Functional Roles of DDX3 on Regulating Cell Stemness and Its Impact on Hepatic Tumorigenesis
LEE WU YAN-HWA
|關鍵字:||RNA 解螺旋酶 DDX3;肝癌癌源幹細胞;CD133;肝臟再生;miRNA生合成;肝細胞癌;RNA helicase DDX3;cancer-initiating stem cells (CISCs);CD133;liver regeneration;miRNA biogenesis;hepatocellular carcinoma (HCC)|
然而目前對於肝癌癌源幹細胞產生之分子機制仍未明瞭。RNA 解螺旋酶DDX3 參與
miRNA。以上結果暗示DDX3 可藉由透過調節miRNA 生合成，進而調控肝癌源細胞
miRNA 生合成進而調控癌源特徵的機制，闡明DDX3 抑制肝癌癌源幹細胞生成的功
Hepatocellular carcinoma (HCC) is an aggressive malignancy with poor prognosis. Growing evidence support that cancer-initiating stem cells (CISCs), a small portion of cells responsible for tumorigenesis, could be a therapeutic target. In addition to self-renewal and differentiation capacity, CISCs exhibit features of enhanced invasiveness and chemoresistance. To date, the existence of CISCs has been proven in many malignancies, including HCC. Recently, several hepatic CISC populations have been identified by their specific phenotype, such as the expression of CD133 surface marker. Characterization of the source of hepatic CISCs suggests that they could originate from hepatic progenitor cells or hepatocytes with genetic alteration. Although aberrant expression of certain miRNA could result in CISC-associated features in HCC, the molecular details about the regulation of hepatic CISC generation remains elusive. The DEAD-box RNA helicase DDX3 plays important roles in various cellular function via its engagement in RNA metabolism. Our previous studies suggest a tumor suppressor role of DDX3 in HCC. Recently, our preliminary data revealed reduction of DDX3 expression in CD133+ hepatic CISC cells. Moreover, DDX3 knockdown led to generation of CD133+ cells along with up-regulation of stem cell-related transcription factors. On the contrary, DDX3 overexpression suppressed certain CISC-associated features. Most interestingly, according to our miRNA microarray analysis, DDX3 could regulate the expression of a group of miRNAs predicted or proved to suppress CISC-associated genes. These evidences strongly suggest that DDX3 may regulate hepatic CISC generation by modulating miRNA biogenesis. Thus, in this proposal, efforts will be made to elaborate the functional role of DDX3 on regulating cell stemness and its impact on HCC tumorigenesis. In the first part of this proposal, we will clarify the regulatory role of DDX3 on generation of CISCs in HCC. The expression levels of DDX3 in defined hepatic CISC populations will be delineated. Moreover, effect of DDX3 on CISC features and CISC generation will also be examined in vitro, validated in clinical samples and correlated to patients’ clinical outcome. Secondly, the functional role of Ddx3x on hepatocytic- and hepatic progenitor cells-mediated hepatocarcinogenesis will be investigated in mouse liver regeneration model. Finally, the DDX3-mediated regulation of miRNAs targeting CISC-associated genes will be addressed. We will validate the effect of DDX3 on the expression of miRNAs predicted to suppress CISC-associated genes. Additionally, the targeting effect of these miRNA candidates will be certified. Furthermore, we will explore the functional role of DDX3 on miRNA biogenesis. The interplay among DDX3 and miRNA processing complexes will also be investigated. Collectively, the approaches outlined above will allow envisaging DDX3-mediated regulation on CISC-associated gene and hepatic CISC generation, which may be informative for the future research on HCC carcinogenesis and ultimate development of diagnostic or therapeutic strategies for hepatic malignancy.