The researchers in the Key Laboratory of Space Radiobiology at Institute of Modern Physics (IMP), Chinese Academy of Sciences have investigated the methylation of promoter of RBL1 enhances the radioresistance of three dimensional cultured carcinoma cells. 

Three dimensional (3D) culture in vitro is a new cell culture model that more closely mimics the physiology features of the in vivo environment and is being used widely in the field of medical and biological research (Figure 1). It has been demonstrated that cancer cells cultured in 3D matrices are more radioresistant compared with cells in monolayer (2D). However, the mechanisms causing this difference remain largely unclear. DNA methylation is an important epigenetic modification of the genome. It involves in the regulation of many cellular processes via gene silencing without alteration in DNA sequences. 

The researchers found that the cell cycle distribution and expression of cell cycle regulation genes in 3D A549 cells are different from the 2D. The higher levels of the promotor methylation of cell cycle regulation genes such as RBL1 were observed in 3D A549 cells compared with cells in 2D. The treatments of irradiation or 5-Aza-CdR activated the demethylation of RBL1 promotor and resulted in the increased expression of RBL1 only in 3D A549 cells. Inhibition of RBL1 enhanced the radioresistance and decreased the G2/M phase arrest induced by irradiation in 2D A549 and MCF7 cells. Overexpression of RBL1 sensitized 3D cultured A549 and MCF7 cells to irradiation (Figure 2). Taken together, to our knowledge, it is the first time to reveal that the low expression of RBL1 due to itself promotor methylation in 3D cells enhances the radioresistance. This finding sheds a new light on understanding the features of the 3D cultured cell model and its application in basic research into cancer radiotherapy and medicine development. 

The work has been published in Oncotarget, 2016 (DOI: 10.18632/oncotarget.12647).The article can be linked as follows:http://www.impactjournals.com/oncotarget/index.php?journal=oncotarget&page=article&op=view&path[]=12647&author-preview=9rb 

This work was supported by National Natural Science Foundation of China [11635013, U1432121, 31170803] and the National Key Scientific Instrument and Equipment Development Project of China [2012YQ03014210 .

Figure 1 Different morphological features and physiological characteristics between 3D and 2D cultured cells (Image by IMP) 

Figure 2 Methylation of promoter of RBL1 responses to radiation and enhances the radioresistance of three dimensional cultured carcinoma cells (Image by IMP)