CDK6 is activated by the atypical cyclin I to promote E2F-mediated gene expression and cancer cell proliferation.

Cyclin-dependent kinases (CDKs), together with their cyclin partners, are the master cell cycle regulators. Remarkably, the cyclin family was extended to include atypical cyclins, characterized by distinctive structural features, but their partner CDKs remain elusive. Here, we conducted a yeast two-hybrid screen to identify new atypical cyclin-CDK complexes. We identified 10 new complexes, including a complex between CDK6 and cyclin I (CCNI), which was found to be active against retinoblastoma protein. CCNI upregulation increased the proliferation of breast cancer cells in vitro and in vivo, with a magnitude similar to that seen upon cyclin D upregulation, an effect that was abrogated by CDK6 silencing or palbociclib treatment. In line with these findings, CCNI downregulation led to a decrease in cell number and a reduction in the percentage of cells reaching S phase. Finally, CCNI upregulation correlated with the high expression of E2F target genes in large panels of cancer cell lines and tissue samples from breast cancer patients. In conclusion, we unveil CCNI as a new player in the pathways that activate CDK6, enriching the wiring of cell cycle control.

CCNI2 plays a promoting role in the progression of colorectal cancer.

Colorectal cancer (CRC) is one of the most common malignancies and most of the patients diagnosed with advanced CRC have unsatisfactory treatment effect and poor prognosis. The purpose of this study was to investigate the effect of CCNI2 on the development of CRC. In this sutdy, immunohistochemical staining was used to detect CCNI2 expression levels in clinical samples, meanwhile, the Kaplan-Meier survival analysis was conducted. Celigo cell counting assay was used for screening shCCNI2s. QPCR and WB were performed to verify knockdown efficiency of CCNI2. Cell proliferation, colony formation, cell cycle, apoptosis, and mechanism investigation of CCNI2 knockdown were investigated by MTT assay, colony formation assay, fluorescence-activated cell sorting, and human apoptosis antibody array, respectively. Otherwise, the mouse model of CCNI2 knockdown was also constructed. The results of immunohistochemical staining and qPCR indicated that CCNI2 had a high expression level in the CRC tissues and cell lines. Kaplan-Meier survival analysis manifested that the high expression of CCNI2 suggested poor prognosis. The expression of CCNI2 was significantly reduced by CCNI2-siRNAs, and the downregulated expression level of CCNI2 inhibited CRC cell proliferation and colony formation, arrested cell cycle in G2 phase, as well as promoted cell apoptosis. The various indexes of solid tumor in mice models indicated that CCNI2 knockdown could suppress the growth of CRC tumor. Based on the comprehensive analysis of the above results, CCNI2 was contributed to the progression of CRC and could serve as a prognostic marker for CRC.

RNA editing derived epitopes function as cancer antigens to elicit immune responses.

In addition to genomic mutations, RNA editing is another major mechanism creating sequence variations in proteins by introducing nucleotide changes in mRNA sequences. Deregulated RNA editing contributes to different types of human diseases, including cancers. Here we report that peptides generated as a consequence of RNA editing are indeed naturally presented by human leukocyte antigen (HLA) molecules. We provide evidence that effector CD8+ T cells specific for edited peptides derived from cyclin I are present in human tumours and attack tumour cells that are presenting these epitopes. We show that subpopulations of cancer patients have increased peptide levels and that levels of edited RNA correlate with peptide copy numbers. These findings demonstrate that RNA editing extends the classes of HLA presented self-antigens and that these antigens can be recognised by the immune system.

Cyclin I promotes cisplatin resistance via Cdk5 activation in cervical cancer.

