title: Lysosomal function in the degradation of defective collagen in cultured lung fibroblasts.
abstract: Human fibroblasts when induced to make nonhelical , 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 [3H]-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 [3H]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 nonhelical [14C]procollagen. About 3% of the total intracellular hydroxy[14C]proline was found in lysosomes. If, however, the cells were also treated with NH4Cl, 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.
mesh_terms: D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007976:Leupeptins / Q000378:metabolism; D008168:Lung / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D010436:Pepstatins / Q000378:metabolism; D011247:Pregnancy; D011347:Procollagen / Q000378:metabolism; D014107:Tosyllysine Chloromethyl Ketone / Q000494:pharmacology
chemical_list: D007976:Leupeptins; D010436:Pepstatins; D011347:Procollagen; C014195:Streptomyces pepsin inhibitor; D014107:Tosyllysine Chloromethyl Ketone; D003094:Collagen; D010450:Endopeptidases; C032854:leupeptin; C031375:pepstatin