Disease relevance of E2F4

• Herpes simplex virus induces intracellular redistribution of E2F4 and accumulation of E2F pocket protein complexes [1].
• Functional interaction between E2F-4 and p130: evidence for distinct mechanisms underlying growth suppression by different retinoblastoma protein family members [2].
• Consistent with this observation, immunochemical staining of cell lines and of 364 samples of ovarian cancer tissue show that the expression of E2F1 and E2F4 proteins is much higher in ovarian cancer cells than in normal ovarian epithelial cells, and that increased expression of E2Fs was negatively correlated with ARHI expression (P < 0.05) [3].
• These results suggest that mutations of the E2F4 gene, presumably caused by an abnormality of one of the DNA repair genes, may play an important role in development of ATL and childhood ALL [4].
• Mutations of the E2F4 gene in hematological malignancies having microsatellite instability [4].

High impact information on E2F4

• Previously known as the ultimate recipients of cdk regulatory signals, E2F4/5 and p107 act here as transducers of TGFbeta receptor signals upstream of cdk [5].
• Among approximately 1200 genes expressed during cell cycle entry, we found that the promoters of 127 were bound by the E2F4 transcription factor in primary fibroblasts [6].
• Probing a human CpG microarray with chromatin immunoprecipitated using an antibody to E2F4, we have identified 68 unique target loci; 15% are bidirectional promoters and 25% recruit E2F via a mechanism distinct from the defined consensus site [7].
• E2F4 and DP2 interact through an extensive protein-protein interface, and structural features of this interface suggest it contributes to the preference for heterodimers over homodimers in DNA binding [8].
• The asymmetry in the extended binding site TTTc/gGCGCc/g is associated with an amino-terminal extension of E2F4, in which an arginine binds in the minor groove near the TTT stretch [8].

Chemical compound and disease context of E2F4

• We observed previously that all-trans retinoic acid (t-RA) arrests the growth of HBE cells in the G0 phase of the cell cycle through activation of retinoic acid receptor-dependent pathways, which enhances the association of E2F-4 with retinoblastoma protein family members, converting E2F into a transcriptional suppressor [9].
• N-Acetylcysteine enhances UV-mediated caspase-3 activation, fragmentation of E2F-4, and apoptosis in human C8161 melanoma: inhibition by ectopic Bcl-2 expression [10].
• It is interesting to note that the mutations of the serine (AGC)13 repeats within the E2F-4 gene were found only in the squamous cell carcinoma portions of them, whereas such alterations were not detected in any of the adenocarcinomatous portions [11].

Biological context of E2F4

• We found that p130 and E2F4 cooperatively repress a common set of genes under each growth arrest condition and showed that growth arrest is achieved through repression of a core set of genes involved not only in cell cycle control but also mitochondrial biogenesis and metabolism [12].
• We also show that in quiescent normal human cells this entire RBP1-mSIN3-SAP30-HDAC complex colocalizes with both RB family members and E2F4 in a limited number of discrete regions of the nucleus that in other studies have been shown to represent the initial origins of DNA replication following growth stimulation [13].
• Genotoxic stress induces expression of E2F4, leading to its association with p130 in prostate carcinoma cells [14].
• To test the functional implications of these observations, we transfected HaCaT keratinocytes with plasmids coding for E2F1 and E2F4 [15].
• Concomitant with its redistribution, the apparent molecular weight of total and p107-associated E2F4 increased, at least partially as a result of protein phosphorylation [1].

Anatomical context of E2F4

• By gel shift analysis, we show that in mitogen-dependent normal melanocytes, external growth factors tightly controlled the levels of growth-promoting free E2F DNA binding activity, composed largely of E2F2 and E2F4, and the growth-suppressive E2F4-p130 complexes [16].
• In contrast, overexpression of E2F2 or E2F3a results in only a marginal delay of chondrocyte maturation, and increased E2F4 levels have no effect [17].
• Opposite functions for E2F1 and E2F4 in human epidermal keratinocyte differentiation [15].
• We also observed an increase in electrophoretic mobility of the predominant E2F components, DP1 and E2F4, as B-lymphocytes progressed from G0 into early G1 [18].
• E2F1 induces PPARgamma transcription during clonal expansion, whereas E2F4 represses PPARgamma expression during terminal adipocyte differentiation [19].

