The POU transcription factor OCT4 is a pleiotropic regulator of gene expression 
in embryonic stem cells. Recent studies demonstrated that OCT4 is aberrantly 
expressed in multiple types of human cancer; however, the underlying molecular 
mechanism remains largely unknown. In this study, we report that OCT4-pg4, a 
pseudogene of OCT4, is abnormally activated in hepatocellular carcinoma (HCC). 
The expression level of OCT4-pg4 is positively correlated with that of OCT4, and 
both gene transcripts can be directly targeted by a tumor-suppressive micro RNA 
miR-145. We find that the non-coding RNA OCT4-pg4 is biologically active, as it 
can upregulate OCT4 protein level in HCC. Mechanistic analysis revealed that 
OCT4-pg4 functions as a natural micro RNA sponge to protect OCT4 transcript from 
being inhibited by miR-145. In addition, our study also showed that OCT4-pg4 can 
promote growth and tumorigenicity of HCC cells, thus exerting an oncogenic role 
in hepatocarcinogenesis. Furthermore, survival analysis suggests that high 
OCT4-pg4 level is significantly correlated with poor prognosis of HCC patients. 
Taken together, our finding adds a new layer of post-transcriptional regulation 
of OCT4 and sheds new light on the treatment of human HCC.