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C Albanese

Publications and source records attributed to C Albanese.

At least 19 recordsLinked to original sources
PubMed2000

The cyclin D1 gene is transcriptionally repressed by caveolin-1.

The cyclin D1 gene encodes the regulatory subunit of the holoenzyme that phosphorylates and inactivates the retinoblastoma pRB protein. Cyclin D1 protein levels are elevated by mitogenic and oncogenic signaling pathways, and antisense mRNA to cyclin D1 inhibits transformation by the ras, neu, and src oncogenes, thus linking cyclin D1 regulation to cellular transformation. Caveolins are the principal protein components of caveolae, vesicular plasma membrane invaginations that also function in signal transduction. We show here that caveolin-1 expression levels inversely correlate with cyclin D1 abundance levels in transformed cells. Expression of antisense caveolin-1 increased cyclin D1 levels, whereas caveolin-1 overexpression inhibited expression of the cyclin D1 gene. Cyclin D1 promoter activity was selectively repressed by caveolin-1, but not by caveolin-3, and this repression required the caveolin-1 N terminus. Maximal inhibition of the cyclin D1 gene promoter by caveolin-1 was dependent on the cyclin D1 promoter T-cell factor/lymphoid enhancer factor-1-binding site between -81 to -73. The T-cell factor/lymphoid enhancer factor sequence was sufficient for repression by caveolin-1. We suggest that transcriptional repression of the cyclin D1 gene may contribute to the inhibition of transformation by caveolin-1.

Amino Acid Sequence↗
PubMed2000

Sustained mammary gland-directed, ponasterone A-inducible expression in transgenic mice.

The ability to regulate temporal- and spatial-specific expression of target genes in transgenic mice will facilitate analysis of gene function and enable the generation of murine models of human diseases. The genetic analysis of mammary gland tumorigenesis requires the development of mammary gland-specific transgenics, which are tightly regulated throughout the adult mammary epithelium. Analysis of genes implicated in mammary gland tumorigenesis has been hampered by mosaic transgene expression and the findings that homozygous deletion of several candidate genes (cyclin D1, Stat5A, prolactin receptor) abrogates normal mammary gland development. We describe the development of transgenic mouse lines in which sustained transgene expression was inducibly regulated, both specifically and homogeneously, in the adult mammary gland epithelium. Transgenes encoding RXRalpha and a chimeric ecdysone receptor under control of a modified MMTV-LTR, which targets mammary gland expression, were used. These transgenic 'receptor' lines were crossed with transgenic 'enhancer' lines in which the ecdysone/RXR binding site induced ligand-dependent expression of transgenic beta-galactosidase. Pharmacokinetic analysis of a highly bioactive ligand (ponasterone A), identified through screening ecdysteroids from local plants, demonstrated sustained release and transgene expression in vivo. This transgenic model with both tightly regulated and homogeneous transgene expression, which was sustained in vivo using ligands readily extracted from local flora, has broad practical applicability for genetic analysis of mammary gland disease.

Animals↗
PubMed2000

Cyclin D1 is required for transformation by activated Neu and is induced through an E2F-dependent signaling pathway.

The neu (c-erbB-2) proto-oncogene encodes a tyrosine kinase receptor that is overexpressed in 20 to 30% of human breast tumors. Herein, cyclin D1 protein levels were increased in mammary tumors induced by overexpression of wild-type Neu or activating mutants of Neu in transgenic mice and in MCF7 cells overexpressing transforming Neu. Analyses of 12 Neu mutants in MCF7 cells indicated important roles for specific C-terminal autophosphorylation sites and the extracellular domain in cyclin D1 promoter activation. Induction of cyclin D1 by NeuT involved Ras, Rac, Rho, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38, but not phosphatidylinositol 3-kinase. NeuT induction of the cyclin D1 promoter required the E2F and Sp1 DNA binding sites and was inhibited by dominant negative E2F-1 or DP-1. Neu-induced transformation was inhibited by a cyclin D1 antisense or dominant negative E2F-1 construct in Rat-1 cells. Growth of NeuT-transformed mammary adenocarcinoma cells in nude mice was blocked by the cyclin D1 antisense construct. These results demonstrate that E2F-1 mediates a Neu-signaling cascade to cyclin D1 and identify cyclin D1 as a critical downstream target of neu-induced transformation.

Animals↗
PubMed1999

Activation of the cyclin D1 gene by the E1A-associated protein p300 through AP-1 inhibits cellular apoptosis.

