Oral Presentations - Pathology and Laboratory Medicine - University ...

Graduate StudentAbstract # 61Suzanne Cheng 1,4 , Guobin Sun 2,4 , Catherine J. Pallen 1,2,3,4Departments of Pathology and Laboratory Medicine 1 , Medicine 2 , Pediatrics 3 , and Child andFamily Research Institute 4 , University of British ColumbiaSuzanne Chengintegrin-induced protein tyrosine phosphatase alpha(PTPa) tyrosine phosphorylation regulates casmediatedcell migrationBackround/ObjectivesIntegrins are transmembrane receptors that bind to extracellular matrix (ECM) components to regulate cell adhesion,survival, and migration. The integrin signaling cascade is characterized by a series of protein tyrosine phosphorylationevents that are regulated by protein tyrosine kinases (PTKs) and phosphatases (PTPs). Deregulation of these signalingpathways is associated with tumor cell behaviors such as angiogenesis and metastasis. Thus, a precise understandingof integrin signaling mechanisms may lead to the identification of novel molecular targets for anti-cancer therapies.PTPa is a receptor PTP that plays two roles in integrin signaling: It acts proximal to activated integrins to activatethe PTK Src, which interacts with focal adhesion kinase (FAK) to initiate multiple downstream signaling events. PTPais phosphorylated by the active Src-FAK complex on a tyrosine residue in its C-terminal tail, Tyr789, and this iscritical for a second undefined role of PTPa in regulating actin stress fiber assembly, focal adhesion formation, and cellmigration.Our objective is to elucidate the role of PTPa-Tyr789 phosphorylation in integrin signaling. We hypothesizethat PTPa-phosphoTyr789 functions as a site to recruit integrin signaling molecules involved in cytoskeletalreorganization.MethodsAn in vitro model with wild type and PTPa knockout mouse embryonic fibroblasts (MEFs) is adopted to study themolecular mechanisms of PTPa phosphorylation in integrin signaling. We used an adenoviral system to re-expresswild type and mutant (Y789F) PTPa in the knockout cells in order to study the function of PTPa-phosphoTyr789.We performed co-immunoprecipitations and immuno-fluorescent staining to identify defective signaling events thatare dependent on phosphoPTPa.ResultsWe found that tyrosine phosphorylation of the p130Cas (Cas) adaptor protein, a key player in focal adhesion (FA)formation and cell migration, is dependent on integrin-induced PTPa-Tyr789 phosphorylation. The PTK Srccatalyzes Cas phosphorylation. In cells expressing mutant PTPa-Y789F, integrin-induced Src activation is normal but the association of Src with Cas is reduced, indicating that thislikely underlies the Cas phosphorylation defect. Since the Cas-Src complex forms in FAs, this suggests that PTPaphosphoTyr789may be required for Cas or Src localization to FAs. Our preliminary data indicate that PTPa islocalized to FAs in integrin-stimulated cells, supportive of a role for PTPa in potentially regulating the localization ofother proteins to these sites. Whether PTPa-Tyr789 phosphorylation is required for FA localization of PTPa, Cas,and/or Src, and the mechanism by which this is effected, is under investigation.ConclusionWe are delineating a second role of PTPa in integrin-stimulated cell migration. PTPa-Tyr789 phosphorylation isrequired for the association of Src with Cas and for Cas phosphorylation that is essential for downstream signaling topromote cell migration.72 2 0 1 0 * P o s t e r P r e s e n t a t i o n s