Rhomboid family member 2 regulates cytoskeletal stress-associated Keratin 16

Thiviyani Maruthappu,Diana Blaydon,Anissa Chikh,Matthew A Brooke,Matthew Freeman,Paul J Delaney,David P Kelsell,Angela Moncada-Pazos,Clemence Levet,Akemi Ishida-Yamamoto,Benjamin Fell,Irene M Leigh,Ahmad Waseem

doi:10.1038/ncomms14174

Abstract

Keratin 16 (K16) is a cytoskeletal scaffolding protein highly expressed at pressure-bearing sites of the mammalian footpad. It can be induced in hyperproliferative states such as wound healing, inflammation and cancer. Here we show that the inactive rhomboid protease RHBDF2 (iRHOM2) regulates thickening of the footpad epidermis through its interaction with K16. K16 expression is absent in the thinned footpads of irhom2−/− mice compared with irhom2+/+mice, due to reduced keratinocyte proliferation. Gain-of-function mutations in iRHOM2 underlie Tylosis with oesophageal cancer (TOC), characterized by palmoplantar thickening, upregulate K16 with robust downregulation of its type II keratin binding partner, K6. By orchestrating the remodelling and turnover of K16, and uncoupling it from K6, iRHOM2 regulates the epithelial response to physical stress. These findings contribute to our understanding of the molecular mechanisms underlying hyperproliferation of the palmoplantar epidermis in both physiological and disease states, and how this ‘stress’ keratin is regulated.

Highlights

Keratin 16 (K16) is a cytoskeletal scaffolding protein highly expressed at pressure-bearing sites of the mammalian footpad
We demonstrate for the first time that inactive rhomboid protease RHBDF2 (iRHOM2) binds to K16, and that this interaction is increased in Tylosis with oesophageal cancer (TOC) keratinocytes, where it is associated with robust downregulation of K16’s binding partner K6
As keratins comprise a major component of the footpad epidermis and are known to be altered in palmoplanter keratodermas[16], we performed immunohistochemical staining for the palmoplantarexpressed keratins; K6, K16 and Keratin 9 (K9)

Summary

Introduction

Keratin 16 (K16) is a cytoskeletal scaffolding protein highly expressed at pressure-bearing sites of the mammalian footpad. 27); K16 did not bind iRHOM1 in pull-down assays using TOC and CTRL cells (Fig. 2d and Supplementary Fig. 2b), suggesting that, unlike ADAM17, the interaction with K16 is iRHOM2 specific. Graph depicting fold change of iRHOM2 pull-down by K16 in TOC cells compared with CTRL (n 1⁄4 3); error bars denote s.d., *Po0.05 (Student’s t-test).

Results

Conclusion