Biology Reference
In-Depth Information
Fig. 21.6 IQGAP is not essential for MTOC polarization in activated Jurkat T cells. Either
normal Jurkat T cells (a, b, c), Jurkat cells expressing GFP-IQGAP (d, e, f), or Jurkat cells
expressing GFP-IQGAP G75Q (g, h, i) were paired with SEE-coated Raji B cells (R). Pairs were
immunostained for IQGAP (a) and/or tubulin (b, e, h). IQGAP is seen at the immunological
synapse (a). Tubulin staining marked the MTOC (bright spot), which was localized at the synapse
in all cell lines. Since GFP-IQGAP G75Q cannot bind actin and the MTOC was still polarized in
these cells, this indicates that IQGAP is not essential for MTOC polarization in this system. The
merged images show IQGAP in red and tubulin in green (c), or GFP-IQGAP or IQGAP G75Q in
green and tubulin in red (f, i). Overlap between green and red is colored yellow
phosphorylated, they recruit the Syk-family kinase ZAP-70 leading to its activa-
tion. ZAP-70 then phosphorylates a number of critical scaffold proteins including
LAT and SLP-76 (Wang et al.
2010
). Studies have shown that this cascade,
especially the kinase lck, is essential for MTOC translocation (Davis and van der
Merwe
2011
; Lowin-Kropf et al.
1998
; Kuhne et al.
2003
; Tsun et al.
2011
;
Morgan et al.
2001
; Blanchard et al.
2002
).
One of the enzymes triggered through TcR activation is phospholipase Cc.This
enzyme cleaves phosphatidylinositol 4,5-biosphosphate (PIP2) into the second
messengers inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). These in
turn trigger calcium release from the ER and activation of protein kinase C (PKC).
Sustained calcium signaling is achieved by the opening of CRAC channels at the
plasma membrane through the interaction of the Stim and Orai proteins (Hogan
et al.
2010
). Interestingly, both calcium and diacylglycerol have been implicated in
MTOC translocation (Quann et al.
2009
; Quintana et al.
2009
; Nesic et al.
1998
).
