Association of Hsp47, Grp78, and Grp94 with procollagen supports the successive or coupled action of molecular chaperones

Abstract

Hsp47, Grp78, and Grp94 have been implicated with procollagen maturation events. In particular, Hsp47 has been shown to nascent procollagen alpha 1(I) chains in the course of synthesis and/or translocation into the endoplasmic reticulum (ER). Although, Hsp47 binding to gelatin and collagen has previously been suggested to be independent of ATP. Grp78 and Grp94 are known to dissociate from its substrates by an ATP-dependent release mechanism. The early association of Hsp47 with procollagen and its relatively late release suggested that other chaperones, Grp78 and Grp94, interact successively or concurrently with Hsp47. Herein, we examined how these events occur in cells metabolically stressed by depletion of ATP. In cells depleted of ATP, the release of Hsp47, Grp78, and Grp94 from maturing procollagen is delayed. Thus, in cells experiencing metabolic stress, newly synthesized procollagen unable to properly fold became stably bound to a complex of molecular chaperones. In that Hsp47, Grp78, and Grp94 could be recovered with nascent procollagen and as oligomers in ATP depleted cells suggests that these chaperones function in a series of coupled or successive reactions.

Functional Linkage between the Endoplasmic Reticulum Protein Hsp47 and Procollagen Expression in Human Vascular Smooth Muscle Cells

“…These include its specificity for procollagens as well as an atypical binding profile whereby it interacts with both folded and unfolded conformations of its target protein (11,13,14,16). The results of the current study indicate that Hsp47 can act as a primary stimulator of type I collagen production.…”

“…Hsp47 is expressed only by collagen-producing cells (8,9) and in vitro binds to collagens type I to V as well as gelatin (10). Within the ER, Hsp47 has been found to interact with nascent type I procollagen chains (11,12), with fully translated pro␣ collagen chains (13), with non-helical and poorly hydroxylated procollagen trimers (14) and with well-hydroxylated, triple helical procollagen (15,16). Once the procollagen-Hsp47 complex reaches the cis-Golgi, Hsp47 dissociates and is recycled back to the ER (13,17).…”

“…The exact mechanism by which Hsp47 contributes to the production of procollagen is unclear, however. Several possible roles have been proposed including facilitating pro␣ collagen chain elongation, preventing improper association of unassembled and possibly underhydroxylated pro␣ collagen chains (11,13,14), winding of the triple helix (24), maintaining thermal stability of the triple helix once formed (16,25), and diverting assembled procollagen into the cisternal maturation transport pathway (15,26). Although there is experimental support for each of these potential roles, a cohesive model has yet to emerge and not all of the data are consistent.…”

New Endoplasmic Reticulum Stress Regulator, Gipie, Regulates the Survival of Vascular Smooth Muscle Cells and the Neointima Formation After Vascular Injury

“…17,18 Collagen I is one of the most abundantly secreted proteins in the synthetic phenotype hVSMCs, and the modification of procollagen I in the ER and Golgi apparatus is essential for the maturation of collagen I. [19][20][21] Thus, we examined the effects of Gipie knockdown on the maturation of collagen I in hVSMCs to elucidate the participation of Gipie in the ER function under mild or physiological ER stress. A Western blot analysis showed that knockdown of Gipie decreased the production of the mature forms of collagen I incubated in the presence of ascorbate ( Figure 2C).…”

The molecular chaperone Hsp47 is essential for cartilage and endochondral bone formation

“…In the case of procollagen biosynthesis in the ER, these molecular chaperones include BiP (Grp78), Grp94, PDI, P4H and Hsp47 (Chessler and Byers, 1993;Ferreira et al, 1994;Lamande et al, 1995;Wilson et al, 1998;Walmsley et al, 1999;Nagata, 2003). Hsp47 was first identified as a collagen binding protein that resides in the ER and functions as a collagen-specific molecular chaperone (Nagata et al, 1986).…”