Quantification of hTERT alternatively spliced isoforms in resting and activated human T cell subsets

Abstract

Abstract The activity of telomerase is regulated at multiple levels of the reverse transcriptase (hTERT) subunit. In T cells, it is well documented that telomerase activity is not detected in resting cells while it is high in activated cells. However, it is unclear whether full-length (FL) hTERT mRNA and AS products (ASPs) are expressed in resting T cells and how they affect T cell differentiation and function. Here, we analyzed hTERT mRNA (full-length and 3 types of ASPs) in CD4 and CD8 T cell subsets (naïve, central and effector memory) isolated from 66 healthy human adults. We detected hTERT FL mRNA in resting CD4 and CD8 T cell subsets and found that the level of hTERT FL mRNA decreased from naïve (N) to central memory (CM) to effector memory (EM) cells. Furthermore, hTERT FL mRNA levels were higher in CD4 than in corresponding CD8 subsets and undetectable in CD8 EM of most donors. In vitro stimulation with anti-CD3/CD28 antibody-coated beads induced a high level of hTERT mRNA in all subsets without changing the order of hTERT abundance in CD4 and CD8 T cell subsets. Finally, we measured telomerase activity in these T cell subsets and confirmed that resting T cells did not have detectable telomerase activity, but activated T cells did and the levels of telomerase activity concurred with expression levels of hTERT FL mRNA. In conclusion, quantifying hTERT FL and ASPs in T cell subsets confirmed no telomerase activity in the presence of FL hTERT mRNA in resting T cells and revealed a decrease of hTERT levels with T cell differentiation from naïve to memory. Currently, we are assessing which transcription factors are responsible for regulating hTERT expression levels in T cell differentiation.