Urokinase-type plasminogen-activator receptor associates to a cell surface molecule in monocytic cells

The monocyte-like THP-1 cells express on their surface the urokinase-type plasminogen activator receptor (uPA-R). This receptor, chemically cross-linked to its possible ligands, migrates, in SDS PAGE, slower than the uPA-R expressed on the epithelial thyroid cell line TAD-2, cross-linked to the same ligands. The different migration corresponds to a difference in molecular weight of 15 kDa. Similar results were obtained with peripheral monocytes and primary cultures of thyroid cells. The molecular weight of the native receptor is about 50 kDa and appears to be identical in these two cell types. Such results suggest that, in monocytic cells, uPA-R associates to a 15 kDa molecule. This molecule is probably linked to the cell surface by a glyco-phospho-inositol anchor since, by phospholipase-C treatment, it is co-eluted with the urokinase-type plasminogen activator receptor from THP-1 cells.