Vav2 Inhibits T Cell Calcium Signaling by Activating Cdc42.
proteins are tyrosine kinase-dependent guanine nucleotide exchange factors (GEFs)
essential for a functional immune system. This family of proteins consists of three
mammalian isoforms, Vav1, Vav2, and Vav3. Studies in mice have shown that knocking out
all three of these isoforms leads to an almost complete loss in the number and function
of T and B cells (Fujikawa et al., 2003)... read more, serious defects in innate immune cells, and
impacts on the cardiovascular and nervous systems (Bustelo, 2012). The different Vav
isoforms have unique signaling properties: in T cells, Vav1 promotes and Vav2 opposes
TCR-induced calcium entry despite their structural similarity. I show here that, while
Vav1 facilitates calcium entry via non-catalytic mechanisms, the suppressive activity of
Vav2 is largely dependent on its catalytic activity and can be transferred into Vav1 by
exchanging the catalytic cores of these proteins. Although Vav1 and Vav2 have been
reported to target identical Rho family GTPases, my data indicate that this cannot be
the case. Among the GTPase targets of Vav proteins, I find that only active Cdc42
potently inhibits TCR-induced calcium entry. Using a novel in vivo 'GEF trapping' assay
to screen GEF-GTPase interactions, I demonstrate that Cdc42 interacts with the catalytic
surface of Vav2, but not Vav1. I further identify a single amino acid that prevents the
recognition of Cdc42 by Vav1. Lastly, I show that the pharmacological suppression of
Cdc42 activation prevents the inhibition of TCR-induced calcium entry by Vav2. Since
Vav2 and Cdc42 both contribute to the initiation of immunoreceptor-dependent calcium
signals in B cells, these observations suggest a profound point of divergence in the
signaling pathways of T cells and other immune
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Immunology.
Advisor: Stephen Bunnell.
Committee: David Thorley-Lawson, Henry Wortis, and Joan Mecsas.
Keywords: Immunology, and Cellular biology.read less