p12(CDK2-AP1) mediates DNA damage responses induced by cisplatin

To control or to be controlled? Dual roles of CDK2 in DNA damage and DNA damage response

CDK2 (cyclin-dependent kinase 2), a member of the CDK family, has been shown to play a role in many cellular activities including cell cycle progression, apoptosis and senescence. Recently, accumulating evidence indicates that CDK2 is involved in DNA damage and DNA repair response (DDR). When DNA is damaged by internal or external genotoxic stresses, CDK2 activity is required for proper DNA repair in vivo and in vitro, whereas inactivation of CDK2 by siRNA techniques or by inhibitors could result in DNA damage and stimulate DDR. Hence, CDK2 seems to play dual roles in DNA damage and DDR. On one aspect, it is activated and stimulates DDR to repair DNA damage when DNA damage occurs; on the other hand, its inactivation directly leads to DNA damage and evokes DDR. Here, we describe the roles of CDK2 in DNA damage and DDR, and discuss the potential application of CDK2 inhibitors as anti-cancer agents.

mRNA Expression of CDK2AP1 in Human Breast Cancer: Correlation with Clinical and Pathological Parameters

BACKGROUND

Cyclin-dependent kinase 2-associated protein 1 (CDK2AP1) interacts with CDK2AP2, modulates the actions of transforming growth factor-B1, cyclin-dependent kinase 2 and retinoblastoma protein, and closely interacts with micro-RNA21 and micro-RNA25. Our objective was to determine if CDK2AP1 mRNA expression levels were consistent with tumour-suppressive functions in breast cancer.

MATERIALS AND METHODS

A total of 134 samples were analysed. CDK2AP1 mRNA levels were measured using quantitative polymerase chain reaction (RT-PCR) and normalised against glyceraldehyde 3-phosphate dehydrogenase mRNA. Levels in breast cancer and adjacent non-cancerous breast tissue were analysed against pathological and clinical parameters (TNM staging, survival over a 10-year follow-up period).

RESULTS

Normalised CDK2AP1 expression was 38-fold higher in adjacent non-cancerous breast tissue than in breast cancer. CDK2AP1 expression in disease-free patients at 10 years was more than threefold that of patients who died of breast cancer. However, neither of these differences in expression levels reached statistical significance. CDK2AP1 mRNA levels were higher in TNM1 compared to TNM3 (p=0.016) and with TNM4 (p=0.016). There were no significant associations between CDK2AP1 expression and estrogen receptor status, tumour grade and tumour type. There was no significant difference in overall survival between patients with high and those with low CDK2AP1 mRNA levels after a median follow-up of 10 years (Kaplan-Meier analysis, p=0.872).

CONCLUSION

To our knowledge, this is the first study in the literature to examine the mRNA expression of CDK2AP1 in human breast cancer over a long-term follow-up period. A compelling relationship exists between high CDK2AP1 mRNA expression and lower TNM classification of breast cancer, which is consistent with CDK2AP1 having a tumour-suppressive function.

Clinical aggressiveness of myxofibrosarcomas associates with down-regulation of p12CDK2AP1: prognostic implication of a putative tumor suppressor that induces cell cycle arrest and apoptosis via mitochondrial pathway

BACKGROUND

Attenuated endogenous protein levels of cyclin-dependent kinase 2 associated protein 1 (p12(CDK2AP1)) and its active homodimer p25(CDK2AP1) were found in myxofibrosarcoma-derived cell lines. Clinical and biological significances of this putative tumor suppressor in myxofibrosarcoma were studied.

METHODS

Plasmids carrying the CDK2AP1 gene and small hairpin RNA interference (shRNAi) targeting CDK2AP1 were transfected into NMFH-1 and/or OH931 cells to evaluate the effects on the CDK2, active caspase 3 (CASP3), cleaved-CASP8 and -CASP9 levels, cell cycle regulation, and/or apoptotic responses. Immunostaining of p12(CDK2AP1) was interpretable in 102 primary myxofibrosarcomas and correlated with clinicopathological variables, CDK2, Ki-67 and active CASP3 protein levels, and disease-specific survival.

