CDK1 and cyclin A expression is linked to cell proliferation and associated with prognosis in non-Hodgkin's lymphomas

CDK1 inhibitor RO-3306 enhances BTKi potency in diffuse large B-cell lymphoma by suppressing JAK2/STAT3 signaling

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma in adults, which characterized by a high degree of heterogeneity in terms of clinical presentation, molecular phenotype, and genetic features. However, approximately 30 %-40 % of patients are refractory to standard chemotherapy, and their prognosis is poor. The emergence of small-molecule inhibitors, such as Bruton's tyrosine kinase inhibitors (BTKi), has greatly improved the treatment of DLBCL; however, drug resistance associated with small-molecule inhibitors has greatly limited their clinical application. In this study, we elucidated the principal genes influencing BTKi sensitivity in DLBCL and delineated the underlying mechanisms. This study identified cyclin-dependent kinase 1 (CDK1) as the central gene influencing BTKi sensitivity in DLBCL cells. The application of RO-3306 effectively promoted the growth and increased the apoptotic rate of DLBCL cells. Furthermore, RO-3306 increased the susceptibility of DLBCL cells to BTKis in both in vitro and xenograft experimental models. RNA-seq analyses suggested the potential modulation of the JAK2/STAT3 signaling cascade by RO-3306, a finding further confirmed by the diminished phosphorylation documented by western blotting. This study provides pivotal insights into the mechanisms governing BTKi sensitivity in DLBCL and potentially reveals new avenues for targeted therapeutic strategies.

Prognostic significance of CDK1 expression in diffuse large B-Cell lymphoma

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma in adult, characterized by uncontrolled cell proliferation and strong aggressiveness. Previous studies have found that cyclin-dependent kinase 1(CDK1) are related to tumor growth and metastasis. However, the role of CDK1 in DLBCL is exclusive. This study investigated the clinical implications and expression of CDK1 in DLBCL.

METHODS

Gene expression data for healthy subjects were sourced from the Genotype-Tissue Expression repository. Clinical details and survival statistics of patients with DLBCL were obtained from the Gene Expression Omnibus archive (GSE10846). Patients were categorized based on CDK1 expression levels, and differences in clinical outcomes between the groups were examined. Univariate and multivariate Cox regression analyses were used to ascertain whether CDK1 expression independently predicted DLBCL prognosis. The protein expression of CDK1 was gauged by immunohistochemistry. Additionally, we investigated the effect of CDK1 inhibition on DLBCL cell growth and death using the Cell Counting Kit-8 and flow cytometry.

RESULTS

In the control group, CDK1 expression was predominantly observed in the hematopoietic and reproductive systems. CDK1 levels in patients with DLBCL were notably elevated compared with those in controls. Significant differences were noted in the lactate dehydrogenase ratio and overall survival based on CDK1 expression. Statistical analyses confirmed that CDK1 was an independent predictor of DLBCL outcomes. Elevated CDK1 protein levels were observed in a significant number of DLBCL samples, in contrast to normal lymph node samples from individuals without lymphoma. The inhibitor Ro-3306 curtails DLBCL cell growth and enhances cell death in vitro.

CONCLUSIONS

Elevated CDK1 levels are correlated with poor prognosis in patients with DLBCL.

Insight into the potential candidate genes and signaling pathways involved in lymphoma disease in dogs using a comprehensive whole blood transcriptome analysis

Lymphoma is one of the most prevalent hematological cancers, accounting for 15-20 % of new cancer diagnoses in dogs. Therefore, this study aims to explore the important genes and pathways involved in canine lymphoma progression and understand the underlying molecular mechanisms using RNA sequencing. In this study, RNAs acquired from seven pairs of lymphoma and non-lymphoma blood samples were sequenced from different breeds of dogs. Sequencing reads were preprocessed, aligned with the reference genome, assembled and expressions were estimated through bioinformatics approaches. At a false discovery rate (FDR) < 0.05 and fold change (FC) ≥ 1.5, a total of 625 differentially expressed genes (DEGs) were identified between lymphoma and non-lymphoma samples, including 347 up-regulated DEGs such as SLC38A11, SCN3A, ZIC5 etc. and 278 down-regulated DEGs such as LOC475937, CSMD1, KRT14 etc. GO enrichment analysis showed that these DEGs were highly enriched for molecular function of ATP binding and calcium ion binding, cellular process of focal adhesion, and biological process of immune response, and defense response to virus. Similarly, KEGG pathways analysis revealed 11 significantly enriched pathways such as ECM-receptor interaction, cell cycle, PI3K-Akt signaling pathway, ABC transporters etc. In the protein-protein interaction (PPI) network, CDK1 was found to be a top hub gene with highest degree of connectivity. Three modules selected from the PPI network showed that canine lymphoma was highly associated with cell cycle, ECM-receptor interaction, hypertrophic cardiomyopathy, dilated cardiomyopathy and RIG-I-like receptor signaling pathway. Overall, our findings highlighted new candidate therapeutic targets for further testing in canine lymphoma and facilitate the understanding of molecular mechanism of lymphoma's progression in dogs.