The adenovirus E1A protein interferes with regulators of apoptosis and growth by physically interacting with cell cycle regulatory proteins including the retinoblastoma tumor suppressor protein and the coactivator proteins p300/CBP (where CBP is the CREB-binding protein). The p300/CBP proteins occupy a pivotal role in regulating mitogenic signaling and apoptosis. The mechanisms by which cell cycle control genes are directly regulated by p300 remain to be determined. The cyclin D1 gene, which is overexpressed in many different tumor types, encodes a regulatory subunit of a holoenzyme that phosphorylates and inactivates PRB. In the present study E1A12S inhibited the cyclin D1 promoter via the amino-terminal p300/CBP binding domain in human choriocarcinoma JEG-3 cells. p300 induced cyclin D1 protein abundance, and p300, but not CBP, induced the cyclin D1 promoter. cyclin D1 or p300 overexpression inhibited apoptosis in JEG-3 cells. The CH3 region of p300, which was required for induction of cyclin D1, was also required for the inhibition of apoptosis. p300 activated the cyclin D1 promoter through an activator protein-1 (AP-1) site at -954 and was identified within a DNA-bound complex with c-Jun at the AP-1 site. Apoptosis rates of embryonic fibroblasts derived from mice homozygously deleted of the cyclin D1 gene (cyclin D1(-/-)) were increased compared with wild type control on several distinct matrices. p300 inhibited apoptosis in cyclin D1(+/+) fibroblasts but increased apoptosis in cyclin D1(-/-) cells. The anti-apoptotic function of cyclin D1, demonstrated by sub-G(1) analysis and annexin V staining, may contribute to its cellular transforming and cooperative oncogenic properties.

Adenovirus E1A Proteins↗
PubMed1999

Down-regulation of cyclin D1 by transcriptional repression in MCF-7 human breast carcinoma cells induced by flavopiridol.

Flavopiridol is a novel flavonoid that induces cell cycle arrest at different stages of the cell cycle because of the inhibition of cyclin-dependent kinases (cdks). In previous studies from our laboratory, (B. A. Carlson et al., Cancer Res., 56: 2973-2978, 1996), we observed that exposure of the MCF-7 breast carcinoma cell line to flavopiridol resulted in G1-S arrest, which was associated with the loss of cdk4 and cdk2 activity by 24 h of exposure. Along with this inhibition, flavopiridol decreased total cyclin-D protein levels in this cell line. In this work, we demonstrate that using isoform-specific antibodies, flavopiridol induces an early (by 6 h) decrease in cyclin D1 protein levels. This decline is followed by a decline in cyclin D3 with no effect on cyclin D2 or cyclin E levels by 10 h. Furthermore, at early time points (up to 8 h), the activity of cdk4 and the expression of endogenous phosphorylated retinoblastoma species from intact cells exposed to flavopiridol are unchanged. Thus, the decline in cdk4 activity and the induction of retinoblastoma hypophosphorylation follows cyclin D1 decline. Turnover studies demonstrate that the half-life of cyclin D1 (approximately 30 min) is not shortened in flavopiridol-exposed cells, and that the turnover of cdk4-bound cyclin D1 is unaltered. However, steady-state levels of cyclin D1 mRNA display a significant decrease by 4 h of flavopiridol treatment, with total disappearance by 8 h. This mRNA decline is not abrogated by the presence of cycloheximide. Furthermore, we have found that flavopiridol specifically represses the activity of the full-length cyclin D1 promoter linked to a luciferase reporter gene. In summary, we have found that the flavopiridol-induced decline in cyclin D1 is an early event, specific and, at least in part, due to the transcriptional repression of the cyclin D1 promoter. These results extend our understanding of flavopiridol's action to include regulation of cyclin D1 transcription.

Antineoplastic Agents↗
PubMed1999

Integration of Rac-dependent regulation of cyclin D1 transcription through a nuclear factor-kappaB-dependent pathway.

