Detergent solubility defines an alternative itinerary for a subpopulation of PDCF β receptors

Current models of platelet-derived growth factor (PDGF) β receptor itinerary are based upon the properties of receptors recovered from nonionic detergent-solubilized cellular extracts. Comparing several commonly used cell extraction procedures, we have determined that up to 50% of immunoreactive PDGF β receptors reside in a Triton X-100 insoluble pool in a wide distribution of cultured cell lines, including Balb/c-3T3, NIH 3T3, and Swiss fibroblasts, primary murine and human fibroblasts, and primary human glial cells. Many properties of Tritan insoluble receptors are distinct from the well-characterized PDGF β receptors, including 1) delayed arrival of newly synthesized receptors into the Triton insoluble fraction, 2) prolonged half-life in the presence of PDGF, 3) increased abundance with increasing cell density, 4) inaccessibility to modification by extracellular compartment enzymes, 5) cofractionation with cytoskeletal proteins, and 6) a higher basal tyrosine phosphorylation state. PDGF stimulates accumulation of tyrosine phosphorylated PDGF β receptors in the Triton X-100 insoluble fraction. Cell surface PDGF β receptors modified by enzymatic desialylation redistribute to the insoluble fraction. These findings distinguish the itinerary of a large subpopulation of PDGF β receptors from those characterized previously. Receptors in this fraction represent a long-lived tyrosine phosphorylated population that may effect responses for extended periods following ligand activation.