Pro-prion Binds Filamin A, Facilitating Its Interaction with Integrin β1, and Contributes to Melanomagenesis

Neena Singh,Wei Xin,Shaoman Yin,Fumihiko Nakamura,Shuiliang Yu,Olli T. Pentikäinen,Man-Sun Sy,Chaoyang Li

doi:10.1074/jbc.m110.147413

Abstract

Filamin A (FLNA) is an integrator of cell mechanics and signaling. The spreading and migration observed in FLNA sufficient A7 melanoma cells but not in the parental FLNA deficient M2 cells have been attributed to FLNA. In A7 and M2 cells, the normal prion (PrP) exists as pro-PrP, retaining its glycosylphosphatidyl-inositol (GPI) anchor peptide signal sequence (GPI-PSS). The GPI-PSS of PrP has a FLNA binding motif and binds FLNA. Reducing PrP expression in A7 cells alters the spatial distribution of FLNA and organization of actin and diminishes cell spreading and migration. Integrin β1 also binds FLNA. In A7 cells, FLNA, PrP, and integrin β1 exist as two independent, yet functionally linked, complexes; they are FLNA with PrP or FLNA with integrin β1. Reducing PrP expression in A7 cells decreases the amount of integrin β1 bound to FLNA. A PrP GPI-PSS synthetic peptide that crosses the cell membrane inhibits A7 cell spreading and migration. Thus, in A7 cells FLNA does not act alone; the binding of pro-PrP enhances association between FLNA and integrin β1, which then promotes cell spreading and migration. Pro-PrP is detected in melanoma in situ but not in melanocyte. Invasive melanoma has more pro-PrP. The binding of pro-PrP to FLNA, therefore, contributes to melanomagenesis.

Highlights

Filamin A (FLNA)3 is a cytolinker, which links cell surface receptors, such as integrins to F-actin filaments, creating an orthogonal actin network that is important in maintaining membrane integrity, cell-cell, and cell-matrix interactions [1, 2]
We report that in M2 and A7 cells, PrP exists as pro-PrP and binds FLNA
PrP was present on the cell surface of M2 and A7 cells at a comparable level, as judged by immunofluorescent staining of M2 and A7 cells with multiple anti-PrP mAbs with distinct epitopes (Fig. 1A)

Summary

Introduction

Filamin A (FLNA) is a cytolinker, which links cell surface receptors, such as integrins to F-actin filaments, creating an orthogonal actin network that is important in maintaining membrane integrity, cell-cell, and cell-matrix interactions [1, 2]. We discovered that in human pancreatic ductal adenocarcinoma (PDAC) cell lines, PrP existed as pro-PrP, retaining its GPI-PSS. The binding of pro-PrP to FLNA altered the cytoskeleton and signaling events, providing a growth advantage to the PDAC cell lines [15]. This conclusion is based on our findings that down-regulation of PrP expression in the PDAC cell lines reduces their proliferation and invasiveness in vitro and their growth in vivo as xenografts in nude mice. We hypothesized that the presence of pro-PrP and its binding to FLNA provided a growth advantage to human pancreatic cancer cells, enabling the tumor cell to become more aggressive. The underlying mechanism by which the binding of pro-PrP to FLNA provided a growth advantage to a cancer cell was not known

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