The small GTP-binding protein Rac1, a member of the Ras superfamily, plays a fundamental role in cytoskeleton reorganization, cellular transformation, the induction of DNA synthesis, and superoxide production. Cyclin D1 abundance is rate-limiting in normal G(1) phase progression, and the abundance of cyclin D1 is induced by activating mutations of both Ras and Rac1. Nuclear factor-kappaB (NF-kappaB) proteins consist of cytoplasmic hetero- or homodimeric Rel-related proteins complexed to a member of the IkappaB family of inhibitor proteins. In the current studies, activating mutants of Rac1 (Rac(Leu-61), Rac(Val-12)) induced cyclin D1 expression and the cyclin D1 promoter in NIH 3T3 cells. Induction of cyclin D1 by Rac1 required both an NF-kappaB and an ATF-2 binding site. Inhibiting NF-kappaB by overexpression of an NF-kappaB trans-dominant inhibitor (nonphosphorylatable IkappaBalpha) reduced cyclin D1 promoter activation by the Rac1 mutants, placing NF-kappaB in a pathway of Rac1 activation of cyclin D1. Specific amino acid mutations in the amino-terminal effector domain of Rac(Leu-61) had comparable effects on NF-kappaB transcriptional activity and activation of the cyclin D1 promoter. The NF-kappaB factors Rel A (p65) and NF-kappaB(1) (p50) induced the cyclin D1 promoter, requiring both the NF-kappaB binding site and the ATF-2 site. Stable overexpression of Rac(Leu-61) increased binding of Rel A and NF-kappaB(1) to the cyclin D1 promoter NF-kappaB site. Activation of Rac1 in NIH 3T3 cells induces both NF-kappaB binding and activity and enhances expression of cyclin D1 through an NF-kappaB and ATF-2 site in the proximal promoter, suggesting a critical role for NF-kappaB in cell cycle regulation through cyclin D1 and Rac1.

3T3 Cells↗
PubMed1999

Stat3 as an oncogene.

STATs are latent transcription factors that mediate cytokine- and growth factor-directed transcription. In many human cancers and transformed cell lines, Stat3 is persistently activated, and in cell culture, active Stat3 is either required for transformation, enhances transformation, or blocks apoptosis. We report that substitution of two cysteine residues within the C-terminal loop of the SH2 domain of Stat3 produces a molecule that dimerizes spontaneously, binds to DNA, and activates transcription. The Stat3-C molecule in immortalized fibroblasts causes cellular transformation scored by colony formation in soft agar and tumor formation in nude mice. Thus, the activated Stat3 molecule by itself can mediate cellular transformation and the experiments focus attention on the importance of constitutive Stat3 activation in human tumors.

3T3 Cells↗
PubMed1999

Protein kinase Cdelta inhibition of S-phase transition in capillary endothelial cells involves the cyclin-dependent kinase inhibitor p27(Kip1).

Distinct protein kinase C (PKC) isoforms differentially regulate cellular proliferation in rat microvascular endothelial cells (EC). Overexpression of PKCalpha has little effect on proliferation, whereas PKCdelta slows endothelial cell proliferation and induces S-phase arrest. Analyses were performed on EC overexpressing PKCalpha (PKCalphaEC) or PKCdelta (PKCdeltaEC) to determine the role of specific cell cycle regulatory proteins in the PKCdelta-induced cell cycle arrest. Serum-induced stimulation of cyclins D1, E, and A-associated kinase activity was delayed by 12 h in the PKCdeltaEC line in association with S-phase arrest. However, the protein levels for cyclins D1, E, and A were similar. Nuclear accumulation of cyclin D1 protein in response to serum was also delayed in PKCdeltaEC. In the PKCdeltaEC line, serum induced p27(Kip1) but not p16(Ink4a) or p21(Cip1). Serum did not affect p27(Kip1) levels in the control vascular endothelial cell line. Immunoprecipitation-Western blotting analysis of p27(Kip1) showed serum stimulation of the vascular endothelial cell line resulted in increased amounts of cyclin D1 bound to p27(Kip1). In the PKCdeltaEC line, serum did not increase the amount of cyclin D1 bound to p27(Kip1). Transfection of full-length p27(Kip1) antisense into the PCKdeltaEC line reversed the S-phase arrest and resulted in normal cell cycle progression, suggesting a critical role for p27(Kip1) in the PKCdelta-mediated S-phase arrest.

Animals↗
PubMed1999

The cyclin D1 gene is a target of the beta-catenin/LEF-1 pathway.

beta-Catenin plays a dual role in the cell: one in linking the cytoplasmic side of cadherin-mediated cell-cell contacts to the actin cytoskeleton and an additional role in signaling that involves transactivation in complex with transcription factors of the lymphoid enhancing factor (LEF-1) family. Elevated beta-catenin levels in colorectal cancer caused by mutations in beta-catenin or by the adenomatous polyposis coli molecule, which regulates beta-catenin degradation, result in the binding of beta-catenin to LEF-1 and increased transcriptional activation of mostly unknown target genes. Here, we show that the cyclin D1 gene is a direct target for transactivation by the beta-catenin/LEF-1 pathway through a LEF-1 binding site in the cyclin D1 promoter. Inhibitors of beta-catenin activation, wild-type adenomatous polyposis coli, axin, and the cytoplasmic tail of cadherin suppressed cyclin D1 promoter activity in colon cancer cells. Cyclin D1 protein levels were induced by beta-catenin overexpression and reduced in cells overexpressing the cadherin cytoplasmic domain. Increased beta-catenin levels may thus promote neoplastic conversion by triggering cyclin D1 gene expression and, consequently, uncontrolled progression into the cell cycle.

