TNFR-associated factor family protein expression in normal tissues and lymphoid malignancies

TNFR-associated factors (TRAFs) constitute a family of adapter proteins tha t associate with particular TNF family receptors, Humans and mice contain s ix TRAF genes, but little is known about their in vivo expression at the si ngle cell level, The in vivo locations of TRAF1, TRAF2, TRAF5, and TRAF6 we re determined in human and mouse tissues by immunohistochemistry. Striking diversity was observed in the patterns of immunostaining obtained for each TRAF family protein, suggesting their expression is independently regulated in a cell type-specific manner, Dynamic regulation of TRAFs was observed i n cultured PBLs, where anti-CD3 Abs, mitogenic lectins, and ILs induced mar ked increases in the steady-state levels of TRAF1, TRAF2, TRAF5, and TRAF6. TRAF1 was also highly inducible by CD40 ligand in cultured germinal center B cells, whereas THAF2, TRAF3, TRAF5, and TRAF6 were relatively unchanged. Analysis of 83 established human tumor cell lines by semiquantitative immu noblotting methods revealed tendencies of certain cancer types to express p articular TRAFs, For example, expression of TRAF1 was highly restricted, wi th B cell lymphomas consistently expressing this TRAF family member. Consis tent with results from tumor cell lines, immunohistochemical analysis of 23 2 non-Hodgkin lymphomas revealed TRAF1 overexpression in 112 (48%) cases, T RAF1 protein levels were also elevated in circulating B cell chronic lympho cytic leukemia specimens (n = 49) compared with normal peripheral blood B c ells (p = 0.01), as determined by immunoblotting, These findings contribute to an improved understanding of the cell-specific roles of TRAFs in normal tissues and provide evidence of altered TRAF1 expression in lymphoid malig nancies.