Abstract
<title>Abstract</title> <p> <bold>Background</bold> The high mortality rate of colorectal cancer (CRC) is mainly attributed to the invasion and metastasis process of the tumor, among which epithelial-mesenchymal transition (EMT) is the key mechanism. Our research team previously discovered that mesenchymal stem cells (MSC) in the tumor microenvironment(TME) of CRC exhibit senescent states. Senescent MSC are more capable of promoting the progression of colorectal cancer. However, the mechanism of their action in SMAD4-deficient CRC remains unclear. <bold>Methods</bold> In this study, we used H₂O₂-induced senescent MSCs, collected conditioned media (CM), established SMAD4-knockdown LoVo and HCT116 cells, and treated these cells with young MSC-CM, senescent MSC-CM, and LY-2109761. The expression of EMT markers and the activation of the PI3K/AKT signaling pathway were analyzed. Cell migration, invasion, proliferation, and in vivo xenograft tumor growth were evaluated. <bold>Results</bold> This study reveals for the first time that senescent MSC activates the non-classical PI3K/AKT signaling pathway by secreting transforming growth factor-β (TGF-β), thereby inducing EMT and subsequently driving the migration and invasion of SMAD4-deficient CRC cells. Mechanistic studies have shown that in the context of SMAD4 absence, TGF-β derived from senescent MSC activates the PI3K/AKT signaling, leading to key phenotypic changes in EMT such as down-regulation of E-Cadherin and up-regulation of N-Cadherin and Vimentin. It has been confirmed through in vitro and in vivo functional experiments that the TGF-β receptor inhibitor LY-2109761 can effectively reverse the activation of this signaling axis, the EMT process and the malignant phenotype of cancer cells. <bold>Conclusion</bold> This study not only clarifies a new mechanism by which stromal cells reshape tumor behavior in the senescent microenvironment, but also provides a potential targeted intervention strategy for the treatment of SMAD4-deficient CRC with a poor prognosis. </p>