An N-terminal truncated carboxypeptidase E splice isoform induces tumor growth and is a biomarker for predicting future metastasis in human cancers
Terence K. Lee, … , Ronnie T. Poon, Y. Peng Loh
Terence K. Lee, … , Ronnie T. Poon, Y. Peng Loh
Published February 1, 2011
Citation Information: J Clin Invest. 2011;121(3):880-892. https://doi.org/10.1172/JCI40433.
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Research Article Oncology

An N-terminal truncated carboxypeptidase E splice isoform induces tumor growth and is a biomarker for predicting future metastasis in human cancers

Abstract

Metastasis is a major cause of mortality in cancer patients. However, the mechanisms governing the metastatic process remain elusive, and few accurate biomarkers exist for predicting whether metastasis will occur, something that would be invaluable for guiding therapy. We report here that the carboxypeptidase E gene (CPE) is alternatively spliced in human tumors to yield an N-terminal truncated protein (CPE-ΔN) that drives metastasis. mRNA encoding CPE-ΔN was found to be elevated in human metastatic colon, breast, and hepatocellular carcinoma (HCC) cell lines. In HCC cells, cytosolic CPE-ΔN was translocated to the nucleus and interacted with histone deacetylase 1/2 to upregulate expression of the gene encoding neural precursor cell expressed, developmentally downregulated gene 9 (Nedd9) — which has been shown to promote melanoma metastasis. Nedd9 upregulation resulted in enhanced in vitro proliferation and invasion. Quantification of mRNA encoding CPE-ΔN in HCC patient samples predicted intrahepatic metastasis with high sensitivity and specificity, independent of cancer stage. Similarly, high CPE-ΔN mRNA copy numbers in resected pheochromocytomas/paragangliomas (PHEOs/PGLs), rare neuroendocrine tumors, accurately predicted future metastasis or recurrence. Thus, CPE-ΔN induces tumor metastasis and should be investigated as a potentially powerful biomarker for predicting future metastasis and recurrence in HCC and PHEO/PGL patients.

Authors

Terence K. Lee, Saravana R.K. Murthy, Niamh X. Cawley, Savita Dhanvantari, Stephen M. Hewitt, Hong Lou, Tracy Lau, Stephanie Ma, Thanh Huynh, Robert A. Wesley, Irene O. Ng, Karel Pacak, Ronnie T. Poon, Y. Peng Loh

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Figure 2

Elevated expression of CPE-ΔN and NEDD9 in metastatic tumor cell lines.

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Elevated expression of CPE-ΔN and NEDD9 in metastatic tumor cell lines. ...
(A) qRT-PCR quantification of hCPE-ΔN mRNA in HCC tumor cell lines. Graphs show fold difference in expression of CPE-ΔN mRNA in tumor cell lines relative to primary tumor cells with lowest hCPE-ΔN mRNA expression (first blue bar) made equal to 1. Red bars, highly metastatic cell lines; blue bars, low metastatic cell lines. Note higher expression of hCPE-ΔN mRNA in the highly metastatic cell lines compared with low metastatic cells. Asterisks indicate known highly metastatic or aggressive cell lines. Assays were done in quadruplicate. (B) Top: Western blots showing approximately 40 kDa hCPE-ΔN and 70 kDa NEDD9 in HCC tumor cell lines. Bottom: The intensities of the bands from the Western blots were quantified by densitometry. Graphs show expression levels of hCPE-ΔN (blue) and NEDD9 (red) for each cell line, corrected for actin levels and expressed as mean ± SEM in arbitrary units (n = 3 experiments). (C) Western blot showing approximately 40 kDa CPE-ΔN and 70 kDa NEDD9 in highly metastatic HCC cells (MHCCLM3). Cells were infected with si-Scr or CPE-ΔN siRNA (sequences 1, 2, 3) to downregulate CPE-ΔN mRNA expression. All 3 clones showed coordinated downregulation of CPE-ΔN and NEDD9 protein.