Comparison of human mammary skin cells immortalized by simian virus 40 T-Antigen or by the telomerase catalytic subunit.
We directly compared two methods of immortalizing human mammary skin cells Cells were altered by transferring an independently replicating, piece of extrachromosomal cytoplasmic DNA either for hTERT, the catalytic subunit of telomerase, or for the cancer causing simian virus 40 (SV40) early region genes. Under standard culture conditions, human mammary skin cells were not immortalized by hTERT unless they had spontaneously ceased expression of the p16(INK4a) tumor suppressor gene.
Human mammary skin cells without the added DNA had normal (low) levels of telomerase expression, and immortalization by both methods was associated with an increase in telomerase activity and prevention of telomere shortening. SV40-induced immortalization was accompanied by aberrant differentiation, loss of DNA damage response, instability of the typical arrangement of chromosomes in the cell and, in some cases caused tumor growth.
hTERT-immortalized cells had fewer changes in the typical arrangement of their chromosomes, but had intact DNA damage responses, and features of normal differentiation. Although SV40-immortalized cells are useful for studies of thecauses of cancer, hTERT-immortalized cells retain more properties of normal cells.
Sorry I had to look up all the words and paste them in.
That seems to be the case, BTW, the quote: "Under standard culture conditions, human mammary skin cells were not immortalized by hTERT unless they had spontaneously ceased expression of the p16(INK4a) tumor suppressor gene" may be true. However, I believe Dr. Shay and colleagues (UTSWMC) have published a paper where they demonstarte that such "standard culture conditions" are inadequate and that under 'appropriate' culture conditions, HMECs do not require loss of p16(INK4a) for immortalization - hTERT expression is sufficient.