Hsp47 and the translation-translocation machinery cooperate in the production of alpha 1(I) chains of type I procollagen.

Hsp47, an endoplasmic reticulum resident protein, has gelatin-binding and procollagen-binding properties and has been hypothesized to function as a molecular chaperone in regulating procollagen folding and/or assembly. In this report, we further investigate the interaction of Hsp47 with polysome-associated alpha 1(I) procollagen chains following antisense treatment of 3T6 cells. For these studies, we employed phosphorothioate oligodeoxynucleotides directed to the first five codons of Hsp47 that straddle the predicted translation initiation site of mouse Hsp47. Cells depleted of Hsp47 in this manner were observed to produce diminished amounts of fully elongated nascent alpha 1(I) procollagen while accumulating shorter procollagen peptides associated with peptidyl-tRNA. Pulse-labeling of cells with [35S]methionine followed by treatment with puromycin and immunoprecipitation with anti-Hsp47 and anti-procollagen antibodies revealed that Hsp47 is associated with alpha 1(I) procollagen at a very early point during translocation of the nascent procollagen chains. Although Hsp47 appears to possess properties similar to grp78/BiP, Hsp47 binding early during translocation favors a more specialized specific function relative to chain selection or completion of stable folding in type I procollagen.