The Cytosolic Domain of Protein-tyrosine Kinase 7 (PTK7), Generated from Sequential Cleavage by a Disintegrin and Metalloprotease 17 (ADAM17) and γ-Secretase, Enhances Cell Proliferation and Migration in Colon Cancer Cells

• Published in: The Journal of biological chemistry 2012-07, Vol.287 (30), p.25001-25009
• Main Authors: Na, Hye-Won, Shin, Won-Sik, Ludwig, Andreas, Lee, Seung-Taek
• Format: Article
• Language: English
• Subjects: ADAM Proteins - genetics; ADAM Proteins - metabolism; ADAM17; ADAM17 Protein; Amyloid Precursor Protein Secretases - genetics; Amyloid Precursor Protein Secretases - metabolism; Cell Adhesion Molecules - genetics; Cell Adhesion Molecules - metabolism; Cell Biology; Cell Line, Tumor; Cell Movement; Cell Proliferation; Cell Transformation, Neoplastic; Colon Cancer; Colon Cancer Cells; Colonic Neoplasms - genetics; Colonic Neoplasms - metabolism; HEK293 Cells; Humans; Neoplasm Proteins - genetics; Neoplasm Proteins - metabolism; Protein Processing; Protein Structure, Secondary; Protein Structure, Tertiary; Protein-tyrosine Kinase (Tyrosine Kinase); Proteolysis; PTK7; Receptor Protein-Tyrosine Kinases - genetics; Receptor Protein-Tyrosine Kinases - metabolism; Shedding; Tumorigenesis; γ-Secretase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.348904

Background: A shedding product of PTK7 was detected in the culture media from colon cancer cells. Results: PTK7 is sequentially processed by ADAM17 and γ-secretase, and its cytosolic domain enhances oncogenic properties of colon cancer cells. Conclusion: The cytosolic domain of PTK7 generated by sequential cleavage of ADAM17 and γ-secretase promotes tumorigenesis. Significance: We provide a novel oncogenic mechanism of PTK7 upon its processing. Protein-tyrosine kinase 7 (PTK7) is a member of the defective receptor protein-tyrosine kinases and is known to function as a regulator of planar cell polarity during development. Its expression is up-regulated in some cancers including colon carcinomas. A 100-kDa fragment of PTK7 was detected in the culture media from colon cancer cells and HEK293 cells. The shed fragment was named sPTK7-Ig1–7 because its molecular mass was very similar to that of the entire extracellular domain of PTK7 that contains immunoglobulin-like loops 1 to 7 (Ig1–7). The shedding of sPTK7-Ig1–7 was enhanced by treatment with phorbol 12-myristate 13-acetate. In addition to the sPTK7-Ig1–7 found in the culture medium, two C-terminal fragments of PTK7 were detected in the cell lysates: PTK7-CTF1, which includes a transmembrane segment and a cytoplasmic domain, and PTK7-CTF2, which lacks most of the transmembrane segment from PTK7-CTF1. Analysis of PTK7 processing in the presence of various protease inhibitors or after knockdown of potential proteases suggests that shedding of PTK7 into sPTK7-Ig1–7 and PTK7-CTF1 is catalyzed by ADAM17, and further cleavage of PTK7-CTF1 into PTK7-CTF2 is mediated by the γ-secretase complex. PTK7-CTF2 localizes to the nucleus and enhances proliferation, migration, and anchorage-independent colony formation. Our findings demonstrate a novel role for PTK7 in the tumorigenesis via generation of PTK7-CTF2 by sequential cleavage of ADAM17 and γ-secretase.