The apoptosis-inducing granulocyte-macrophage colony-stimulating factor (GM-CSF) analog E21R functions through specific regions of the heterodimeric GM-CFS receptor and requires interleukin-1β-converting enzyme-like proteases

Abstract

The granulocyte-macrophage colony-stimulating factor (GM-CSF) analog E21R induces apoptosis of hemopoietic cells. We examined the GM-CSF receptor subunit requirements and the signaling molecules involved. Using Jurkat T cells transfected with the GM-CSF receptor we found that both receptor subunits were necessary for E21R-induced apoptosis. Specifically, the 16 membrane-proximal residues of the α subunit were sufficient for apoptosis. This sequence could be replaced by the corresponding sequence from the interleukin-2 receptor common y subunit, identifying this as a conserved cytokine motif necessary for E21R-induced apoptosis. Cells expressing the α subunit and truncated βc mutants showed that the 96 membrane-proximal residues of βc were sufficient for apoptosis. E21R, in contrast to GM-CSF, did not alter tyrosine phosphorylation of βc, suggesting that receptor- associated tyrosine kinases were not activated. Consistent with this, E21R decreased the mitogen-activated protein kinase ERK (extracellular signal- regulated kinase). E21R-induced apoptosis was independent of Fas/APO-1 (CD95) and required interleukin-1β-converting enzyme (ICE)-like proteases. In contrast, Bcl-2, which protects cells from growth factor deprivation-induced cell death, did not prevent this apoptosis. These findings demonstrate the GM-CSF receptor and ICE-like protease requirements for E21R-induced apoptosis.