Interferon-γ has dual potentials in inhibiting or promoting cell proliferation

Abstract

Many cytokines have dual functions of promoting or inhibiting cell proliferation; however, the molecular mechanism of the dual functions of cytokines is not well understood. Under normal conditions, interleukin (IL)-3 is required for Ba/F3 cell proliferation, whereas interferon (IFN)-γ inhibits Ba/F3 cell proliferation. It is known that Stat1 play a major role in inhibition of cell growth in response to IFN-γ. We have examined the possibility of whether IFN-γ can act as a growth-promoting cytokine if the Stat1 function is selectively blocked. We have established variant Ba/F3 cell lines in which Stat1 function is inhibited by a dominant-negative Stat1 mutant. Intriguingly, once Stat1 function is inhibited, IFN-γ can replace IL-3 acting as an essential growth factor for cell proliferation. To understand the molecular mechanism of regulation of cell proliferation by the cytokines, the signaling pathways and gene induction by IL-3 and IFN-γ are further studied. Although IL-3 activates mitogenic-activated protein kinase and Akt kinase, IFN-γ does not. Interestingly, both IL-3 and IFN-γ induce expression of the c-Myc gene that is not dependent on the Stat1 activity. Expression of a dominant-negative mutant Myc can block IFN-γ-mediated Ba/F3 cell proliferation, suggesting that c-Myc gene induction is required for IFN- γ-mediated cell proliferation. These findings suggest that IFN-γ intrinsically and simultaneously induces specific and conflicting signaling pathways and transcriptional programs that contribute to the potential dual effects of IFN-γ in promoting or inhibiting cell proliferation.