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.jpg): Failed to open stream: No such file or directory in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 117 J+Biol+Chem
2015 ; 290
(48
): 28915-31
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p21-activated Kinases (PAKs) Mediate the Phosphorylation of PREX2 Protein to
Initiate Feedback Inhibition of Rac1 GTPase
#MMPMID26438819
Barrows D
; Schoenfeld SM
; Hodakoski C
; Silkov A
; Honig B
; Couvillon A
; Shymanets A
; Nürnberg B
; Asara JM
; Parsons R
J Biol Chem
2015[Nov]; 290
(48
): 28915-31
PMID26438819
show ga
Phosphatidylinositol 3,4,5-trisphosphate (PIP3)-dependent Rac exchanger 2 (PREX2)
is a guanine nucleotide exchange factor (GEF) for the Ras-related C3 botulinum
toxin substrate 1 (Rac1) GTPase, facilitating the exchange of GDP for GTP on
Rac1. GTP-bound Rac1 then activates its downstream effectors, including
p21-activated kinases (PAKs). PREX2 and Rac1 are frequently mutated in cancer and
have key roles within the insulin-signaling pathway. Rac1 can be inactivated by
multiple mechanisms; however, negative regulation by insulin is not well
understood. Here, we show that in response to being activated after insulin
stimulation, Rac1 initiates its own inactivation by decreasing PREX2 GEF
activity. Following PREX2-mediated activation of Rac1 by the second messengers
PIP3 or G??, we found that PREX2 was phosphorylated through a PAK-dependent
mechanism. PAK-mediated phosphorylation of PREX2 reduced GEF activity toward Rac1
by inhibiting PREX2 binding to PIP3 and G??. Cell fractionation experiments also
revealed that phosphorylation prevented PREX2 from localizing to the cellular
membrane. Furthermore, the onset of insulin-induced phosphorylation of PREX2 was
delayed compared with AKT. Altogether, we propose that second messengers activate
the Rac1 signal, which sets in motion a cascade whereby PAKs phosphorylate and
negatively regulate PREX2 to decrease Rac1 activation. This type of regulation
would allow for transient activation of the PREX2-Rac1 signal and may be relevant
in multiple physiological processes, including diseases such as diabetes and
cancer when insulin signaling is chronically activated.