A novel human phosphatidylethanolamine-binding protein resists tumor necrosis factor alpha-induced apoptosis by inhibiting mitogen-activated protein kinase pathway activation and phosphatidylethanolamine externalization.
The phosphatidylethanolamine (PE)-binding proteins (PEBPs) are an evolutionarily conserved family of proteins with pivotal biological functions. Here we describe the cloning and functional characterization of a novel family member, human phosphatidylethanolamine-binding protein 4 (hPEBP4). hPEBP4 is expressed in most human tissues and highly expressed in tumor cells. Its expression in tumor cells is further enhanced upon tumor necrosis factor (TNF) alpha treatment, whereas hPEBP4 normally co-localizes with lysosomes, TNFalpha stimulation triggers its transfer to the cell membrane, where it binds to Raf-1 and MEK1. L929 cells overexpressing hPEBP4 are resistant to both TNFalpha-induced ERK1/2, MEK1, and JNK activation and TNFalpha-mediated apoptosis. Co-precipitation and in vitro protein binding assay demonstrated that hPEBP4 interacts with Raf-1 and MEK1. A truncated form of hPEBP4, lacking the PE-binding domain, maintains lysosomal co-localization but has no effect on cellular responses to TNFalpha. Given that MCF-7 breast cancer cells expressed hPEBP4 at a high level, small interfering RNA was used to silence the expression of hPEBP4. We demonstrated that down-regulation of hPEBP4 expression sensitizes MCF-7 breast cancer cells to TNFalpha-induced apoptosis. hPEBP4 appears to promote cellular resistance to TNF-induced apoptosis by inhibiting activation of the Raf-1/MEK/ERK pathway, JNK, and PE externalization, and the conserved region of PE-binding domain appears to play a vital role in this biological activity of hPEBP4.
Wang
Xiaojian
X
Institute of Immunology, Zhejiang University, Hangzhou 310031, People's Republic of China.
Li
Nan
N
Liu
Bin
B
Sun
Hongying
H
Chen
Taoyong
T
Li
Hongzhe
H
Qiu
Jianming
J
Zhang
Lihuang
L
Wan
Tao
T
Cao
Xuetao
X
D000595:Amino Acid Sequence; D000727:Androgen-Binding Protein; D017209:Apoptosis / Q000187:drug effects*; D002352:Carrier Proteins / Q000502:physiology*; D045744:Cell Line, Tumor; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008969:Molecular Sequence Data; D049488:Phosphatidylethanolamine Binding Protein; D010714:Phosphatidylethanolamines / Q000378:metabolism*; D021381:Protein Transport; D012333:RNA, Messenger / Q000032:analysis; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D000727:Androgen-Binding Protein; D002352:Carrier Proteins; C511482:PEBP1 protein, human; D049488:Phosphatidylethanolamine Binding Protein; D010714:Phosphatidylethanolamines; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; C483858:phosphatidylethanolamine; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3