Control of IL-2Ralpha gene expression: structural changes within the proximal enhancer/core promoter during T-cell development

Abstract

During T-cell development in thymus, CD25, the IL-2 receptor alpha chain (IL-2Ralpha) is already expressed in early double-negative (DN) thymocytes where commitment to T-cell lineage has been established, but subsequently IL-2Ralpha is dramatically down-regulated for the remainder of T-cell development. The loss of IL-2Ralpha expression after expression of the pre-TCR alpha:beta complex on the cell surface is essential for the later specific responses of mature T cells. Using appropriate mouse models and DMS genomic footprinting, we showed that the TATA box in the core promoter region of the murine IL-2Ralpha locus was occupied only in DN CD25+ T cells. Further, by chromatin immunoprecipitation assays, we evidenced that down-regulation of IL-2Ralpha transcription correlated with (i) loss of the basal transcriptional machinery; (ii) dissociation of histone acetylase p300 and BRG1, a member of the ATP-dependent chromatin remodeling complex SWI/SNF; and (iii) histone N-termini dephosphorylation plus deacetylation. In contrast, occupancy of the proximal enhancer region (positive regulatory region I) was not detected by in vivo genomic footprinting though constitutive accessibility of the promoter region for DNase I digestion both in the DN and double-positive stages correlated with the constitutive association of CBP and PCAF to the IL-2Ralpha core promoter. These results exemplify one mechanism by which a promoter enables transcription to switch on and off during T-cell differentiation.

An AP-1 Binding Site in the Enhancer/Core Element of the HIV-1 Promoter Controls the Ability of HIV-1 To Establish Latent Infection

“…Latency is then maintained due to continuous transcription factor restriction. At that time, nucleosomes form on the LTR and are positioned by interaction with other cellular factors such as the SWI/ SNF complex BAF or PBAF (24), similar to reports for cellular genes, such as CD25, that are also not actively expressed in resting T cells but can be induced following T cell activation (10,25,64).…”

“…In many ways, the HIV-1 promoter is highly similar to a series of promoters of cellular genes that are not active in resting T cells but are upregulated following T cell activation. Among these, the most notable are cellular promoters for the interleukin-2 (IL-2) receptor (CD25), tumor necrosis factor alpha (TNF-␣), IL-2, IL-6, and IL-8 (9,10). All of these, as in the case of HIV-1, have a CD28-responsive element (CD28RE) that is crucial for efficient gene expression, and as for HIV-1 reactivation, stimulation of CD28 is essential for the efficient activation of these genes.…”

A General Survey of Thymocyte Differentiation by Transcriptional Analysis of Knockout Mouse Models

“…Notch1 has also been proposed as a Cd25 regulator, although the promoter region of Cd25 does not display canonical CBF1/Su(H) binding sites (49). Because Smarca4/Brg1 is recruited in the promoter region of Cd25 (23), this supports the notion that multiple pathways overlap in this cluster. The transcriptional analysis of Notch1 and Smarca4/Brg1 conditional targeting would be of great interest to resolve such a complexity and to help us to temporally organize these transcriptional processes.…”

“…Smarca4/Brg1 encoding a component of the SWI/SNF chromatinremodeling complex showed a coordinated expression with Cd25. Interestingly, Smarca4/Brg1 is known to be recruited in the Cd25 core promoter at the CD25 ϩ DN stages (23). The notion of functional links between genes of cluster B was reinforced by the simultaneous expression of several genes involved in calcium-dependent signaling pathways, as illustrated with the following: Calpain5/Capn5, FK506-bp5, the calcium/calmodulin-dependent eukaryotic elongation factor-2 kinase/Eef2k, and Camk2a/ CaMKII, which directly regulates the calcium channel, Cacna1h, also found in this cluster (24).…”

Transcription Factor Binding and Histone Modifications on the Integrated Proviral Promoter in Human T-cell Leukemia Virus-I-infected T-cells

“…The absence of PCAF was unexpected, since two previous studies have shown that PCAF interacts with Tax and stimulates viral transcription in transfection assays (50,51). Therefore, we performed immunoprecipitations using two additional anti-PCAF antibodies that have been successfully used in the past for ChIP analysis (52,53). In all cases, we were unable to immunoprecipitate HTLV-I promoter sequences (Fig.…”