Ets-2 Repressor Factor (ERF) mediates repression of the human cytomegalovirus major immediate-early promoter in undifferentiated non-permissive cells

Abstract

The repression of human cytomegalovirus immediate-early (IE) lytic gene expression is crucial for the maintenance of the latent viral state. By using conditionally permissive cell lines, which provide a good model for the differentiation state-dependent repression of IE gene expression, we have identified several cellular factors that bind to the major immediate-early promoter (MIEP) and whose expression is down-regulated after differentiation to a permissive phenotype. Here we show that the cellular protein Ets-2 Repressor Factor (ERF) physically interacts with the MIEP and represses MIEP activity in undifferentiated non-permissive T2 embryonal carcinoma cells. This factor binds to the dyad element and the 21 bp repeats within the MIEP -regions known to be important for the negative regulation of MIEP activity. Finally, we show that following differentiation to a permissive phenotype ERF's repressive effects are severely abrogated. INTRODUCTIONHuman cytomegalovirus (HCMV) is a betaherpesvirus whose sero-prevalence can vary from 50 to 90 % depending on the socio-economic status of the population. Following primary infection, which rarely causes disease in the immunocompetent, HCMV maintains a latent infection throughout the lifetime of the infected host. However, infection or reactivation in the immunocompromised, such as transplant recipients or AIDS patients, is associated with morbidity and mortality (reviewed in Alford & Britt, 1993).Productive HCMV infection and reactivation require an ordered cascade of gene expression and are dependent on the expression of the immediate-early (IE) gene products IE72 and IE86 (also known as IE1 and IE2 respectively). These IE proteins are potent and promiscuous transactivators of both cellular and viral genes, and serve to activate the viral early (E) gene promoters (Pizzorno et al., 1988;Malone et al., 1990), ultimately leading to viral DNA replication, expression of the viral late (L) genes and virus assembly. The expression of IE72 and IE86 is under the control of the major immediate-early promoter (MIEP), a highly complex region comprising a TATA box, an upstream imperfect dyad symmetry element (also termed the modulator), and an extremely powerful enhancer region made up of a series of 17, 18, 19 and 21 bp repeat motifs (reviewed in Meier & Stinski, 1996). MIEP activity is regulated by a myriad of positively and negatively acting cellular and viral proteins. For example, there are numerous nuclear factor-1 (NF-1) sites within the MIEP and the 18 and 19 bp repeat sequences contain NF-kB and cyclic AMPresponsive element binding protein (CREB) binding sites respectively (Meier & Stinski, 1996). Conversely, several studies using non-permissive cells have shown that the modulator and the 21 bp repeats are responsible for the inhibition of MIEP activity in such cells (Nelson et al., 1987;Lubon et al., 1989;Kothari et al., 1991).In vivo, monocytes have been identified as an important site of HCMV latency (Taylor-Wiedeman et al., 1991); these cells carry the viral genome in t...

Spi-C Has Opposing Effects to PU.1 on Gene Expression in Progenitor B Cells

“…Combined with the results discussed above that PU.1 and Spi-C have opposing activities on the Fc␥RIIb and IgH genes, our data suggest that Spi-C can inhibit PU.1 DNA binding either directly or indirectly. This type of inhibition is also observed with Ets-2 repressor factor, which acts as a repressor to Ets-2 activity (64). Therefore, we propose that when Spi-C expression is induced during normal B cell development, it inhibits PU.1 binding to target genes.…”

Differential Repression ofc-mycandcdc2Gene Expression by ERF and PE-1/METS

“…While ERF was previously shown to bind to and repress the human cytomegalovirus major immediate-early promoter, 31,32 endogenous cellular target genes have not been defined. The present studies demonstrating the ability of ERF to repress c-myc, and cdc2, previously identified as transcriptional targets of METS, is consistent with the high degree of sequence conservation of the ETS domains of METS and ERF that mediate sequence-specific DNA binding.…”

“…When growth factors are removed, ERF is dephosphorylated and transported back to the nucleus. 27,28,30 While inactivation of ERF by Ras/MAPK signaling has been demonstrated to be involved in erythroid differentiation and ERF has been shown to bind to and repress the human cytomegalovirus major immediate-early promoter (MIEP) in undifferentiated cells, 31,32 endogenous cellular targets of ERF and the molecular mechanisms responsible for its repressor function have not have been defined.…”

Analysis of latent viral gene expression in natural and experimental latency models of human cytomegalovirus and its correlation with histone modifications at a latent promoter

“…In direct contrast was the association of the MIEP with markers of transcriptional repression (Fig. 3b, lane 4) - probably due to the continued action of transcriptional repressors YY1 and ERF and the chromatin-remodelling enzymes with which they interact (Bain et al, 2003;Liu et al, 1994;Murphy et al, 2002;Wright et al, 2005).…”