Activation of the ATF6, XBP1 and grp78 genes in human hepatocellular carcinoma: a possible involvement of the ER stress pathway in hepatocarcinogenesis.
OBJECTIVE
We identified the glucose-regulated protein (grp) 78 as a transformation-associated gene in hepatocellular carcinoma (HCC). Grp78 is a molecular chaperone involved in the unfolded protein response, the expression of which can be regulated by the transcription factors ATF6 and XBP1. Thus, we investigated the regulatory mechanisms of the grp78 gene in liver malignancy.


METHODS
Expression of grp78, ATF6 and XBP1 was examined by Northern blot, RT-PCR, immunoblot and immunohistochemical analyses. A reporter assay of the grp78 promoter was also performed.


RESULTS
Elevation of grp78 and ATF6 mRNAs and the splicing of XBP1 mRNA, resulting in the activation of XBP1 product, occurred in HCC tissues with increased histological grading. Higher accumulation of the grp78 product in the cytoplasm, concomitantly with marked nuclear localization of the activated ATF6 product (p50ATF6), was observed in moderately to poorly differentiated HCC tissues. Cooperation between the distal DNA segment and the proximal endoplasmic reticulum stress response elements was essential for maximum transcription of the grp78 promoter in HCC cells.


CONCLUSIONS
The endoplasmic reticulum stress pathway mediated by ATF6 and by IRE1-XBP1 systems seems essential for the transformation-associated expression of the grp78 gene in HCCs.
Shuda
Masahiro
M
Department of Microbiology and Cell Biology, The Tokyo Metropolitan Institute of Medical Science, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo 113-8613, Japan.
Kondoh
Nobuo
N
Imazeki
Nobuo
N
Tanaka
Kenji
K
Okada
Tetsuya
T
Mori
Kazutoshi
K
Hada
Akiyuki
A
Arai
Masaaki
M
Wakatsuki
Toru
T
Matsubara
Osamu
O
Yamamoto
Naoki
N
Yamamoto
Mikio
M
D051702:Activating Transcription Factor 6; D000328:Adult; D000368:Aged; D006528:Carcinoma, Hepatocellular / Q000503:physiopathology* / Q000601:surgery; D002352:Carrier Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics*; D004721:Endoplasmic Reticulum / Q000502:physiology; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006360:Heat-Shock Proteins; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008113:Liver Neoplasms / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D018832:Molecular Chaperones / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012326:RNA Splicing; D012333:RNA, Messenger / Q000032:analysis; D000071701:Regulatory Factor X Transcription Factors; D013312:Stress, Physiological / Q000503:physiopathology; D014157:Transcription Factors / Q000235:genetics*; D000071717:X-Box Binding Protein 1
C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human