Mcl-1 and Bcl-xL are co-regulated by IL-6 in human myeloma cells

Multiple myeloma (MM) is a slowly proliferative malignancy in which malignant plasma cells accumulate within the bone marrow. The expression of several anti-apoptotic proteins was evaluated by immunoblotting in human myeloma cell lines and in highly purified native myeloma cells. Expression of Bcl-x(L), Mcl-1 and Bcl-2 was found in most of the samples; expression of Bcl-x(L) and Mcl-1 seemed to be related on myeloma cells. In a system of apoptosis by growth factor deprivation on myeloma cells, we showed that the effect of Bcl-2 seemed minimal whereas Mcl-1 and Bcl-x(L) were tightly regulated by interleukin (IL)-6. These findings underline the important role of Mcl-1 and Bcl-x(L) instead of Bcl-2 in IL-6-induced survival of myeloma cells.