Effect of interleukin-6 on cell proliferation of FRTL-5 cells.

We studied the effects of interleukin-6(IL-6) on DNA synthesis and cyclic AMP production in rat thyroid FRTL-5 cells. When cells were incubated with IL-6 in the presence or absence of IGF-I, cell proliferation was not observed. By contrast, IL-6 stimulated DNA synthesis in a dose dependent manner when TSH was added concomitantly. On the other hand, IL-6 did not modulate the cAMP accumulation in the presence or absence of TSH. These data demonstrate that, like IGF-I, IL-6 may be able to act as a growth factor through activation of a mitogenic signal transduction pathway different from A-kinase in FRTL-5 cells.