Phosphatidylethanolamine binding protein 4 (PEBP4) is a secreted protein and has multiple functions

Biochim Biophys Acta. 2016 Jul;1863(7 Pt A):1682-9. doi: 10.1016/j.bbamcr.2016.03.022.

Huan He ¹, Dan Liu ², Hui Lin ¹, Shanshan Jiang ³, Ying Ying ⁴, Shao Chun ⁵, Haiteng Deng ⁶, Joseph Zaia ⁵, Rong Wen ⁷, Zhijun Luo ⁸

Affiliations

1 Graduate Program of Internal Medicine, Nanchang University Jiangxi Medical College, Nanchang, China; Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, United States.
2 Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, United States; Department of Pharmacology, Nanchang University School of Pharmaceutic Sciences, Nanchang, China.
3 Graduate Program of Internal Medicine, Nanchang University Jiangxi Medical College, Nanchang, China; Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, United States; Department of Pharmacology, Nanchang University School of Pharmaceutic Sciences, Nanchang, China.
4 Graduate Program of Internal Medicine, Nanchang University Jiangxi Medical College, Nanchang, China; Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, United States; Department of Pathology, Institute of Basic Medical Sciences, Nanchang University Jiangxi Medical College, Nanchang, China.
5 Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, United States.
6 MOE Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University, Beijing, China.
7 Bascom Palmer Eye Institute, University of Miami Miller Medical School, Miami, FL 33136, United States.
8 Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, United States; Department of Pathology, Institute of Basic Medical Sciences, Nanchang University Jiangxi Medical College, Nanchang, China. Electronic address: zluo@bu.edu.

PMID: 27033522 DOI: 10.1016/j.bbamcr.2016.03.022

Abstract

Phosphatidylethanolamine binding proteins (PEBP) represent a superfamily of proteins that are conserved from bacteria to humans. In mammals, four members have been identified, PEBP1-4. To determine the functional differences among PEBP1-4 and the underlying mechanism for their actions, we performed a sequence alignment and found that PEBP4 contains a signal peptide and potential glycosylation sites, whereas PEBP1-3 are intracellular proteins. To test if PEBP4 is secreted, we made constructs with Myc epitope at the amino (N) terminus or carboxyl (C) terminus to mask the signal sequence or keep it free, respectively. Our data revealed that both mouse and human PEBP4 were secreted when the epitope was tagged at their C-terminus. To our surprise, secretion was dependent upon the C-terminal conserved domain in addition to the N-terminal signal sequence. When the epitope was placed to the N-terminus, the recombinant protein failed to secrete and instead, was retained in the cytoplasm. Mass spectrometry detected asparagine (N)-glycosylation on the secreted PEBP4. Although overexpression of N-terminal tagged PEBP4 resulted in an inhibition of ERK activation by EGF, that with a C-terminal epitope tag did not have such an effect. Likewise, transfection of PEBP4 shRNA did not appear to affect ERK activation, suggesting that PEBP4 does not participate in the regulation of this pathway. In contrast, PEBP4 siRNA suppressed phosphorylation of Act at S473. Therefore, our results suggest that PEBP4 is a multifunctional protein and can be secreted. It will be important to investigate the mechanism by which PEBP4 is secreted and regulates cellular events.

Keywords

Act; ERK; Glycosylation; PEBP4; Secretion; Signal peptide.

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