My interest in post-transcriptional controls and their deregulation in tumorigenesis is long-standing (Grosset C et al, Cell 2000; Grosset C et al, JBC, 2004; Sagliocco F et al; Biochem J 2006; Laloo B et al, Mol & Cell Prot 2009; Simon D et al, Hum Mol Genet 2010; Laloo B et al, Biochem Soc Trans 2010). Since 2006, I am heading an autonomous research team which is working on the post-transcriptional regulation of genes mediated by RNA-binding proteins and microRNAs in the context of liver cancer. Our favorite gene is Glypican-3 (GPC3), a membrane-anchored protein that regulates key signaling pathways (e.g. Wnt/beta-catenin pathway) and is overexpressed in liver cancer. In collaboration with Jessica Zucman Rossi's lab (U674 INSERM, Paris, France), we identified several microRNAs and one endoribonuclease which differentially regulates GPC3 expression in hepatic cells (Maurel M et al, Hepatology, accepted for publication). We recently obtained a three-year competitive grant from INCa, entitled "Glypican-3: a therapeutic target in liver cancer treatment" (July 2012). I also collaborate with Pr Benoît Arveiler (EA 4137, Bordeaux, France) on the study of a single mutation localized in the hdac6 3’ untranslated region (UTR) and segregating with a dominant X-linked chondrodysplasia where family members harbor deleterious and disabling developmental defects. We showed that this mutation abrogates the posttranscriptional regulation of hdac6 by miR-433 leading to an increased expression of this gene in affected cells. This collaboration led to an original publication (Simon D et al, Hum Mol Genet 2010) and an ANR grant (ANR 2010; Acronym: CHONDRO-X).
To facilitate the study of post-transcriptional mechanisms in various human cell types including primary cells, we developed a functional method named FunREG (functional, integrated and quantitative method to measure post-transcriptional regulations) (Laloo B et al, Mol & Cell Prot 2009; Simon D et al, Hum Mol Genet 2010; Laloo B et al, Biochem Soc Trans 2010). This method enables (i) the quantitative measurements of post-transcriptional regulations mediated by either selected 3’UTRs, siRNA or microRNAs, and (ii) the comparison of these regulatory processes in physiologically relevant systems (e.g. cancerous versus primary cells). Applied to the study of liver cancer, FunREG reported for the first time post-transcriptional gene deregulations in tumoral hepatic cells compared to normal hepatocytes (Laloo B et al, Mol & Cell Prot 2009; Maurel M et al, Hepatology, accepted for publication).
To identify GPC3-regulating microRNAs in tumoral hepatic cells, we developed a functional screening system named Dual-Fluorescence FunREG (DF-FunREG). Using DF-FunREG, we screened a library of 876 microRNAs and identified 5 microRNAs controlling GPC3 expression through its 3' untranslated region (UTR). Whereas miR-96 and miR-1271 down-regulated GPC3 expression through a direct microRNA:3'UTR recognition process, miR-129-1-3p, miR-1291 and miR-1303 had an inducible effect (Jalvy-Delvaille S et al, Nucl Acids Res 2012; Maurel M et al, Hepatology, accepted for publication). Further investigations showed that miR-1291 enhances GPC3 expression by recognizing the 5'UTR of an endoribonuclease, thereby decreasing its cellular expression. As this endoribonuclease binds GPC3 3'UTR and cuts the mRNA, miR-1291 induces GPC3 expression by attenuating the mRNA degradation process regulated by this endoribonuclease. Collectively, our work demonstrates that GPC3 expression is controlled by multiple microRNAs and one endoribonuclease illustrating the fascinating notion of post-transcriptional gene regulation network.