Adenomatous Polyposis Coli Protein↗
PubMed1999

pp60(v-src) induction of cyclin D1 requires collaborative interactions between the extracellular signal-regulated kinase, p38, and Jun kinase pathways. A role for cAMP response element-binding protein and activating transcription factor-2 in pp60(v-src) signaling in breast cancer cells.

The cyclin D1 gene is overexpressed in breast tumors and encodes a regulatory subunit of cyclin-dependent kinases that phosphorylate the retinoblastoma protein. pp60(c-src) activity is frequently increased in breast tumors; however, the mechanisms governing pp60(c-src) regulation of the cell cycle in breast epithelium are poorly understood. In these studies, pp60(v-src) induced cyclin D1 protein levels and promoter activity (48-fold) in MCF7 cells. Cyclin D1-associated kinase activity and protein levels were increased in mammary tumors from murine mammary tumor virus-pp60(c-src527F) transgenic mice. Optimal induction of cyclin D1 by pp60(v-src) involved the extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase members of the mitogen-activated protein kinase family. Cyclin D1 promoter activation by pp60(v-src) involved a cAMP response element-binding protein (CREB)/activating transcription factor 2 (ATF-2) binding site. Dominant negative mutants of CREB and ATF-2 but not c-Jun inhibited pp60(v-src) induction of cyclin D1. pp60(v-src) induction of CREB was blocked by the p38 inhibitor SB203580 or by mutation of CREB at Ser133. pp60(v-src) induction of ATF-2 was abolished by the c-Jun N-terminal kinase inhibitor JNK-interacting protein-1 or by mutation of ATF-2 at Thr69 and Thr71. CREB and ATF-2, which bind to a common pp60(v-src) response element, are transcriptionally activated by distinct mitogen-activated protein kinases. Induction of cyclin D1 activity by pp60(v-src) may contribute to breast tumorigenesis through phosphorylation and inactivation of the retinoblastoma protein.

Activating Transcription Factor 2↗
PubMed1999

Transcriptional regulation of the cyclin D1 promoter by STAT5: its involvement in cytokine-dependent growth of hematopoietic cells.

STAT5 is a member of a family of transcription factors that participate in the signal transduction pathways of many hormones and cytokines. Although STAT5 is suggested to play a crucial role in the biological effects of cytokines, its downstream target(s) associated with cell growth control is largely unknown. In a human interleukin-3 (IL-3)-dependent cell line F-36P-mpl, the induced expression of dominant-negative (dn)-STAT5 and of dn-ras led to inhibition of IL-3-dependent cell growth, accompanying the reduced expression of cyclin D1 mRNA. Also, both constitutively active forms of STAT5A (1*6-STAT5A) and ras (H-rasG12V) enabled F-36P-mpl cells to proliferate without added growth factors. In NIH 3T3 cells, 1*6-STAT5A and H-rasG12V individually and cooperatively transactivated the cyclin D1 promoter in luciferase assays. Both dn-STAT5 and dn-ras suppressed IL-3-induced cyclin D1 promoter activities in F-36P-mpl cells. Using a series of mutant cyclin D1 promoters, 1*6-STAT5A was found to transactivate the cyclin D1 promoter through the potential STAT-binding sequence at -481 bp. In electrophoretic mobility shift assays, STAT5 bound to the element in response to IL-3. Furthermore, the inhibitory effect of dn-STAT5 on IL-3-dependent growth was restored by expression of cyclin D1. Thus STAT5, in addition to ras signaling, appears to mediate transcriptional regulation of cyclin D1, thereby contributing to cytokine-dependent growth of hematopoietic cells.

Cell Cycle↗
PubMed1999

NF-kappaB controls cell growth and differentiation through transcriptional regulation of cyclin D1.

