PI3K regulates TAZ/YAP and mTORC1 and can synergistically be targeted in sarcomas

Sarcomas encompass heterogenous, difficult to treat cancers, lacking common therapeutic targets. Phosphatidylinositol-3 kinase (PI3K) signaling is activated in sarcomas to a greater degree than previously appreciated due to phosphatase and tensin homolog (PTEN) loss, and could represent such a target. Targeting PI3K signaling has largely focused on targeting mTORC1, considered the main effector of PI3K signaling, but this has not translated to success in the clinic, suggesting that there may be other effectors downstream of PI3K. One gap in our understanding of the PI3K signaling pathway has been the absence of a known oncogenic transcription factor. Herein we implicate TAZ and YAP as additional transcriptional effectors downstream of PI3K signaling regulated by a LATS1/2 dependent mechanism. Using in vitro and in vivo approaches, we show that TAZ and YAP are central oncoproteins in PI3K driven oncogenesis along with mTORC1, providing a rationale for combination therapy. Leveraging these findings, we describe a therapeutic approach that builds upon pre-existing therapeutic strategies utilizing mTORC1 inhibitors and combines them with new TEAD inhibitors that target YAP and TAZ. Combination therapy using everolimus and IK-930, an inhibitor targeting autopalmitoylation of the TEADs, synergistically diminished proliferation and anchorage dependent growth of PI3K activated sarcoma cell lines at low, physiologically achievable doses. In vivo, this combination therapy showed a synergistic effect, contrasting with the lack of effect of the individual single agent therapies, suggesting that an integrated view of PI3K and Hippo signaling can be leveraged therapeutically in PI3K activated sarcomas. RNA was isolated from the tumors of genetically engineered mouse. Where, "Skel" is the control group and "PTEN", "YAP", "TAZ", "Quad" represent the experimental group. Each sample group had 5 replicates. RNA-seq was done to evaluate and study the differentially expressed genes in each group. PTEN: Trp53fl/fl Ptenfl/fl YAP: Trp53fl/fl Ptenfl/flYapfl/fl TAZ: Trp53fl/flPtenfl/flTazfl/fl QUAD: Trp53fl/flPtenfl/flYapfl/flTazfl/fl SKEL: skeletal muscle control

肉瘤（Sarcomas）是一类异质性强、治疗难度极高的癌症，缺乏通用的治疗靶点。磷脂酰肌醇-3激酶（Phosphatidylinositol-3 kinase, PI3K）信号通路在肉瘤中的激活程度远超此前认知，这一现象源于张力蛋白同源磷酸酶（phosphatase and tensin homolog, PTEN）的缺失，而PI3K信号通路正可作为这类癌症的潜在治疗靶点。此前针对PI3K信号通路的靶向治疗大多聚焦于mTORC1——这一被认为是PI3K信号通路主要效应分子的靶点，但这类策略尚未在临床中取得成功，这提示PI3K下游或许存在其他未被发现的效应分子。目前我们对PI3K信号通路的认知空白之一，是尚未发现明确的致癌转录因子。本研究证实TAZ与YAP是PI3K信号通路下游的额外转录效应分子，其表达受LATS1/2依赖的机制调控。通过体外（in vitro）与体内（in vivo）实验手段，我们证实TAZ与YAP是PI3K驱动的肿瘤发生过程中与mTORC1同等关键的致癌蛋白，这为联合治疗提供了坚实的理论依据。基于上述发现，我们提出了一种治疗策略：在现有mTORC1抑制剂治疗方案的基础上，联合靶向YAP与TAZ的新型TEAD抑制剂。使用依维莫司（everolimus）与IK-930——一种靶向TEAD自身棕榈酰化的抑制剂——的联合治疗方案，在低剂量且生理可达到的给药浓度下，可协同抑制PI3K激活的肉瘤细胞系的增殖与锚定依赖性生长。在体内实验中，该联合治疗方案展现出显著的协同效应，而单一药物治疗则无明显效果，这提示我们可以整合PI3K与Hippo信号通路（Hippo signaling）的视角，对PI3K激活型肉瘤开展靶向治疗。我们从基因工程小鼠的肿瘤组织中提取RNA。其中，"Skel"为对照组，"PTEN"、"YAP"、"TAZ"、"Quad"为实验组，每组样本均设置5个生物学重复。通过RNA测序（RNA-seq）分析各组间的差异表达基因。具体基因型如下：PTEN组：Trp53fl/fl Ptenfl/fl；YAP组：Trp53fl/fl Ptenfl/flYapfl/fl；TAZ组：Trp53fl/flPtenfl/flTazfl/fl；QUAD组：Trp53fl/flPtenfl/flYapfl/flTazfl/fl；SKEL组：骨骼肌对照。