| HSP47 (SERPINH1) is an endoplasmic reticulum–resident collagen‑specific molecular chaperone of the serpin superfamily that lacks protease inhibitory activity and is essential for correct folding, stabilization, and secretion of multiple collagen types. The protein contains an N‑terminal signal sequence and an ER retention motif, and adopts a serpin‑like fold that creates a collagen‑binding surface recognizing the triple‑helical conformation and specific Gly‑X‑Y sequence motifs, allowing selective association with procollagen chains once they form stable triple helices. HSP47 binds procollagen in the ER lumen, stabilizes the triple helix against premature unfolding, and escorts collagen molecules through the secretory pathway until they reach the cis‑Golgi, where pH‑dependent dissociation releases collagen for further processing, while unbound or misfolded collagen is targeted to degradation pathways. HSP47 interacts with fibrillar collagens such as type I and type III by binding N‑terminal triple‑helical regions critical for secretion, and also supports proper triple‑helix formation and lateral assembly of selected non‑fibrillar collagens, including collagen XVII and collagen VI, revealing collagen‑subfamily‑specific chaperone functions. Genetic ablation or knockdown of Hsp47 in fibroblasts and keratinocytes reduces secretion of fibrillar collagens, alters assembly of collagen VI, and leads to accumulation of incompletely folded transmembrane collagen XVII fragments at the plasma membrane, defects that can be corrected by addition of recombinant HSP47. HSP47 expression is strongly induced by TGF‑β and other profibrotic and ER‑stress–related signals in fibroblasts and myofibroblasts, and elevated HSP47 levels are a consistent feature of fibrotic tissues where excessive collagen deposition and extracellular matrix remodeling occur. Suppression of HSP47 in models of lung, liver, and kidney fibrosis reduces collagen I expression and deposition and attenuates matrix accumulation and tissue stiffening. Increased HSP47 expression is associated with collagen‑rich tumor stroma, higher grade, and poor prognosis. |
