An epigenetic role for PRL-3 as a regulator of H3K9 methylation in colorectal cancer

Objective This study investigated the epigenetic role of PRL-3, a key metastasis gene in colorectal cancer (CRC), as a regulator of histone demethylation and the functions of Jumonji domain-containing protein 1B (JMJD1B) and JMJD2B in the progression of CRC. Methods PRL-3-associated proteins were analysed using functional distribution and category enrichment analysis. Western blotting and immunofluorescence were used to detect nuclear PRL-3. The relationship between PRL-3 and JMJD1B or JMJD2B and the roles of JMJD1B, JMJD2B and PRL-3 in histone demethylation were determined after these proteins were knocked down using RNA interference. Case-control studies on JMJD1B and JMJD2B in patients with CRC were performed using immunohistochemical analysis. The in vitro functional effects of JMJD2B and JMJD1B were examined further. Results JMJD1B and JMJD2B, two histone demethylases, were enriched among PRL-3-associated proteins. Nuclear PRL-3 was observed in CRC cells and clinical samples of CRC. The expression of nuclear PRL-3 was increased in patients with CRC at more advanced Dukes' stages. PRL-3 was involved in the regulation of histone methylation by affecting the activities of JMJD1B and JMJD2B. A low expression of the JMJD1B protein was positively correlated with the lymph node status (p=0.032), Dukes' classification (p=0.008) and TNM staging (p=0.022) of patients with CRC. A high expression of JMJD2B was positively correlated with the lymph node status (p=0.03), Dukes' classification (p=0.036) and tumour invasion (p=0.003) of patients with CRC. A loss-of-function analysis confirmed that JMJD2B promoted the proliferation, colony formation and migration of human CRC cells. Conclusion Our data reveal a new role for PRL-3 as a key regulator of histone demethylation. JMJD1B seems to be a candidate tumour suppressor and JMJD2B seems to be a potential oncoprotein in the development and progression of CRC.