n = 12, 18; 60%, 36%) cases of EH and EC, respectively with no significant difference obtained.

Conclusion:

Not all cases of PTEN negative EC showing p27 loss and vice versa. Despite many studies reacted with PTEN and p27 expression in EC, none of them is confirmatory to adjust the correlation between them in EC. So, more studies must be done to correlate between the degree of PTEN loss and p27 comprising all subtypes and grading of EC.

p27 and its ubiquitin ligase Skp2 expression in endometrium of IVF patients with repeated hormonal stimulation

This preliminary study examined a possible effect of long duration repeated hormonal stimulation on the endometrium using a molecular tool. The expression of the hormone stimulated, cell cycle regulators, p27 and its ligase S-phase kinase-interacting protein2 (Skp2), were assessed in 46 endometrial samples of patients who underwent repeated IVF cycles (3-21). Skp2 protein is usually undetectable in normal tissue and can be demonstrated only in rapidly dividing cells. Samples from non-stimulated, normal cycling women served as control group A. Samples of endometrial carcinoma served as control group B. In secretory endometrium, the expression of p27 was found to be lower and Skp2 higher in the study group compared with control group A. Moreover, in 25% of patients of the study group, Skp2 expression was significantly higher (P < 0.05) compared with control group A, reaching concentrations demonstrated in endometrial carcinoma. The findings of this study suggest that repeated hormone stimulation cycles may disrupt endometrial physiology, potentially towards abnormal proliferation. These changes in protein expression are described for the first time in IVF patients and should be further investigated.

An essential role of p27 downregulation in fenvalerate-induced cell growth in human uterine leiomyoma and smooth muscle cells

Previously, we reported that fenvalerate (Fen) promotes proliferation of human uterine leiomyoma (UtLM) cells by enhancing progression of cells from G(0)-G(1) to S phase through molecular mechanisms independent of estrogen receptor-α and -β. The cyclin-dependent kinase (CDK) inhibitor p27, which blocks G(1) to S phase transitions and is an important regulator of CDK2, is often decreased in hormonally regulated diseases, including uterine leiomyomas. Therefore, we were interested in whether Fen could regulate the expression of p27 and whether p27 might play a role in Fen-induced cell proliferation. Expression of p27 in Fen-treated UtLM and uterine smooth muscle cells (UtSMCs) was examined. We found that p27 mRNA was significantly downregulated and that protein levels were decreased in both cell types treated with 10 μM Fen for 24 h compared with respective controls. Overexpression of p27 in UtLM cells and UtSMCs using an adenovirus doxycycline (Dox)-regulated Tet-off system abrogated the proliferative effects of Fen, as evidenced by decreased total cell numbers and BrdU incorporation. Fen treatment increased CDK2 mRNA expression levels; however, overexpression of p27 also abolished this effect. In contrast, Dox treatment dramatically restored the above muted responses. Finally, we utilized siRNA to knock down p27 expression. After transfection, mRNA levels of p27 were downregulated in UtLM cells and UtSMCs and total cell numbers and BrdU incorporation increased significantly compared with nontransfected cells. Fen treatment in the presence of p27 silencing enhanced the increased cell counts and BrdU labeling in UtLM cells and UtSMCs. Taken together, these results indicate that p27 downregulation is critical for Fen-induced cell proliferation.

Loss of WT1 expression in the endometrium of infertile PCOS patients: a hyperandrogenic effect?

CONTEXT

In fertile patients the endometrial Wilms tumor suppressor gene (WT1) is expressed during the window of implantation. Polycystic ovary syndrome (PCOS) patients suffer from hyperandrogenemia and infertility and have elevated endometrial androgen receptor (AR) expression. WT1 is known to be down-regulated by AR. Therefore, the expression of WT1 and its targets may be altered in PCOS endometrium.

OBJECTIVE

The objective of the study was to assess the expression and regulation of WT1 and selected downstream targets in secretory endometrium from ovulatory PCOS (ovPCOS) and fertile women.

DESIGN AND PATIENTS

Endometrial samples were obtained from 25 ovPCOS and 25 fertile patients.

MAIN OUTCOME MEASURE

Endometrial expression of WT1 and selected downstream targets were assessed by immunohistochemistry and RT-PCR. The androgen effect on WT1 expression was determined in vitro by immunoblots and RT-PCR. The expression of WT1 and its targets was quantified in fertile and ovPCOS stromal cells in the presence of androgens by RT-PCR. Caspase-3/7 activity was measured to evaluate sensitivity to drug-induced apoptosis.

