The unusual yin-yang fashion of RIZ1/RIZ2 contributes to the progression of esophageal squamous cell carcinoma

Retinoblastoma protein-interacting zinc finger gene RIZ encodes two different protein products, RIZ1 and RIZ2. Observations suggest that RIZ1 is a tumor suppressor, while RIZ2 acts as a negative regulator of RIZ1 and may play a positive role in oncogenesis. The imbalance amount of RIZ1 and RIZ2 may be involved in cancer development. In this study we detected the expression levels of RIZ1 and RIZ2 mRNA in human esophageal squamous cell carcinoma (ESCC) tissue specimens, reexpressed RIZ1 in the human ESCC cell line EC109 in which RIZ1 mRNA level was not detected, examined the changes of RIZ1 and RIZ2 mRNA expression, investigated the changes of proliferation, and apoptosis of the cells. We found that RIZ1 mRNA expression is commonly decreased or at undetectable level in human esophageal squamous cancer tissue specimens compared to the normal tissue specimens, while RIZ2 is usually expressed. With the forced expression of RIZ1, RIZ2 mRNA expression did not change, The ESCC cell proliferation was inhibited and apoptosis was induced. This unusual yin-yang fashion of RIZ1/RIZ2 may contribute to the progression of ESCC.