Transmembrane adaptor protein PAG1 is a novel tumor suppressor in neuroblastoma.

Saurabh Agarwal,Rajib Ghosh,Jason M Shohet,Preethi H Gunaratne,Anna Lakoma,Eugene S Kim,Zaowen Chen

doi:10.18632/oncotarget.8116

Abstract

(NB) is the most common extracranial pediatric solid tumor with high mortality rates. The tyrosine kinase c-Src has been known to play an important role in differentiation of NB cells, but the mechanism of c-Src regulation has not been defined. Here, we characterize PAG1 (Cbp, Csk binding protein), a central inhibitor of c-Src and other Src family kinases, as a novel tumor suppressor in NB. Clinical cohort analysis demonstrate that low expression of PAG1 is a significant prognostic factor for high stage disease, increased relapse, and worse overall survival for children with NB. PAG1 knockdown in NB cells promotes proliferation and anchorage-independent colony formation with increased activation of AKT and ERK downstream of c-Src, while PAG1 overexpression significantly rescues these effects. In vivo, PAG1 overexpression significantly inhibits NB tumorigenicity in an orthotopic xenograft model. Our results establish PAG1 as a potent tumor suppressor in NB by inhibiting c-Src and downstream effector pathways. Thus, reactivation of PAG1 and inhibition of c-Src kinase activity represents an important novel therapeutic approach for high-risk NB.

Highlights

Neuroblastoma (NB) is a highly aggressive pediatric malignancy and accounts for 13% of cancer morbidity in children with current cure rates less than 50% [1]
Our findings demonstrate potent tumor suppressor functions for PAG1 and suggest transcriptional repression of PAG1 is a major mechanism for c-Src hyperactivity in NB
MYCN non-amplified samples in clinical cohorts show worse overall survival with low PAG1 levels (p

Summary

Introduction

Neuroblastoma (NB) is a highly aggressive pediatric malignancy and accounts for 13% of cancer morbidity in children with current cure rates less than 50% [1]. The MYCN oncogene is a primary driver of this malignancy and is amplified in almost 50% of high-risk cases. Additional oncogenes including c-Src (cellular-Src) are known to increase NB invasiveness and proliferation in vitro [2, 3]. We present in vitro, in vivo, and clinical data defining the major repressor of c-Src, PAG1 (Phosphoprotein Associated with Glycosphingolipidenriched microdomains 1), as a novel tumor suppressor in high-risk NB. PAG1 (Csk binding protein, Cbp) is a ubiquitous lipid-raft associated scaffold protein that inhibits Src. Family Kinases (SFKs) including c-Src [4]. PAG1 can inhibit c-Src independent of Csk by directly sequestering this kinase to lipid-rafts. PAG1 represses c-Src and prevents activation of multiple downstream effector proteins controlling cellular adhesion, proliferation, inflammation and differentiation [2, 6]. Negative feedback activation of PAG1 controls potent proliferative and oncogenic functions of c-Src in non-transformed cells [7, 8]

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