Role of microRNAs in B-Cell Compartment: Development, Proliferation and Hematological Diseases

B-cell development is a very orchestrated pathway that involves several molecules, such as transcription factors, cytokines, microRNAs, and also different cells. All these components maintain the ideal microenvironment and control B-cell differentiation. MicroRNAs are small non-coding RNAs that bind to target mRNA to control gene expression. These molecules could circulate in the body in a free form, protein-bounded, or encapsulated into extracellular vesicles, such as exosomes. The comprehension of the role of microRNAs in the B-cell development was possible based on microRNA profile of each B-cell stage and functional studies. Herein, we report the knowledge about microRNAs in the B-cell the differentiation, proliferation, and also in hematological malignancies.

CDK1 interacts with iASPP to regulate colorectal cancer cell proliferation through p53 pathway

CDK1 (cyclin-dependent kinase 1) is a critical regulator of the G2-M checkpoint. CDK1 is considered a possible target for cancer treatment. In addition to CDK1, iASPP plays essential role in maintaining cancer cell proliferation. In the present study, we monitored the expression of CDK1 and iASPP at mRNA and protein levels in CRC tissues and cell lines; we also predicted that iASPP protein might interact with CDK1 protein. By performing GST pull-down assay and Co-IP assay, we confirmed the interaction of CDK1 and iASPP protein. In CRC cell lines, CDK1 interacted with iASPP to affect CRC cell proliferation and apoptosis; moreover, the p53 apoptosis pathway was involved in this progression. Taken together, we revealed that CDK1 and iASPP was up-regulated in CRC tissues and cell lines; CDK1 protein interacted with iASPP protein to affect CRC cell proliferation and apoptosis through the p53 apoptosis pathway. CDK1 and iASPP might serve as not only promising targets in CRC treatment, but also efficient prognostic markers. From the perspective of protein interactions, we provided a novel theoretical basis for targeted therapy of CRC.

Loss of Cdk2 and cyclin A2 impairs cell proliferation and tumorigenesis

Cell-cycle inhibition has yet to offer a generally effective approach to cancer treatment, but a full evaluation of different combinations of cell-cycle inhibitors has not been evaluated. Cyclin A2, a core component of the cell cycle, is often aberrantly expressed in cancer where it may impact cell proliferation. In this study, we investigated the role of cyclin A2 in tumorigenesis using a conditional genetic knockout mouse model. Cyclin A2 deletion in oncogene-transformed mouse embryonic fibroblasts (MEF) suppressed tumor formation in immunocompromised mice. These findings were confirmed in mice with cyclin A2-deficient hepatocytes, where a delay in liver tumor formation was observed. Because cyclin A2 acts in complex with Cdk2 in the cell cycle, we explored a hypothesized role for Cdk2 dysregulation in this effect through conditional deletions of both genes. In oncogene-transformed MEFs lacking both genes, tumor formation was strongly suppressed in a manner associated with decreased proliferation, premature senescence, and error-prone recovery from serum deprivation after immortalization. Whereas loss of cyclin A2 led to a compensatory increase in Cdk1 activity, this did not occur with loss of both Cdk2 and cyclin A2. Our work offers a rationale to explore combinations of Cdk1 and Cdk2 inhibitors as a general approach in cancer therapy.

