Effects of wortmannin and rapamycin on CSF-1-mediated responses in macrophages

There are differing views regarding the roles of phosphatidylinositol 3- kinases (PI3-kinases) and p70 S6 kinase (p76(s6k)) in growth factor-induced cellular responses. One approach that is widely employed to investigate these roles is to use the inhibitors, wortmannin and rapamycin, respectively. This approach is used here to study the responses in macrophages to colony stimulating factor-1 (CSF-1). Wortmannin (≤30 nM) and rapamycin (≤3 nM) both weakly inhibited CSF-1-stimulated DNA synthesis in murine bone marrow- derived macrophages (BMM), suggesting that there are PI3-kinase- and p70(s6k)-independent pathways required for the onset of the S phase; interestingly the combination of the drugs gave dramatic suppression. Inhibition of DNA synthesis by rapamycin on the BMM was much less than that observed with the CSF-1-dependent cell line, BAC1.2F5. In BMM, wortmannin suppressed CSF-1-stimulated increase in p70(s6k) activity indicating that PI3-kinase activity may lie upstream. In contrast to some other growth factor/cell systems, no evidence was obtained using the inhibitors for the involvement of PI3-kinase or p70(s6k) in CSF-1-mediated induction of c-fos mRNA expression or Erk-1 activity; in addition no evidence was found for an involvement in the CSF-1-mediated increase in cyclin D1 expression or STAT activation. The findings reinforce the need to study the signal transduction cascades relevant to each individual growth factor and preferably not in cell lines.