|ZFIN ID: ZDB-PUB-120802-13|
|Source:||Gastroenterology 143(5): 1341-1351 (Journal)|
|Registered Authors:||Kim, Cheol-Hee, Kim, Hyun-Taek|
|Keywords:||liver cancer, chemotherapy resistance mechanisms, tumor cell death|
|PubMed:||22841785 Full text @ Gastroenterology|
Background & Aims
The TOR signaling pathway regulator-like (TIPRL) protein, the mammalian ortholog of yeast TIP41, was identified in an expression profiling screen for factors that regulate human liver carcinogenesis. We investigated the role of human TIPRL in hepatocellular carcinoma (HCC).
We measured the level of TIPRL in HCC and adjacent non-tumor tissues from patients. We used small interfering (si)RNAs and zebrafish to study the function of TIPRL. We used annexin V propidium iodide staining and immunoblot analyses to measure apoptosis and activation of apoptotic signaling pathways. We used confocal microscopy, co-immunoprecipitation, and glutathione-S transferase pull-down analyses to determine interactions among mitogen-activated protein kinase kinase 7 (MKK7or MAP2K7), TIPRL, and the protein phosphatase 2 catalytic subunit (PP2Ac). We studied the effects of TIPRL in tumor xenografts in mice.
Levels of TIPRL were higher in HCC tissues and cell lines than non-tumor tissues and primary hepatocytes. Knockdown of tiprl expression in zebrafish led to large amounts of apoptosis throughout the embryos. Incubation of HCC cells, but not primary human hepatocytes, with siRNA against TIPRL (siTIPRL) and tumor necrosis factor-related apoptosis inducing ligand (TRAIL) caused prolonged activation (phosphorylation) of MKK7 and c-Jun N-terminal kinase (JNK) and led to apoptosis, indicated by cleavage of procaspase-8,-3, and of poly-(ADP-ribose) polymerase (PARP). TIPRL bound to MKK7 and PP2Ac and promoted the interaction between MKK7 and PP2Ac. In mice, injection of HCC xenograft tumors with siTIPRL and TRAIL led to tumor apoptosis and regression.
TIPRL is highly upregulated in human HCC samples and cell lines, compared with non-cancerous liver tissues. TIPRL prevents prolonged activation of MKK7 and JNK and TRAIL-induced apoptosis by mediating the interaction between MKK7 and PP2Ac.