Mast cells,
mastocytoma cells and basophil leukaemia cells are well-established producers of
leukotrienes when grown and stimulated appropriately. I report that the cells' ability to produce
leukotrienes is dependent on the cells' proliferative status or their provision with
growth factors. Proliferating MC/9 and subconfluent RBL2H3 cells respond maximally to stimulation by 1 microM
ionomycin with the production of 56 and 32 pmol of cysteinyl-
leukotrienes/10(6) cells respectively. In contrast, confluent RBL2H3 or growth-arrested MC/9 cells lose their ability to generate
leukotrienes in response to
ionomycin treatment. This rapid down-regulation of
leukotriene synthesis is also observed when proliferating RBL2H3 cells are transferred to
growth-factor-free medium, wherein cellular
leukotriene-synthesis capacity has an apparent half-lifetime of 60 min. Transfer back into growth medium results in the regeneration of
leukotriene synthesis capacity within 6 h. In growth-arrested MC/9 cells,
leukotriene production ability can at least partially be restored by priming the cells with
interleukin 3, but not with
interleukin 4. In RBL2H3 cells, pretreatment with
protein tyrosine kinase inhibitors such as
genistein (5 min, 37 microM),
herbimycin A (6 h, 3 microM) or
tyrphostin 25 (16 h, 100 microM) completely inhibits
leukotriene generation, whereas
okadaic acid (15 min, 0.5 microM) has no effect. Under these conditions, both
genistein and
herbimycin A strongly impair
ionomycin-induced
protein tyrosine phosphorylation. Our study indicates that
leukotriene generation in these tumour cells is tightly regulated by their proliferation status and supply with
growth factors, and cell stimulation towards
leukotriene synthesis appears to involve
protein tyrosine kinase activity.