Cell lines are critical for many uses involving microbiological research and for the development of new drugs. The first 10 generations of cells or less are known as primary cells. These cells are believed to be exact copies of the original cell. However, after 10 generations, due to imperfections of the DNA/RNA copy process, the cells from the 11th generation on are considered defective and therefore unusable by researchers looking to study the original cell line. Clearly, methods to keep the original cell line intact over a longer period of time would be quite useful since a cell generation usually takes less that 24 hours in most cases. Are there any “natural” techniques that could extend the life of a cell line, essentially immortalizing it for a long period of time? Yes, in fact there are over 60 cell lines of immortalized cells.
Use of a Virus Gene to Immortalize Cell Lines
Cells have specific tumor suppressor genes that help control the cell’s growth and reproduction. Some viral genes act specifically on these types of suppressor areas, thus permitting their changed cells to reproduce at rapid rates. During infection, the gene from the virus connects to and immobilizes part of the infected cell, causing the cell to generate more viral cells in the body. Using a number of viruses to infect a new cell culture can generate cells equivalent to the original cell line that will reproduce exactly for an extended period of time. Thus, these cell lines are available for long term use and study. Some of the viruses used are EBV, HPV-16 E6/7 gene, and the Simian Virus 40 (SV40) T antigens.
hTERP Suppression
Another method to immortilize cells is to activate the Telemerease Reverse Transcriptase Protein or hTERP. This enzyme prevents the loss of telomeres at the end of each DNA strand. The telomere keeps the strands from sticking together or breaking into parts. Activating this enzyme in some cell lines keeps the cells able to continue to reproduce indefinitely. This is especially useful when the length of the DNA strands plays an important part in cell reproduction, which is common in human DNA.
Inactivation of Tumor Suppressor Genes
It has been noted that the inactivation of co-expressive tumor genes can lead a prime cell line to immortalize itself. This is done using hTERP to assist reproduction of new cells without the suppressor genes. This is successful in a limited number of cases to develop immortalized cell lines.