MicroRNAs in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a rare and aggressive subtype of non-Hodgkin lymphoma. New treatment modalities, including intensive induction regimens with immunochemotherapy and autologous stem cell transplant, have improved survival. However, many patients still relapse, and there is a need for novel therapeutic strategies. Recent progress has been made in the understanding of the role of microRNAs (miRNAs) in MCL. Comparisons of tumor samples from patients with MCL with their normal counterparts (naive B-cells) have identified differentially expressed miRNAs with roles in cellular growth and survival pathways, as demonstrated in various biological model systems. In addition, MCL clinico-pathological and prognostic subtypes can be identified using individual miRNAs or miRNA classifiers. miRNA based therapies have now shown efficacy in animal models, and many efforts are currently being made to further develop these drugs for use in patients. Thus, there is hope that specific targeting of pathogenic miRNAs may be used in cases of MCL when conventional therapies fail. Here, we review the current knowledge about the role of miRNAs in MCL, and highlight the perspectives for clinical use.

Temsirolimus in the treatment of relapsed and/or refractory mantle cell lymphoma

Patients with mantle cell lymphoma (MCL) have a poor prognosis; consequently, new therapeutic approaches, such as rapamycin and its derivates, mammalian target of rapamycin (mTOR) inhibitors, are warranted. Temsirolimus (also known as CCI-779), a dihydroester of rapamycin, in MCL cell lines inhibited mTOR, downregulated p21 and v-Raf, and induced autophagy. The first clinical trial in MCL patients was performed using 250 mg of temsirolimus weekly for 6-12 cycles. The overall response rate was 38%; the median time to progression was 6.5 months, median overall survival was 12 months, and the median duration of response was 6.9 months. At lower dose (25 mg/week), the overall response rate was 41%, median overall survival was 14 months, and time to progression was 6 months. In another trial, 162 patients were randomly assigned to receive temsirolimus at 2 different doses (175 mg/week for 3 weeks, then 75 mg or 25 mg/week) or a treatment chosen by the investigator among the most frequently adopted single agents for treatment of relapsed MCL. Patients treated with 175/75 mg of temsirolimus had significantly higher response rates and longer progression-free survival than those treated with investigator's choice therapy. These data support the use of mTOR inhibitors for the treatment of MCL, probably in combination with other agents, such as antiangiogenic drugs or histone acetylase inhibitors.

A molecular risk score based on 4 functional pathways for advanced classical Hodgkin lymphoma

Despite improvement in the treatment of advanced classical Hodgkin lymphoma, approximately 30% of patients relapse or die as result of the disease. Current predictive systems, determined by clinical and analytical parameters, fail to identify these high-risk patients accurately. We took a multistep approach to design a quantitative reverse-transcription polymerase chain reaction assay to be applied to routine formalin-fixed paraffin-embedded samples, integrating genes expressed by the tumor cells and their microenvironment. The significance of 30 genes chosen on the basis of previously published data was evaluated in 282 samples (divided into estimation and validation sets) to build a molecular risk score to predict failure. Adequate reverse-transcription polymerase chain reaction profiles were obtained from 262 of 282 cases (92.9%). Best predictor genes were integrated into an 11-gene model, including 4 functional pathways (cell cycle, apoptosis, macrophage activation, and interferon regulatory factor 4) able to identify low- and high-risk patients with different rates of 5-year failure-free survival: 74% versus 44.1% in the estimation set (P < .001) and 67.5% versus 45.0% in the validation set (P = .022). This model can be combined with stage IV into a final predictive model able to identify a group of patients with very bad outcome (5-year failure-free survival probability, 25.2%).

Differences in protein expression and gene amplification of cyclins between colon and rectal adenocarcinomas

Adenocarcinomas of rectum and colon may be different with regard to the cellular biological basis for cancer development. A material of 246 rectal cancers removed surgically at Akershus University Hospital in the years 1992–2000 was investigated and was compared to a material of 219 colon cancers operated on at Akershus University Hospital during the years 1988, 1990 and 1997–2000. There were highly significant differences between the rectal and the colon cancers in the protein expression of cyclin D1, cyclin D3, cyclin E, nuclear β-catenin, and c-Myc and in gene amplification of cyclin A2, cyclin B1, cyclin D1, and cyclin E. Gene amplification and protein expression in the rectal cancers correlated significantly for the cyclins B1, D3, and E. A statistically significant relation was observed between overexpression of cyclin A2 and local relapse of rectal carcinomas, as higher expression of cyclin A2 was associated with lower local recurrence rate.

