TRAF1 is involved in the classical NF-κB activation and CD30-induced alternative activity in Hodgkin's lymphoma cells

Abstract

TNFR-associated factors (TRAFs) participate in diverse biological processes, such as adaptive and innate immunity, stress response, and bone metabolism. We report that all TRAFs except TRAF3 are expressed at mRNA and protein levels in B cell-derived Hodgkin's lymphoma cell lines (L428 and KM-H2). Both the classical (p50–RelA) and the alternative NF-κB activity (p52–RelB) are sustained in L428 and KM-H2 cells. A successful depletion of TRAF1 protein expression by means of RNA interference abrogates the anti-apoptosis activity in L428 cells. The TRAF1-deficiency reduces the classical NF-κB activity but not the alternative activity. The expression of the NF-κB targeting genes, such as ICAM- 1, c- Flip, and Cyclin D1, is suppressed in the TRAF1-depleted cells. On the other hand, CD30 signaling upregulates the TRAF1 expression while reducing the expression of TRAF2 and TRAF5. Importantly, the CD30-induced alternative NF-κB activation is inhibited by the depletion of the TRAF1 expression. We also demonstrate that the phosphorylation of the extracellular signal-regulated kinase (ERK) upon CD30 stimulation in Hodgkin's lymphoma cells is independent of TRAF1 expression. Our data shed new light on the function of TRAF1 in B cell-derived lymphoma cells. We conclude that TRAF1 is an important molecule mediating both the CD30 signaling-dependent and independent NF-κB activation, which prevents the lymphoma cells from spontaneous and induced apoptosis.