RESULTS

Exogenous expression of p12(CDK2AP1) in NMFH-1 and OH931 cells significantly induced G0/G1 cell cycle arrest and down-regulated CDK2 protein level. In NMFH-1 cells, these aspects were reversed by shRNAi targeting CDK2AP1 gene. Increased active CASP3 and cleaved-CASP9, but not -CASP8, were detected after CDK2AP1 overexpression, suggesting the cellular apoptosis were induced through the mitochondrial pathway. Immunostains of p12(CDK2AP1) were aberrantly decreased in 56.9 % of cases; positively and negatively correlated with protein levels of CDK2 (p = 0.023), Ki-67 (p = 0.001) and active CASP3 (p < 0.001), respectively. Following by high histological grades, p12(CDK2AP1) down-regulation was predictive of worse disease-specific survival in univariate (p = 0.003) and multivariate (p = 0.004) analyses.

CONCLUSIONS

Through down-regulation of CDK2, high p12(CDK2AP1) level induced cell cycle arrest and the mitochondrial-dependent apoptotic pathway. Low p12(CDK2AP1) level represents a poor prognostic factor in patients with myxofibrosarcoma.

CDK2-AP1 inhibits growth of breast cancer cells by regulating cell cycle and increasing docetaxel sensitivity in vivo and in vitro

Background

Cell cycle regulatory pathway is a well-established pathway mainly dependent on cyclin-dependent kinases (CDKs), which are regulated positively by cyclins and negatively by cyclin-dependent kinase inhibitors(CKIs). Cyclin-dependent kinase 2 associate protein 1(CDK2-AP1) is a specific negative regulatory protein for CDK2, is important in the cancer cell cycle. However, the function of CDK2-AP1 in breast cancer remains unclear. We designed therefore explored the effects of CDK2-AP1 on breast cancer growth and its chemo-sensitivity.

Methods

Expression of CDK2-AP1, CDK2 and CyclinD1 in 209 cases of pathological specimens using IHC staining was measured. Lost-of-function and Gain-of-function assays were used in vivo and in vitro relating to the specific role of CDK2-AP1 in breast cancer. We analyzed in vivo and in vitro the impact of CDK2-AP1 on chemotherapy sensitivity in breast cancer.

Results

The positive ratio of CDK2-AP1 expression was reduced successively in normal breast tissue, DCIS, invasive breast cancer and relapsed breast cancer, however, with CDK2 and CyclinD1 it was suggested that CDK2-AP1 was correlated closely with the tumorigenesis and progress, and might work as a tumor suppressor. After down-regulating CDK2-AP1 in breast cancer cells, the cell cycle was accelerated and cell proliferation enhanced. The cell cycle was arrested in G0/G1 phase and G2/M phase after up-regulating CDK2-AP1 in breast cancer cells, inhibiting cell proliferation. The expression of CDK2 and CyclinD1 changed accordingly after downregulation or upregulation of CDK2-AP1 by western blot, suggesting a role of the CDK2-AP1/CDK2/CyclinD1 cell cycle pathway in the initiation and progression of breast cancer. Similar results were obtained in animal assays. The data indicates that CDK2-AP1 can induce sensitivity to docetaxel treatment in breast cancer cells.

Conclusions

CDK2-AP1 affects tumorigenesis, tumor growth and chemo-sensitivity by cell cycle regulation, which can potentially to be a therapeutical agent in breast cancer.

Efavirenz induces autophagy and aberrant differentiation in normal human keratinocytes

Although efavirenz (EFV) is efficacious as an anti-retroviral therapy when combined with other antiretroviral drugs, it may cause adverse clinical effects, including skin and mucosal eruptions, central nervous system complications, hepatotoxicity, renal failure and pulmonary complications. The present study investigated the phenotypic alterations caused by EFV in normal human keratinocytes (NHKs) and determined the cell death pathways leading to the lack of epithelial proliferation and regeneration. Replication kinetics, cellular morphology, and protein and mRNA levels of cell cycle regulatory genes and cell death markers were compared between the EFV-exposed cells and the untreated control. EFV treatment led to cell proliferation arrest and cell death of the NHKs by inducing autophagy mediated by proteasome-dependent degradation of p53. EFV also reduced the levels of mTOR and active ERK signaling in NHKs. Chemical inhibition of p53 degradation with a proteasome inhibitor led to reduced autophagic response of NHKs to EFV. In addition, EFV triggered terminal differentiation of NHKs by inducing the expression of involucrin, filaggrin, loricrin and genes involved in cornified envelope formation. Inhibition of autophagy in the EFV-treated NHKs with 3-methylalanine reduced the levels of involucrin and the extent of cell death. Our data indicate that EFV elicits cytotoxic effects on NHKs in part through induction of autophagy and aberrant differentiation of cells.