Knocking-down cyclin A(2) by siRNA suppresses apoptosis and switches differentiation pathways in K562 cells upon administration with doxorubicin

Cyclin A₂ is critical for the initiation of DNA replication, transcription and cell cycle regulation. Cumulative evidences indicate that the deregulation of cyclin A₂ is tightly linked to the chromosomal instability, neoplastic transformation and tumor proliferation. Here we report that treatment of chronic myelogenous leukaemia K562 cells with doxorubicin results in an accumulation of cyclin A₂ and follows by induction of apoptotic cell death. To investigate the potential preclinical relevance, K562 cells were transiently transfected with the siRNA targeting cyclin A₂ by functionalized single wall carbon nanotubes. Knocking down the expression of cyclin A₂ in K562 cells suppressed doxorubicin-induced growth arrest and cell apoptosis. Upon administration with doxorubicin, K562 cells with reduced cyclin A₂ showed a significant decrease in erythroid differentiation, and a small fraction of cells were differentiated along megakaryocytic and monocyte-macrophage pathways. The results demonstrate the pro-apoptotic role of cyclin A₂ and suggest that cyclin A₂ is a key regulator of cell differentiation. To the best of our knowledge, this is the first report that knocking down expression of one gene switches differentiation pathways of human myeloid leukemia K562 cells.

Prognostic significance of cyclin A in gastric cancer

High level of cyclin A promotes carcinogenesis, and overexpression of cyclin A has been associated with poor prognosis of cancer patients. We validated the prognostic role of cyclin A in gastric cancer and evaluated its correlation with expression of an mRNA stability factor HuR. From 342 consecutive histologically confirmed gastric cancer patients were obtained 325 representative tissue specimens for cyclin A and 316 for HuR immunohistochemistry. Specimens were stained by cyclin A and HuR specific monoclonal antibodies. Nuclear immunostaining detected in > or =5% of the tumor cells was considered the cut-off for cyclin A positivity. Positive HuR immunoreactivity was scored as nuclear or cytoplasmic. Associations between scores, clinicopathological factors and survival were calculated by the chi2-test, Fisher's exact test, Kaplan-Meier test and Cox model. Cyclin A detected in the nuclei of cancer cells was positive in 55% (179 of 325) of the specimens; 40% (127 of 316) of the specimens had cytoplasmic and 88% (279 of 316) nuclear immunoreactivity of HuR. Cyclin A expression was an independent prognostic factor for poor survival. Cyclin A immunoreactivity was associated with old age, high stage, proximal location of the tumor, intestinal type, noncurative resection, advanced penetration depth and with nodal metastases but not distant metastases. Furthermore, cyclin A expression was associated with cytoplasmic HuR expression, whereas no association with nuclear HuR was evident. Cyclin A is an independent prognostic factor in gastric cancer, and one mechanism for its overexpression may depend on cytoplasmic localization of HuR.

The feasibility of gene expression profiling generated in fine-needle aspiration specimens from patients with follicular lymphoma and diffuse large B-cell lymphoma

Lymphoma of germinal center cell (GC) origin generally is an indolent malignancy that transforms progressively into a more aggressive disease. According to the World Health Organization classification, lymphomas of follicular center cell origin are classified as either large B-cell lymphoma (LBCL) or follicular lymphoma (FL). The authors tested the feasibility of performing gene expression profiling using amplified RNA from fine-needle aspirates (FNA) obtained from lymph nodes. Twenty-four samples from patients with a diagnosis of FL or LBCL were obtained after Institutional Review Board-approved informed consent was obtained. The diagnoses were confirmed by 2 pathologists and were classified into 2 groups (10 LBCL samples and 14 FL samples) by using conventional morphology and immunophenotyping. One hundred nanograms of total RNA were subjected to 2 cycles of standard, double-stranded complementary DNA synthesis and in vitro transcription for target amplification using a small-sample target-labeling protocol. The biotinylated cRNA from each sample was hybridized to gene chips. Gene expression profiling results were analyzed first by principal-component analysis (PCA) by using a list of 146 probe sets that represented 62 genes that are characteristic of an activated B-cell (ABC) signature or a GC signature. The analysis identified 5 LBCL samples with an ABC cell signature. Using a list of 207 probe sets that represented 113 genes involved in FL transformation, PCA analysis identified 2 overlapping clusters corresponding to FL and GC-diffuse LBCL. To improve this classification further, the authors generated a list of 72 genes that were expressed differentially between FL and GC-LBCL. Using this list of genes, PCA analysis demonstrated a clear separation between FL and GC-LBCL. However, five FL samples clustered as an intermediate group between FL and GC-DLBCL. These samples were characterized morphologically by a mixed cell pattern with relatively fewer large, noncleaved lymphocytes and more small, cleaved lymphocytes. The results support the feasibility of FNA-based transcription profiles in patients with FL or LBCL, which, in combination with morphology and immunophenotyping, can help in the subtyping of these entities.

