Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously showed that the rate of hepatocyte proliferation in livers from newborn C/EBPalpha knockout mice was increased. An examination of cell cycle-related proteins showed that the cyclin-dependent kinase (CDK) inhibitor p21 level was reduced in the knockout animals compared to that in wild-type littermates. Here we show additional cell cycle-associated proteins that are affected by C/EBPalpha. We have observed that C/EBPalpha controls the composition of E2F complexes through interaction with the retinoblastoma (Rb)-like protein, p107, during prenatal liver development. S-phase-specific E2F complexes containing E2F, DP, cdk2, cyclin A, and p107 are observed in the developing liver. In wild-type animals these complexes disappear by day 18 of gestation and are no longer present in the newborn animals. In the C/EBPalpha mutant, the S-phase-specific complexes do not diminish and persist to birth. The elevation of levels of the S-phase-specific E2F-p107 complexes in C/EBPalpha knockout mice correlates with the increased expression of several E2F-dependent genes such as those that encode cyclin A, proliferating cell nuclear antigen, and p107. The C/EBPalpha-mediated regulation of E2F binding is specific, since the deletion of another C/EBP family member, C/EBPbeta, does not change the pattern of E2F binding during prenatal liver development. The addition of bacterially expressed, purified His-C/EBPalpha to the E2F binding reaction resulted in the disruption of E2F complexes containing p107 in nuclear extracts from C/EBPalpha knockout mouse livers. Ectopic expression of C/EBPalpha in cultured cells also leads to a reduction of E2F complexes containing Rb family proteins. Coimmunoprecipitation analyses revealed an interaction of C/EBPalpha with p107 but none with cdk2, E2F1, or cyclin A. A region of C/EBPalpha that has sequence similarity to E2F is sufficient for the disruption of the E2F-p107 complexes. Despite its role as a DNA binding protein, C/EBPalpha brings about a change in E2F complex composition through a protein-protein interaction. The disruption of E2F-p107 complexes correlates with C/EBPalpha-mediated growth arrest of hepatocytes in newborn animals.
Mol Cell Biol 1999 Apr
PMID:C/EBPalpha regulates formation of S-phase-specific E2F-p107 complexes in livers of newborn mice. 1008 61

The human UV-damaged-DNA binding protein DDB has been linked to the repair deficiency disease xeroderma pigmentosum group E (XP-E), because a subset of XP-E patients lack the damaged-DNA binding function of DDB. Moreover, the microinjection of purified DDB complements the repair deficiency in XP-E cells lacking DDB. Two naturally occurring XP-E mutations of DDB, 82TO and 2RO, have been characterized. They have single amino acid substitutions (K244E and R273H) within the WD motif of the p48 subunit of DDB, and the mutated proteins lack the damaged-DNA binding activity. In this report, we describe a new function of the p48 subunit of DDB, which reveals additional defects in the function of the XP-E mutants. We show that when the subunits of DDB were expressed individually, p48 localized in the nucleus and p125 localized in the cytoplasm. The coexpression of p125 with p48 resulted in an increased accumulation of p125 in the nucleus, indicating that p48 plays a critical role in the nuclear localization of p125. The mutant forms of p48, 2RO and 82TO, are deficient in stimulating the nuclear accumulation of the p125 subunit of DDB. In addition, the mutant 2RO fails to form a stable complex with the p125 subunit of DDB. Our previous studies indicated that DDB can associate with the transcription factor E2F1 and can function as a transcriptional partner of E2F1. Here we show that the two mutants, while they associate with E2F1 as efficiently as wild-type p48, are severely impaired in stimulating E2F1-activated transcription. This is consistent with our observation that both subunits of DDB are required to stimulate E2F1-activated transcription. The results provide insights into the functions of the subunits of DDB and suggest a possible link between the role of DDB in E2F1-activated transcription and the repair deficiency disease XP-E.
Mol Cell Biol 1999 Jul
PMID:The naturally occurring mutants of DDB are impaired in stimulating nuclear import of the p125 subunit and E2F1-activated transcription. 1037 43

The members of the Sp1 transcription factor family can act as both negative and positive regulators of gene expression. Here we show that Sp1 can be a target for histone deacetylase 1 (HDAC1)-mediated transcriptional repression. The histone deacetylase inhibitor trichostatin A activates the chromosomally integrated murine thymidine kinase promoter in an Sp1-dependent manner. Coimmunoprecipitation experiments with Swiss 3T3 fibroblasts and 293 cells demonstrate that Sp1 and HDAC1 can be part of the same complex. The interaction between Sp1 and HDAC1 is direct and requires the carboxy-terminal domain of Sp1. Previously we have shown that the C terminus of Sp1 is necessary for the interaction with the transcription factor E2F1 (J. Karlseder, H. Rotheneder, and E. Wintersberger, Mol. Cell. Biol. 16:1659-1667, 1996). Coexpression of E2F1 interferes with HDAC1 binding to Sp1 and abolishes Sp1-mediated transcriptional repression. Our results indicate that one component of Sp1-dependent gene regulation involves competition between the transcriptional repressor HDAC1 and the transactivating factor E2F1.
Mol Cell Biol 1999 Aug
PMID:Histone deacetylase 1 can repress transcription by binding to Sp1. 1040 40

