Astrocyte elevated gene‐1 and c‐Myc cooperate to promote hepatocarcinogenesis in mice

Abstract

Astrocyte elevated gene-1 (AEG-1) and c-Myc are overexpressed in human hepatocellular carcinoma (HCC) functioning as oncogenes. AEG-1 is transcriptionally regulated by c-Myc and AEG-1 itself induces c-Myc by activating Wnt/β-catenin signaling pathway. We now document cooperation of AEG-1 and c-Myc in promoting hepatocarcinogenesis by analyzing hepatocyte-specific transgenic mice expressing either AEG-1 (Alb/AEG-1), c-Myc (Alb/c-Myc) or both (Alb/AEG-1/c-Myc). WT and Alb/AEG-1 mice did not develop spontaneous HCC. Alb/c-Myc mice developed spontaneous HCC without distant metastasis while Alb/AEG-1/c-Myc mice developed highly aggressive HCC with frank metastasis to the lungs. Induction of carcinogenesis by N-nitrosodiethylamine (DEN) significantly accelerated the kinetics of tumor formation in all groups. However, in Alb/AEG-1/c-Myc the effect was markedly pronounced with lung metastasis. In vitro analysis showed that Alb/AEG-1/c-Myc hepatocytes acquired increased proliferation and transformative potential with sustained activation of pro-survival and epithelialmesenchymal transition (EMT) signaling pathways. RNA-sequencing analysis identified a unique gene signature in livers of Alb/AEG-1/c-Myc mice that was not observed when either AEG-1 or c-Myc was overexpressed. Specifically Alb/AEG-1/c-Myc mice overexpressed maternally imprinted non-coding RNAs, such as Rian, Meg-3 and Migr, which are implicated in hepatocarcinogenesis. Knocking down these ncRNAs significantly inhibited proliferation and invasion by Alb/AEG-1/c-Myc hepatocytes. Conclusion Our studies reveal a novel cooperative oncogenic effect of AEG-1 and c-Myc that might explain the mechanism of aggressive HCC. Alb/AEG-1/c-Myc mice provide a useful model to understand the molecular mechanism of cooperation between these two oncogenes and other molecules involved in hepatocarcinogenesis. This model might also be of use for evaluating novel therapeutic strategies targeting HCC.

The emerging role of astrocyte-elevated gene-1 in hepatocellular carcinoma (Review)

“…Previous studies as well as our study manipulating AEG-1 expression in HCC cells showed that overexpression of AEG-1 promotes proliferation and increases anchorageindependent growth in soft agar (16,46); knockdown of AEG-1 was found to suppress proliferation and inhibit colony formation as well as induce apoptosis through suppression of IL-6 secretion (47,48). Further studies also demonstrated that enhanced AEG-1 expression in HCC cells generated large and highly vascular subcutaneous tumors compared to the control; correspondingly, downregulation of the expression of AEG-1 decreased the tumor formation rate and the growth of subcutaneous tumors in nude mice and the tumor volumes were found to be smaller than the control (16,47).…”

“…As mentioned above, AEG-1 is regulated by Ha-ras through the PI3K/Akt/GSK3β/c-Myc pathway (62) in HCC. AEG-1 is transcriptionally regulated by c-Myc, and cooperates with c-Myc maternally imprinted non-coding RNAs, such as Rian, Meg-3 and Migr, which are implicated in the promotion of hepatocarcinogenesis (46). AEG-1-dependent anoikis resistance is also activated via the PI3K/Akt pathway and Bcl-2, and the PI3K inhibitor LY294002 was found to reverse the AEG-1-dependent effects on Akt phosphorylation, expression and anoikis resistance (54).…”

Astrocyte Elevated Gene-1 (AEG-1) Contributes to Non-thyroidal Illness Syndrome (NTIS) Associated with Hepatocellular Carcinoma (HCC)

“…Overexpression of AEG-1 in the poorly aggressive HCC cell line HepG3, which expresses a low level of AEG-1, significantly increases in vitro proliferation, invasion, anchorage-independent growth and chemoresistance, and in vivo tumorigenesis, angiogenesis, and metastasis in nude mice (7, 9 -11). These observations were further corroborated in a transgenic mouse with hepatocyte-specific overexpression of AEG-1 (Alb/AEG-1) that develops highly aggressive metastatic HCC in a diethylnitrosamine-induced HCC model (12,13). Conversely, knockdown of AEG-1 in highly aggressive QGY-7703 cells, expressing high levels of AEG-1, significantly abrogates in vivo tumorigenesis (7,10).…”

“…Alb/AEG-1 and AEG-1KO Mice-Generation and characterization of a hepatocyte-specific AEG-1 transgenic mouse (Alb/ AEG-1) and an AEG-1 knock-out (AEG-1KO) mouse have been described previously (12)(13)(14) Patient Samples-Serum samples were collected from hepatitis C virus-HCC patients (n ϭ 23) and 14 healthy volunteers. These studies are approved by the Institutional Review Board of the University of Virginia.…”

Astrocyte Elevated Gene 1 Interacts with Acetyltransferase p300 and c-Jun To Promote Tumor Aggressiveness

“…Recently, Li et al demonstrated that AEG-1 promotes gastric cancer progression through a positive-feedback Toll-like receptor 4/NF-B signaling-related mechanism (14). Moreover, Robertson and colleagues found that AEG-1-deficient mice display resistance to N-nitrosodiethylamine-induced hepatocellular carcinoma and lung metastasis (18).…”