Background & Aims
Breast tumor kinase (BRK) augments proliferation and promotes cell survival in breast
cancers via interactions with SH2 and SH3 ligand-containing proteins, such as receptor
tyrosine kinases (RTK; e.g. EGFR, ErbB2/neu). Since RTK contribute to cholangiocarcinoma
(CC) evolution we probed BRK protein expression and function in normal and CC livers.
Methods
Immunohistochemical staining of normal livers and CC (n = 93) in a tissue microarray and three CC and an immortalized human cholangiocyte cell
lines (real-time PCR, Western blotting, siRNA) were used to study the functional relationships
between BRK, EGFR, ErbB2, SAM68, and SPRR2a.
Results
BRK protein was expressed in normal human intrahepatic bile ducts; all CC cell lines
and a majority of CC showed strong BRK protein expression. Multiplex immunostaining/tissue
cytometry and immunoprecipitation studies showed: 1) BRK co-localized with EGFR and
ErbB2/neu; 2) BRKhigh/EGFRhigh-co-expressing CC cells had significantly higher Ki67 labeling and; 3) stronger BRK
protein expression was seen in perihilar and distal CC than intrahepatic CC and directly
correlated with CC differentiation. In cell lines, BRK expression augmented proliferation
in response to exogenous EGF, whereas BRK siRNA significantly reduced growth. The
SH3 ligand-containing, SPRR2A activated pTyr342 BRK, which in turn, phosphorylated
SAM68, causing nuclear localization and increased cell proliferation similar to observations
in breast cancers.
Conclusion
BRK expression in a majority of CC can interact with RTK, augmenting growth and interfering
with proliferation inhibitors (SAM68). Therapeutically targeting BRK function (in
addition to RTK) should be of benefit for CC treatment.
Abbreviations:
BRK (breast tumor kinase), CC (cholangiocarcinoma), SPRR2A (small proline-rich protein 2A), SH2 and SH3 (Src- homology domain 2 and 3), ErbB2/neu (human epidermal growth factor receptor 2), STAT (signal transducer and activator of transcription), non-RTK (non-receptor tyrosine kinase), STAR (signal transducer and activator of RNA), SAM68 (Src-associated in mitosis 68kDa protein), SLM (SAM68-like mammalian protein)Keywords
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Article info
Publication history
Published online: March 11, 2015
Accepted:
February 25,
2015
Received in revised form:
January 23,
2015
Received:
August 14,
2014
Identification
Copyright
© 2015 European Association for the Study of the Liver. Published by Elsevier Inc. All rights reserved.
