TRAF6 Stimulates the Tumor-Promoting Effects of TGFβ Type I Receptor Through Polyubiquitination and Activation of Presenilin 1

Abstract

Transforming growth factor-β (TGFβ) can be both a tumor promoter and suppressor, although the mechanisms behind the protumorigenic switch remain to be fully elucidated. The TGFβ type I receptor (TβRI) is proteolytically cleaved in the ectodomain region. Cleavage requires the combined activities of tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) and TNF-α-converting enzyme (TACE). The cleavage event occurs selectively in cancer cells and generates an intracellular domain (ICD) of TβRI, which enters the nucleus to mediate gene transcription. Presenilin 1 (PS1), a γ-secretase catalytic core component, mediates intramembrane proteolysis of transmembrane receptors, such as Notch. We showed that TGFβ increased both the abundance and activity of PS1. TRAF6 recruited PS1 to the TβRI complex and promoted lysine-63-linked polyubiquitination of PS1, which activated PS1. Furthermore, PS1 cleaved TβRI in the transmembrane domain between valine-129 and isoleucine-130, and ICD generation was inhibited when these residues were mutated to alanine. We also showed that, after entering the nucleus, TβRI-ICD bound to the promoter and increased the transcription of the gene encoding TβRI. The TRAF6- and PS1-induced intramembrane proteolysis of TβRI promoted TGFβ-induced invasion of various cancer cells in vitro. Furthermore, when a mouse xenograft model of prostate cancer was treated with the γ-secretase inhibitor DBZ {(2S)-2-[2-(3,5-difluorophenyl)-acetylamino]-N-(5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl)-propionamide}, generation of TβRI-ICD was prevented, transcription of the gene encoding the proinvasive transcription factor Snail1 was reduced, and tumor growth was inhibited. These results suggest that γ-secretase inhibitors may be useful for treating aggressive prostate cancer.

TRAF6 promotes TGFβ-induced invasion and cell-cycle regulation via Lys63-linked polyubiquitination of Lys178 in TGFβ type I receptor

“…23,24 To further explore the set of genes regulated by TGFb-induced and TRAF6-mediated polyubiquitination of TbRI, we performed quantitative reverse transcription polymerase chain reaction (qRT-PCR) to analyze the mRNA expression of Vimentin, Twist1, N-cadherin, p73, cyclin D1 (CCND1), and Plasminogen activator inhibitor-1 (PAI1) (Fig. 3).…”

“…[19][20][21][22] We recently reported a mechanism whereby TGFb promotes the invasiveness of cancer cells. [23][24][25] TGFb induces the activation of TRAF6, which ubiquitinates TbRI in a Lys63-dependent manner and promotes proteolytic cleavage of the receptor by TNF a-converting enzyme (TACE) and presenilin-1, resulting in the release of the intracellular domain (ICD) of TbRI. [23][24][25] The TbRI ICD is then translocated to the nucleus, where it associates with the transcriptional co-activator p300 and promotes tumor-cell invasion by inducing the expression of genes encoding TbRI, Snail1, and matrix metallopeptidase 2 (MMP2).…”

“…[23][24][25] TGFb induces the activation of TRAF6, which ubiquitinates TbRI in a Lys63-dependent manner and promotes proteolytic cleavage of the receptor by TNF a-converting enzyme (TACE) and presenilin-1, resulting in the release of the intracellular domain (ICD) of TbRI. [23][24][25] The TbRI ICD is then translocated to the nucleus, where it associates with the transcriptional co-activator p300 and promotes tumor-cell invasion by inducing the expression of genes encoding TbRI, Snail1, and matrix metallopeptidase 2 (MMP2). 23,24,26 In the present study, we identified the acceptor lysine in TbRI that is ubiquitinated by TRAF6, and determined the biological significance of this ubiquitination.…”

“…[23][24][25] The TbRI ICD is then translocated to the nucleus, where it associates with the transcriptional co-activator p300 and promotes tumor-cell invasion by inducing the expression of genes encoding TbRI, Snail1, and matrix metallopeptidase 2 (MMP2). 23,24,26 In the present study, we identified the acceptor lysine in TbRI that is ubiquitinated by TRAF6, and determined the biological significance of this ubiquitination.…”

Targeting TGF-β Signaling for Therapeutic Gain

“…Moreover, because these inhibitors block TbRI kinase activity, they will not prevent signaling independent of the kinase activity, such as TRAF6-p38 MAPK signaling (Hocevar et al 2005;Gudey et al 2014;Sundar et al 2015). SMIs have poor pharmacokinetics and are generally cleared from the body with a t 1/2 of 2-3 h, whereas pharmacodynamic markers, such as inhibition of Smad2 phosphorylation, persist for up to 8 h postdosing (Bueno et al 2008;Gueorguieva et al 2014).…”