Distinct roles for the α, β and γ1 isoforms of protein phosphatase 1 in the outside-in αIIbβ3 integrin signalling-dependent functions

Nawaf Alrehani; Subhashree Pradhan; Tanvir Khatlani; Lavanya Kailasam; Vinod K. Vijayan

doi:10.1160/TH12-04-0237

Thrombosis and Haemostasis, Table of Contents

Thromb Haemost 2013; 109(01): 118-129
DOI: 10.1160/TH12-04-0237

Platelets and Blood Cells

Schattauer GmbH

Distinct roles for the α, β and γ1 isoforms of protein phosphatase 1 in the outside-in α_IIbβ₃ integrin signalling-dependent functions

Authors

Nawaf Alrehani^*

¹Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
Subhashree Pradhan^*

¹Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
Tanvir Khatlani

¹Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
Lavanya Kailasam

¹Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
Vinod K. Vijayan

¹Department of Medicine, Baylor College of Medicine, Houston, Texas, USA

Abstract

Summary

Although protein kinases and phosphatases participate in integrin α_IIbβ₃ signalling, whether integrin functions are regulated by the catalytic subunit of protein phosphatase 1 (PP1c) isoforms are unclear. We show that siRNA mediated knockdown of all PP1c isoforms (α, β and γ1) in 293 α_IIbβ₃ cells decreased adhesion to immobilised fibrinogen and fibrin clot retraction. Selective knockdown of only PP1cγ1 did not alter adhesion or clot retraction, while depletion of PP1cβ decreased both functions. Unexpectedly, knockdown of PP1cα enhanced α_IIbβ₃ adhesion to fibrinogen and clot retraction. Protein interaction studies revealed that all PP1c isoforms can interact with the integrin α_IIb subunit. Phospho-profiling studies revealed an enhanced activation of mitogen- activated protein kinase (MAPK) p38 in the PP1cα depleted cells. Enhanced adhesive phenotype displayed by the PP1cα-depleted 293 α_IIbβ₃ cells was blocked by pharmacological inhibition of p38. Conversely, the decreased adhesion of PP1cα overexpressing cells was rescued by the expression of constitutively active p38α or p38γ. Thus, PP1c isoforms have distinct contribution to the outside-in α_IIbβ3 signalling- dependent functions in 293 α_IIbβ₃ cells. Moreover, PP1cα negatively regulates integrin function by suppressing the p38 pathway.

Keywords

Protein phosphatase 1 - adhesion - clot retraction - fibrinogen

Full Text

References

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