Amphiregulin induces the alternative splicing of p73 into its oncogenic isoform DeltaEx2p73 in human hepatocellular tumors.
OBJECTIVE
Inactivation of the product of the tumor suppressor gene TP73 does not usually occur by mutation but rather through expression of truncated isoforms that have dominant-negative effects on p73 and p53. The truncated oncogenic isoform DeltaEx2p73 is expressed in hepatocellular carcinomas (HCC) and is produced through the alternative splicing of p73 pre-messenger RNA (pre-mRNA); however, the underlying mechanisms regulating this process are unknown.


METHODS
We used human normal and diseased liver tissue samples, as well as human HCC cell lines, to examine the association between activation of epidermal growth factor receptor (EGFR) by its ligand amphiregulin (AR) and the alternative splicing of p73 pre-mRNA into the tumorigenic isoform DeltaEx2p73, via c-Jun N-terminal-kinase-1-mediated signaling.


RESULTS
DeltaEx2p73 was expressed in a subset of premalignant cirrhotic livers and in otherwise healthy livers that harbored a primary tumor, as well as in HCC tissues. DeltaEx2p73 expression was correlated with that of the EGFR ligand AR, which was previously shown to have a role in hepatocarcinogenesis. Autocrine activation of the EGFR by AR triggered c-Jun N-terminal kinase-1 activity and inhibited the expression of the splicing regulator Slu7, leading to the accumulation of DeltaEx2p73 transcripts in HCC cells.


CONCLUSIONS
This study provided a mechanism for the generation of protumorigenic DeltaEx2p73 during liver tumorigenesis, via activation of EGFR signaling by AR and c-Jun N-terminal kinase-1 activity, leading to inhibition of the splicing regulator Slu7.
Castillo
Josefa
J
Division of Hepatology and Gene Therapy, CIMA-University of Navarra, Pamplona, Spain.
Goñi
Saioa
S
Latasa
María Ujue
MU
Perugorría
María J
MJ
Calvo
Alicia
A
Muntané
Jordi
J
Bioulac-Sage
Paulette
P
Balabaud
Charles
C
Prieto
Jesús
J
Avila
Matías A
MA
Berasain
Carmen
C
D017398:Alternative Splicing / Q000187:drug effects*; D066258:Amphiregulin; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D018929:Cell Culture Techniques; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D066255:EGF Family of Proteins; D066246:ErbB Receptors / Q000378:metabolism; D006023:Glycoproteins / Q000494:pharmacology*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
C587848:AREG protein, human; D066258:Amphiregulin; D004268:DNA-Binding Proteins; D066255:EGF Family of Proteins; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins; D066246:ErbB Receptors; D048055:Mitogen-Activated Protein Kinase 8