Cyclin-dependent kinase 2-associated protein 1 suppresses growth and tumorigenesis of lung cancer

Cyclin-dependent kinase 2-associated protein 1 (CDK2AP1), a growth suppressor that negatively regulates CDK2 activity, has been implicated in various types of cancer; yet its role in lung cancer remains unclear. In the present study, a lentivirus-based system was used to specifically downregulate or upregulate CDK2AP1 expression. A549 lung cancer cells were treated with RNAi (RNA interference) or lentiviral vectors for overexpression. Ectopic overexpression of CDK2AP1 in A549 cells in vitro greatly impaired their proliferation and colony-forming ability and enhanced their chemosensitivity to cisplatin and paclitaxel and caused cell cycle arrest at G1/S transition accompanied by the reduction of expression of CDK4 and CDK7. Injection of the ectopically CDK2AP1-overexpressing A549 cells into nude mice resulted in growth arrest of solid lung cancer tumors in vivo. Knockdown of CDK2AP1 in A549 cells, however, gave rise to the opposite effects including promoting cell proliferation/growth, cell cycling in vitro and enhancing tumorigenesis in vivo. These results suggest that CDK2AP1 plays an important role in modulating the growth and tumorigenesis of lung cancer cells and also has significant effects on the chemosensitivity of pulmonary malignancies to chemotherapeutics. Hence, this study extends our knowledge on the relationship between CDK2AP1 and oncogenesis of lung cancer, indicating that CDK2AP1 may serve as a new molecular target for future lung cancer therapy.

Expression of cyclin-dependent kinase 2-associated protein 1 confers an independent prognosticator in nasopharyngeal carcinoma: a cohort study

BACKGROUND AND AIM

Low expression of cyclin-dependent kinase 2-associated protein (CDK2AP1) is associated with tumour progression in oral and oesophageal carcinomas, but is not well studied in patients with head and neck cancer and nasopharyngeal carcinoma (NPC).

METHODS

A rabbit anti-human CDK2AP1 polyclonal antibody was prepared. Immunoblotting of CDK2AP1 was examined in three cell lines and immunoexpression was retrospectively assessed in biopsies of 124 consecutive NPC patients without initial distant metastasis and treated with consistent guidelines.

RESULTS

Higher CDK2AP1 expression level was identified in dysplastic oral keratinocytes, compared with two NPC-derived HONE-1 and TW01 cell lines. Low expression of CDK2AP1 (50.8%) was correlated with advanced nodal status (p=0.002) and American Joint Committee on Cancer (AJCC) stage (p=0.004). In multivariate analyses, low CDK2AP1 expression emerged as an independent prognosticator for worse disease-specific survival (DSS; p=0.037) and local recurrence-free survival (LRFS; p=0.042), along with AJCC stage III-IV (p=0.034, DSS; p=0.029, LRFS).

CONCLUSIONS

Low CDK2AP1 expression is common and associated with adverse prognosticators, conferring tumour aggressiveness through cycle cycle, cell growth or apoptosis cellular processes.

Cyclin-dependent kinase 2-associating protein 1 commits murine embryonic stem cell differentiation through retinoblastoma protein regulation

Mouse embryonic stem cells (mESCs) maintain pluripotency and indefinite self-renewal through yet to be defined molecular mechanisms. Leukemia inhibitory factor has been utilized to maintain the symmetrical self-renewal and pluripotency of mESCs in culture. It has been suggested that molecules with significant cellular effects on retinoblastoma protein (pRb) or its related pathways should have functional impact on mESC proliferation and differentiation. However, the involvement of pRb in pluripotent differentiation of mESCs has not been extensively elaborated. In this paper, we present novel experimental data indicating that Cdk2ap1 (cyclin-dependent kinase 2-associating protein 1), an inhibitor of G(1)/S transition through down-regulation of CDK2 and an essential gene for early embryonic development, confers competency for mESC differentiation. Targeted disruption of Cdk2ap1 in mESCs resulted in abrogation of leukemia inhibitory factor withdrawal-induced differentiation, along with altered pRb phosphorylation. The differentiation competency of the Cdk2ap1(-/-) mESCs was restored upon the ectopic expression of Cdk2ap1 or a nonphosphorylatable pRb mutant (mouse Ser(788) --> Ala), suggesting that the CDK2AP1-mediated differentiation of mESCs was elicited through the regulation of pRb. Further analysis on mESC maintenance or differentiation-related gene expression supports the phosphorylation at serine 788 in pRb plays a significant role for the CDK2AP1-mediated differentiation of mESCs. These data clearly demonstrate that CDK2AP1 is a competency factor in the proper differentiation of mESCs by modulating the phosphorylation level of pRb. This sheds light on the role of the establishment of the proper somatic cell type cell cycle regulation for mESCs to enter into the differentiation process.