RESULTS

WT1 expression was down-regulated in secretory-phase ovPCOS endometrium. Stromal expression of Bcl-2 and p27 was higher, and epidermal growth factor receptor was lower in ovPCOS than in fertile patients. Endometrial stromal expression of WT1, Bcl-2, Bcl-2-associated X protein, and β-catenin was regulated by androgens. Apoptosis levels were reduced in ovPCOS samples and androgen-treated fertile samples.

CONCLUSION

WT1 expression is down-regulated in ovPCOS endometrium during the window of implantation. Androgens regulate the expression of WT1 and its targets during endometrial decidualization. The altered balance between WT1 and AR in the endometrium of PCOS patients may jeopardize the success of decidualization and endometrial receptivity.

The diversity of sex steroid action: the role of micro-RNAs and FOXO transcription factors in cycling endometrium and cancer

The rise and fall in ovarian oestrogen and progesterone production orchestrates a series of events that are indispensable for reproduction, including ovulation, implantation, decidualisation and menstruation. In the uterus, these events involve extensive tissue remodelling, characterised by waves of endometrial cell proliferation, differentiation, recruitment of inflammatory cells, apoptosis, tissue breakdown, menstruation and regeneration. The ability of ovarian hormones to trigger such diverse physiological responses is foremost dependent upon interaction of activated steroid receptors with specific transcription factors, such as Forkhead box class O (FOXO) proteins, involved in cell fate decisions. Furthermore, micro-RNAs (miRNAs), small non-coding RNAs that function as posttranscriptional regulators of gene expression, have emerged as a major regulator system of steroid hormone responses in the female reproductive tract. Consequently, increasing evidence shows that deregulated uterine miRNA expression underpins a spectrum of common reproductive disorders, ranging from implantation failure to endometriosis. Furthermore, by targeting FOXO transcription factors and other key regulators of tissue homeostasis, oncogenic endometrial miRNAs promote tumourigenesis and cancer progression.

Proteasome system of protein degradation and processing

In eukaryotic cells, degradation of most intracellular proteins is realized by proteasomes. The substrates for proteolysis are selected by the fact that the gate to the proteolytic chamber of the proteasome is usually closed, and only proteins carrying a special "label" can get into it. A polyubiquitin chain plays the role of the "label": degradation affects proteins conjugated with a ubiquitin (Ub) chain that consists at minimum of four molecules. Upon entering the proteasome channel, the polypeptide chain of the protein unfolds and stretches along it, being hydrolyzed to short peptides. Ubiquitin per se does not get into the proteasome, but, after destruction of the "labeled" molecule, it is released and labels another molecule. This process has been named "Ub-dependent protein degradation". In this review we systematize current data on the Ub-proteasome system, describe in detail proteasome structure, the ubiquitination system, and the classical ATP/Ub-dependent mechanism of protein degradation, as well as try to focus readers' attention on the existence of alternative mechanisms of proteasomal degradation and processing of proteins. Data on damages of the proteasome system that lead to the development of different diseases are given separately.

Macrophage migration inhibitory factor regulates proliferation of gastric cancer cells via the PI3K/Akt pathway

AIM

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Definition of microRNAs that repress expression of the tumor suppressor gene FOXO1 in endometrial cancer

Endometrial cancer is the most common malignancy of the lower female reproductive tract. The tumor suppressor FOXO1 is downregulated in endometrial cancer compared with normal endometrium but the underlying mechanisms are not well understood. Using microRNA (miR) target prediction algorithms, we identified several miRs that potentially bind the 3'-untranslated region of FOXO1 transcripts. Expression profiling of normal and malignant endometrial samples by quantitative real-time PCR and Northern blot analysis revealed an inverse correlation between the levels of FOXO1 protein and the abundance of several of the in silico-predicted miRs, suggesting that loss of FOXO1 expression in endometrial cancer may be mediated by miRs. To determine the role of candidate miRs, we used the endometrial cancer cell lines HEC-1B and Ishikawa, which express FOXO1 at high and low levels, respectively. Expression of miR-9, miR-27, miR-96, miR-153, miR-182, miR-183, or miR-186, but not miR-29a, miR-128, miR-152, or miR-486 mimetics in HEC-1B cells was sufficient to significantly reduce the abundance of FOXO1. Conversely, FOXO1 expression was efficiently restored in the Ishikawa cell line upon simultaneous inhibition of miR-9, miR-27, miR-96, miR-153, miR-183, and miR-186. Moreover, induction of FOXO1 in Ishikawa cells by miR inhibitors was accompanied by G1 cell cycle arrest and cell death, and was attenuated by the small interfering RNA-mediated downregulation of FOXO1 expression. Our findings identify several miRs overexpressed in endometrial cancer that function in concert to repress FOXO1 expression. Further, aberrant miR expression results in deregulated cell cycle control and impaired apoptotic responses, and thus, may be central to endometrial tumorigenesis.

