YAP1 Depletion Enhances TAZ and its Complexation with TEAD4 and AP-1 Heterodimer C-JUN/FOSB to Promote Gastric Cancer Progression and Metastases

Background

Dysregulation of the Hippo signaling pathway, characterized by aberrant activation of the transcriptional coactivators YAP1 and TAZ, drives tumour progression, immunosuppression and metastasis. Hippo pathway components are emerging therapeutic targets in several solid tumours, however, the expression profiles of Hippo coactivators YAP1, TAZ and their transcriptional factors TEAD1-4 in gastric cancer peritoneal metastases (GCPMs) and their therapeutic value are unknown.

Objective

To determine expression status of YAP1, TAZ and TEAD1-4 in GCPMs; and to evaluate whether dual targeting of YAP1 and TAZ provides superior antitumour activity compared with inhibition of either coactivator alone.

Design

Expression of YAP1, TAZ and TEAD1–4 was examined in GCPMs by single-cell RNA sequencing and co-immunofluorescent staining. Functional studies using genetic knockout and antisense oligonucleotide (ASO) inhibition of YAP1 or TAZ were performed to assess antineoplastic effects in vitro and in vivo. Co-immunoprecipitation and luciferase reporter assays were used to characterize YAP1/TAZ interactions with TEADs and AP-1 components (JUN and FOSB) and to quantify transcriptional activity. Antitumour efficacy was validated in patient-derived xenograft (PDX) and KP-Luc2 syngeneic models.

Results

YAP1, TAZ, and TEADs1- 4 were highly coexpressed in GCPMs and correlated with poor survival. YAP1 inhibition alone elicited compensatory upregulation of TAZ, while combined inhibition of both coactivators maximally repressed cell proliferation and invasion in vitro , and tumor growth in vivo . Increased TAZ complexation with TEAD4 and AP-1 (c-JUN and FOSB) heterodimer was observed following YAP1 knockdown or pharmacological ASO inhibition. Dual inhibition of YAP1 and TAZ was required to maximally suppress YAP1/TAZ expression and reduce their nuclear accumulation, transactivation of TEAD, and activation of downstream genes.

Conclusions

These findings show that combined YAP1 and TAZ inhibition holds promise for the treatment of GCPMs, a highly lethal disease with an urgent need for novel treatment options.

WHAT IS ALREADY KNOWN ON THIS TOPIC

• Gastric cancer with peritoneal metastasis (GCPM), occurring in > 45% of gastric cancer (GC) patients, is a highly lethal malignancy with limited therapeutic options.

• The Hippo pathway mediator Yes-associated protein 1 (YAP1) is intimately involved in chemoresistance, cancer stemness properties, and the epithelial-to-mesenchymal transition in gastric and other cancers.

• While YAP1 represents a promising therapeutic target, clinical trial of YAP1 antisense oligonucleotides has been disappointing.

WHAT THIS STUDY ADDS

• Hippo coactivators YAP1, TAZ and their main transcription factors TEAD1-4 are markedly upregulated in GCPMs and associated with poor prognosis.

• Antisense targeting of YAP1 results in compensatory upregulation of its paralog TAZ.

• Upon YAP1 depletion, TAZ forms transcriptional complexes with TEAD4 and the AP-1 heterodimer (JUN and FOSB).

• Dual targeting of YAP1 and TAZ, by oligonucleotides, achieves maximal suppression of tumour growth in vitro and in vivo .

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

• These findings provide a strong mechanistic rationale for co-targeting YAP1 and TAZ as a therapeutic approach in metastatic gastric cancer.

• Dual Hippo coactivator inhibition could inform the design of future clinical trials aimed at improving outcomes for patients with GCPMs.