PTK6 inhibition promotes apoptosis of Lapatinib-resistant Her2 breast cancer cells by inducing BimReportar como inadecuado

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Breast Cancer Research

, 17:86

First Online: 19 June 2015Received: 14 February 2015Accepted: 02 June 2015DOI: 10.1186-s13058-015-0594-z

Cite this article as: Park, S.H., Ito, K., Olcott, W. et al. Breast Cancer Res 2015 17: 86. doi:10.1186-s13058-015-0594-z


IntroductionProtein tyrosine kinase 6 PTK6 is a non-receptor tyrosine kinase that is highly expressed in Human Epidermal Growth Factor 2 Her2 breast cancers. Overexpression of PTK6 enhances anchorage-independent survival, proliferation, and migration of breast cancer cells. We hypothesized that PTK6 inhibition is an effective strategy to inhibit growth and survival of Her2 breast cancer cells, including those that are relatively resistant to Lapatinib, a targeted therapy for Her2 breast cancer, either intrinsically or acquired after continuous drug exposure.

MethodsTo determine the effects of PTK6 inhibition on Lapatinib-resistant Her2 breast cancer cell lines UACC893R1 and MDA-MB-453, we used short hairpin ribonucleic acid shRNA vectors to downregulate PTK6 expression. We determined the effects of PTK6 downregulation on growth and survival in vitro and in vivo, as well as the mechanisms responsible for these effects.

ResultsLapatinib treatment of -sensitive- Her2 cells induces apoptotic cell death and enhances transcript and protein levels of Bim, a pro-apoptotic Bcl2 family member. In contrast, treatment of relatively -resistant- Her2 cells fails to induce Bim or enhance levels of cleaved, poly-ADP ribose polymerase PARP. Downregulation of PTK6 expression in these -resistant- cells enhances Bim expression, resulting in apoptotic cell death. PTK6 downregulation impairs growth of these cells in in vitro 3-D Matrigel cultures, and also inhibits growth of Her2 primary tumor xenografts. Bim expression is critical for apoptosis induced by PTK6 downregulation, as co-expression of Bim shRNA rescued these cells from PTK6 shRNA-induced death. The regulation of Bim by PTK6 is not via changes in Erk-MAPK or Akt signaling, two pathways known to regulate Bim expression. Rather, PTK6 downregulation activates p38, and pharmacological inhibition of p38 activity prevents PTK6 shRNA-induced Bim expression and partially rescues cells from apoptosis.

ConclusionsPTK6 downregulation induces apoptosis of Lapatinib-resistant Her2 breast cancer cells by enhancing Bim expression via p38 activation. As Bim expression is a critical biomarker for response to many targeted therapies, PTK6 inhibition may offer a therapeutic approach to treating patients with Her2 targeted therapy-resistant breast cancers.


Bcl2B cell lymphoma 2

BKSbreast tumor kinase substrate

cleaved PARPcleaved poly ADP ribose polymerase

DMEMDulbecco’s modified Eagle’s medium

DMSOdimethyl sulfoxide

ECLenhanced chemiluminescence

EGFRepidermal growth factor receptor

ERestrogen receptor

FACSfluorescence-activated cell sorting

FITCFluorescein isothiocyanate

HER2human epidermal growth factor receptor 2

hsp27heat shock protein 27

IGF-R1insulin-like growth factor 1 receptor


JNKc-Jun N-terminal kinase

MAPKmitogen-activated protein kinase

PBSphosphate-buffered saline

PCRpolymerase chain reaction

PIpropidium iodide

PP2Aprotein phosphatase-2A

PTK6protein tyrosine kinase 6

shRNAshort hairpin RNA

TCGAThe Cancer Genome Atlas

TKItyrosine kinase inhibitor


Electronic supplementary materialThe online version of this article doi:10.1186-s13058-015-0594-z contains supplementary material, which is available to authorized users.

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Autor: Sun Hee Park - Koichi Ito - William Olcott - Igor Katsyv - Gwyneth Halstead-Nussloch - Hanna Y. Irie


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