Differential expression of human telomerase-associated genes in human hematopoietic cells

Telomerase is a ribonucleoprotein which specifically extends the telomeric strand in an RNA-templated reaction. Recently, human telomerase-associated proteins have been described; telomerase-associated protein 1 (TP1) and human telomerase reverse transcriptase (hTERT), homologous to the Tetrahymena telomerase protein p80 and to the yeast telomerase catalytic subunit respectively. We investigated the role of hTERT and TP1 in normal hematopoiesis by assessing mRNA expression level using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). TP1 mRNA was present in all normal hematopoietic cells. On the other hand, hTERT mRNA was expressed only in CD34 positive cells which have known telomerase activity. During the course of myeloid differentiation from normal CD34 positive cells cultured in IMDM, hTERT mRNA expression was downregulated before day 10, closely correlated with telomerase activity. In HL60 cells induced to differentiate into granulocyte-like cells with ATRA, hTERT mRNA expression was downregulated in accordance with the telomerase activity. TP1 mRNA expression, however, showed no apparent change. These data indicate that hTERT mRNA expression relates directly with telomerase activity itself and telomerase activity may be regulated in hTERT mRNA expression step.