Protein kinase C alpha-dependent signaling mediates endometrial cancer cell growth and tumorigenesis

Endometrial cancer is the most common invasive gynecologic malignancy, yet molecular mechanisms and signaling pathways underlying its etiology and pathophysiology remain poorly characterized. We sought to define a functional role for the protein kinase C (PKC) isoform, PKCalpha, in an established cell model of endometrial adenocarcinoma. Ishikawa cells depleted of PKCalpha protein grew slower, formed fewer colonies in anchorage-independent growth assays and exhibited impaired xenograft tumor formation in nude mice. Consistent with impaired growth, PKCalpha knockdown increased levels of the cyclin-dependent kinase (CDK) inhibitors p21(Cip1/WAF1) (p21) and p27(Kip1) (p27). Despite the absence of functional phosphatase and tensin homolog (PTEN) protein in Ishikawa cells, PKCalpha knockdown reduced Akt phosphorylation at serine 473 and concomitantly inhibited phosphorylation of the Akt target, glycogen synthase kinase-3beta (GSK-3beta). PKCalpha knockdown also resulted in decreased basal ERK phosphorylation and attenuated ERK activation following EGF stimulation. p21 and p27 expression was not increased by treatment of Ishikawa cells with ERK and Akt inhibitors, suggesting that PKCalpha regulates CDK expression independently of Akt and ERK. Immunohistochemical analysis of Grade 1 endometrioid adenocarcinoma revealed aberrant PKCalpha expression, with foci of elevated PKCalpha staining, not observed in normal endometrium. These studies demonstrate a critical role for PKCalpha signaling in endometrial tumorigenesis by regulating expression of CDK inhibitors p21 and p27 and activation of Akt and ERK-dependent proliferative pathways. Thus, targeting PKCalpha may provide novel therapeutic options in endometrial tumors.

Macrophage migration inhibitory factor regulates proliferation of gastric cancer cells via the PI3K/Akt pathway

AIM: 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.

METHODS: Gastric cancer MGC-803 cells were cultured and then treated with 50 μg/L recombinant human MIF (rhMIF) with and without a PI3K inhibitor, LY294002 (25 μmol/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.

RESULTS: 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.

CONCLUSION: 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.

Functional significance of cytochrome P450 1B1 in endometrial carcinogenesis

Cytochrome P450 1B1 (CYP1B1) catalyzes estrogen hydroxylation and activation of potential carcinogens. Here we explored the role of CYP1B1 in endometrial carcinogenesis. Immunohistochemical staining of endometrial carcinomas showed that CYP1B1 is up-regulated in endometrial cancers. To understand the functional significance of CYP1B1 up-regulation in endometrial cancers with regard to tumorigenesis, we used small interfering RNA-mediated approach to knockdown CYP1B1 in endometrial carcinoma cell line followed by functional assays. Further, to understand the molecular basis of the role of CYP1B1 in endometrial carcinomas, we profiled the expression of key pathway-specific genes and identified several components of cell cycle, apoptosis, and cell adhesion pathways that are potentially regulated by CYP1B1. CYP1B1 depletion in endometrial carcinoma cells leads to decreased cellular proliferation and induces G(0)-G(1) cell cycle arrest. Significantly, CYP1B1 knockdown leads to down-regulated expression of cyclin E1, S-phase kinase-associated protein 2 (SKP2), minichromosome maintenance complex component 4 (MCM4), and RAD51 and up-regulation of p27(Kip1). Also, we identified cyclin E-binding protein (CEBP1) as a novel CYP1B1 target. Attenuation of CYP1B1 expression in endometrial carcinoma cells induces apoptosis and increases expression of IFN-beta (IFNbeta), granzyme A (GRZA), and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Importantly, CYP1B1 depletion decreased the invasive potential of the endometrial cancer cells and expression of melanoma cell adhesion molecule (MCAM). In conclusion, our data suggest that CYP1B1 up-regulation plays a crucial role in endometrial carcinogenesis by targeting multiple pathways. We speculate that CYP1B1 inhibition in endometrial carcinomas could be a useful therapeutic approach as it regulates several potential anticancer targets like cyclin E1, Skp2, and TRAIL.

