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 functi on as a molecular chaperone in regulating procollagen folding and/or a ssembly. In this report, we further investigate the interaction of Hsp 47 with polysome associated alpha 1(I) procollagen chains following an tisense treatment of 3T6 cells. For these studies, we employed phospho rothioate oligo-deoxynucleotides 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 produc e diminished amounts of fully elongated nascent alpha 1(I) procollagen while accumulating shorter procollagen peptides associated with pepti dyl-tRNA. Pulse-labeling of cells with [S-35]methionine followed by tr eatment with puromycin and immunoprecipitation with anti-Hsp47 and ant i-procollagen antibodies revealed that Hsp47 is associated with alpha 1(I) procollagen at a very early point during translocation of the nas cent 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 co mpletion of stable folding in type I procollagen.