Examination of the Localization and Function of the Protein Leupaxin in Cytotoxic T Lymphocytes

• Author / Creator

  Yao, Shugang

• Cytotoxic T lymphocytes (CTL) play an essential role in the immune surveillance of intracellular pathogen-infected cells and transformed tumor cells. Cytotoxic mechanisms include the direct killing of target cells and release of cytokines such as IFN-γ and TNF-α. One of the direct killing mechanisms is called degranulation, which is characterized by the directional release of lytic granules towards the target cells. Another mechanism is mediated by the interaction between FasL on the CTL and the Fas receptor on target cells, thereby inducing apoptosis. Both of these mechanisms are cell adhesion-dependent, and the adhesion between CTL and target cells is mediated by integrins, primarily LFA-1.
  My research is to study the localization, molecular regulation and function of leupaxin in CTL. Leupaxin belongs to the paxillin family of proteins and is a cytoskeletal protein downstream of integrin signaling. I found that leupaxin was recruited to the contact surface, and regulated CTL spreading and migration on ICAM-1. At the contact surface, leupaxin was a component of focal adhesion-like structures and colocalized with paxillin, vinculin and talin. The focal adhesion-like structures were assembled at the leading edge and disassembled at the trailing edge. Although leupaxin was also recruited to the MTOC, it was more dynamic than paxillin at the MTOC.
  I found that leupaxin was both tyrosine and serine phosphorylated upon TCR engagement, and the serine phosphorylation at Ser54 caused a leupaxin mobility shift. Both tyrosine and serine phosphorylation were dependent on the tyrosine kinase Pyk2. Corresponding to its involvement in the TCR signaling, leupaxin was recruited to the immunological synapse during CTL conjugation. Separation of TCR signaling and LFA-1 signaling showed that this recruitment was mainly mediated by LFA-1.
  To study the function of leupaxin in CTL, we generated leupaxin deficient mice. Deletion of leupaxin did not affect T cell development or animal viability. However, Pyk2 had reduced tyrosine phosphorylation at its activation sites when leupaxin was absent in CTL. Furthermore, leupaxin deficient CTL showed impaired MTOC reorientation during CTL conjugation with the target cells. These results suggested that leupaxin was required for optimal TCR signaling and MTOC reorientation in CTL.

• Subjects / Keywords

  • leupaxin, cytotoxic T lymphocytes

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3862BT3H

• License

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