Acquisition of a lysosomal enzyme by myoblasts in tissue culture

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Abstract
Skeletal muscle myoblasts from different sources acquired high levels of the lysosomal enzyme β-glucuronidase, when they were cultured together with mitogen-activated lymphocytes. Immunofluorescent staining, thermal stability, and electrophoretic mobility showed that the increase in enzyme activity in the myoblasts was due to the presence of the lymphocyte form of the enzyme. Although myoblasts were able to take up exogenous β-glucuronidase from the culture medium by mannose 6-phophate receptor-mediated endocytosis, enzyme acquisition during co-culture with lymphocytes was independent of this pathway. Enzyme transfer from the lymphocytes was found to require direct cell-cell contact with the muscle cells, and was accompanied by an increase in β-glucuronidase activity in the lymphocytes themselves. Since this additional activity was also due to the presence of the lymphocyte form of the enzyme, these results indicate that interaction with the muscle cells induced the de novo synthesis of β-glucuronidase in the lymphocytes.