Decreased expression of telomerase-associated RNAs in the proliferation ofstem cells in comparison with continuous expression in malignant tumors

Telomerase, an enzyme associated with cellular immortality, is expressed by malignant tumor and stem cells, especially germ cells. Normal somatic cell s, however, usually do not express telomerase. In the malignant tumor, dere gulation of telomerase is thought to facilitate tumorigenesis and cellular immortality by providing cancer cells unlimited proliferation capacity. We investigated the relationship between proliferation activity and in situ ex pression of the telomerase RNA component (human telomerase RNA component, h TERC). In addition, in situ hybridization of the telomerase-associated prot eins (telomerase-associated protein 1, TEP1; human telomerase reverse trans criptase, TERT), and MIB-1 immunohistochemistry for proliferation activity were performed, using the malignant tumors of adenocarcinoma, squamous cell carcinoma, and malignant lymphoma, and somatic tissues of testis, endometr ium, stomach, skin, and lymph nodes. In the somatic tissues, the stem cells expressed telomerase-associated RNA, but no proliferation activity. When t he proliferation activity of the stem cells increased, however, the telomer ase-associated expressions decreased. In the malignant tumors, both prolife ration activity and expression of the telomerase-associated RNA significant ly increased. Deregulation of telomerase, in addition to proliferation acti vity, is associated with tumorigenesis.