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Immortalization of bovine capillary endothelial cells by hTERT alone involves inactivation of endogenous p16 INK4A /pRb
Author(s) -
Veitonmäki Niina,
Fuxe Jonas,
Hultdin Magnus,
Roos Göran,
Pettersson Ralf F.,
Cao Yihai
Publication year - 2003
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.02-0599fje
Subject(s) - telomerase , telomerase reverse transcriptase , telomere , biology , transfection , senescence , population , retinoblastoma protein , microbiology and biotechnology , cancer research , dna methylation , somatic cell , cell culture , cell cycle , cell , gene expression , genetics , dna , gene , demography , sociology
Recent studies show that stable expression of the human telomerase catalytic subunit, hTERT, alone can lead several types of normal human somatic cells to bypass replicative senescence and become immortal. The molecular mechanisms by which telomerase immortalizes cells are not fully understood, although a key function of telomerase is to maintain a critical length of telomeres in order to preserve the stability and integrity of the genome. Here we report that stable transfection of hTERT alone was sufficient to allow bovine capillary endothelial (BCE) cells to bypass senescence and acquire immortality. Surprisingly, telomere lengths in these stable transfectants were progressively shortened during an increasing number of population doublings (PDLs), despite high telomerase activity. The expression of the cyclin‐dependent kinase inhibitors (CDKIs) p16 INK4A and p21 CIP1/WAF1 was concomitantly repressed, and the retinoblastoma protein (pRb) was maintained in a hyperphosphorylated state in the telomerase‐expressing cells. Re‐expression of p16 INK4A in these cells by either treatment with a demethylating agent or by adenovirus‐mediated expression reinduced a senescence‐like phenotype, suggesting that the inactivation of p16 INK4A was due to DNA methylation and was crucial for the immortalization process. In agreement with this finding, the expression levels of the prototypic DNA methyltransferase DNMT1 were elevated in the hTERT‐positive cells.