Effect of p27mt gene on apoptosis of the colorectal cancer cell line Lovo

AIM: To construct p27mt recombinant adenovirus, transfect the colorectal cell line Lovo and observe the effects of p27mt on Lovo cell apoptosis and cell cycle inhibition.

METHODS: We constructed recombinant adenovirus containing p27mt by homologous recombination in bacteria. The colorectal cancer cell line Lovo was infected with recombinant replication-defective adenovirus Ad-p27mt, and expression of p27mt was determined by Western blotting; the inhibitory effect of p27mt on Lovo cells was detected by cytometry. Cell cycle was determined by flow cytometry. DNA fragment analysis identified the occurrence of apoptosis.

RESULTS: The recombinant adenovirus which already contained p27mt target gene was successfully constructed. When multiplicity of infection was ≥ 50, the infection efficiency was 100%. After transfection of Lovo cells with Ad-p27mt the cells had high p27 expression which was identified by immunoblotting assay. PI staining and flow cytometry showed that 77.96% of colorectal cancer cells were inhibited in phase G₀/G₁, while in the Ad-LacZ group and blank control group, 27.57% and 25.29% cells were inhibited in the same phase, respectively. DNA fragment analysis, flow cytometry and TUNEL assay demonstrated that p27mt is able to induce apoptosis in colorectal cancer cells.

CONCLUSION: p27mt has an obvious blocking effect on colorectal cancer cell cycle, and most cells were inhibited in phase G₀/G₁. Therefore, p27mt can induce apoptosis in colorectal cells.

FOXO transcription factors: from cell fate decisions to regulation of human female reproduction

All key reproductive events in the human ovary and uterus, including follicle activation, ovulation, implantation, decidualization, luteolysis and menstruation, are dependent upon profound tissue remodelling, characterised by cyclical waves of cell proliferation, differentiation, apoptosis, tissue breakdown and regeneration. FOXO transcription factors, an evolutionarily conserved subfamily of the forkhead transcription factors, have emerged as master regulators of cell fate decision capable of integrating avariety of stress, growth factor and cytokine signaling pathways with the transcription machinery. The ability of FOXOs to regulate seemingly opposing cellular responses, ranging from cell cycle arrest and oxidative stress responses to differentiation and apoptosis, renders these transcription factors indispensable for cyclic tissue remodelling in female reproduction. Conversely, perturbations in the expression or activity of FOXO transcription factors are increasingly linked to common reproductive disorders, such as pregnancy loss, endometriosis, endometrial cancer and primary ovarian insufficiency.

Cyclin-dependent kinase inhibitor p27Kip1 controls growth and cell cycle progression in human uterine leiomyoma

The molecular mechanism of the cell-cycle machinery in uterine leiomyoma has not yet been fully elucidated. Among the various types of cell-cycle regulators, p27(Kip1) (p27) is considered to be a potent tumor suppressor. To provide further molecular basis for understanding the progression of uterine leiomyoma, our objective was to evaluate the expression level of p27 in normal myometrium and uterine leiomyoma tissue and its effect on cytogenic growth. Western blot analysis, real-time polymerase chain reaction (PCR) and immunohistochemical staining revealed that p27 protein and messenger RNA were down-regulated in uterine leiomyoma tissue and cultured cells compared to normal myometrium. Full-length human p27 cDNA was transferred using a replication-deficient recombinant adenoviral vector (Ad.p27) into uterine leiomyoma cells and evaluated the effect on cell proliferation. Transfection of Ad.p27 into uterine leiomyoma cells resulted in the induction of apoptosis, reduction in viability and proliferation of uterine leiomyoma cells. Our results suggest a new paradigm that down-regulated p27 protein expression is the possible underlying mechanism for the growth of uterine leiomyoma and over-expression of p27 induces cell death. This study provides better understanding of the control exerted by p27 in regulating growth and disease progression of uterine leiomyoma.

