Researchers from the Indian Institute of Science Education and Research (IISER), Pune, have for the first time studied the early stages of normal cells transforming into cancerous cells. Using breast epithelial cells (on the surface) grown in 3D cultures, a team led by Mayurika Lahiri also found a particular protein (DNA-dependent protein kinase, DNA-PK), which normally repairs any damage to cell DNA, playing a central role in the transformation process. The results of the study have been published in the Journal of Cell Science .
While cells are continually exposed to DNA-damaging agents, the surveillance system in place in cells checks for any errors on the DNA and immediately repairs them. But when either one of them gets compromised, the errors on the DNA tend to accumulate in the genome. After a while, the cells appear abnormal and have most of the characteristics of cancerous cells.
In the study, an alkylating agent (a drug used in chemotherapy) was used to induce the transformation of breast epithelial cells into cancerous cells by activating the DNA-PK gene. The activated DNA-PK was found to disrupt the structure and function of the Golgi, an organelle found in the cell.
“Observing the abnormal Golgi was sheer serendipity. Cancer-causing agents cause damage to the DNA, which is found inside the nucleus. But in this case, we found the alkylating agent to also disrupt the Golgi, which is found outside the nucleus,” says Prof. Lahiri.
As a result of the disruption of the Golgi morphology, the movement of proteins (trafficking) from the endoplasmic reticulum to the cell membrane via Golgi was found to be impaired. As a result, the polarity — ability to distinguish the top and bottom sides of the epithelial cell — was disrupted and the cells were no longer epithelial cells, thus resulting in their transformation to cancerous cells. “Disruption of polarity is one of the hallmarks of cancerous cells,” she says.
The cells treated with the alkylating agent were found to be forming colonies; the ability of cells to form colonies is one of the important characteristics of transformation.
To confirm that activation of DNA-PK was causing the phenomena of transformation, the researchers used a small molecule to inhibit the activity of DNA-PK. “The inhibitor was able to partially reverse the polarity disruption and the Golgi regained its normal morphology. But the trafficking could not be reversed at all,” says Prof. Lahiri.