TAF5L functions as transcriptional coactivator of MITF involved in the immune response of the clam Meretrix petechialis

TAF5L is a component of the P300/CBP-associated factor (PCAF) histone acetylase complex, which serves as a coactivator and takes part in basal transcription such as promoter recognition, complex assembly and transcription initiation. In our study, the full-length sequence of MpTAF5L was identified and characterized in the clam M. petechialis. Sequence analysis showed that the predicted MpTAF5L protein had a N-terminal TAF5-NTD2 domain and a C-terminal WD40-repeats domain. The annotation and evolutionary analysis revealed MpTAF5L had close evolutionary relationship with other invertebrate species. Tissue distribution analysis of TAF5L claimed that it was highly expressed in the mantle, adductor muscle, foot and hepatopancreas. The mRNA expression of MpTAF5L was significantly up-regulated after Vibrio parahaemolyticus challenge, indicating its involvement in the immune response of clam. Yeast two-hybrid assays verified that MpTAF5L can interact with MpMITF (a critical immune-related transcription factor), and our further research clarified this interaction depended upon the N-terminal TAF5-NTD2 domain of MpTAF5L. Moreover, the mRNA expression of MpBcl-2 (a target gene of MITF) was significantly decreased but the mRNA expression of MpMITF was not significantly changed after knockdown of MpTAF5L, which indicated the reduction of MpMITF regulating activity at the same time. These results revealed that MpTAF5L interacted with MpMITF and enhanced the activation of MpMITF, which plays roles in the immune defense against V. parahaemolyticus.

Inhibition of p300/CBP-Associated Factor Attenuates Renal Tubulointerstitial Fibrosis through Modulation of NF-kB and Nrf2

p300/CBP-associated factor (PCAF), a histone acetyltransferase, is involved in many cellular processes such as differentiation, proliferation, apoptosis, and reaction to cell damage by modulating the activities of several genes and proteins through the acetylation of either the histones or transcription factors. Here, we examined a pathogenic role of PCAF and its potential as a novel therapeutic target in the progression of renal tubulointerstitial fibrosis induced by non-diabetic unilateral ureteral obstruction (UUO) in male C57BL/6 mice. Administration of garcinol, a PCAF inhibitor, reversed a UUO-induced increase in the renal expression of total PCAF and histone 3 lysine 9 acetylation and reduced positive areas of trichrome and α-smooth muscle actin and collagen content. Treatment with garcinol also decreased mRNA levels of transforming growth factor-β, matrix metalloproteinase (MMP)-2, MMP-9, and fibronectin. Furthermore, garcinol suppressed nuclear factor-κB (NF-κB) and pro-inflammatory cytokines such as tumor necrosis factor-α and IL-6, whereas it preserved the nuclear expression of nuclear factor erythroid-derived 2-like factor 2 (Nrf2) and levels of Nrf2-dependent antioxidants including heme oxygense-1, catalase, superoxide dismutase 1, and NAD(P)H:quinone oxidoreductase 1. These results suggest that the inhibition of inordinately enhanced PCAF could mitigate renal fibrosis by redressing aberrant balance between inflammatory signaling and antioxidant response through the modulation of NF-κB and Nrf2.

LPS depletes PHLPP levels in macrophages through the inhibition of SP1 dependent transcriptional regulation

We have previously reported that bacterial endotoxin LPS attenuates expression of PHLPP, a ser/thr phosphatase, at both transcript and protein levels in different immune cells, however the underlying molecular mechanism is unknown and is of significant interest. Here, in line with the decreased transcript levels upon LPS treatment, we observed that LPS caused significant reduction in PHLPP promoter activity. We observed that SP1, a transcription factor frequently associated with inflammation, was recruited to the PHLPP promoter region. Ectopic expression of SP1 enhanced both transcript and protein levels of PHLPP while knockdown of SP1 or pharmacological inhibition of SP1 DNA binding by mithramycin reduced PHLPP expression. Moreover, over-expression of SP1 co-activators CBP/p300 augmented SP1 driven PHLPP promoter activity. Of note, LPS treatment depleted SP1 and CBP protein levels due to which recruitment of SP1 to PHLPP promoter was reduced. Further, we found that re-introduction of SP1 restored promoter activity and transcript levels of PHLPP in LPS stimulated cells. Collectively, our data revealed the molecular mechanism underlying the regulation of PHLPP expression during LPS induced macrophage inflammatory response.

Ubiquitin-mediated NFκB degradation pathway

The nuclear factor κB (NFκB) transcription factor plays critical roles in inflammation and immunity. The dysregulation of NFκB is associated with inflammatory and autoimmune diseases and cancer. NFκB activation is negatively regulated by the ubiquitin-dependent proteasomal degradation pathway. In the present review, we discuss recent advances in our understanding of how ubiquitin ligases regulate the NFκB degradation pathway.

