THE APOPTOSIS-INDUCING GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR (GM-CSF) ANALOG E21R FUNCTIONS THROUGH SPECIFIC REGIONS OF THE HETERODIMERIC GM-CSF RECEPTOR AND REQUIRES INTERLEUKIN-1-BETA-CONVERTING ENZYME-LIKE PROTEASES

The granulocyte macrophage colony-stimulating factor (GM-CSF) analog E 21R induces apoptosis of hemopoietic cells. We examined the GM-CSF rec eptor subunit requirements and the signaling molecules involved. Using Jurkat T cells transfected with the GM-CSF receptor we found that bot h receptor subunits were necessary for E21R-induced apoptosis. Specifi cally, the 16 membrane-proximal residues of the alpha subunit were suf ficient for apoptosis. This sequence could be replaced by the correspo nding sequence from the interleukin-2 receptor common gamma subunit, i dentifying this as a conserved cytokine motif necessary for E21R-induc ed apoptosis. Cells expressing the alpha subunit and truncated beta c mutants showed that the 96 membrane-proximal residues of beta c were s ufficient for apoptosis, E21R, in contrast to GMCSF, did not alter tyr osine phosphorylation of beta c, suggesting that receptor-associated t yrosine kinases were not activated. Consistent with this, E21R decreas ed the mitogen-activated protein kinase ERK (extracellular signal-regu lated kinase). E21R-induced apoptosis was independent of Fas/APO-1 (CD 95) and required interleukin-1 beta-converting enzyme (ICE)-like prote ases. In contrast, Bcl-2, which protects cells from growth factor depr ivation-induced cell death, did not prevent this apoptosis. These find ings demonstrate the GM-CSF receptor and ICE-like protease requirement s for E21R-induced apoptosis.