Mechanisms of Actomyosin-Mediated T Cell Activation.
recognition by the T cell receptor (TCR) complex and engagement of costimulatory
ligands, such as CD28 and Very Late Antigen-4 (VLA-4), are essential for sustained
activation of T lymphocytes. These receptor interactions induce extensive cytoskeletal
rearrangement that forms the immune synapse and shapes discrete nucleation sites of
activating SLP-76 (SH2 domain containing ... read moreleukocyte protein of 76kDa) microclusters (MC).
Previous studies suggest that retrograde actin flow contributes to SLP-76 MC
centralization over time; however, the precise mechanism of SLP-76 MC locomotion is not
fully elucidated. Myosin II is a non-muscle motor protein that contracts along actin
filaments and is critical for lymphocyte migration and cell crawling. We proposed that
myosin II controls the locomotion and activating potential of SLP-76 MC. To investigate
the structure and behavior of myosin II, fluorescent chimeras of myosin II were imaged
in Jurkat T cells stimulated by plate-bound TCR and VLA-4 ligands. We found that myosin
II forms filaments that flow centripetally in response to TCR stimulation. Notably, the
contraction of myosin II filaments is slowed by VLA-4 coligation, suggesting a close
relationship between integrin adhesion and cytoskeletal contraction in T cells. In cells
treated with blebbistatin, a drug that inhibits myosin II contraction, we found that
TCR-induced SLP-76 MC do not centralize. In contrast, cells with no myosin II expression
exhibit mobile SLP-76 MC with weakened stability. Additionally, we determined that the
production of IL-2 is dependent on the expression of myosin II. Together, these results
suggest that myosin II expression and contractile activity drive productive T cell
signaling and effector function.
Thesis (M.S.)--Tufts University, 2011.
Submitted to the Dept. of Immunology.
Advisor: Stephen Bunnell.
Committee: Cheleste Thorpe, Joan Mecsas, and Ananda Roy.
Keyword: Immunology.read less