OBJECTIVE: Cisplatin (cis-diamminedichloroplatinum II, CDDP) is one of the most effective chemotherapeutic agents and is widely used in the treatment of cervical cancer (CC), but cancer cell acquired resistance to this drug during the course of its treatment. The aim of this study was to investigate the role of cyclin I to cisplatin resistance in CC cell. PATIENTS AND METHODS: Cervical tumor specimens from 30 patients were recruited in this study. We analyzed the expression of cyclin I by real-time polymerase chain reaction (qRT-PCR), Western blotting examination of downstream effectors. Cell proliferation assay and xenograft experiments were performed for cisplatin cytotoxicity assay. Lentivirus-mediated and siRNA-mediated genes overexpression or knockdown were applied to investigate the role of cyclin I to cisplatin resistance in CC cell. RESULTS: We found that high level of cyclin I was associated with cisplatin resistance in CC. Here, we described that cyclin I protein becomes highly expressed in human CC patients resistant to cisplatin chemotherapy. Stable overexpressed cyclin I promotes Hela cell resistance to higher concentrations of cisplatin. In addition, upregulated level of cyclin I increased tumor cells growth in vitro and enhanced tumor resistance to cisplatin in vivo. The further mechanism investigated showed that cyclin I upregulated the expression of cyclin-dependent kinase 5 (Cdk5) promoting cisplatin resistance by preventing apoptosis in CC cell line. Consistently, the cyclin I overexpressed Hela cell lines produce increased sensitivity to cisplatin treatment through knockdown of Cdk5 protein with siRNA. CONCLUSIONS: These data suggest that a cyclin I-Cdk5 complex forms a critical antiapoptotic factor in the process of generating cisplatin resistance in cervical cancer.

Cyclin I mRNA expression correlates with kinase insert domain receptor expression in human epithelial ovarian cancer.

BACKGROUND/AIM: Ovarian cancer is the second most common gynecological malignancy after cancer of the uterine corpus, and the fifth leading cause of cancer-related death among women. It has been discovered that cyclin I (CCNI) protein expression correlates with the proliferation of cancer cells and expression of angiogenesis-related proteins, such as vascular endothelial growth factor (VEGF) and VEGF receptor 2/kinase insert domain receptor (VEGFR2/KDR). We examined whether any association exists between mRNA expression of CCNI and KDR genes in epithelial ovarian cancer (EOC) tissues, clinicopathological parameters and patients' response to chemotherapy. MATERIALS AND METHODS: Expression of CCNI and KDR genes was analyzed by quantitative real-time reverse transcription PCR in 40 human primary EOC tissues and four human ovarian cancer cell lines (TOV-112D, OV-90, OVCAR-3 and Caov-3). RESULTS: CCNI and KDR mRNA expression was detected in all EOC tissues and ovarian cancer cell lines. The mRNA levels of both genes were significantly higher in EOC than in ovarian cancer cell lines (p<0.001). Neither CCNI nor KDR mRNA expression in EOC tissues was significantly associated with variables such as age, menopausal status, International Federation of Gynecology and Obstetrics (FIGO) stage, residual disease, patients' response to chemotherapy, tumor histology, grade or sensitivity to chemotherapy. However, we demonstrated a significant positive correlation between the mRNA expression of KDR and CCNI in EOC tissues (R=0.530, p<0.001). CONCLUSION: Neither CCNI nor KDR mRNA expression predicts response of patients with EOC to platinum-based first-line chemotherapy. Cyclin I may be involved in angiogenesis in EOC, which needs further investigation.

Cyclin I and p35 determine the subcellular distribution of Cdk5.

The atypical cyclin-dependent kinase 5 (Cdk5) serves an array of different functions in cell biology. Among these are axonal guidance, regulation of intercellular contacts, cell differentiation, and prosurvival signaling. The variance of these functions suggests that Cdk5 activation comes to pass in different cellular compartments. The kinase activity, half-life, and substrate specificity of Cdk5 largely depend on specific activators, such as p25, p35, p39, and cyclin I. We hypothesized that the subcellular distribution of Cdk5 activators also determines the localization of the Cdk5 protein and sets the stage for targeted kinase activity within distinct cellular compartments to suit the varying roles of Cdk5. Cdk5 localization was analyzed in murine kidney and brain slices of wild-type and cyclin I- and/or p35-null mice by immunohistochemistry and in cultured mouse podocytes using immunofluorescence labeling, as well as cell fractionation experiments. The predominance of cyclin I mediates the nuclear localization of Cdk5, whereas the predominance of p35 results in a membranous localization of Cdk5. These findings were further substantiated by overexpression of cyclin I and p35 with altered targeting characteristics in human embryonic kidney 293T cells. These studies reveal that the subcellular localization of Cdk5 is determined by its specific activators. This results in the directed Cdk5 kinase activity in specific cellular compartments dependent on the activator present and allows Cdk5 to serve multiple independent roles.

Expression of genes encoding matrilin-3 and cyclin-I during the impairment and recovery of chicken growth plate in tibial dyschondroplasia.

