Down-regulation of Pim-1 and Bcl-2 is accompanied with apoptosis of interleukin-6-depleted mouse B-cell hybridoma 7TD1 cells.

Here we report, interleukin-6 (IL-6) dependent mouse B-cell hybridoma, 7TD1 cells underwent apoptotic cell death with the starvation of IL-6. First, 7TD1 cells cultured without IL-6 arrested at G0/G1 phase (maximum accumulation at 24 h ) of the cell cycle. After that, the parameters of apoptosis namely, decreased mitochondrial transmembrane potential (DeltaPsi(m)), activation of caspases, DNA fragmentation and morphological changes (condensed nucleus and formation of apoptotic bodies) were observed. As evidents by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses, down-regulation of Pim-1 (a serine/threonine kinase) and Bcl-2 was observed in the IL-6-depleted 7TD1 cells. There was no change in the expression of c-Myc, Bcl-xL and Mcl-1, even at 48 h of IL-6-depletion. Taken together, these results indicate that IL-6 withdrawn from the 7TD1 cells resulted in G0/G1 arrest and then caspase-dependent apoptosis via mitochondrial pathway by down-regulation of Pim-1 and Bcl-2, which may be essential for anti-apoptotic signals of IL-6.