Lysosomal Function in the Degradation of Defective Collagen in Cultured Lung Fibroblasts

Richard A. Berg, Martin L. Schwartz, Ronald Crystal, Leonard H. Rome

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Human fibroblasts when induced to make non-helical, defective collagen have mechanisms for degrading up to 30% of their newly synthesized collagen intracellularly prior to secretion. To determine if at least a portion of the degradation of defective collagen occurs by lysosomes, extracts of cultured HFL-1 fibroblasts were examined for proteinases capable of degrading denatured type I [3H] procollagen. The majority of the proteolytic activity against denatured [H]-procollagen had a pH optimum of 3.5-4; it was stimulated by dithiothreitol and inhibited 95% by leupeptin, 10% by pepstatin, and 98% by leupeptin and pepstatin together. Extracts of purified lysosomes from the fibroblasts were active in degrading denatured [H] procollagen and were completely inhibited by leupeptin and pepstatin. To demonstrate directly that human lung fibroblasts can translocate a portion of their defective collagen to lysosomes, cultured cells were incubated with cis-4-hydroxyproline and labeled with [14C]proline to cause the cells to make nonhehcal [C]procollagen. About 3% of the total intracellular hydroxy[14C]proline was found in lysosomes. If, however, the cells were also treated with NH4CI, an inhibitor of lysosomal function, 18% of the intracellular hydroxy[14C]proline was found in lysosomes. These results demonstrate that cultured human lung fibroblasts induced to make defective collagen are capable of shunting a portion of such collagen to their lysosomes for intracellular degradation.

Original languageEnglish
Pages (from-to)2134-2138
Number of pages5
Issue number10
Publication statusPublished - 1 Jan 1984
Externally publishedYes


ASJC Scopus subject areas

  • Biochemistry

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