HSP47: Introduction

Hsp47, also known as Serpin H1, is an ER-resident procollagen-specific molecular chaperone essential for the biosynthesis and structural assembly of collagen 1-3. Beside its role in collagen biosynthesis, Hsp47 represents an essential factor in the mammalian Golgi stress response 4. Hsp47 belongs to clade H of the SERPIN superfamily of proteinase inhibitors, but it does not exhibit serine proteinase inhibitory activity. Apart from its location to the ER, Hsp47 can also be found in several extra-ER compartments, including the Golgi  5, membrane rafts 6, on the cell surface 7-10, the extracellular matrix (ECM) 11, as well as in the serum of healthy and diseased human individuals 12-14. Membrane-associated Hsp47 was proposed to serve two functions: as a receptor for extracellular collagens 8 and as regulator of immune responses particularly in autoimmune diseases 7. The expression of Hsp47 varies with tissue type, developmental stage and stress conditions. While Hsp47 is constitutively expressed under normal conditions, its expression is up-regulated by cellular stress including heat shock 15. Constitutive expression of Hsp47 tightly correlates with that of collagens in numerous tissues and cell types;  thus, Hsp47 is predominantly expressed in collagen-synthesizing cells 1. In the course of the last years, several diseases have been linked to Hsp47 and its interaction partners, such as collagen-related and neurodegenerative diseases as well as cancer in which Hsp47 levels are often up-regulated. Targeting Hsp47 in certain types of fibrosis is being evolved into an excellent therapeutic tool in collagen-related diseases and hold promise for application in other disorders. Herein, the biology of Hsp47 and its role in disease and therapy is compiled.