Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Microbiology and Immunology

Abstract

T lymphocytes are a critical component of the adaptive immune system and their responses in pathogenic and steady state conditions require strict regulation. One mechanism involved in this regulation is Transforming Growth Factor-β (TGF-β) signaling. TGF-β can act on activated T cells to facilitate the differentiation of TGF-β dependent T helper subsets or the suppression of T cell activation and proliferation. However, the molecular mechanism(s) by which TGF-β signaling controls T cell differentiation vs T cell suppression remain poorly understood.TGF-β signaling is propagated by initially binding to the TGF-β type II receptor, which subsequently activates TGF-β type I receptor (TGF-βRI) that phosphorylates the transcription factors Smad2/Smad3. This induces nuclear localization of Smad complexes and transcription of target genes. To understand how TGF-β signaling functions to control T cell fate, we generated TGF-βRI deficient Jurkat T cells using the CRISPR/cas9 genome editing system.Unexpectedly, TGF-βRI deficient Jurkat demonstrate a hyperactivation phenotype and showed highly elevated expression of surface antigens (CD69, CD25), and secreted significantly increased levels of IL-2 and TNF. Analysis of signaling events in TGF-βRI deficient Jurkat reveal a highly elevated and constitutive activity of the critical transcription factor, activator protein-1 (AP-1), constitutive activation of the upstream kinase for AP-1, jun-amino-terminal kinase (JNK), and increased expression of the transcriptional target for c-Jun, JUN. Similarly, in primary T cells, transient expression of a dominant negative mutant of TGF-βRI revealed elevated AP-1 activity, while a constitutively active TGF-βRI mutant reduced this activity. Further, the upstream kinase for JNK, MKK7, and critical scaffold proteins upstream of JNK activation, CARMA1 and Bcl10, are upregulated in the TGF-βRI deficient Jurkat. Correspondingly, primary T cells stimulated in the presence of TGF-β exhibit robustly reduced levels of CARMA1 and Bcl10 expression.Taken together, these data describe a novel TGF-β-mediated pathway that functions to suppress the activation of JNK by suppressing the CARMA1/Bcl10 signalosome. Because JNK signaling is involved in T cell activation, differentiation and apoptosis, the suppression of JNK activation by TGF-β signaling could serve as a mechanism used to control T cell functions.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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