Targeted inactivation of p12, CDK2 associating protein 1, leads to early embryonic lethality

Targeted disruption of murine Cdk2ap1, an inhibitor of CDK2 function and hence G1/S transition, results in the embryonic lethality with a high penetration rate. Detailed timed pregnancy analysis of embryos showed that the lethality occurred between embryonic day 3.5 pc and 5.5 pc, a period of implantation and early development of implanted embryos. Two homozygous knockout mice that survived to term showed identical craniofacial defect, including a short snout and a round forehead. Examination of craniofacial morphology by measuring Snout Length (SL) vs. Face Width (FW) showed that the Cdk2ap1(+/-) mice were born with a reduced SL/FW ratio compared to the Cdk2ap1(+/+) and the reduction was more pronounced in Cdk2ap1(-/-) mice. A transgenic rescue of the lethality was attempted by crossing Cdk2ap1(+/-) animals with K14-Cdk2ap1 transgenic mice. Resulting Cdk2ap1(+/-:K14-Cdk2ap1) transgenic mice showed an improved incidence of full term animals (16.7% from 0.5%) on a Cdk2ap1(-/-) background. Transgenic expression of Cdk2ap1 in Cdk2ap1(-/-:K14-Cdk2ap1) animals restored SL/FW ratio to the level of Cdk2ap1(+/-:K14-Cdk2ap1) mice, but not to that of the Cdk2ap1(+/+:K14-Cdk2ap1) mice. Teratoma formation analysis using mESCs showed an abrogated in vivo pluripotency of Cdk2ap1(-/-) mESCs towards a restricted mesoderm lineage specification. This study demonstrates that Cdk2ap1 plays an essential role in the early stage of embryogenesis and has a potential role during craniofacial morphogenesis.

Cdk2ap1 is required for epigenetic silencing of Oct4 during murine embryonic stem cell differentiation

Oct4 is a known master regulator of stem cell renewal and differentiation. Expression of Oct4 during differentiation is regulated by promoter methylation by the nucleosome remodeling and histone deacetylation (NuRD) complex. Here, we show that Cdk2ap1, a negative regulator of Cdk2 function and cell cycle, promotes Oct4 promoter methylation during murine embryonic stem cell differentiation to down-regulate Oct4 expression. We further show that this repressor function of Cdk2ap1 is dependent on its physical interaction with the methyl DNA-binding protein, Mbd3. Our data support a potential molecular link between the known differentiation promoters, including bone morphogenetic proteins and transforming growth factor signaling, and embryonic stem cell differentiation.

Ultraviolet B light stimulates interleukin-20 expression by human epithelial keratinocytes

The proinflammatory cytokine interleukin-20 (IL-20) may exert the majority of its activity in the skin. We examined the effect of various treatments including several forms of phototherapy on IL-20 expression using cultured normal human epithelial keratinocytes (NHEK). Broadband UVB light, recombinant (r) IL-1 and rIL-8 increased, while hydrocortisone reduced, NHEK supernatant IL-20 levels. Elevation of NHEK IL-20 mRNA and maximal supernatant IL-20 levels occurred with a UVB light dose (40 mJ cm(-2)) that reduced cell viability by approximately 50%. While this UVB light dose also elevated supernatant IL-1 alpha and IL-8 levels, antibody neutralization studies indicated that neither of these cytokines was directly responsible for this increase in IL-20 expression. However, the elevation in IL-20 levels was fully inhibited by the p38 mitogen-activated protein kinase (MAPK) inhibitor SB-203580, suggesting involvement of this stress signaling pathway in this UVB light response. Photodynamic therapy (PDT) with the photosensitizer lemuteporfin, UVA light, cisplatin, lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) or recombinant interferon-gamma (rIFN-gamma) either had little effect or decreased NHEK supernatant IL-20 levels. Reduced IL-20 levels paralleled the cytotoxic actions of PDT, UVA light or cisplatin and the antiproliferative effect of rIFN-gamma. Neither rIL-20 supplementation nor anti-IL-20 antibody treatments affected cell viability indicating that soluble IL-20 did not affect the short-term survival of UVB light-irradiated NHEK. Stimulation of IL-20 expression in keratinocytes by UVB light suggests that this cytokine might participate in skin responses to this ever-present environmental factor and potentially has a role in UV light-associated dermatoses.