17beta-Estradiol (E2) stimulated proliferation and DNA synthesis in MCF-7 human breast cancer cells, and this was accompanied by induction of E2F1 mRNA and protein levels. Analysis of the E2F1 gene promoter showed that the -146 to -54 region was required for E2-responsiveness in transient transfection assays, and subsequent deletion/mutation analysis showed that a single upstream GC-rich and two downstream CCAAT-binding sites were required for transactivation by E2. Gel mobility shift assays with multiple oligonucleotides and protein antibodies (for supershifts) showed that the -146 to -54 region of the E2F1 gene promoter bound Sp1 and NF-Y proteins in MCF-7 cells. The estrogen receptor (ER) protein enhanced Sp1 interactions with upstream GC-rich sites, and interactions of ER, Sp1, and ER/Sp1 with downstream DNA bound-NF-Y was investigated by kinetic analysis for protein-DNA binding (on- and off-rates), coimmunoprecipitation, and pulldown assays using wild-type and truncated glutathione S-transferase (GST)-Sp1 chimeric proteins. The results showed that Sp1 protein enhanced the Bmax of NF-Y-DNA binding by more than 5-fold (on-rate); in addition, the Sp1-enhanced NF-Y-DNA complex was further stabilized by coincubation with ER and the rate of dissociation (t1/2) was decreased by approximately 50%. Sp1 antibodies immunoprecipitated [35S]NF-YA after coincubation with unlabeled Sp1 protein. Thus, transcriptional activation of E2F1 gene expression in MCF-7 cells by E2 is regulated by multiprotein ER/Sp1-NF-Y interactions at GC-rich and two CCAAT elements in the proximal region of the E2F1 gene promoter. This represents a unique trans-acting protein complex in which ligand-dependent transactivation by the ER is independent of direct ER interactions with promoter elements.
Mol Endocrinol 1999 Aug
PMID:Transcriptional activation of E2F1 gene expression by 17beta-estradiol in MCF-7 cells is regulated by NF-Y-Sp1/estrogen receptor interactions. 1044 10

The E2F family of transcription factors regulates the expression of genes needed for DNA synthesis and cell-cycle control. However, the individual contributions of the different E2F family members in regulating proliferation in various tissues have not been well characterized. Mouse liver is an excellent system for investigating proliferation because its growth state can be experimentally manipulated. As observed in cell culture systems, E2F1 protein is present at low levels in the quiescent liver, with an increase in expression during proliferation. Therefore, we expected that E2F1 may play an important role in cell-growth control during periods of robust proliferation. Using E2F1-nullizygous mice, we performed partial hepatectomies to investigate the role of E2F1 in the synchronous proliferation of adult hepatocytes. We found that E2F1 deficiency resulted in only minor changes in gene expression and that the timing of liver regeneration was not altered in E2F1 nullizygous mice. E2F1 has displayed properties of both a tumor suppressor and an oncogene in different model systems. Therefore, we investigated the role of E2F1 in rapidly growing liver tumor cells in strains of mice that have high (C3H/HeJ) and low (C57BL/6J) rates of hepatocarcinogenesis. We observed no significant differences in the number of liver tumors that developed after diethylnitrosamine treatment of wild type versus E2F1-nullizygous mice. We suggest that abundant levels of E2F4 in the mouse liver compensate for loss of E2F1.
Mol Carcinog 1999 Aug
PMID:No effect of loss of E2F1 on liver regeneration or hepatocarcinogenesis in C57BL/6J or C3H/HeJ mice. 1044 36

E2F transcription factors play a critical role in cell cycle progression through the regulation of genes required for G(1)/S transition. They are also thought to be important for growth arrest; however, their potential role in the cell differentiation process has not been previously examined. Here, we demonstrate that E2F4 is highly upregulated following the neuronal differentiation of PC12 cells with nerve growth factor (NGF), while E2F1, E2F3, and E2F5 are downregulated. Immunoprecipitation and subcellular fractionation studies demonstrated that both the nuclear localization of E2F4 and its association with the Rb family member p130 increased following neuronal differentiation. The forced expression of E2F4 markedly enhanced the rate of PC12 cell differentiation induced by NGF and also greatly lowered the rate at which cells lost their neuronal phenotype following NGF removal. Importantly, this effect occurred in the absence of any significant change in the growth regulation of PC12 cells by NGF. Further, the downregulation of E2F4 expression with antisense oligodeoxynucleotides inhibited NGF-induced neurite outgrowth, indicating an important role for this factor during PC12 cell differentiation. Finally, E2F4 expression was found to increase dramatically in the developing rat cerebral cortex and cerebellum, as neuroblasts became postmitotic and initiated terminal differentiation. These findings demonstrate that, in addition to its effects on cell proliferation, E2F4 actively promotes the neuronal differentiation of PC12 cells as well as the retention of this state. Further, this effect is independent of alterations in cell growth and may involve interactions between E2F4 and the neuronal differentiation program itself. E2F4 may be an important participant in the terminal differentiation of neuroblasts.
Mol Cell Biol 1999 Sep
PMID:E2F4 actively promotes the initiation and maintenance of nerve growth factor-induced cell differentiation. 1045 52

