1026

CDKN1A

CAP20|CDKN1|CIP1|MDA-6|P21|SDI1|WAF1|p21CIP1;cyclin-dependent kinase inhibitor 1A (p21, Cip1);CDKN1A;cyclin-dependent kinase inhibitor 1A (p21, Cip1)

CDK-interacting protein 1|CDK-interaction protein 1|DNA synthesis inhibitor|cyclin-dependent kinase inhibitor 1|melanoma differentiation associated protein 6|wild-type p53-activated fragment 1

6p21.2

protein-coding

Count: 3; Pubmed_search,TAG,Generif

BACKGROUND: The esophageal carcinoma related gene 4 (ECRG4) was initially identified and cloned from human normal esophageal epithelium in our laboratory (GenBank accession no.AF325503). ECRG4 has been described as a novel tumor suppressor gene associated with prognosis in esophageal squamous cell carcinoma (ESCC). METHODS: In this study, binding affinity assay in vitro and co-immunoprecipitation experiment in vivo were utilized to verify the physical interaction between ECRG4 and transmembrane protease, serine 11A (TMPRSS11A, also known as ECRG1, GenBank accession no. AF 071882). Then, p21 protein expression, cell cycle and cell proliferation regulations were examined after ECRG4 and ECRG1 co-transfection in ESCC cells. RESULTS: We revealed for the first time that ECRG4 interacted directly with ECRG1 to inhibit cancer cell proliferation and induce cell cycle G1 phase block in ESCC. Binding affinity and co-immunoprecipitation assays demonstrated that ECRG4 interacted directly with ECRG1 in ESCC cells. Furthermore, the ECRG4 and ECRG1 co-expression remarkably upregulatd p21 protein level by Western blot (P < 0.001), induced cell cycle G1 phase block by flow cytometric analysis (P < 0.001) and suppressed cell proliferation by MTT and BrdU assay (both P < 0.01) in ESCC cells. CONCLUSIONS: ECRG4 interacts directly with ECRG1 to upregulate p21 protein expression, induce cell cycle G1 phase block and inhibit cancer cells proliferation in ESCC.

Tumor suppression by p53 and BRCA1 involves regulation of cell cycle, apoptosis, and DNA repair and is influenced by transcriptional coactivators and post-translational modifications. Here we show that coactivator-associated arginine methyltransferase 1 (CARM1) methylates Arg 754 in the KIX region of coactivator p300. Methylated p300 and p300 protein fragments are preferentially recognized by BRCT domains of BRCA1, identifying the BRCT domain as a novel methylarginine-binding module. CARM1 and p300 cooperate with BRCA1 and p53 to induce expression of the critical cell cycle and proliferation regulator p21(WAF1/CIP1) in response to DNA damage. This induction was severely attenuated by elimination of CARM1 or its methyltransferase activity, or by mutation of Arg 754 of p300. Absence of CARM1 methyltransferase activity led to failure of cells to arrest in the G1 phase of the cell cycle in response to DNA damage. CARM1 methyltransferase activity was required for induction of some p53 target genes (p21 and Gadd45) but not others (Bax) by DNA damage. Recruitment of BRCA1 to the p53-binding region of the p21 promoter in response to DNA damage required methylation of Arg 754 of p300 by CARM1. Thus, coactivator methylation may be crucial for fine-tuning the tumor suppressor function of BRCA1 and other BRCT domain proteins.

The oncogenic human gammaherpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) expresses 12 viral microRNAs (miRNAs) in latently infected cells. Here, we report that cellular mRNAs encoding the cellular cyclin-dependent kinase inhibitor p21, a key inducer of cell cycle arrest, are direct targets for KSHV miR-K1. Ectopically expressed KSHV miR-K1 specifically inhibited the expression of endogenous p21 in KSHV-negative cells and strongly attenuated the cell cycle arrest that normally occurs upon p53 activation, yet miR-K1 did not prevent the induction of other p53-responsive genes. Stable knockdown of miR-K1 in latently KSHV-infected human primary effusion lymphoma (PEL) B cells revealed a derepression of p21 expression and enhanced cell cycle arrest following activation of p53. Our data demonstrate that miR-K1 represses the expression of p21, a protein with known tumor suppressor functions, and suggest that this KSHV miRNA is likely to contribute to the oncogenic potential of this opportunistic viral pathogen.

