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. Implications: The SH2-domain of PTK6 is a potent effector of advanced cancer phenotypes in TNBC via RhoA and AhR, identified herein as novel therapeutic targets in PTK6+ breast tumors.

中文翻译：

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乳腺肿瘤激酶 (Brk/PTK6) 通过 RhoA 和芳烃受体 (AhR) 信号传导的 SH2 域依赖性激活介导晚期癌症表型

蛋白酪氨酸激酶 6（PTK6；也称为 Brk）在 86% 的乳腺癌患者中过度表达；高 PTK6 表达预示不良结果。我们报道了 HIF/GR 复合物对细胞或宿主应激的反应对 PTK6 的诱导。然而，在 TNBC 的背景下，PTK6 驱动的信号事件仍未定义。在 TNBC 的小鼠模型中，PTK6 水平的操作（即通过敲除或添加）对原发肿瘤体积几乎没有影响，但会改变肺转移。为了描述 PTK6 下游信号转导的机制，我们通过 N 末端 SH3 或 SH2 结构域的框内缺失创建了 PTK6 的激酶死亡 (KM) 和激酶完整结构域结构突变体。虽然 PTK6 激酶结构域有助于软琼脂菌落形成，但 PTK6 激酶活性对于细胞迁移是完全可有可无的。具体来说，相对于 SH3-del、KM 或野生型 PTK6 对照，表达缺乏 SH2 结构域的 PTK6 变体 (SH2-del PTK6) 的 TNBC 模型对生长因子刺激的细胞运动没有反应。反相蛋白阵列 (RPPA) 显示，虽然完整的 PTK6 通过 p38 MAPK 信号传导介导球体形成，但 PTK6 的 SH2 结构域限制了这种生物学，而是通过激活 RhoA 和/或 AhR 信号通路介导 TNBC 细胞运动。RhoA 和/或 AhR 的抑制阻断了 TNBC 细胞迁移以及 PTK6+/AhR+ 原发性乳腺肿瘤组织类器官的分支/侵袭形态。RhoA 的抑制也增强了紫杉醇在 TNBC 细胞中的细胞毒性，包括在紫杉烷难治性 TNBC 模型中。启示：PTK6 的 SH2 结构域是 TNBC 中晚期癌症表型通过 RhoA 和 AhR 的有效效应物，