TLK1>Nek1 Axis Promotes Nuclear Retention and Activation of YAP with Implications for Castration-Resistant Prostate
Damilola Olatunde1, Arrigo De Benedetti1
1Department of Biochemistry and Molecular Biology, The Feist Weiller Cancer Center, Louisiana State University Health Shreveport, Shreveport, LA 71103, USA.
Abstract:
Despite some advances in controlling the progression of prostate cancer (PCa) that is refractory to the use of ADT/ARSI, most patients eventually succumb to the disease, and there is a pressing need to understand the mechanisms that lead to the development of CRPC. A common mechanism is the ability to integrate AR signals from vanishing levels of testosterone, with the frequent participation of YAP as a co-activator, and pointing to the deregulation of the Hippo pathway as a major determinant. We have recently shown that YAP is post-transcriptionally activated via the TLK1>NEK1 axis by stabilizing phosphorylation at Y407. We are now solidifying this work by showing the following: (1) The phosphorylation of Y407 is critical for YAP retention/partition in the nuclei, and J54 (TLK1i) reverses this along with YAP-Y407 dephosphorylation. (2) The enhanced degradation of (cytoplasmic) YAP is increased by J54 counteracting its Enzalutamide-induced accumulation. (3) The basis for all these effects, including YAP nuclear retention, can be explained by the stronger association of pYAP-Y407 with its transcriptional co-activators, AR and TEAD1. (4) We demonstrate that ChIP for GFP-YAP-wt, but hardly for the GFP-YAP-Y407F mutant, at the promoters of typical ARE- and TEAD1-driven genes is readily detected but becomes displaced after treatment with J54. (5) While xenografts of LNCaP cells show rapid regression following treatment with ARSI+J54, in the VCaP model, driven by the TMPRSS2-ERG oncogenic translocation, tumors initially respond well to the combination but subsequently recur, despite the continuous suppression of pNek1-T141 and pYAP-Y407. This suggests an alternative parallel pathway for CRPC progression for VCaP tumors in the long term, which may be separate from the observed ENZ-driven YAP deregulation, although clearly some YAP gene targets like PD-L1, that are found to accumulate following prolonged ENZ treatment, are still suppressed by the concomitant addition of J54.
Insights
Targeting the TLK1>NEK1 axis with J54 inhibits prostate cancer progression by dephosphorylating YAP and preventing its nuclear retention, offering a new therapeutic strategy for castration-resistant prostate cancer (CRPC).
Area of Science:
- Oncology
- Molecular Biology
- Cancer Therapeutics
Background:
- Prostate cancer (PCa) progression to castration-resistant PCa (CRPC) remains a significant clinical challenge, necessitating a deeper understanding of underlying mechanisms.
- The Hippo pathway, particularly the co-activator YAP, plays a crucial role in CRPC by enabling androgen receptor (AR) signaling even at low testosterone levels.
- Recent findings implicate the TLK1>NEK1 axis in the post-transcriptional activation of YAP through phosphorylation at Y407.
Purpose of the Study:
- To elucidate the functional significance of YAP phosphorylation at Y407 in CRPC.
- To investigate the therapeutic potential of inhibiting the TLK1>NEK1 axis using J54 (TLK1 inhibitor) in preclinical models of prostate cancer.
Main Methods:
- Investigated the effect of J54 on YAP phosphorylation, nuclear retention, and degradation in prostate cancer cells.
- Utilized chromatin immunoprecipitation (ChIP) to assess YAP binding to target gene promoters.
- Evaluated the efficacy of combined ARSI and J54 treatment in LNCaP and VCaP xenograft models.
Main Results:
- J54 treatment reversed YAP phosphorylation at Y407, reduced nuclear YAP, and promoted cytoplasmic YAP degradation, counteracting Enzalutamide-induced YAP accumulation.
- Phosphorylated YAP (pYAP-Y407) enhances association with AR and TEAD1, promoting transcription of YAP/AR target genes; J54 disrupts this interaction.
- Combination therapy with ARSI and J54 induced tumor regression in LNCaP xenografts, but VCaP tumors recurred, suggesting alternative CRPC pathways despite YAP suppression.
Conclusions:
- YAP phosphorylation at Y407 is critical for nuclear retention and co-activation of AR/TEAD1 target genes in prostate cancer.
- Inhibition of the TLK1>NEK1 axis via J54 represents a promising strategy to overcome AR signaling in CRPC, particularly in models sensitive to this pathway.
- The recurrence of VCaP tumors highlights the complexity of CRPC and the potential for alternative signaling pathways that may require combination therapies beyond targeting YAP.
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