NORE1B Is a Putative Tumor Suppressor in Hepatocarcinogenesis and May Act via RASSF1A

Abstract

Recently, we found epigenetic silencing of the Ras effector genes NORE1B and/or RASSF1A in 97% of the hepatocellular carcinoma (HCC) investigated. This is strong evidence that the two genes are of major significance in hepatocarcinogenesis. Although RASSF1A serves as a tumor suppressor gene, the functions of NORE1B are largely unknown. Here, we studied the role of NORE1B for growth and transformation of cells. To understand the molecular mechanisms of action of the gene, we used the wild-type form and deletion mutants without the NH 2 terminus and CENTRAL domain, the Ras association (RA) domain, or the COOH-terminal SARAH-domain. Intact RA and SARAH-domains were found to be necessary for NORE1B (a) to increase the G 0 -G 1 fraction in hepatoma cells, (b) to suppress c-Myc/Ha-Ras-induced cell transformation, and (c) to interact closely with RASSF1A, as determined with fluorescence resonance energy transfer. In further studies, cell cycle delay by NORE1B was equally effective in hepatocyte cell lines with wild-type or mutant Ras suggesting that NORE1B does not interact with either Ras. In conclusion, NORE1B suppresses replication and transformation of cells as effectively as RASSF1A and thus is a putative tumor suppressor gene. NORE1B interacts physically with RASSF1A and functional loss of one of the interacting partners may lead to uncontrolled growth and transformation of hepatocytes. This may explain the frequent epigenetic silencing of NORE1B and/or RASSF1A in HCC.

Bimodal expression of Sprouty2 during the cell cycle is mediated by phase-specific Ras/MAPK and c-Cbl activities

“…Images were acquired with filters for CFP (cyan), YFP (yellow), and for FRET using identical microscope and camera settings. After determination of the correction factor for CFP (donor) and YFP (acceptor), the intensity of the FRET signal (green) was calculated [25]. Representative examples are shown.…”

“…Fluorescence resonance energy transfer (FRET) analysis was performed as described previously [25]. For quantitative analysis calculated FRET images were exported and analysed using ImageQuant software.…”

RASSF5 inhibits growth and invasion and induces apoptosis in osteosarcoma cells through activation of MST1/LATS1 signaling

“…A loss-of-function experiment revealed that loss of RASSF5 leads to uncontrolled growth and transformation of HCC, but overexpression of RASSF5 suppresses cell replication and transformation (22). RASSF5 is suppressed in pheochromocytoma and abdominal paraganglioma, resulting in enhanced apoptosis and impaired colony formation (23).…”

Integrated Analysis of Prognostic Gene Expression Profiles from Hepatitis B Virus-Positive Hepatocellular Carcinoma and Adjacent Liver Tissue

“…For example, expression of both AKR1B10 and RASSF1 has been reported to be related to the prognosis of human tumors including HCC. [21][22][23][24][25][26][27] Hierarchical clustering of gene expression separated HCC patients into 2 subclasses, with a striking survival difference between subclasses (P \ 0.0001) (Fig. 3a, b).…”