Receptor tyrosine kinases (RTKs) are important drivers of cancers. In addition to genomic alterations, aberrant activation of WT RTKs plays an important role in driving cancer progression. However, the mechanisms underlying how RTKs drive prostate cancer remain incompletely characterized. Here we show that non-proteolytic ubiquitination of RTK regulates its kinase activity and contributes to RTK-mediated prostate cancer metastasis. TRAF4, an E3 ubiquitin ligase, is highly expressed in metastatic prostate cancer. We demonstrated here that it is a key player in regulating RTK-mediated prostate cancer metastasis. We further identified TrkA, a neurotrophin RTK, as a TRAF4-targeted ubiquitination substrate that promotes cancer cell invasion and found that inhibition of TrkA activity abolished TRAF4-dependent cell invasion. TRAF4 promoted K27- and K29-linked ubiquitination at the TrkA kinase domain and increased its kinase activity. Mutation of TRAF4-targeted ubiquitination sites abolished TrkA tyrosine autophosphorylation and its interaction with downstream proteins. TRAF4 knockdown also suppressed nerve growth factor (NGF) stimulated TrkA downstream p38 MAPK activation and invasion-associated gene expression. Furthermore, elevated TRAF4 levels significantly correlated with increased NGF-stimulated invasion-associated gene expression in prostate cancer patients, indicating that this signaling axis is significantly activated during oncogenesis. Our results revealed a posttranslational modification mechanism contributing to aberrant non-mutated RTK activation in cancer cells.

Highlights d Tw2 + cells are a type IIb/x fiber-specific muscle progenitor d Nrp1 is a membrane receptor enriched in Tw2 + cells compared to Pax7 + cells d Sema3a is a type-I-and-IIa-myofiber-specific chemorepellent that binds Nrp1 d Overexpression of Sema3a in type IIb myofibers prevents Tw2 + cell fusion

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Receptor tyrosine kinases (RTKs) are important drivers of cancers. In addition to genomic alterations, aberrant activation of wild type RTKs play an important role in driving cancer progression. However, the underlying mechanisms of how RTKs drive prostate cancer remains incompletely characterized. Here we show that non-proteolytic ubiquitination of RTK regulates its kinase activity and contributes to RTK-mediated prostate cancer metastasis. TRAF4, a RING domain E3 ubiquitin ligase, is highly expressed in metastatic prostate cancer. We demonstrated here that it is a key player in regulating RTK mediated prostate cancer metastasis. We further identified TrkA, a neurotrophin receptor tyrosine kinase, as a TRAF4-targeted ubiquitination substrate that promotes cancer cell invasion and genetic ablation of TrkA abolished TRAF4-dependent cell invasion. TRAF4 promoted atypical K27 and K29-linked ubiquitination at the TrkA kinase domain and increased its kinase activity. Mutation of TRAF4-targeted ubiquitination sites abolished TrkA tyrosine auto-phosphorylation and its interaction with downstream effector proteins. TRAF4 knockdown also suppressed nerve growth factor-stimulated TrkA downstream p38 MAPK activation and subsequent invasion-associated gene expression. Furthermore, elevated TRAF4 levels significantly correlated with increased NGF-stimulated invasion-associated gene expression in prostate cancer patients, indicating this signaling axis is significantly activated during oncogenesis. Our results revealed a post-translational modification mechanism contributing to aberrant non-mutated receptor tyrosine kinase activation in cancer cells. Citation Format: Ramesh Singh, Dileep Karri, Jiangyong Shao, Subhamoy Dasgupta, Shixia Huang, Dean P. Edwards, Bert W. O'Malley, Ping Yi. TRAF4-mediated NGF receptor TrkA ubiquitination regulates prostate cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1084.