Immunohistochemical detection of cdc2 is useful in predicting survival in patients with mantle cell lymphoma

Recent cDNA microarray studies have reported the prognostic value of several genes in mantle cell lymphoma patients. We aimed to validate the prognostic significance of three of these genes: alpha-tubulin, cdc2, and CENP-F. The protein expression of alpha-tubulin, cdc2, and CENP-F was assessed using immunohistochemistry. Their immunoreactivity in 48 formalin-fixed/paraffin-embedded mantle cell lymphoma tumors was determined by estimating the percentage of positive cells. These results were correlated with the expression of proliferation marker Ki67 and survival. Of these 48 mantle cell lymphoma patients, 41 were men and seven were women. The median age at time of diagnosis was 64.5 years, and the overall median survival was 40 months. In benign lymph nodes, the expression of cdc2 and alpha-tubulin was restricted to the germinal centers; mantle zones were negative. Expression of CENP-F was more uniformly distributed. In mantle cell lymphoma, Ki67 significantly correlated with all three markers (P<0.05, Spearman), but only Ki67 (>50%) and cdc2 (>25%) significantly correlated with shorter survival (P<0.0006, Spearman). Of several clinical parameters examined, international prognostic index of >or=2 correlated with worse clinical outcome, and high clinical stage (ie 4 vs <or=3) showed a trend for shorter survival. The prognostic significance of cdc2 and Ki67 was independent of international prognostic index and clinical stage. We have validated the prognostic value of cdc2, and confirmed that of Ki67, in a cohort of mantle cell lymphoma patients. Immunohistochemical detection of cdc2 and Ki67 may be a useful and simple method in evaluating the prognosis of mantle cell lymphoma patients.

High expression of cyclin B1 predicts a favorable outcome in patients with follicular lymphoma

Substantial research has been dedicated to the study of the relationship between genetic mechanisms regulating cell functions in tumors and how those tumors respond to various treatment regimens. Because these mechanisms are still not well understood, we have chosen to study the genetic makeup of 57 tumor samples from patients with follicular lymphoma (FL). Our goal was to develop a prognostic tool, which can be used as an aid in determining FL patients with tumors genetically predisposed to a successful treatment with the CHOP (cyclophosphamide, vincristine, doxorubicin, prednisone) regimen. To select relevant genes, high-density oligonucleotide arrays were used. There were 14 genes highly expressed in FL patients that responded well to CHOP chemotherapy, and 11 of these were involved in G2/M transition of the cell cycle, in mitosis, or in DNA modulation. A high expression of CCNB1 (cyclin B1), CDC2, CDKN3A, CKS1B, ANP32E, and KIAA0101, but not of the proliferation-related antigen Ki-67, was associated with better survival rate in a univariate analysis. CCNB1 expression had an independent prognostic value when included in a multivariate analysis together with the 5 parameters of the follicular lymphoma international prognostic index.

A low toxicity maintenance regime, using eicosapentaenoic acid and readily available drugs, for mantle cell lymphoma and other malignancies with excess cyclin D1 levels