Coordinated histone H3 methylation and acetylation regulate physiologic and pathologic fas ligand gene expression in human CD4+ T cells

Activation-induced Fas ligand (FasL) mRNA expression in CD4+ T cells is mainly controlled at transcriptional initiation. To elucidate the epigenetic mechanisms regulating physiologic and pathologic FasL transcription, TCR stimulation-responsive promoter histone modifications in normal and alcohol-exposed primary human CD4+ T cells were examined. TCR stimulation of normal and alcohol-exposed cells led to discernible changes in promoter histone H3 lysine trimethylation, as documented by an increase in the levels of transcriptionally permissive histone 3 lysine 4 trimethylation and a concomitant decrease in the repressive histone 3 lysine 9 trimethylation. Moreover, acetylation of histone 3 lysine 9 (H3K9), a critical feature of the active promoter state that is opposed by histone 3 lysine 9 trimethylation, was significantly increased and was essentially mediated by the p300-histone acetyltransferase. Notably, the degree of these coordinated histone modifications and subsequent recruitment of transcription factors and RNA polymerase II were significantly enhanced in alcohol-exposed CD4+ T cells and were commensurate with the pathologic increase in the levels of FasL mRNA. The clinical relevance of these findings is further supported by CD4+ T cells obtained from individuals with a history of heavy alcohol consumption, which demonstrate significantly greater p300-dependent H3K9 acetylation and FasL expression. Overall, these data show that, in human CD4+ T cells, TCR stimulation induces a distinct promoter histone profile involving a coordinated cross-talk between histone 3 lysine 4 and H3K9 methylation and acetylation that dictates the transcriptional activation of FasL under physiologic, as well as pathologic, conditions of alcohol exposure.

Nrf2 expression and activity in human T lymphocytes: stimulation by T cell receptor activation and priming by inorganic arsenic and tert-butylhydroquinone

The transcription factor nuclear factor-erythroid 2-related-2 (Nrf2) controls cellular redox homeostasis and displays immunomodulatory properties. Nrf2 alters cytokine expression in murine T cells, but its effects in human T lymphocytes are unknown. This study investigated the expression and activity of Nrf2 in human activated CD4(+) T helper lymphocytes (Th cells) that mediate the adaptive immune response. Th cells were isolated from peripheral blood mononuclear cells and activated with antibodies against CD3 and CD28, mimicking physiologic Th cell stimulation by dendritic cells. Nrf2 is hardly detectable in unstimulated Th cells. Activation of Th cells rapidly and strongly increases the levels of Nrf2 protein by increasing NRF2 gene transcription. Th cell activation also enhances mRNA and protein levels of Nrf2 target genes encoding antioxidant enzymes. Blocking Nrf2 expression using chemical inhibitors or siRNAs prevents these gene inductions. Pretreatment with inorganic arsenic, a Nrf2 inducer that does not alter NRF2 gene expression, increases protein level and transcriptional activity of Nrf2 induced by Th cell stimulation. Inorganic arsenic enhances nuclear translocation of Nrf2, its interaction with the coactivator protein p300, and its DNA binding activity. Inhibition of Nrf2 expression abrogates the effects of inorganic arsenic on mRNA levels of antioxidant genes, but does not alter the expression of IL-2, TNF-α, interferon-γ, or IL-17 in Th cells activated in the absence or presence of the metalloid. In conclusion, this study demonstrates for the first time that stimulation of human Th cells increases transcription of the NRF2 gene and activity of the Nrf2 protein. However, modulation of Nrf2 levels does not modify the secretion of inflammatory cytokines from these T lymphocytes.

Polycomb antagonizes p300/CREB-binding protein-associated factor to silence FOXP3 in a Kruppel-like factor-dependent manner

Inducible gene expression underlies the epigenetically inherited differentiation program of most immune cells. We report that the promoter of the FOXP3 gene possesses two distinct functional states: an "off state" mediated by the polycomb histone methyltransferase complex and a histone acetyltransferase-dependent "on state." Regulating these states is the presence of a Kruppel-like factor (KLF)-containing Polycomb response element. In the KLF10(-/-) mouse, the FOXP3 promoter is epigenetically silenced by EZH2 (Enhancer of Zeste 2)-mediated trimethylation of Histone 3 K27; thus, impaired FOXP3 induction and inappropriate adaptive T regulatory cell differentiation results in vitro and in vivo. The epigenetic transmittance of adaptive T regulatory cell deficiency is demonstrated throughout more than 40 generations of mice. These results provide insight into chromatin remodeling events key to phenotypic features of distinct T cell populations.

Transcriptional activation of mouse TCR Jγ4 germline promoter by STAT5

The IL-7 receptor (IL-7R) controls the accessibility of mouse TCRgamma locus, by recruiting STAT5 and transcriptional coactivators to the Jgamma1 germline promoter and inducing histone acetylation at nearby chromatin. Although a STAT motif is present in Jgamma4 germline promoter, it is still unknown whether STAT5 regulates the transcription of the Jgamma4 promoter. Here, we showed that cytokine stimulation induced Jgamma4-Cgamma4 germline transcripts in a pre-T cell line, Scid.adh, and a hematopoietic cell line, Ba/F3. A STAT consensus motif was present in 5' region of Jgamma4 gene segment. We found that STAT5 bound to the STAT motif of the Jgamma4 germline promoter in vitro by EMSA. In addition, we detected by chromatin immunoprecipitation assay that STAT5 was recruited to the endogenous Jgamma4 chromatin in Ba/F3 cells after cytokine stimulation. Finally, using reporter assay, we showed that the Jgamma4 germline promoter was activated by STAT5 and that mutation in the STAT motif abrogated the activity. Furthermore, this transactivation was augmented by transcriptional coactivators, CBP and p300. Collectively, these results demonstrate that STAT5 binds to the STAT motif in the Jgamma4 promoter and induces germline transcription. Thus, this study indicates that the IL-7R/STAT5 signal controls the transcription and accessibility of different clusters in the TCRgamma locus.