CD133-mediated TM4SF5 expression enhances growth and survival of liver cancer spheres

TM4SF5;CD133;β-catenin;Src;Akt;sphere formation and growth;615

약학대학 약학과 ;

University:서울대학교 대학원

关键词: TM4SF5;    CD133;    β-catenin;    Src;    Akt;    sphere formation and growth;    615;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/133663/1/000000141364.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

Transmembrane 4 L six family member 5 (TM4SF5) is a member of the tetraspanin L6 superfamily and highly expressed in various cancers including hepatocarcinoma. Previous study showed that TM4SF5 physically interacts with CD44, one of the cancer stem cell (CSC) markers, and this interaction leads to self-renewal stemness and activates circulating properties via an involvement of Epithelial-Mesenchymal Transition (EMT) phenotypes. In this study, I investigated how TM4SF5 and CD44 could be regulated while leading to their collaboration for cellular stemness-like and circulating properties. Since CD133 is also well-known to be a cancer stem cell surface marker and a pentaspan transmembrane protein expressed by a broad range of cancers including hepatocarcinoma, I studied here how the expression of TM4SF5 and CD44 are regulated by CD133 related to their stemness-like and circulating properties. In this study, I found that overexpression of CD133 in liver cancer cells increases expression of TM4SF5 and CD44. However, neither overexpression nor knockdown of TM4SF5 affects CD133 expression. As overexpression of CD44 does not change the expression of CD133 and TM4SF5, our results suggest that CD133 regulates TM4SF5 and CD44 as an upstream molecule of them. Then, two tyrosine residues (Y828 and Y852) present in the cytoplasmic tail of CD133 were substituted by a phenylalanine residue individually, or simultaneously, Y828/852F, or the c-terminal cytoplasmic domain of CD133 (52 amino acids) was completely deleted. Under both conditins, c-Src and Akt activities and expression level of TM4SF5 decreased, compared to CD133 wildtype. Topflash reporter assays showed that the transcriptional activity of β-catenin by CD133 mutants decreased, compared to the wildtype. TM4SF5 reporter assays also showed that the activated β-catenin promoted TM4SF5 expression subsequently, suggesting that CD133 regulates TM4SF5 expression by c-Src, Akt, and β-catenin signaling cascades. In 3D aqueous condition, CD133-overexpressing cells formed more and bigger spheres than cells expressing C-terminal mutants of CD133. In addition, treatment of TSAHC, a specific TM4SF5 inhibitor, showed that CD133-overexpressing cells showed more effective inhibitory response to form spheres upon TSAHC treatment, suggesting that CD133 regulates TM4SF5 expression required for sphere formation and growth. Taken together, the expression of TM4SF5 increase by CD133 expression. Tyrosine phosphorylation and activation of c-Src, Akt, and β-catenin signaling pathways triggers liver cancer cells to adopt characteristics of circulating tumor cells.