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PTK6 domain mutants modulates action in Triple-negative breast cancer

ABSTRACT: Protein tyrosine kinase 6 (PTK6; also called Brk) is overexpressed in 86% of breast cancer patients; high PTK6 expression predicts poor outcome. We reported PTK6 induction by HIF/GR complexes in response to either cellular or host stress. However, PTK6-driven signaling events in the context of TNBC remain undefined. In a mouse model of TNBC, manipulation of PTK6 levels (i.e. via knock-out or add-back) had little effect on primary tumor volume but altered lung metastasis. To delineate the mechanisms of PTK6 downstream signaling, we created kinase-dead (KM) and kinase-intact domain structure mutants of PTK6 via in frame deletions of the N-terminal SH3 or SH2 domains. While the PTK6 kinase domain contributed to soft-agar colony formation, PTK6 kinase activity was entirely dispensable for cell migration. Specifically, TNBC models expressing a PTK6 variant lacking the SH2 domain (SH2-del PTK6) were unresponsive to growth factor-stimulated cell motility relative to SH3-del, KM or wild-type PTK6 controls. Reverse phase protein array (RPPA) revealed that while intact PTK6 mediates spheroid formation via p38 MAPK signaling, the SH2 domain of PTK6 limits this biology, and instead mediates TNBC cell motility via activation of the RhoA and/or AhR signaling pathways. Inhibition of RhoA and/or AhR blocked TNBC cell migration as well as the branching/invasive morphology of PTK6+/AhR+ primary breast tumor tissue organoids. Inhibition of RhoA also enhanced paclitaxel cytotoxicity in TNBC cells, including in a taxane-refractory TNBC model. Together, these studies reveal that the SH2-domain of PTK6 is a potent effector of advanced cancer phenotypes in TNBC and identify RhoA and AhR as novel therapeutic targets in PTK6+ breast tumors.

ORGANISM(S): Homo sapiens

PROVIDER: GSE156676 | GEO | 2020/08/31

REPOSITORIES: GEO

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Project description:Src family kinases are often overexpressed and constitutively active in cancer cells, where they represent promising targets for therapeutic intervention. In myeloid hematopoietic cells, Hck, Lyn, and Fgr are associated with both chronic and acute forms of myeloid leukemia. All three of these kinases are expressed in acute myeloid leukemia (AML), where high-level expression correlates with poor survival. The pyrrolopyrimidine Src-family kinase inhibitor A-419259 (also known as RK-20449) has been shown to significantly inhibit patient-derived AML bone marrow cell growth in immunocompromised mice. Recent work has identified an N-phenylbenzamide kinase inhibitor, known as TL02-59, which potently inhibited Fgr kinase activity in vitro and reversed orthotopic engraftment of AML cells in the bone marrow and spleen of immunocompromised mice following oral administration. The inhibitory mechanism of this compound with Fgr or other Src-family members has not been reported. Both wild-type Fgr and a tail mutant (i.e., replacement of Tyr527 with Phe) were shown to produce equal numbers of transformed colonies when expressed in rodent fibroblasts, whereas wild-type Hck transforming activity was completely repressed. In both Hck and Fgr, however, the tail tyrosine residue was shown to be phosphorylated, and hydrogen deuterium exchange mass spectrometry (HDX MS) of near-full-length Fgr was consistent with the closed conformation in solution, with the SH3 domain bound to the SH2-kinase linker and the tail bound to SH2. Here we present the first X-ray crystal structures of near-full-length Fgr bound to the ATP site inhibitors A-419259 and TL02-59. Structural changes induced by the inhibitors in the crystalline state were validated in solution using HDX MS, with A-419259 stabilizing the closed conformation and TL02-59 enhancing exposure of the SH3 domain to solvent. These new structures help to explain the constitutive activity of wild-type Fgr in cells as well as its unique sensitivity to TL02-59, which is currently in development for AML and other maladies.

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PTK6 domain mutants modulates action in Triple-negative breast cancer

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