Plakophilin3 loss leads to an increase in PRL3 levels promoting K8 dephosphorylation, which is required for transformation and metastasis.

Nileema Khapare,Mugdha Sawant,Nishigandha Naik,Rashmi Priya,Prajakta Gosavi,Neha Gupta,Sorab N Dalal,Madhura Karkhanis,Lalit Sehgal,Hunain Alam,Milind M Vaidya,Samrat T Kundu,Cara Gottardi

doi:10.1371/journal.pone.0038561

Abstract

The desmosome anchors keratin filaments in epithelial cells leading to the formation of a tissue wide IF network. Loss of the desmosomal plaque protein plakophilin3 (PKP3) in HCT116 cells, leads to an increase in neoplastic progression and metastasis, which was accompanied by an increase in K8 levels. The increase in levels was due to an increase in the protein levels of the Phosphatase of Regenerating Liver 3 (PRL3), which results in a decrease in phosphorylation on K8. The increase in PRL3 and K8 protein levels could be reversed by introduction of an shRNA resistant PKP3 cDNA. Inhibition of K8 expression in the PKP3 knockdown clone S10, led to a decrease in cell migration and lamellipodia formation. Further, the K8 PKP3 double knockdown clones showed a decrease in colony formation in soft agar and decreased tumorigenesis and metastasis in nude mice. These results suggest that a stabilisation of K8 filaments leading to an increase in migration and transformation may be one mechanism by which PKP3 loss leads to tumor progression and metastasis.

Highlights

Changes in cytoskeletal architecture and cell-cell adhesion are often observed in cells undergoing neoplastic transformation
Our results suggest that the increase in K8 levels is required, at least in part, to mediate the tumor progression and metastasis induced upon PKP3 loss
Metastatic colonies in the lungs showed equivalent expression of K8 in mice injected with all three clones. These results suggest that an increase in K8 expression upon PKP3 knockdown is required for tumor progression and metastasis

Summary

Introduction

Changes in cytoskeletal architecture and cell-cell adhesion are often observed in cells undergoing neoplastic transformation. The aberrant over-expression of K8 and K18 has been observed in a number of squamous cell carcinomas irrespective of their origin [9,12,13,14]. Increased expression of K8/18 could lead to tumor formation. Over-expression of K8 in the immortal foetal buccal mucosal cell line, FBM, led to increased transformation in vitro and in vivo [18]. A decrease in K8 and K18 levels leads to a decrease in transformation in tumor cell lines derived from stratified epithelia due to alterations in a6b4 integrin signalling [19]. A knockdown in K8 leads to decreases in a6b4 levels which are accompanied by a decrease in invasion, transformation and a6b4 mediated signalling

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Results

Conclusion