Aj. Garton et al., IDENTIFICATION OF P130(CAS) AS A SUBSTRATE FOR THE CYTOSOLIC PROTEIN-TYROSINE-PHOSPHATASE PTP-PEST, Molecular and cellular biology, 16(11), 1996, pp. 6408-6418
PTP-PEST is a ubiquitously expressed, cytosolic, mammalian protein tyr
osine phosphatase (PTP) which exhibits high specific activity in vitro
, We have investigated the substrate specificity of PTP-PEST by a nove
l substrate-trapping approach in combination within vitro dephosphoryl
ation experiments. We initially identified a prominent 130-kDa tyrosin
e-phosphorylated protein in pervanadate-treated HeLa cell lysates whic
h was preferentially dephosphorylated by PTP-PEST in vitro, In order t
o identify this potential substrate, mutant (substrate-trapping) forms
of PTP-PEST were generated which lack catalytic activity but retain t
he ability to bind substrates. These mutant proteins associated in sta
ble complex-es exclusively with the same 130-kDa protein, which was id
entified as p130(cas) by immunoblotting. This exclusive association wa
s observed in lysates from several cell lines and in transfected COS c
ells, but was not observed with other members of the PTP family, stron
gly suggesting that p130(cas) represents a major physiologically relev
ant substrate for PTP-PEST. Our studies suggest potential roles for PT
P-PEST in regulation of p130(cas) function, These functions include mi
togen- and cell adhesion-induced signalling events and probable roles
in transformation by various oncogenes. These results provide the firs
t demonstration of a PTP having an inherently restricted substrate a s
pecificity in vitro and in vivo. The methods used to identify p130(cas
) as a specific substrate for PTP-PEST are potentially applicable to a
ny PTP and should therefore prove useful in determining the physiologi
cal substrates of other members of the PTP family.