STAT5 and BATF Promote Chromatin Accessibility in Helper T Cells
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The human immune system is made up of a complex set of biological processes and mechanisms that help our bodies fight against pathogens. When a foreign stimulus enters our body and slips past our innate immune cells, the immune system sends lymphocytes as a more advanced approach to attack.
There are 2 types of lymphocytes: B cells and T cells -- both of which mark the pathogen and create a tailored response to destroy it. B cells achieve this by producing antibodies specific to the pathogen to neutralize the threat, whereas cytotoxic T cells produce powerful enzymes that induce cell death.
Perhaps the most important part of the lymphocyte response belongs to the helper T cell (Th). Th cells help activate B cells and T cells by creating small proteins called cytokines, providing a blueprint for the lymphocytes to follow.
In order for Th cells to be effective in the immune response, they must be differentiated. Th cell differentiation is a lineage-based process that can be reversed and will vary depending on the immune response needed. It begins when cytokine signals and transcription factors open up the chromatin, allowing a group of transcription proteins called STAT to dictate which type of helper T cell it becomes.
In a study out of Indiana University, a team of researchers examined Th9 cells—a particular subset of Th cells constant in the immune response of humans and mice. These cells demonstrate antitumor activity, and help promote immunity to certain parasites and allergies.
The team led by Drs. Yongyao Fu and Mark Kaplan wanted to determine the factors that allow Th9 cells to produce a cytokine called interleukin-9 (IL-9), which aids cell proliferation and prevents apoptosis. Specifically, they focused on transcription factors STAT5 and BATF, and how they affect chromatin accessibility and gene expression, with hopes of finding potential therapies for IL-9-dependent immune response.
D.FACS analysis of IL-9 and pSTAT5 expression in Th9 cells transduced with control (Scr), STAT5a-specific, or STAT5b-specific shRNA. E. Chromatin accessibility analysis of Il9 gene locus in Th9 cells transduced with Scr-shRNA or STAT5a-shRNA retrovirus. F, G. H3K27me3 modification and BATF binding at the Il9 gene locus in Th9 cells transduced with Scr-shRNA or STAT5a-shRNA retrovirus on day 5.
The researchers performed a ChIP-seq on Th9 cells and identified BATF as a required factor in cell development and IL-9 production, but they discovered that BATF could only access the IL9 gene in a euchromatin state.
To determine the role STAT5 plays in accessibility of the IL9 gene, the researchers isolated Th9 cells from human peripheral blood mononuclear cells. In total, they collected between 0.4 million and 1 million Th9 cells. They added a STAT5 inhibitor on day 1 and monitored the cells for 5 days. On day 5, the team used the EpiQuik Chromatin Accessibility Kit to determine the chromatin state.
Then, they converted different Th9 cell cultures with short hairpin RNA (shRNA) that were specific for genes Stat5a and Stat5b. In these cultures, they found that both STAT5 activation and IL9 production had drastically decreased, implying that STAT5 is required to allow access to the IL9 locus.
D, E. Kinetic analysis of IL9 gene accessibility from naive human CD4+ cells to D5 Th9 culture. F. IL-9 expression in Th9 cells transduced with Scr-shRNA or STAT5b-shRNA lentivirus, cells were analyzed on day 5. G. Th9 cells treated with DMSO or STAT5 inhibitor on day 1, IL-9 and pSTAT5 were analyzed on day 5.
Next, they wanted to find out the cooperative relationship between STAT5 and BATF. Using the same experimental design as above, the researchers noticed a gradual increase in STAT5 presence through day four. After the STAT5 inhibitor was added, both the IL9 locus accessibility and the BATF binding dramatically decreased. Upon further examination, they found that STAT5 and BATF shared the same biding region on 289 genes, indicating their cooperative function in regulating IL-9 expression.
There are many moving parts to our immune system. When the body senses a foreign pathogen, it sets off a cascade of regulatory processes to ensure that the pathogen is met and terminated early to prevent further infection or disease development. The findings in this study highlight the importance of helper T cell differentiation and how it could be a potential therapeutic target for immune health and disease prevention.
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