Mantle cell lymphoma is a difficult to treat non-Hodgkin's lymphoma (NHL) whose biochemistry is unusually well characterised. Almost all and perhaps all patients overexpress the cyclin D1 protein which is crucial in driving cells from the G1 to the S phase. This overexpression may be responsible for the refractoriness. Despite this understanding, treatments for mantle cell lymphoma are based on standard NHL regimes of cyclophosphamide, doxorubicin, vincristine and prednisone, perhaps supplemented with the monoclonal antibody rituximab. There has never been any attempt to direct treatment to the cyclin D1 mechanism or to angiogenesis which is now known to be important in all lymphomas. Both these targets lend themselves to long-term maintenance regimes of relatively low toxicity which can be used as adjuvants to standard therapy. Agents which have recently been shown to block cyclin D1 translation by regulating calcium levels are the unsaturated essential fatty acid, eicosapentaenoic acid (EPA), the antidiabetic thiazolidinediones, and the antifungal agent, clotrimazole. Two types of agent which have been shown to inhibit angiogenesis are the teratogen, thalidomide, and the selective inhibitors of cyclo-oxygenase 2 (COX-2). Retinoids exert synergistic effects with EPA and have been shown to inhibit both tumour growth and angiogenesis. The mechanisms of action of these various agents are discussed, and specific suggestions are made for low toxicity maintenance therapy of mantle cell lymphoma and of other tumours which overexpress cyclin D1.

Glomerulonephritis and malignancy: a population-based analysis

BACKGROUND

An association between glomerulonephritis and malignant tumors has previously both been found and discarded in clinical series, but to our knowledge never has been tested in a population-based setting.

METHODS

The Danish Kidney Biopsy Registry includes all kidney biopsies performed from 1985. Using a unique personal identification number, each person in the registry to the National Population Registry and the Danish Cancer Registry were linked. Cancer occurrence after the biopsy was compared in patients with morphological, glomerular diseases with that of the general Danish population, taking into account sex, age, calendar period and time since biopsy, and the 95% confidence interval (95% CI) for the observed-to-expected rates was calculated, assuming a Poisson distribution. Cancer occurrence was stratified to <1 year, 1 to 4, and >or=5 years after a biopsy.

RESULTS

A total of 102 de novo cancers were found in 1958 patients. These cancers represent a two- to threefold excess of the expected number at <1 and 1 to 4, but not >or=5 years after a biopsy. Non-Hodgkin's lymphomas were observed six to eight times more than expected. Cancer excess was seen in glomerulonephritides with a known or suspected virus etiology.

CONCLUSIONS

The excess cancer rate could be the result of underlying undiagnosed tumors whose antigens have initiated glomerulonephritis, or the immunosuppressive therapy that initiated or energized tumor cells. Based on the findings in our study, there is some support for an association to persistent viruses causing first the glomerulonephritides and then the malignancies, perhaps through a common pathogenesis. This calls for other studies to be done that are specifically designed to investigate this issue, with more data on patient characteristics and confounders.

Low expression of p27 protein combined with altered p53 and Rb/p16 expression status is associated with increased expression of cyclin A and cyclin B1 in diffuse large B-cell lymphomas

The expression of the cyclin-dependent kinase inhibitor (CDKI) p27 protein was investigated in relation to (1) the expression of the cell cycle regulators p53, Rb and p16 and (2) the proliferation profile as determined by the expression of Ki67, cyclin A, and cyclin B1 in 80 cases of de novo diffuse large B-cell lymphomas (DLBCL). P27 expression was low/null in large tumor cells in 58/80 cases and intermediate/high in 22/80 cases. Increased expression of p53 protein was observed in 39/80 cases. Decreased expression of Rb and p16 proteins was mutually exclusive and was observed in 5/80 and 14/80 cases, respectively. The analysis of the p27 expression status (low/null versus intermediate/high) with respect to the p53 and/or Rb/p16 expression status showed that low/null p27 expression was significantly correlated with increased p53 expression (P =.018) and showed a strong trend for correlation with concurrent increased p53 expression and decreased Rb or p16 expression (P =.050). These findings suggest a tendency for concurrent alterations of the cell cycle regulators p27, p53, and Rb or p16 in DLBCL, which might result in impaired tumor growth control. Indeed, the analysis of the combined p27/p53/Rb/p16 expression status with respect to the proliferation profile showed that (1) three alterations in the combined p27/p53/Rb/p16 status (i.e., low/null P27 expression, increased expression of p53, and decreased expression of Rb or p16) were significantly correlated with increased expression of cyclin B1 (P =.005) and (2) two or three alterations were significantly correlated with increased expression of cyclin A (P =.014). These findings suggest combined impairment of a complex cell-cycle control network involving the CDK inhibitor p27, the P53 pathway, and the Rb1 pathway, which exerts a cooperative effect resulting in enhanced tumor cell proliferation.