Accumulating evidence implicates the transcription factor NF-kappaB as a positive mediator of cell growth, but the molecular mechanism(s) involved in this process remains largely unknown. Here we use both a skeletal muscle differentiation model and normal diploid fibroblasts to gain insight into how NF-kappaB regulates cell growth and differentiation. Results obtained with the C2C12 myoblast cell line demonstrate that NF-kappaB functions as an inhibitor of myogenic differentiation. Myoblasts generated to lack NF-kappaB activity displayed defects in cellular proliferation and cell cycle exit upon differentiation. An analysis of cell cycle markers revealed that NF-kappaB activates cyclin D1 expression, and the results showed that this regulatory pathway is one mechanism by which NF-kappaB inhibits myogenesis. NF-kappaB regulation of cyclin D1 occurs at the transcriptional level and is mediated by direct binding of NF-kappaB to multiple sites in the cyclin D1 promoter. Using diploid fibroblasts, we demonstrate that NF-kappaB is required to induce cyclin D1 expression and pRb hyperphosphorylation and promote G(1)-to-S progression. Consistent with results obtained with the C2C12 differentiation model, we show that NF-kappaB also promotes cell growth in embryonic fibroblasts, correlating with its regulation of cyclin D1. These data therefore identify cyclin D1 as an important transcriptional target of NF-kappaB and reveal a mechanism to explain how NF-kappaB is involved in the early phases of the cell cycle to regulate cell growth and differentiation.

3T3 Cells↗
PubMed1999

Activator protein-2 mediates transcriptional activation of the CYP11A1 gene by interaction with Sp1 rather than binding to DNA.

The ovine P45 side chain cleavage (CYP11A1) enzyme gene, which catalyzes the initial enzymatic step in steroid hormone biosynthesis is transcriptionally regulated in cultured steroidogenic human trophoblastic JEG-3 cells. The ovine CYP11A1 promoter contains two GC-rich footprinted regions referred to as ovine footprints 5 (OF5) and OF3, which are well conserved among the CYP11A1 promoters of different species. These GC-rich sequences resemble activator protein-2 (AP-2)/Sp1 binding sites and were previously implicated in basal and cAMP-regulated activity of the bovine and ovine CYP11A1 promoters. In the current studies, AP-2 induced the ovine CYP11A1 promoter 4.5-fold in JEG-3 cells with full induction requiring the previously defined cAMP-responsive elements. Point mutation of OF3 abolished induction by AP-2, and OF3 was sufficient for induction by AP-2 when linked to a heterologous promoter. AP-2 induction of the CYP11A1 promoter required the basic region (N165-N278) and the carboxy terminus of AP-2 (N413-N437). In the course of investigating the mechanisms by which OF5 and OF3 regulated CYP11A1 transcription, we found that OF5 and OF3 bound Sp1 and Sp3 in JEG-3 cells. AP-2 did not bind OF5 or OF3 directly but rather formed a multiprotein complex with Sp1 in JEG-3 cells. AP-2 associated directly with Sp1 in vitro requiring the AP-2 basic region and the Sp1 carboxy terminus. AP-2 induced Sp1/Sp3 activity independently of AP-2 binding to DNA using a GAL4 paradigm. The Sp1 and Sp3 transactivation domains were linked to the DNA-binding domain of GAL4, and their activity was assessed using a luciferase reporter gene containing only the GAL4 DNA-binding sites linked to the minimal TATA site. AP-2 induced Sp1/ Sp3-GAL4 activity 3- to 4-fold, requiring both the amino and extreme carboxy terminus of AP-2. We conclude that AP-2 can bind to and stimulate Sp1 activity and induces the ovine CYP11A1 promoter through conserved Sp1/Sp3-binding sites in JEG-3 cells. The induction of Sp1 activity by AP-2 may contribute to the induction of other genes that bind Sp1.

Animals↗
PubMed1998

Amyloid beta-peptide stimulates nitric oxide production in astrocytes through an NFkappaB-dependent mechanism.

