Fig. 11

A model for ectodomain shedding and secretion of DPF. DPF is synthesized as an ~ 160-kDa protein that is inserted into the plasma membrane, following signal peptide cleavage. The transmembrane TM domain near the C-terminus anchors the single-pass DPF in the membrane. The long N-terminal ~ 150-kDa extracellular domain is glycosylated. Extracellular proteolytic cleavage, N-terminal to the TM domain, releases a p150 fragment into the media; The residual p10 TM/cytoplasmic fragment is retained in the plasma membrane. The secreted p150 possesses density-dependent aggregation activity and at high levels promotes aggregation at sub-optimal cellular densities and defines centers for aggregation. Membrane-anchored DPF has cell-autonomous activity for growth and adhesion