TPA INDUCES APOPTOSIS IN MPC-11 MOUSE PLASMACYTOMA CELLS GROWN IN SERUM-FREE MEDIUM

Apoptotic-like events could be rapidly induced by the phorbol ester 12 -O-tetradecanoylphorbol-13-acetate (TPA) in cells of the mouse plasmac ytoma cell line MPC-11 grown in serum-free medium. Indicators for apop tosis were morphological changes visualized by light and electron micr oscopy, such as chromatin condensation and the formation of cellular b uds and fragments, as well as biochemical indices like the appearance of the so-called 'DNA ladder'. Additionally, in these cells which are usually devoid of significant amounts of cytoplasmic intermediate fila ment (cIF) proteins, synthesis and accumulation of the cIF protein vim entin was rapidly induced by TPA treatment and almost all cells became vimentin-positive. Later on, substantial amounts of vimentin and lami n B degradation products appeared, and an increasing fraction of cells displayed low or even undetectable quantities of intact vimentin. Thi s subpopulation was characterized via microscopy to be in the late sta ges of apoptosis. We suggest that in MPC-11 cells undergoing apoptosis in response to TPA treatment vimentin as well as lamin B are degraded , leading to a rearrangement and eventual loss of their respective fil ament networks.