Genistein (4',5,7-trihydroxyisoflavone) is the most abundant isoflavone found in the soybean. The effects of genistein on various cancer cell lines have been extensively studied but the precise molecular mechanisms are not known. We report here the epigenetic mechanism of the action of genistein on androgen-sensitive (LNCaP) and androgen-insensitive (DuPro) human prostate cancer cell lines. Genistein induced the expression of tumor suppressor genes p21 (WAF1/CIP1/KIP1) and p16 (INK4a) with a concomitant decrease in cyclins. There was a G(0)-G(1) cell cycle arrest in LNCaP cells and a G(2)-M arrest in DuPro cells after genistein treatment. Genistein also induced apoptosis in DuPro cells. DNA methylation analysis revealed the absence of p21 promoter methylation in both cell lines. The effect of genistein on chromatin remodeling has not been previously reported. We found that genistein increased acetylated histones 3, 4, and H3/K4 at the p21 and p16 transcription start sites. Furthermore, we found that genistein treatment also increased the expression of histone acetyl transferases that function in transcriptional activation. This is the first report on epigenetic regulation of various genes by genistein through chromatin remodeling in prostate cancer. Altogether, our data provide new insights into the epigenetic mechanism of the action of genistein that may contribute to the chemopreventive activity of this dietary isoflavone and have important implications for epigenetic therapy.

Screening for tumor suppressor genes in breast cancer revealed multiple truncating mutations of PB1, which encodes the BAF180 subunit of the PBAF chromatin remodeling complex. mutation was associated with loss of heterozygosity of the wild-type allele. BAF180 complementation of BAF180-mutant tumor cells caused G(1) arrest that was dependent on increased expression of the cyclin/cyclin-dependent kinase inhibitor p21/WAF1/CIP1. Endogenous wild-type BAF180 bound to the p21 promoter and was required for proper p21 expression and G(1) arrest after transforming growth factor-beta and gamma-radiation treatment. BAF180 thus functions on two tumor suppressor signaling pathways as a physiologic mediator of p21 expression. We conclude that BAF180 suppresses tumorigenesis, at least in part, through its ability to regulate p21.

BACKGROUND: Androgen receptor (AR) functions in normal prostate epithelium as a tumor suppressor to inhibit continuous proliferation of these cells. Such tumor suppressor function of AR is lost in androgen depletion independent (ADI) prostate cancers. In type-I ADI cancers AR is not expressed, while in type-II ADI cancers AR is recaptured as an oncogene. The PC3 and DU145 human prostate cancer cell lines are representative of the earlier type-I ADI prostate cancers. While these cells do not express AR, it is unclear whether they retained the coactivators necessary for AR-dependent tumor suppression. To answer this question the response to AR protein expression by PC3 and DU145 cells was evaluated. METHODS: To do this, a lentiviral AR (Lenti-AR) expression system was engineered to encode an AR transcript which includes appropriate 5' and 3' untranslated regions (UTRs) containing all previously identified post-transcriptional regulatory sequences. AR expression and transcriptional activity were evaluated in Lenti-AR transduced cells by Western blot and luciferase assay, respectively. Cell growth in culture and in mouse xenografts was evaluated in correlation to expression changes in p21, p27, and p45(SKP2) proteins. RESULTS: Lenti-AR transduced PC3 and DU145 lines expressed transcriptionally functional AR protein at appropriate physiological levels. expression and engagement of AR protein in PC3-Lenti-AR cells resulted in transactivation of p21 and subsequent growth inhibition of these cells in culture and in mouse xenografts. Such inhibition was due to induced G1 arrest of these cells as documented by expression changes in p27 and p45(SKP2) proteins. Such growth inhibition was not observed in DU145-Lenti-AR cells. CONCLUSIONS: These results document that PC3, but not DU145 cells retain the coregulators needed for AR tumor suppressor ability.CI - (c) 2005 Wiley-Liss, Inc.

