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Phosphorylation of RAB7 by TBK1/IKKε regulates innate immune signaling in triple negative breast cancer

Authors

  • J.L. Ritter
  • Z. Zhu
  • T.C. Thai
  • N.R. Mahadevan
  • P. Mertins
  • E.H. Knelson
  • B.P. Piel
  • S. Han
  • J.D. Jaffe
  • S.A. Carr
  • D.A. Barbie
  • T.U. Barbie

Journal

  • Cancer Research

Citation

  • Cancer Res

Abstract

  • Triple negative breast cancer (TNBC) is a heterogeneous disease enriched for mutations in PTEN and dysregulation of innate immune signaling. Here we demonstrate that Rab7, a recently identified substrate of PTEN phosphatase activity, is also a substrate of the innate immune signaling kinases TBK1/IKKε on the same serine-72 site. An unbiased search for novel TBK1/IKKε substrates using stable isotope labeling with amino acids in cell culture (SILAC) phosphoproteomic analysis identified Rab7 serine-72 (S72) as a top hit. PTEN-null TNBC cells expressing a phosphomimetic version of Rab7-S72 exhibited diffuse cytosolic Rab7 localization and enhanced innate immune signaling, in contrast to a kinase-resistant version, which localized to active puncta that promote lysosomal-mediated STING degradation. Thus, convergence of PTEN loss and TBK1/IKKε activation on Rab7-S72 phosphorylation limited STING turnover and increased downstream production of IRF3 targets including CXL10, CCL5, and IFN-b. Consistent with this data, PTEN-null TNBC tumors expressed higher levels of STING, and PTEN-null TNBC cell lines were hyper-responsive to STING agonists. Together these findings begin to uncover how innate immune signaling is dysregulated downstream of TBK1/IKKε in a subset of TNBCs and reveals previously unrecognized cross-talk with STING recycling that may have implications for STING agonism in the clinic.


DOI

doi:10.1158/0008-5472.CAN-19-1310