TIE2 Associates with Caveolae and Regulates Caveolin-1 To Promote Their Nuclear Translocation

ABSTRACT

DNA repair pathways are aberrant in cancer, enabling tumor cells to survive standard therapies—chemotherapy and radiotherapy. Our group previously reported that, upon irradiation, the membrane-bound tyrosine kinase receptor TIE2 translocates into the nucleus and phosphorylates histone H4 at Tyr51, recruiting ABL1 to the DNA repair complexes that participate in the nonhomologous end-joining pathway. However, no specific molecular mechanisms of TIE2 endocytosis have been reported. Here, we show that irradiation or ligand-induced TIE2 trafficking is dependent on caveolin-1, the main component of caveolae. Subcellular fractionation and confocal microscopy demonstrated TIE2/caveolin-1 complexes in the nucleus, and using inhibitor or small interfering RNAs (siRNAs) against caveolin-1 or Tie2 inhibited their trafficking. TIE2 was found in caveolae and directly phosphorylated caveolin-1 at Tyr14 in vitro and in vivo. This modification regulated the generation of TIE2/caveolin-1 complexes and was essential for TIE2/caveolin-1 nuclear translocation. Our data further demonstrate that the combination of TIE2 and caveolin-1 inhibitors resulted in significant radiosensitization of malignant glioma cells, which will guide the development of combinatorial treatment with radiotherapy for patients with glioblastoma.

KEYWORDS:

• TIE2
• caveolin-1
• nuclear translocation
• radioresistance
• brain tumor
• nuclear transport
• radiosensitivity

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at https://doi.org/10.1128/MCB.00142-17.

ACKNOWLEDGMENTS

We thank Ann M. Sutton (Department of Scientific Publications, MD Anderson, Houston, TX) for scientific editorial assistance and Xuejun Fan and Joy Gumin (Brain Tumor Program, MD Anderson, Houston, TX) for technical assistance. We acknowledge Federico Bussolino (University of Turin, Turin, Italy) for providing the pcDNA3-Tie2 plasmid and William A. Barton (Virginia Commonwealth University, Richmond, VA) for providing pcDNA3.1-Tie2-myc.

We declare that we have no conflict of interest.

Author contributions were as follows: M.B.H., R.S., J.F., and C.G.-M. developed the original hypothesis. M.B.H., R.S., J.F., C.G.-M., and J.L. designed the study, performed experiments, and analyzed data. X.L. carried out and interpreted the mass spectrometry experiments. K.R.H. carried out the statistical analysis. Y.R.-M., F.P.M., H.J., and M.-C.H. participated with the discussion of results. F.F.L. provided GSCs. The manuscript was written by M.B.H., R.S., J.F., and C.G.-M.

This work was supported by National Institutes of Health (NIH) grant R01 NS069964, grant P50 CA127001, and Cancer Center Support Grant P30CA016672 (Sequencing and Microarray Facility).