Tibial dyschondroplasia (TD) is a skeletal disease characterized by the disruption ofendochondral bone formation in avian species. The aim of this study was to determine the expression of Matrilin-3 and Cyclin-I genes in chicken growth plate during impairment and recovery from TD. Gene expressions were analyzed by polymerase chain reaction, and proteins by immunohistochemistry and in situ hybridizations. Expression of genes encoding Matrilin-3 and Cyclin-I were diminished with parallel decrease in proteins during TD, with fewer signs of cartilage cell differentiation. In contrast, there was an increase in mRNA expressions and protein levels of both genes during the recovery phase. These findings suggest that the Matrilin-3 and Cyclin-I genes also play a role in chondrocyte differentiation during the impairment and recovery of growth plate in TD.

Characterizing of functional human coding RNA editing from evolutionary, structural, and dynamic perspectives.

A-to-I RNA editing has been recently shown to be a widespread phenomenon with millions of sites spread in the human transcriptome. However, only few are known to be located in coding sequences and modify the amino acid sequence of the protein product. Here, we used high-throughput data, variant prediction tools, and protein structural information in order to find structural and functional preferences for coding RNA editing. We show that RNA editing has a unique pattern of amino acid changes characterized by enriched stop-to-tryptophan changes, positive-to-neutral and neutral-to-positive charge changes. RNA editing tends to have stronger structural effect than equivalent A-to-G SNPs but weaker effect than random A-to-G mutagenesis events. Sites edited at low level tend to be located at conserved positions with stronger predicted deleterious effect on proteins comparing to sites edited at high frequencies. Lowly edited sites tend to destabilize the protein structure and affect amino acids with larger number of intra-molecular contacts. Still, some highly edited sites are predicted also to prominently affect structure and tend to be located at critical positions of the protein matrix and are likely to be functionally important. Using our pipeline, we identify and discuss several novel putative functional coding changing editing sites in the genes COPA (I164V), GIPC1 (T62A), ZN358 (K382R), and CCNI (R75G).

Cyclin I is involved in the regulation of cell cycle progression.

Cyclins control cell cycle progression by regulating the activity of cyclin-dependent kinases (Cdks). Cyclin I is a member of the cyclin family because of the presence of a cyclin box motif. It has been suggested that Cyclin I is involved in various biological processes, such as cell survival, angiogenesis, and cell differentiation. However, whether or not Cyclin I has a role in regulating the cell cycle similarly to other cyclins has yet to be clarified. Therefore, we investigated the role for Cyclin I in cell cycle progression. We showed that the protein level of Cyclin I oscillated during the cell cycle, and that Cyclin I was subjected to ubiquitination and degradation in cells. The interaction between Cyclin I and Cdk5 was detected in cells overexpressed with both proteins. Furthermore, depletion of Cyclin I by siRNAs prevented cell proliferation, suggesting the positive role of Cyclin I for the cell cycle progression. In addition, flow cytometric analysis revealed that cells depleted of Cyclin I were accumulated at G2/M phases. By using HeLa.S-Fucci (fluorescent ubiquitination-based cell cycle indicator) cells, we further confirmed that knockdown of Cyclin I induced cell cycle arrest at S/G2/M phases. These results strongly suggest that Cyclin I has the role in the regulation of cell cycle progression.

Both cyclin I and p35 are required for maximal survival benefit of cyclin-dependent kinase 5 in kidney podocytes.

Cyclin-dependent kinase (Cdk)-5 is activated by both cyclin I and the noncyclin activator p35 in terminally differentiated cells such as kidney podocytes and neurons. Cyclin I and p35 are restricted to podocytes in the kidney, and each limit podocyte apoptosis by activating Cdk5. To determine whether both activators are necessary, or whether they serve backup roles, a double cyclin I-p35 null mouse was generated. Experimental glomerular disease characterized by podocyte apoptosis was then induced by administering an anti-podocyte antibody. The results showed that under nonstressed conditions double mutants had normal kidney structure and function and were indistinguishable from wild-type, cyclin I(-/-), or p35(-/-) mice. In contrast, when stressed with disease, podocyte apoptosis increased fourfold compared with diseased cyclin I(-/-) or p35(-/-) mice. This resulted in a more pronounced decrease in podocyte number, proteinuria, and glomerulosclerosis. Under normal states and nephritic states, levels for the prosurvival protein Bcl-2 were lower in double cyclin I(-/-) p35(-/-) mice than the other mice. Similarly, levels of Bcl-xL, another prosurvival member, were lower in normal and nephritic double cyclin I(-/-) p35(-/-) mice but similar to single-cyclin I(-/-) mice. Moreover, levels of ERK1/2 and MEK1/2 activation were lower in nephritic double cyclin I(-/-) p35(-/-) mice but similar to single-cyclin I(-/-) mice. The results demonstrate that the activators of Cdk5, p35, and cyclin I are not required for normal kidney function. However, they play pivotal coordinated roles in maintaining podocyte survival during stress states in disease.

