Cytoplasmic retention of protein tyrosine kinase 6 promotes growth of prostate tumor cells

Cell Cycle. 2010 Oct 15;9(20):4190-9. doi: 10.4161/cc.9.20.13518. Epub 2010 Oct 30.

Abstract

Protein tyrosine kinase 6 (PTK6) is an intracellular tyrosine kinase that is nuclear in epithelial cells of the normal prostate, but cytoplasmic in prostate tumors and in the PC3 prostate tumor cell line. The impact of altered PTK6 intracellular localization in prostate tumor cells has not been extensively explored. Knockdown of endogenous cytoplasmic PTK6 resulted in decreased PC3 cell proliferation and colony formation, suggesting that cytoplasmic PTK6 stimulates oncogenic pathways. In contrast, reintroduction of PTK6 into nuclei of PC3 cells had a negative effect on growth. Enhanced tyrosine phosphorylation of the PTK6 substrate Sam68 was detected in cells expressing nuclear-targeted PTK6. We found that mechanisms regulating nuclear localization of PTK6 are intact in PC3 cells. Transiently overexpressed PTK6 readily enters the nucleus. Ectopic expression of ALT-PTK6, a catalytically inactive splice variant of PTK6, did not affect localization of endogenous PTK6 in PC3 cells. Using leptomycin B, we confirmed that cytoplasmic localization of endogenous PTK6 is not due to Crm-1/exportin-1 mediated nuclear export. In addition, overexpression of the PTK6 nuclear substrate Sam68 is not sufficient to bring PTK6 into the nucleus. While exogenous PTK6 was readily detected in the nucleus when transiently expressed at high levels, low-level expression of inducible wild type PTK6 in stable cell lines resulted in its cytoplasmic retention. Our results suggest that retention of PTK6 in the cytoplasm of prostate cancer cells disrupts its ability to regulate nuclear substrates and leads to aberrant growth. In prostate cancer, restoring PTK6 nuclear localization may have therapeutic advantages.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Active Transport, Cell Nucleus / physiology
  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • Cell Line, Tumor
  • Cell Nucleus / metabolism
  • Cytoplasm / enzymology*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Gene Knockdown Techniques
  • Humans
  • Karyopherins / metabolism
  • Male
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism*
  • Nuclear Localization Signals
  • Prostatic Neoplasms / enzymology*
  • Prostatic Neoplasms / pathology*
  • Protein-Tyrosine Kinases / genetics
  • Protein-Tyrosine Kinases / metabolism*
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism
  • Receptors, Cytoplasmic and Nuclear / metabolism
  • Signal Transduction / physiology

Substances

  • Adaptor Proteins, Signal Transducing
  • DNA-Binding Proteins
  • KHDRBS1 protein, human
  • Karyopherins
  • Neoplasm Proteins
  • Nuclear Localization Signals
  • RNA-Binding Proteins
  • Receptors, Cytoplasmic and Nuclear
  • exportin 1 protein
  • Protein-Tyrosine Kinases
  • PTK6 protein, human