Cyclin E-Cdk2 is an evolutionary conserved cyclin-dependent kinase (CDK) complex that drives the G1 to S phase transition of the cell cycle. A novel cDNA encoding a HECT family protein also containing RCC1-like repeats was isolated by a yeast two-hybrid screening using both cyclin E and its inhibitor p21. The protein product of this cDNA, Ceb1, interacts with various cyclin subunits of CDKs in mammalian cells. expression of Ceb1 is specifically detected in testis and ovary and is highly elevated when the functions of the tumor suppressor proteins, p53 and RB, are compromised by mutations or viral oncoproteins. The present results suggest that Ceb1 may play a critical role when its expression and the CDK activity are upregulated by inactivation of p53 and RB.CI - Copyright 1999 Academic Press.

The p21CKI forms a physical complex with the retinoblastoma protein (pRb) both in vitro and in vivo. The A/B pocket region of pRb and the N-terminal region of p21 were indispensable for this interaction. Among p21 family members, p57, but not p27, associated with pRb. Overexpression of cyclin D1, Cdk4, and E2F1 in the cells expressing pRb and p21 did not perturb the interaction between p21 and pRb. Coexpression of p21 in cells expressing pRb, cyclin D1, and Cdk4 prevented pRb hyperphosphorylation by cyclin D1/Cdk4. On the other hand, hyperphosphorylation of pRb by an excess amount of cyclin/Cdk disrupted pRb/p21 complex formation in vitro. These findings suggest that pRb may be dynamically regulated by the relative binding and activities of p21 and Cdks.CI - Copyright 1999 Academic Press.

mutations of the BRCA1 gone in humans are associated with predisposition to breast and ovarian cancers. We show here that Brca1+/- mice are normal and fertile and lack tumors by age eleven months. Homozygous Brca1(5-6) mutant mice die before day 7.5 of embryogenesis. Mutant embryos are poorly developed, with no evidence of mesoderm formation. The extraembryonic region is abnormal, but aggregation with wild-type tetraploid embryos does not rescue the lethality. In vivo, mutant embryos do not exhibit increased apoptosis but show reduced cell proliferation accompanied by decreased expression of cyclin E and mdm-2, a regulator of p53 activity. The expression of cyclin-dependent kinase inhibitor p21 is dramatically increased in the mutant embryos. Buttressing these in vivo observations is the fact that mutant blastocyst growth is grossly impaired in vitro. Thus, the death of Brca1(5-6) mutant embryos prior to gastrulation may be due to a failure of the proliferative burst required for the development of the different germ layers.

The E7 oncoprotein of the high-risk human papillomaviruses (HPV) is thought to contribute to cervical carcinogenesis at least in part by abrogating cell cycle regulation. E7 can dysregulate the cell cycle through its interaction with several cellular proteins including the retinoblastoma suppressor protein pRb, as well as the cyclin-dependent kinase inhibitor p21(Cip1). Inactivation of pRb in cervical epithelia is not sufficient to explain the ability of E7 to cause cervical cancers in transgenic mice. In the current study, we focused on the role of p21(Cip1) in cervical cancer. Cervical disease was significantly increased in p21(-/-) mice compared with p21(+/+) mice, showing that p21(Cip1) can function as a tumor suppressor in this tissue. Importantly, the ability of E7 to induce cervical cancers was not significantly enhanced on the p21-null background, consistent with the hypothesis that the ability of E7 to inhibit p21(Cip1) contributes to its carcinogenic properties. Further supportive of this hypothesis, cervical carcinogenesis in mice expressing a mutant form of HPV-16 E7, E7(CVQ), which fails to inactivate p21(Cip1), was significantly reduced compared with that in K14E7(WT) mice expressing wild-type HPV-16 E7. However, K14E7(CVQ) mice still displayed heightened levels of cervical carcinogenesis compared with that in nontransgenic mice, indicating that activities of E7 besides its capacity to inactivate p21(Cip1) also contribute to cervical carcinogenesis. Taken together, we conclude that p21(Cip1) functions as a tumor suppressor in cervical carcinogenesis and that p21(Cip1) inactivation by HPV-16 E7 partially contributes to the contribution of E7 to cervical carcinogenesis.