Differential expression of genes in co-cultured versus separately cultured fibroblasts and epithelial cells from human benign hyperplastic prostate tissues.

The prostate is composed mainly of epithelial and stromal cells, whose dynamic interaction is vital to a broad array of cellular processes, including proliferation, differentiation, growth, and apoptosis. To understand intercellular communication in the development and progression of prostatic diseases, we examined gene expression in tissues from five patients diagnosed with benign prostatic hyperplasia (BPH). Fibroblasts and epithelial cells derived from these tissues were grown in a primary co-culture system that retains many characteristics of the intact human prostate. The mRNA levels of expressed genes as assessed by differential-display reverse transcription-PCR revealed that 110 genes were differentially expressed in co-cultured fibroblasts and epithelial cells, compared with expression in separately cultured cells. Eighty-four of these were confirmed by reverse Northern blotting, and 68 were successfully sequenced. Of the sequenced genes, 43 were differentially expressed in epithelial cells (37 upregulated, 6 downregulated), and 25 were differentially expressed in fibroblasts (6 upregulated, 19 downregulated) in co-cultures versus separate cultures. Semi-quantitative RT-PCR analysis of 12 genes with known functions showed that five of these were differentially expressed in co-cultured cells. Human kallikrein gene 7 (KLK7) was markedly upregulated in co-cultured compared with separately cultured epithelial cells (P<0.001), whereas S100 calcium binding protein A11, tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, cyclin I, and latexin were significantly downregulated in co-cultured fibroblasts (P<0.05). Quantitative real-time RT-PCR and Western blot analysis confirmed KLK7 up-regulation at both the mRNA and protein levels, respectively. Thus, epithelial-stromal cell interaction and communication are likely to be important in BPH. Epithelial cells and fibroblasts may interplay coordinately or collaboratively to influence cellular growth and death through dynamically differential gene expression in response to physiological and pathophysiological changes.

Clinical significance and expression of cyclin kinase subunits 1 and 2 in hepatocellular carcinoma.

BACKGROUND: The mammalian cyclin kinase subunit (Cks) family has two members, Cks1 and Cks2, which were identified based on the protein sequence homology to yeast Cks. Overexpression of Cks1 and Cks2 has been reported to be associated with high aggressiveness and a poor prognosis in various malignancies, including gastric, breast and prostate carcinomas. Yet, whether Cks1 and Cks2 are overexpressed in hepatocellular carcinoma (HCC) remains uncharacterized. AIMS: To investigate whether overexpression of the Cks family is clinically relevant to HCC, and whether expression patterns of Cks1 and Cks2 in HCC have diagnostic and prognostic value. METHODS: Real-time quantitative reverse transcriptase polymerase chain reaction, immunostaining and Western blot analyses were used to detect the expression of Cks1 and Cks2 at the mRNA and protein levels respectively. The associations between Cks1 and Cks2 expressions and clinical features, as well as the association between Cks1 or Cks2 and p27(kip1) expressions in HCC, were analysed. RESULTS: Expressions of Cks1 and Cks2 at both mRNA and protein levels were significantly higher in HCC than those in the adjacent noncancerous tissues (including chronic hepatitis and cirrhosis) and normal liver tissues. Overexpressions of Cks1 and Cks2 in HCC were closely associated with poor differentiation features. The expressions of both Cks1 and Cks2 were negatively associated with p27(kip1) at the protein level. CONCLUSIONS: Overexpression of Cks1 and Cks2 is associated with the aggressive tumour behaviours of HCC, and thus has diagnostic and prognostic value. Further efforts are needed to develop novel biomarkers for HCC based on CKs1 and Cks2 expressions.