p12CDK2-AP1 gene therapy strategy inhibits tumor growth in an in vivo mouse model of head and neck cancer

PURPOSE

To test the potential of p12(CDK2-AP1) (p12), a cell cycle regulator and cyclin-dependent kinase-2-associating protein commonly down-regulated in head and neck squamous cell carcinoma ( approximately 70%), as a gene therapy in inhibiting head and neck squamous cell carcinoma growth in vivo.

EXPERIMENTAL DESIGN

We addressed the effect of p12 expression on tumor growth by using a well-established squamous cell carcinoma VII/SF floor of mouth xenograft mouse model. The effect of therapy on tumor growth was determined for: (a) no treatment, (b) PBS, (c) vehicle (1,2-dioleoyloxy-3-trimethylammonium propane:cholesterol liposomes / 5% dextrose), (d) empty vector controls, and (e) p12-encoding vector experimental groups.

RESULTS

p12 gene therapy significantly induced antitumor effects as compared with controls, including (a) size and weight of p12-treated tumors decreased by 51% to 72% compared with all controls (P < 0.02), (b) tumor growth rate post-therapy was inhibited by 55% to 64% compared with empty vector controls (P < 0.0001), and (c) p12 expression was higher in p12-treated than controls (P < 0.002) by two-tailed t test analyses. Mechanistically, p12 treatment affected cell turnover kinetics as assessed by apoptotic and cell proliferation indices. p12 therapy significantly increased terminal nucleotidyl transferase-mediated nick end labeling (P < 0.05) and morphology-based apoptotic indices (P < 0.05) as well as significantly decreased Ki-67 cell proliferation indices (P < 0.001) compared with controls, resulting in a net cell turnover reduction in p12-treated tumors.

CONCLUSIONS

We show that this novel therapeutic modality can significantly induce antitumor responses in vivo. These results support a role for p12 as a novel tumor growth suppressor gene therapy and suggest that optimization and/or combination with current therapies may hold considerable promise in preparation for clinical trials.

Mutation of Cys105 inhibits dimerization of p12CDK2-AP1 and its growth suppressor effect

p12(CDK2-AP1) (p12) is a CDK2-associated protein that negatively regulates its kinase activity. Growth arrest of normal diploid cells by contact inhibition resulted in an induction of p27(kip1) and reduction of CDK2 levels. Interestingly, we observed concomitantly in growth-arrested cells, there was a reduction of nuclear p12 and the appearance of a nuclear 25-kDa molecule (p25) recognized by anti-p12 polyclonal antibody. Biochemical analysis showed that bacterial His-tagged p12 could be converted into a dimeric p25 in a reducing agent-dependent manner, and mutating the only cysteine residue of p12 (Cys(105) --> Ala(105)) abolished the dimerization. Transient transfection of wild type p12 into U2OS cells showed a reducing agent-sensitive dimerization that was also abolished by the C105A mutation. Furthermore, reduction of p12 expression by a short interfering RNA resulted in a parallel reduction of p25. These data supports the possibility that p25 is a homodimeric form of p12 through the cysteine residue. More interestingly, transient transfection of p12 (C105A) into the normal diploid lung fibroblast CCD18LU cells resulted in a reduction of the growth-inhibitory effect of p12 and abolished the inhibitory effect of p12 on CDK2 kinase activity. In addition, we found that the C105A mutation did not alter nuclear localization of p12, but it prevented association with CDK2. Taken together, our data suggest that p12 forms a nuclear homodimers in contact inhibited normal diploid cells and dimerization of p12 is a necessary process for the growth inhibition effect by p12.