The cyclin-dependent kinase inhibitor p21WAF1/CIP1 was originally considered to be a tumor-suppressor because it was identified as a key mediator of p53-dependent cell cycle arrest. However, it has been suggested that p21 may also act as an oncogene because it often inhibits apoptosis. For example, deletion of p21 from p53-deficient mice resulted in longer survival and in a significantly reduced number of thymic lymphomas that was explained by higher apoptotic rates in these mice. However, recently it has been shown that a p53 mutant that had lost its ability to induce apoptosis, but retained its ability to induce p21 and cell cycle arrest, was able to suppress lymphomagenesis in different cancer models. Tumor suppression by this p53 mutant was modulated by p21, which induced senescence and preserved chromosomal stability. These data suggest that the ability of p21 to induce cell-cycle arrest may lead to tumor suppression in some types of cancer.

Transformation and cancer growth are regulated by the coordinate actions of oncogenes and tumor suppressors. Here, we show that the novel E3 ubiquitin ligase HACE1 is frequently downregulated in human tumors and maps to a region of chromosome 6q21 implicated in multiple human cancers. Genetic inactivation of HACE1 in mice results in the development of spontaneous, late-onset cancer. A second hit from either environmental triggers or genetic heterozygosity of another tumor suppressor, p53, markedly increased tumor incidence in a Hace1-deficient background. Re-expression of HACE1 in human tumor cells directly abrogates in vitro and in vivo tumor growth, whereas downregulation of HACE1 via siRNA allows non-tumorigenic human cells to form tumors in vivo. Mechanistically, the tumor-suppressor function of HACE1 is dependent on its E3 ligase activity and HACE1 controls adhesion-dependent growth and cell cycle progression during cell stress through degradation of cyclin D1. Thus, HACE1 is a candidate chromosome 6q21 tumor-suppressor gene involved in multiple cancers.

The Cdk inhibitor p21 regulates p53-mediated growth arrest following DNA damage. It is expressed during epithelial differentiation in a variety of organs including colon. We investigated susceptibility of p21-deficient mice to the colon carcinogen azoxymethane (AOM). After AOM injections, rodents develop putative premalignant lesions called aberrant crypt foci (ACF) that are localized to the distal three centimeters of the colon. p21-deficient mice developed significantly higher numbers of ACF than wild-type mice in response to AOM, and these were not restricted to distal colon. After AOM treatment, increased numbers of lymphoid aggregates were detected in p21-deficient colon. Proliferation was similar in wild type and p21-deficient colon before and after AOM injection, but AOM-induced apoptosis was detected only in wild-type crypt epithelial cells, and not in the p21-deficient colon. The proapoptotic function uncovered for p21 was unexpected, because p21 acts as an inhibitor of apoptosis in many systems, and is not required for p53-dependent apoptosis. Enhanced formation of ACF in p21-deficient mice supports a tumor suppressor function for p21 in the colon. Reduced apoptosis of colon epithelial cells with deleterious mutations may be an initiating event in the formation of ACF, with inflammatory cell cytokine expression contributing to their further expansion.