Deregulated proteolysis by the F-box proteins SKP2 and beta-TrCP: tipping the scales of cancer

The maintenance and preservation of distinct phases during the cell cycle is a highly complex and coordinated process. It is regulated by phosphorylation--through the activity of cyclin-dependent kinases (CDKs)--and protein degradation, which occurs through ubiquitin ligases such as SCF (SKP1-CUL1-F-box protein) complexes and APC/C (anaphase-promoting complex/cyclosome). Here, we explore the functionality and biology of the F-box proteins, SKP2 (S-phase kinase-associated protein 2) and beta-TrCP (beta-transducin repeat-containing protein), which are emerging as important players in cancer biogenesis owing to the deregulated proteolysis of their substrates.

Oncogenic properties and prognostic implications of the ubiquitin ligase Skp2 in cancer

The expression of Skp2, the ubiquitin ligase subunit that targets p27(Kip1) for degradation, is commonly overexpressed in human cancers. p27(Kip1) is a negative regulator of the cell cycle that plays an important role in tumor suppression. Loss of p27(Kip1) secondary to enhanced ubiquitin-mediated degradation results in uncontrolled proliferation and promotes tumor progression. In the present study the prognostic implications of Skp2 are reviewed and the mechanisms that regulate its expression in different human cancers. A review and analysis of the English literature was undertaken. Overexpression of Skp2 mRNA and protein levels was observed in many aggressive cancers and was commonly associated with down-regulation of p27(Kip1) levels and loss of tumor differentiation. Skp2 is an independent prognostic marker for disease-free and overall survival and may provide additional predictive information to that provided by p27(Kip1) alone. Targeting Skp2 in experimental models resulted in up-regulation of p27(Kip1) and arrested cellular proliferation. Alterations in Skp2 expression have profound effects on cancer progression and may serve as an accurate and independent prognostic marker. Thus, determination of levels of Skp2 and p27(Kip1) by readily available immunohistochemical studies may be a useful tool in the assessment of prognosis, especially in patients with intermediate disease, and may potentially assist in the planning of adjuvant therapy. Skp2 may be an attractive target for the development of novel interventional therapy.

Mechanism and functional consequences of loss of FOXO1 expression in endometrioid endometrial cancer cells

The forkhead transcription factor FOXO1, a downstream target of phosphatidylinositol-3-kinase/Akt signalling pathway, regulates cyclic differentiation and apoptosis in normal endometrium, but its role in endometrial carcinogenesis is unknown. Screening of endometrial cancer cell lines demonstrated that FOXO1 is expressed in HEC-1B cells, but not in Ishikawa cells, which in turn highly express the FOXO1 targeting E3-ubiquitin ligase Skp2. FOXO1 transcript levels were also lower in Ishikawa cells and treatment with the proteasomal inhibitor was insufficient to restore expression. Lack of FOXO1 expression in Ishikawa cells was not accounted for by differential promoter methylation or activity, but correlated with increased messenger RNA (mRNA) turnover. Comparative analysis demonstrated that HEC-1B cells proliferate slower, but are more resistant to paclitaxel-mediated cell death than Ishikawa cells, which were partially reversed upon silencing of FOXO1 in HEC-1B cells or its re-expression in Ishikawa cells. We further show that FOXO1 is required for the expression of the growth arrest- and DNA-damage-inducible gene GADD45alpha. Analysis of biopsy samples demonstrated a marked loss of FOXO1 and GADD45alpha mRNA and protein expression in endometrioid endometrial cancer compared to normal endometrium. Together, these observations suggest that loss of FOXO1 perturbs endometrial homeostasis, promotes uncontrolled cell proliferation and increases susceptibility to genotoxic insults.

Ubiquitin ligases: cell-cycle control and cancer

A driving force of the cell cycle is the activation of cyclin-dependent kinases (CDKs), the activities of which are controlled by the ubiquitin-mediated proteolysis of key regulators such as cyclins and CDK inhibitors. Two ubiquitin ligases, the SKP1-CUL1-F-box-protein (SCF) complex and the anaphase-promoting complex/cyclosome (APC/C), are responsible for the specific ubiquitylation of many of these regulators. Deregulation of the proteolytic system might result in uncontrolled proliferation, genomic instability and cancer. Cumulative clinical evidence shows alterations in the ubiquitylation of cell-cycle regulators in the aetiology of many human malignancies. A better understanding of the ubiquitylation machinery will provide new insights into the regulatory biology of cell-cycle transitions and the development of anti-cancer drugs.

Expression and correlations of S-phase kinase associated protein 2 and P27 protein in pancreatic cancer tissues: an analyses of 51 cases

AIM: To detect the expression of S-phase kinase associated protein 2 (SKP2) and P27 protein in human pancreatic ductal carcinoma and chronic pancreatitis, and to investigate the clinical significance and their correlations in the pancreatic ductal carcinoma.

