title: CD40 ligand-induced apoptosis is Fas-independent in human multiple myeloma cells.
abstract: We and others previously demonstrated that human multiple myeloma (MM) cells express CD40 and have an active CD40-growth regulatory pathway. This study characterizes the growth outcome of soluble (gp39) or membrane-bound recombinant human CD40-ligand (rCD40L) and its relationship with Fas-dependent apoptosis. Contrary to the moderate growth-stimulatory effect of the CD40-MAb G28.5, gp39 inhibited 3H-thymidine uptake of the plasma dyscrasia lines ARH-77, U266, and HS-Sultan in a dose-dependent fashion by up to 82%. By comparison, RPMI 8226 cells were resistant to CD40L-growth modulation, which may be attributable to a single base substitution (TCA-->TTA, serine-->leucine) at the 3rd cysteine-rich extramembrane region of CD40. Gp39 similarly reduced myeloma clonogenic colony (MCC) formation in patient primary bone marrow cultures by 50% (40-76%; n=6). Studies using transfectant L cells that constitutively expressed CD40L showed that membrane-bound CD40L inhibited the growth of ARH-77, U266, and HS-Sultan cells (66%, 63%, and 32%, respectively), whereas untransfected L cells did not. Growth inhibition by gp39 or CD40L+ L cells was neutralized by coincubation with the CD40L antibodies 5c8 or LL48. CD40L-treatment increased apoptotic activity of MM cells, as defined by oligonucleosomal DNA fragmentation and an increased binding to annexin V (16-28%). All three untreated CD40-responsive MM lines expressed the Fas/Apo-1/CD95 antigen (65-92% CD95+). However, only ARH-77 cells responded to the growth inhibitory effect of the CD95-agonistic antibody CH-11. CD95 expression was not affected significantly by gp39 treatment, and growth inhibition by CH-11 was additive to gp39 (from 42% to 64% decrease in 3H-thmidine uptake). Conversely, the CD95 antagonist antibody ZB4 reversed the Fas-dependent growth inhibitory process but did not significantly alter gp39-mediated growth outcome. Gp39 treatment lowered the expression of TNFR-associated factors TRAF4 and TRAF6 by 38% and 32%, respectively, whereas detectable levels of TRAF1,2,3, and 5 levels remained unchanged. Our observations indicate that the CD40L-binding inhibits human MM cell growth and increases its apoptotic activity. This growth inhibitory effect corresponds to lower levels of cytoplasmic TRAF signaling elements, and appears independent of the Fas-signaling pathway. CD40 receptor mutation may lead to unresponsiveness to CD40 growth modulation in multiple myeloma cells.
authors.affiliation: Dept. of Pathology, Baylor-Sammons Cancer Center, Baylor University Medical Center Dallas, TX 75246, USA.
authors.forename: A W
authors.initials: AW
authors.lastname: Tong
authors.forename: B
authors.initials: B
authors.lastname: Seamour
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.forename: D
authors.initials: D
authors.lastname: Su
authors.forename: G
authors.initials: G
authors.lastname: Ordonez
authors.forename: L
authors.initials: L
authors.lastname: Frase
authors.forename: G
authors.initials: G
authors.lastname: Netto
authors.forename: M J
authors.initials: MJ
authors.lastname: Stone
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D023201:CD40 Ligand; D006801:Humans; D007167:Immunotherapy; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000494:pharmacology*; D009101:Multiple Myeloma / Q000276:immunology / Q000378:metabolism / Q000473:pathology* / Q000628:therapy; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D011994:Recombinant Proteins; D019014:fas Receptor; D023201:CD40 Ligand