Blocking of c-FLIPL–independent cycloheximide-induced apoptosis or Fas-mediated apoptosis by the CC chemokine receptor 9/TECK interaction

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Abstract
Chemokines play a pivotal role in regulating leukocyte migration as well as other biological functions. CC chemokine receptor 9 (CCR9) is a specific receptor for thymus-expressed CC chemokine (TECK). It is shown here that engagement of CCR9 with TECK leads to phosphorylation of Akt (protein kinase B), mitogen-activated protein kinases (MAPKs), glycogen synthase kinase–3β (GSK-3β), and a forkhead transcription factor, FKHR, in a human T-cell line, MOLT4, that naturally expresses CCR9. By means of chemical inhibitors, it is shown that phosphoinositide-3 kinase (PI-3 kinase), but not MAPK, is required for CCR9-mediated chemotaxis. Akt, GSK-3β, FKHR, and MAPK have been previously implicated in cell survival signals in response to an array of death stimuli. When MOLT4 cells, which expressed Fas as well as CXCR4, were stimulated with cycloheximide (CHX), an agonistic anti-Fas antibody, or a combination of these, the cells rapidly underwent apoptosis. However, costimulation of MOLT4 cells with TECK or stromal derived factor–1 significantly blocked CHX-mediated apoptosis, whereas stimulation only with TECK partially blocked Fas-mediated apoptosis. Concomitant with this blocking, cleavage of poly (adenosine 5′-diphosphate–ribose) polymerase and activation of caspase 3 were significantly attenuated, but the expression level of FLICE inhibitory protein c-FLIPL, which had been shown to be regulated by CHX, was unchanged. This demonstrates that activation of CCR9 leads to phosphorylation of GSK-3β and FKHR and provides a cell survival signal to the receptor expressing cells against CHX. It also suggests the existence of a novel pathway leading to CHX-induced apoptosis independently of c-FLIPL.