Using a transgenic mouse model expressing the E2F1 gene under the control of a keratin 5 (K5) promoter, we previously demonstrated that increased E2F1 activity can promote tumorigenesis by cooperating with either a v-Ha-ras transgene to induce benign skin papillomas or p53 deficiency to induce spontaneous skin carcinomas. We now report that as K5 E2F1 transgenic mice age, they are predisposed to develop spontaneous tumors in a variety of K5-expressing tissues, including the skin, vagina, forestomach, and odontogenic epithelium. On the other hand, K5 E2F1 transgenic mice are found to be resistant to skin tumor development following a two-stage carcinogenesis protocol. Additional experiments suggest that this tumor-suppressive effect of E2F1 occurs at the promotion stage and may involve the induction of apoptosis. These findings demonstrate that increased E2F1 activity can either promote or inhibit tumorigenesis, dependent upon the experimental context.
Mol Cell Biol 1999 Sep
PMID:E2F1 has both oncogenic and tumor-suppressive properties in a transgenic model. 1045 86

Rb protein inhibits both cell cycle progression and apoptosis. Interaction of specific cellular proteins, including E2F1, with Rb C-terminal domains mediates cell cycle regulation. In contrast, the nuclear N5 protein associates with an Rb N-terminal domain with unknown function. The N5 protein contains a region of sequence similarity to the death domain of proteins involved in apoptotic signaling. We demonstrate here that forced N5 expression potently induces apoptosis in several tumor cell lines. Mutation of conserved residues within the death domain homology compromise N5-induced apoptosis, suggesting that it is required for normal function. Endogenous N5 protein is specifically altered in apoptotic cells treated with ionizing radiation. Furthermore, dominant interfering death domain mutants compromise cellular responses to ionizing radiation. Finally, physical association with Rb protein inhibits N5-induced apoptosis. We propose that N5 protein plays a role in the regulation of apoptosis and that Rb directly coordinates cell proliferation and apoptosis by binding specific proteins involved in each process through distinct protein binding domains.
Mol Biol Cell 1999 Oct
PMID:Apoptosis induced by the nuclear death domain protein p84N5 is inhibited by association with Rb protein. 1051 64

E2F transcription factor is subject to stringent regulation by a variety of molecules. We recently observed that prohibitin, a potential tumor suppressor protein, binds to the retinoblastoma (Rb) protein and represses E2F transcriptional activity. Here we demonstrate that prohibitin requires the marked box region of E2F for repression; further, prohibitin can effectively inhibit colony formation induced by overexpression of E2F1 in T47D cells. Prohibitin was also found to interact with the signaling kinase c-Raf-1, and Raf-1 could effectively reverse prohibitin-mediated repression of E2F activity. Agents such as E1A, p38 kinase, and cyclins D and E had no effect on prohibitin-mediated repression of E2F1, but all of these molecules could reverse Rb function. Similarly, stimulation of the immunoglobulin M signaling pathway in Ramos cells could inactivate prohibitin, but this had no effect on Rb function. Serum stimulation of quiescent Ramos cells inactivated Rb and prohibitin with different kinetics; further, while the serum-dependent inactivation of Rb was dependent on cyclin-dependent kinase activity, the inactivation of prohibitin was not. We believe that prohibitin is a novel regulator of E2F function which channels specific signaling cascades to the cell cycle regulatory machinery.
Mol Cell Biol 1999 Nov
PMID:Rb and prohibitin target distinct regions of E2F1 for repression and respond to different upstream signals. 1052 33

Most E2F-driven promoters are transiently activated around the G(1)/S transition. Although the promoter for the c-myb proto-oncogene harbors an E2F element, it is induced early in G(1) following entry into the cell cycle. Furthermore, this promoter remains active throughout subsequent cell cycles. Since E2F sites function as repressor elements during G(1) (due to the association of pRb with E2F factors), we investigated whether the E2F element in the c-myb promoter is regulated differently than E2F elements in promoters that are repressed during G(1). By gel shift analysis, the E2F element from the c-myb promoter was found to form a unique complex, referred to as E2Fmyb-sp, which was not observed with E2F elements from several other promoters. Antibodies to DP-1, E2F1 to -5, p107, or pRb failed to either supershift or block E2Fmyb-sp complex formation. Methylation interference experiments indicate that the DNA contact residues for the E2Fmyb-sp complex are distinct from but overlapping with residues required for the binding of E2F proteins. In addition to the identification of E2Fmyb-sp, we have found that SP-1 binds to the c-myb E2F element. Functional studies revealed that E2Fmyb-sp and/or SP-1 are required to achieve full activation of the c-myb promoter in different cell types and to maintain elevated expression of the c-myb promoter during G(1) in NIH 3T3 cells. These studies demonstrate that E2F elements can be regulated differently through the binding of unique sets of proteins.
Mol Cell Biol 1999 Dec
PMID:Distinct cellular factors regulate the c-myb promoter through its E2F element. 1056 69


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