Doctor of Philosophy, University of Kansas (2017)
T cell differentiation involves the dynamic regulation of FOXO1 expression, which rapidly declines after activation and is subsequently restored. Reexpression is impaired in na´ve CD4+ T cell responses from older individuals. Here, we show that FOXO1 promotes lysosome function through the induction of the key transcription factor for lysosomal proteins, TFEB. Subdued FOXO1 reexpression in activated CD4+ T cells impairs lysosomal activity, causing an expansion of multivesicular bodies (MVBs). Expansion of the MVB compartment induces the sequestration of glycogen synthase kinase 3? (GSK3?), thereby suppressing protein turnover and enhancing glycolytic activity. As a consequence, older activated CD4+ T cells develop features reminiscent of senescent cells. They acquire an increased cell mass, preferentially differentiate into short-lived effector T cells, and secrete exosomes that harm cells in the local environment through the release of granzyme B.
View details for DOI 10.1126/sciadv.aba1808
View details for PubMedID 32494657
View details for PubMedCentralID PMC7176426
The Gcn5 acetyltransferase functions in multiple acetyltransferase complexes in yeast and metazoans. Yeast Gcn5 is part of the large SAGA (Spt-Ada-Gcn5 acetyltransferase) complex and a smaller ADA acetyltransferase complex. In flies and mammals, Gcn5 (and its homolog pCAF) is part of various versions of the SAGA complex and another large acetyltransferase complex, ATAC (Ada2A containing acetyltransferase complex). However, a complex analogous to the small ADA complex in yeast has never been described in metazoans. Previous studies in Drosophila hinted at the existence of a small complex which contains Ada2b, a partner of Gcn5 in the SAGA complex. Here we have purified and characterized the composition of this complex and show that it is composed of Gcn5, Ada2b, Ada3 and Sgf29. Hence, we have named it the metazoan 'ADA complex'. We demonstrate that the fly ADA complex has histone acetylation activity on histones and nucleosome substrates. Moreover, ChIP-Sequencing experiments identified Ada2b peaks that overlap with another SAGA subunit, Spt3, as well as Ada2b peaks that do not overlap with Spt3 suggesting that the ADA complex binds chromosomal sites independent of the larger SAGA complex.
View details for DOI 10.1093/nar/gkz042
View details for Web of Science ID 000467965900017
View details for PubMedID 30715476
View details for PubMedCentralID PMC6468242
The Spt-Ada-Gcn5-acetyltransferase (SAGA) chromatin-modifying complex is a transcriptional coactivator that contains four different modules of subunits. The intact SAGA complex has been well characterized for its function in transcription regulation and development. However, little is known about the roles of individual modules within SAGA and whether they have any SAGA-independent functions. Here we demonstrate that the two enzymatic modules of Drosophila SAGA are differently required in oogenesis. Loss of the histone acetyltransferase (HAT) activity blocks oogenesis, while loss of the H2B deubiquitinase (DUB) activity does not. However, the DUB module regulates a subset of genes in early embryogenesis, and loss of the DUB subunits causes defects in embryogenesis. ChIP-seq (chromatin immunoprecipitation [ChIP] combined with high-throughput sequencing) analysis revealed that both the DUB and HAT modules bind most SAGA target genes even though many of these targets do not require the DUB module for expression. Furthermore, we found that the DUB module can bind to chromatin and regulate transcription independently of the HAT module. Our results suggest that the DUB module has functions within SAGA and independent functions.
View details for DOI 10.1101/gad.300988.117
View details for Web of Science ID 000410655400007
View details for PubMedID 28887412
View details for PubMedCentralID PMC5630023
Germinal centres support antibody affinity maturation and memory formation. Follicular T-helper cells promote proliferation and differentiation of antigen-specific B cells inside the follicle. A genetic deficiency in the inducible co-stimulator (ICOS), a classic CD28 family co-stimulatory molecule highly expressed by follicular T-helper cells, causes profound germinal centre defects, leading to the view that ICOS specifically co-stimulates the follicular T-helper cell differentiation program. Here we show that ICOS directly controls follicular recruitment of activated T-helper cells in mice. This effect is independent from ICOS ligand (ICOSL)-mediated co-stimulation provided by antigen-presenting dendritic cells or cognate B cells, and does not rely on Bcl6-mediated programming as an intermediate step. Instead, it requires ICOSL expression by follicular bystander B cells, which do not present cognate antigen to T-helper cells but collectively form an ICOS-engaging field. Dynamic imaging reveals ICOS engagement drives coordinated pseudopod formation and promotes persistent T-cell migration at the border between the T-cell zone and the B-cell follicle in vivo. When follicular bystander B cells cannot express ICOSL, otherwise competent T-helper cells fail to develop into follicular T-helper cells normally, and fail to promote optimal germinal centre responses. These results demonstrate a co-stimulation-independent function of ICOS, uncover a key role for bystander B cells in promoting the development of follicular T-helper cells, and reveal unsuspected sophistication in dynamic T-cell positioning in vivo.
View details for DOI 10.1038/nature12058
View details for Web of Science ID 000317984400045
View details for PubMedID 23619696