METHODS: SP immunohistochemical method was used to detect the expression of SKP2 and P27 in the routinely paraffin-embedded sections of specimens from patients with pancreatic ductal carcinoma (n = 51) and chronic pancreatitis (n = 10)..

RESULTS: The positive rate of SKP2 expression in the pancreatic ductal carcinoma (28/51, 54.9%) was significantly higher than that in the chronic pancreatitis (2/10, 20.0%, P < 0.05), while the rate of P27 was significantly lower [25/51(49.0%) vs 9/10(90.0%), P < 0.05]. The positive rates of SKP2 expression was significantly lower in the well-differentiated (7/20, 35.0%) and non-metastasis cases (5/16, 31.2%) than those in the poorly-differentiated (14/19, 73.7%) and metastasis ones (23/35, 65.7%) (P < 0.05), while the rate of P27 expression was significantly higher in the well-differentiated (13/20, 65.0%) and non-metastasis cases (12/16, 75.0%) than those in the poorly-differentiated (6/19, 31.5%) and metastasis ones (13/35, 37.1%) (P < 0.05 or P < 0.01). The expression of SKP2 and P27 were closely correlated in the pancreatic ductal carcinoma tissue (χ² = 14.33, P < 0.01)..

CONCLUSION: SKP2 and P27 are important biological markers for reflecting the carcinogenesis, progression, and prognosis of pancreatic ductal carcinoma. The positive expression of SKP2 or the negative expression of P27 reveals more serious status of the illness, the tendency of metastasis and unfavorable prognosis. There may be a co-regulatory relationship between SKP2 and P27 expression.

High expression of skp2 correlates with poor prognosis in endometrial endometrioid adenocarcinoma

PURPOSE

Skp2 interacts with the degradation of cyclin-dependent kinase inhibitor p27. This study aimed to investigate the correlation of skp2 expression with the expression of p27 and other cell cycle regulators, and clinicopathological parameters in endometrial endometrioid adenocarcinoma.

METHODS

Tissue samples of 136 endometrioid adenocarcinomas, in addition to 20 endometrial hyperplasias and 20 normal endometria, were immunohistochemically stained for skp2. The expression was represented as a labeling index (LI), which indicates the percentage of positive nuclei.

RESULTS

Skp2 staining was localized in the nuclei of the glandular cells of the proliferative phase endometrium, and endometrial hyperplasia and carcinoma cells. Skp2 expression was increased significantly in those of higher histological grade. The high level of skp2 expression was significantly correlated with the presence of lymph node metastasis and lymph-vascular space involvement. The LI of skp2 in endometrial carcinoma was significantly correlated with that of p27, Ki-67, cdk2, cyclin A, cyclin D1, cyclin E, p53 and PTEN. The high level of skp2 expression (LI> or =20%) was significantly correlated with the patients' poor survival.

CONCLUSIONS

The skp2 level might have increased due to p27 accumulation and may be a good indicator of proliferative activity and poor prognosis.

Progestins regulate the expression and activity of the forkhead transcription factor FOXO1 in differentiating human endometrium

Menstruation, or cyclic shedding of nonpregnant endometrial tissue with associated bleeding, occurs only in humans and a few other species. This breakdown of the endometrium in response to falling ovarian progesterone levels is a complex process, characterized by local leukocyte infiltration, expression and activation of matrix metalloproteinases, and apoptosis. Spontaneous decidualization (differentiation) of the stromal compartment precedes the cyclic shedding of the endometrium in various menstruating species but the mechanisms that link these processes are not understood. In this study, we identified FOXO1 as a key transcription factor responsible for mediating apoptosis of decidualized human endometrial stromal cells (HESCs) in response to progesterone withdrawal. We demonstrate that medroxyprogesterone acetate (MPA, a synthetic progestin) enhances the expression of FOXO1 in differentiating HESCs while simultaneously inducing cytoplasmic retention and inactivation of FOXO1. Withdrawal of MPA from decidualized HESCs results in rapid nuclear accumulation of FOXO1, increased BIM expression, a proapoptotic FOXO1 target gene, and cell death. Conversely, silencing of FOXO1 expression completely abolishes cell death induced by MPA withdrawal. In summary, the observation that differentiating HESCs become dependent on progesterone signaling for survival through induction and reversible inactivation of FOXO1 suggests a novel mechanism that links decidualization of the endometrium to menstruation.