Significance of immunological detection of human telomerase reverse transcriptase: re-evaluation of expression and localization of human telomerase reverse transcriptase.
Human telomerase reverse transcriptase (hTERT) is a catalytic subunit of telomerase and is a potentially useful diagnostic marker for cancers. There have been few studies in which immunological detection of hTERT has been attempted and its subcellular localization has not been precisely defined. In the present study, we re-evaluated expression and localization of hTERT in cancer and normal cells using a newly developed antibody. Immunohistochemistry revealed that hTERT is expressed in approximately 80% of gynecological cancers, but some premalignant lesions exhibited weak expression of hTERT. Interestingly, not only nuclei but also cytoplasm of cancer cells were positive for hTERT staining. This finding was supported by the results of Western blot analysis of cell lines, in which both nuclear and cytoplasmic extracts exhibited significant hTERT bands. Cytoplasmic hTERT in cancer cells may be functional because the telomeric repeat amplification protocol assay of cytoplasmic extracts showed high levels of telomerase activity. Unexpectedly, not all normal primary cells and telomerase-negative cancer cell lines lacked hTERT expression; some exhibited weak TERT signals. In Western analysis, hTERT signals did not always correlate with telomerase activity of the various cell types. These findings suggest that functional hTERT is expressed in both the nucleus and cytoplasm of cancer cells and that hTERT expression does not strictly reflect telomerase activity. Further analysis is needed to clarify the biological significance of cytoplasmic hTERT.
Kyo
Satoru
S
Department of Obstetrics and Gynecology, School of Medicine, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8641, Japan. satoruky@med.kanazawa-u.ac.jp
Masutomi
Kenkichi
K
Maida
Yoshiko
Y
Kanaya
Taro
T
Yatabe
Noriyuki
N
Nakamura
Mitsuhiro
M
Tanaka
Masaaki
M
Takarada
Mitsuko
M
Sugawara
Isamu
I
Murakami
Seishi
S
Taira
Takahiro
T
Inoue
Masaki
M
D015153:Blotting, Western; D002467:Cell Nucleus / Q000201:enzymology; D003593:Cytoplasm / Q000201:enzymology; D004268:DNA-Binding Proteins; D005260:Female; D005833:Genital Neoplasms, Female / Q000201:enzymology; D006801:Humans; D007150:Immunohistochemistry; D013347:Subcellular Fractions / Q000201:enzymology; D019098:Telomerase / Q000378:metabolism*; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C509186:TERT protein, human; D019098:Telomerase