PTK6/BRK is expressed in the normal mammary gland and activated at the plasma membrane in breast tumors
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Maoyu Peng1, Rajyasree Emmadi3, Zebin Wang1, Elizabeth L. Wiley3, Peter H. Gann3, Seema A. Khan4, Nilanjana Banerji5, William McDonald5, Szilard Asztalos2, Thao N.D. Pham2, Debra A. Tonetti2 and Angela L. Tyner1
1 Departments of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago IL
2 Department of Biopharmaceutical Sciences University of Illinois at Chicago, Chicago IL
3 Department of Pathology, University of Illinois at Chicago, Chicago IL
4 Department of Surgery, Northwestern Feinberg School of Medicine, Chicago, IL
5 Allina Health, Minneapolis, MN, USA
Angela L. Tyner, email:
Keywords: PTK6, BRK, tyrosine kinase, breast cancer
Received: April 18, 2014 Accepted: June 29, 2014 Published: June 30, 2014
Protein Tyrosine kinase 6 (PTK6/BRK) is overexpressed in the majority of human breast tumors and breast tumor cell lines. It is also expressed in normal epithelial linings of the gastrointestinal tract, skin, and prostate. To date, expression of PTK6 has not been extensively examined in the normal human mammary gland. We detected PTK6 mRNA and protein expression in the immortalized normal MCF-10A human mammary gland epithelial cell line, and examined PTK6 expression and activation in a normal human breast tissue microarray, as well as in human breast tumors. Phosphorylation of tyrosine residue 342 in the PTK6 activation loop corresponds with its activation. Similar to findings in the prostate, we detect nuclear and cytoplasmic PTK6 in normal mammary gland epithelial cells, but no phosphorylation of tyrosine residue 342. However, in human breast tumors, striking PTK6 expression and phosphorylation of tyrosine 342 is observed at the plasma membrane. PTK6 is expressed in the normal human mammary gland, but does not appear to be active and may have kinase-independent functions that are distinct from its cancer promoting activities at the membrane. Understanding consequences of PTK6 activation at the plasma membrane may have implications for developing novel targeted therapies against this kinase.
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