Associations of E2F4 with chemical compounds

• We showed, by performing chromatin immunoprecipitation that, in response to UV irradiation but not doxorubicin treatment, E2F4 accumulated on the MCM10 and TopBP1 promoters [20].
• Vitamin C decreased the expression levels of cyclin D1, E2F1, and E2F4 in B[a]P-stimulated HELF cells [21].
• We have found that E2F4 is actively exported from the nucleus and that leptomycin B, a specific inhibitor of nuclear export, inhibits this process [22].
• This tumor also carried a deletion mutation in the serine (AGC) repeat of the E2F4 gene [23].
• We find that E2F4 levels are diminished following treatment with cyclin dependent kinase inhibitors (flavopiridol, roscovitine and BMS-387032) or with DNA damaging drugs (cisplatin and VP16) [24].

Physical interactions of E2F4

• Free E2F4 was found to be the predominant species bound to the E2F sites in proliferating cells [25].
• The E2F4/p130 pocket protein complex emerges as a new target of radiation in prostate carcinoma cells [14].
• In a first series of experiments, we showed that pRb2/p130 and p107 are not evenly distributed within the nucleus and that cell cycle-dependent binding with E2F4 changes also as a function of their subnuclear localization [26].
• Genomic signature tags designating putative beta-catenin-binding sites mapped to the 3'-untranslated region (3'-UTR) of the E2F4 gene [27].

Regulatory relationships of E2F4

• Conversely, E2F-1 overrode an RB-induced G1 block more efficiently than E2F-4 [2].
• In the present work, we examine the role of both E2F1 and E2F4 in apoptosis induced by three cyclin-dependent kinase inhibitors (roscovitine, BMS-387032, and flavopiridol) as well as by three established chemotherapeutic drugs (VP16, cisplatin and paclitaxel) [24].
• Therefore, TGF-beta signaling may suppress c-myc promoter activity by dissociating p300 from E2F-4 [28].
• Mutations in the HCF-1 kelch domain known to block cell growth abrogated E2F4 binding to the kelch domain in the absence but not in the presence of the juxtaposed basic region [29].

Other interactions of E2F4

• E2F-4, a new member of the E2F transcription factor family, interacts with p107 [30].
• These findings suggest that E2F-4 and E2F-5 may contribute to the regulation of early G1 events including the G0/G1 transition [31].
• Here we describe the characterization of cDNAs encoding two unusual E2Fs, E2F-4 and E2F-5, each identified by the ability of their gene product to interact with p130 in a yeast two-hybrid system [31].
• E2F-1 but not E2F-4 can overcome p16-induced G1 cell-cycle arrest [32].
• The expression levels of cyclin D1, E2F1, and E2F4 in B[a]P-treated transfectants were lower than those in B[a]P-treated HELF cells [21].

Analytical, diagnostic and therapeutic context of E2F4

• Using genome-wide chromatin immunoprecipitation, we show that there are distinct classes of genes directly regulated by unique combinations of E2F4, p107, and p130, including a group of genes specifically regulated in cycling cells [33].
• However, in contrast to E2F-1, E2F-4 and E2F-5 fail to bind pRb in a two-hybrid assay [31].
• Western blot studies showed that expression of cyclin D1, CDK2, and E2F4 were increased, and Rb levels were decreased in these cells [34].
• Northern blot analysis revealed upregulated E2F4 transcript levels in tumor cell lines [35].
• METHODS: Transgenic mice were generated by microinjection of constructs that contained E2F cDNAs (E2F3a, E2F4 or E2F5) linked to the mouse lens-specific alphaA-crystallin promoter [36].

References