Expression of Polyamine Transporter Activity during B Lymphocyte Cell Cycle Progression

The movement of resting B cells into the early stages of the cell cycle is accompanied by elevations in cellular polyamine levels. Our previous results indicate that part of this increase is a consequence of enhanced levels of ornithine decarboxylase activity in activated B cells. However, the levels of ornithine decarboxylase wane within 30 h post-stimulation, suggesting that B cells may acquire polyamines from an alternative source. Results in the present communication indicate that B cells initiate the transport of extracellular polyamines as they enter the G₁ stage of the cell cycle. This induction of polyamine transport activity is seen after the stimulation of B cell cycle progression by both PMA and ionomycin, as well as cognate help from activated Th cells. The transport activities are energy and temperature sensitive, and can be competitively inhibited by unlabeled ligands. The results of the competition studies are compatible with the presence of at least two types of transporters, a low affinity transporter for both putrescine and spermidine, and a higher affinity transporter selective for spermidine. The results are discussed in terms of biochemical events associated with Th cell-mediated, B cell activation.