A ZINC METALLOPROTEINASE IS RESPONSIBLE FOR THE RELEASE OF CD30 ON HUMAN TUMOR-CELL LINES

The activation marker CD30 is expressed on the cell surface of the mal ignant cells in Hodgkin's disease and a few non-Hodgkin lymphomas. We have analyzed the regulation of membrane-bound CD30 and found that the binding of a variety of anti-CD30 antibodies induced down-regulation of CD30 on cell lines. In addition, such down-modulation was also obse rved after treatment of the cell surface proteins with the sulfhydryl reagent iodoacetamide or after stimulation of the second messenger pat hway with phorbol ester or calcium ionophore. This modulation was abol ished at 4 degrees C and strongly inhibited by chelators like EDTA or 1,10-phenanthroline, whereas EGTA, a selective inhibitor of Ca2+-depen dent proteinases and other inhibitors of serine, thiol and acid protei nases, showed no effect. The down-modulation was strengthened by Zn2or Cd2+, but not by other divalent cations such as Fe2+, Mn2+, Mg2+, C a2+ or Co2+, thus indicating the involvement of a zinc metalloproteina se in CD30 modulation which can be activated by protein kinase C and b y alkylation of sulfhydryl groups. Pulse-chase experiments, analysis o f the CD30 glycosylation and specific measurement of the 90-kDa solubl e form of CD30 (sCD30) with a sandwich radioimmunoassay revealed that CD30 downmodulation results from enhanced release of 90-kDa sCD30 by t he site-specific cleavage of CD30 accomplished by a zinc metalloprotei nase. This release occurs at the cell membrane without prior endocytos is. (C) 1995 Wiley-Liss, Inc.