Abstract 4383: CD44s is a crucial ATG7 downstream regulator for formation of sphere, a key stem-like property, invasion and lung metastasis of human bladder cancer/BC cells

Abstract

Abstract Over half a million US residents are suffering with bladder cancer (BC), which costs a total $4 billion in treatment annually. Although recent studies report that autophagy-related gene 7 (ATG7) is overexpressed in BCs, the regulatory effects of ATG7 on stem-like phenotypes and invasion have not been explored yet. Current studies demonstrated that the deficiency of ATG7 by its specific shRNA dramatically reduced Sphere formation and invasion in vitro, as well as lung metastasis in vivo in invasive BC cells. Further studies indicated that the knockdown of ATG7 attenuated the expression of CD44 and CD133, while ectopic introduction of CD44s, but not CD133, was capable of completely restoring sphere formation, invasion, and lung metastasis in T24T(shATG7) cells. Mechanistic studies revealed that ATG7 overexpression stabilized CD44s proteins accompanied with upregulating USP28 proteins. Upregulated USP28 was able to bind to CD44s and remove the ubiquitin group from CD44's protein, resulting in the stabilization of CD44s protein. Moreover, inhibition of ATG7 stabilized AUF1 protein and in turn reduced tet1 mRNA stability and expression, which was able to demethylate usp28 promoter, thereby reduced USP28 expression, finally promoting CD44s degradation. In addition, CD44s was defined to inhibit degradation of RhoGDIβ, which in turn promotes BC invasion. Our results demonstrate that CD44s is a key ATG7 downstream regulator of the sphere formation, invasion, and metastasis of BCs, providing significant insight into understanding the BC invasions, metastasis, and stem-like properties. Citation Format: Xiaohui Hua, Xun Che, Jiheng Xu, Chuanshu Huang, Grace Huang, Wei Dai. CD44s is a crucial ATG7 downstream regulator for formation of sphere, a key stem-like property, invasion and lung metastasis of human bladder cancer/BC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4383.