Objective    To investigate the expression and significance of activating transcription factor 4 (ATF4) in the hepatocyte steatosis models induced by oleic acid

and to explore the relationship between the expression of ATF4 and nonalcoholic fatty liver disease (NAFLD).     Methods    L02 cells were treated by 20 mg/ml oleic acid for 0

24

48 and 72 h respectively  to induce the hepatocytes steatosis

and then the cells were collected and the total RNA and protein were extracted. Reverse transcriptional polymerase chain reaction (RT-PCR) and Western blot analysis were used to detect the expressions of ATF4 gene at different time points.     Results    With the development of deterioration of steatosis

the expression levels of ATF4 mRNA were 1.01±0.12

1.87±0.24

2.01±0.13

and 1.79±0.19 respectively correspondingly from 0 h to 72 h. The peak of ATF4 mRNA expression was reached at the 48th hour

and then showed the tendency of down-regulation. At the same time points

the protein expression of ATF4 were 0.31±0.16

0.57±0.14

0.91±0.20

and 0.89±0.17 separately

and the protein expression was maintained at a high level up to the 72nd hour. There were significantly differences compared with the control group（P0.05）.     Conclusion    In the oleic acidinduced hepatocyte steatosis model

the expression of the ATF4 is enhanced persistently

suggesting where the endoplasmic reticulum stress response may happen. ATF4 may play an important role in the development and progression of NAFLD by up-regulating ATF4 expression.