The major pathological features of Alzheimer's disease (AD) include amyloid plaques composed primarily of the beta-amyloid (Abeta) peptide, degenerating neurons and neurofibrillary tangles, and the presence of numerous activated astrocytes and microglia. Although extensive genetic data implicate Abeta in the neurodegenerative cascade of AD, the molecular mechanisms underlying its effects on neurons and glia and the relationship between glial activation and neuronal death are not well defined. Abeta has been shown to induce glial activation, and a growing body of evidence suggests that activated glia contribute to neurotoxicity through generation of inflammatory cytokines and neurotoxic free radicals, such as nitric oxide (NO), potent sources of oxidative stress known to occur in AD. It is therefore crucial to identify specific Abeta-induced molecular pathways mediating these responses in activated glia. We report that Abeta stimulates the activation of the transcription factor NFkappaB in rat astrocytes, that NFkappaB activation occurs selectively from p65 transactivation domain 2, and that Abeta-induced NO synthase expression and NO production occur through an NFkappaB-dependent mechanism. This demonstration of how Abeta couples an intracellular signal transduction pathway involving NFkappaB to a potentially neurotoxic response provides a key mechanistic link between Abeta and the generation of oxidative damage. Our results also suggest possible molecular targets upon which to focus future drug discovery efforts for AD.

Alzheimer Disease↗
PubMed1998

FSH bioactivity in commercial preparations of gonadotropins.

During the past 2 decades, commercial preparations of FSH have been extensively used to superovulate cattle. The problems that have been encountered in superovulation of cattle include high variability in the ovulation rate and subsequent yield of viable embryos. The lack of predictability in superovulatory trials has been attributed to difficulties in standardizing the potency of commercial FSH preparations. Traditionally, FSH potency has been tested in bioassays that utilize specific responses in whole animals or primary cell cultures. Whole animal bioassays lack sensitivity, while primary cell culture bioassays, which use fresh cells, have inherent variability within each preparation. An FSH bioassay that employed a stable chimeric cell line expressing the human FSH-R was used to provide an accurate measurement of FSH bioactivity. The hormonal potency of 2 commercial preparations of FSH used to superovulate cattle was determined using FSH immuno- and bioassays. Commercial FSH preparations differed in potency. One commercial product, prepared in 4 different years, showed no difference in the immunoactive levels of FSH. In the same product stored under identical conditions, FSH bioactivity varied from year to year. There was variability in FSH bioactivity both between and within commercial products. The lack of correlation between bioactivity and immunoactivity of commercial FSH preparations may explain, in part, the variability observed in superovulation of cattle.

Animals↗
PubMed1998

Papillary cystic neoplasm of the pancreas: a report of three pediatric cases and literature review.

BACKGROUND/PURPOSE: Papillary cystic neoplasms are rare pancreatic tumors that typically present in women in their third decade of life. Few cases have been reported in children. METHODS/RESULTS: The authors report on three pediatric patients: a 10-year-old boy, an 11-year-old girl, and a 14-year-old girl. The authors have reviewed the existing literature on papillary cystic neoplasms of the pancreas and suggest that these tumors probably arise early in life, grow slowly, and metastasize infrequently. CONCLUSION: Even when these tumors metastasize, patients seldom die as a result of the malignancy.

Adolescent↗
PubMed1998

Inhibition of cyclin D1 kinase activity is associated with E2F-mediated inhibition of cyclin D1 promoter activity through E2F and Sp1.

Coordinated interactions between cyclin-dependent kinases (Cdks), their target "pocket proteins" (the retinoblastoma protein [pRB], p107, and p130), the pocket protein binding E2F-DP complexes, and the Cdk inhibitors regulate orderly cell cycle progression. The cyclin D1 gene encodes a regulatory subunit of the Cdk holoenzymes, which phosphorylate the tumor suppressor pRB, leading to the release of free E2F-1. Overexpression of E2F-1 can induce apoptosis and may either promote or inhibit cellular proliferation, depending upon the cell type. In these studies overexpression of E2F-1 inhibited cyclin D1-dependent kinase activity, cyclin D1 protein levels, and promoter activity. The DNA binding domain, the pRB pocket binding region, and the amino-terminal Sp1 binding domain of E2F-1 were required for full repression of cyclin D1. Overexpression of pRB activated the cyclin D1 promoter, and a dominant interfering pRB mutant was defective in cyclin D1 promoter activation. Two regions of the cyclin D1 promoter were required for full E2F-1-dependent repression. The region proximal to the transcription initiation site at -127 bound Sp1, Sp3, and Sp4, and the distal region at -143 bound E2F-4-DP-1-p107. In contrast with E2F-1, E2F-4 induced cyclin D1 promoter activity. Differential regulation of the cyclin D1 promoter by E2F-1 and E2F-4 suggests that E2Fs may serve distinguishable functions during cell cycle progression. Inhibition of cyclin D1 abundance by E2F-1 may contribute to an autoregulatory feedback loop to reduce pRB phosphorylation and E2F-1 levels in the cell.

3T3 Cells↗