Proteolytic cleavage of phospholipase C-gamma1 during apoptosis in Molt-4 cells.
Apoptosis is a cell suicide mechanism that requires the activation of cellular death proteases for its induction. We examined whether the progress of apoptosis involves cleavage of phospholipase C-gamma1 (PLC-gamma1), which plays a pivotal role in mitogenic signaling pathway. Pretreatment of T leukemic Molt-4 cells with PLC inhibitors such as U-73122 or ET-18-OCH(3) potentiated etoposide-induced apoptosis in these cells. PLC-gamma1 was fragmented when Molt-4 cells were treated with several apoptotic stimuli such as etoposide, ceramides, and tumor necrosis factor alpha. Cleavage of PLC-gamma1 was blocked by overexpression of Bcl-2 and by specific inhibitors of caspases such as Z-DEVD-CH(2)F and YVAD-cmk. Purified caspase-3 and caspase-7, group II caspases, cleaved PLC-gamma1 in vitro and generated a cleavage product of the same size as that observed in vivo, suggesting that PLC-gamma1 is cleaved by group II caspases in vivo. From point mutagenesis studies, Ala-Glu-Pro-Asp(770) was identified to be a cleavage site within PLC-gamma1. Epidermal growth factor receptor (EGFR) -induced tyrosine phosphorylation of PLC-gamma1 resulted in resistance to cleavage by caspase-3 in vitro. Furthermore, cleaved PLC-gamma1 could not be tyrosine-phosphorylated by EGFR in vitro. In addition, tyrosine-phosphorylated PLC-gamma1 was not significantly cleaved during etoposide-induced apoptosis in Molt-4 cells. This suggests that the growth factor-induced tyrosine phosphorylation may suppress apoptosis-induced fragmentation of PLC-gamma1. We provide evidence for the biochemical relationship between PLC-gamma1-mediated signal pathway and apoptotic signal pathway, indicating that the defect of PLC-gamma1-mediated signaling pathway can facilitate an apoptotic progression.
Bae
S S
SS
Department of Signal Transduction, Division of Molecular and Life Science, Pohang University of Science and Technology, Kyungbuk, Pohang 790-784, Republic of Korea.
Perry
D K
DK
Oh
Y S
YS
Choi
J H
JH
Galadari
S H
SH
Ghayur
T
T
Ryu
S H
SH
Hannun
Y A
YA
Suh
P G
PG
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3; D053179:Caspase 7; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002518:Ceramides / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008970:Molecular Weight; D009154:Mutation / Q000235:genetics; D051966:Phospholipase C gamma; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D061945:Caspase Inhibitors; D002518:Ceramides; D007527:Isoenzymes; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; D019000:Phosphotyrosine; D005047:Etoposide; D066246:ErbB Receptors; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; C505409:Casp3 protein, mouse; C505524:Casp7 protein, mouse; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases