Protein Tyrosine Kinase 6 (PTK6) is a non-receptor-type
tyrosine kinase known to be expressed in various
cancers, including
pancreatic cancer. The role of PTK6 in
cancer chemoresistance remains unclear. Therefore, it was hypothesized that PTK6 mechanistically regulates
gemcitabine resistance in
pancreatic cancer.
Gemcitabine treatment stimulated endogenous PTK6 overexpression in MIAPaCa2 and Panc1 cells. PTK6 gene silencing increased cell survival after
gemcitabine treatment and decreased apoptosis, whereas PTK6 overexpression decreased cell survival and increased apoptosis. Selection for
gemcitabine resistance revealed substantially lower PTK6 expression in the
gemcitabine-resistant subclones compared with the parental lines, while restoring PTK6 rescued
gemcitabine sensitivity.
Gemcitabine induced phosphorylation of H2AX (γ-H2AX) and
ataxia-telangiectasia mutated
kinase (pATM), specific markers for
DNA double-strand breaks. Both
gemcitabine-induced phosphorylation of H2AX and ATM were reduced by PTK6 knockdown and increased by PTK6 overexpression. PTK6 overexpression also increased the S-phase fraction 48 hours after
gemcitabine treatment. Although
gemcitabine activated both
caspase-8 (CASP8) and
caspase-9 (CASP9), the effect of PTK6 on
gemcitabine-induced apoptosis required CASP8 but not CASP9. In mouse xenografts, PTK6 overexpression in subcutaneous
tumors attenuated
tumor growth after
gemcitabine treatment. In conclusion, PTK6 prolongs S-phase and increases the ability of
gemcitabine to cause DNA damage in vitro and in vivo.
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