PRKG1 and hepatocellular carcinoma: Up to now, several enhancer-promoter combinations have been documented to attain potent and specific transcription in HCC gene therapy studies, such as the hypoxia-specific enhancer in combination with the AFP basal promoter [22], the AFP enhancer in combination with other promoter such as the housekeeping gene phosphoglycerate kinase (pgk) [23], and the AFP enhancer in combination with AFP basal promoter [24,25].