Targeting of a heterologous protein to a regulated secretion pathway in cultured endothelial cells

The stimulation of regulated exocytosis in vascular endothelial cells (EC) by a variety of naturally occurring agonists contributes to the interrelate d processes of inflammation, thrombosis, and fibrinolysis, The Weibel-Palad e body (WPB) is a well-described secretory granule in EC that contains both von Willebrand factor (vWF) and P-selectin, but the mechanisms responsible for the targeting of these proteins into this organelle remain poorly unde rstood. Through adenoviral transduction, we have expressed human growth hor mone (GH) as a model of regulated secretory protein sorting in EC. Immunofl uorescence microscopy of EC infected with GH-containing recombinant adenovi rus (GHrAd) demonstrated a granular distribution of GH that colocalized wit h vWF. In contrast, EC infected with an rAd expressing the IgG(1) heavy cha in (IG), a constitutively secreted protein, did not demonstrate colocalizat ion of IG and vWF. In response to phorbol ester, GH as well as endogenously synthesized vWF were rapidly released from GHrAd-infected EC, By immunoflu orescence microscopy, granular colocalization of GH with endogenous tissue- type plasminogen activator (tPA) was also demonstrated, and most of the tPA colocalized with vWF. These data indicate that EC are capable of selective ly targeting heterologous proteins, such as GH, to the regulated secretory pathway, which suggests that EC and neuroendocrine cells share common prote in targeting recognition signals or receptors. (C) 1999 by The American Soc iety of Hematology.