Using the indirect immunofluorescence technique we have studied the cellular distribution of the protease inhibitor alpha-2-macroglobulin (α2M) in normal and malignant cultured human fibroblasts. Normal fibroblasts take up from the culture medium and accumulate into the cytoplasm large amounts of bovine α2M. We did not detect any human α2M synthesized by the fibroblasts. SV40 transformed human fibroblasts and two cell lines originating from a human fibrosarcoma (HT1080) and from a human rhabdomyosarcoma (RD-2) showed a reduced amount of intracellular α2M. The α2M, controlling the activity of cellular proteases, could play an important role in normal cellular behaviour.
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