Search

Human telomerase reverse transcriptase (hTERT; the catalytic protein subunit of telomerase) is subjected to numerous alternative splicing events, but the regulation and function of these splice variants is obscure. Full-length hTERT includes conserved domains that encode reverse transcriptase activity, RNA binding, and other functions. The major splice variant termed α+β− or β-deletion is highly expressed in stem and cancer cells, where it codes for a truncated protein lacking most of the reverse transcriptase domain but retaining the known RNA-binding motifs. In a breast cancer cell panel, we found that β-deletion was the hTERT transcript that was most highly expressed. Splicing of this transcript was controlled by the splice regulators SRSF11, HNRNPH2, and HNRNPL, and the β-deletion transcript variant was associated with polyribosomes in cells. When ectopically overexpressed, β-deletion protein competed for binding to telomerase RNA (hTR/TERC), thereby inhibiting endogenous telomerase activity. Overexpressed β-deletion protein localized to the nucleus and mitochondria and protected breast cancer cells from cisplatin-induced apoptosis. Our results reveal that a major hTERT splice variant can confer a growth advantage to cancer cells independent of telomere maintenance, suggesting that hTERT makes multiple contributions to cancer pathophysiology. Cancer Res; 73(9); 2817–28. ©2013 AACR.

PDF file - 516K, T1. Breast cell lines used in this study. T2. Summary of results for 45 breast cancer cell lines and 5 non-malignant cell lines. T3. Correlation of hTERT α/β splice variants, telomerase activity, telomere length and hTR in 50 breast cancer cell lines. T4. Sequences of primers used.

PDF file - 236K, S1. hTERT and SRSF3 splice variant enrichment after cycloheximide treatment. S2. Total SRSF3 and hTERT splice variant mRNA abundance in ribosome-containing fractions. S3. Unaltered microscopy image shown in Figure 3. S4. SRSF11 and hnRNPH2 binding sites in pSpliceExpress-hTERT. S5. hTR 3' end co-immunoprecipitates with FLAG-WT-hTERT, FLAG-D868A-hTERT and FLAG-β-deletion. S6. hTERT detection by Western blot in UM-UC-3 lysates from experiment 5C. S7. hTR RNA expression levels in breast cancer cell lines. S8. Modal telomere length stayed relatively constant after 20 continues passages in randomly selected breast cell lines. S9. Telomerase activity and relative expression of hTERT α+β+ and β-deletion mRNAs in breast cancer cell line subtypes.

PDF file - 56K

PDF file - 45K

Human telomerase reverse transcriptase (hTERT; the catalytic protein subunit of telomerase) is subjected to numerous alternative splicing events, but the regulation and function of these splice variants is obscure. Full-length hTERT includes conserved domains that encode reverse transcriptase activity, RNA binding, and other functions. The major splice variant termed α+β− or β-deletion is highly expressed in stem and cancer cells, where it codes for a truncated protein lacking most of the reverse transcriptase domain but retaining the known RNA-binding motifs. In a breast cancer cell panel, we found that β-deletion was the hTERT transcript that was most highly expressed. Splicing of this transcript was controlled by the splice regulators SRSF11, HNRNPH2, and HNRNPL, and the β-deletion transcript variant was associated with polyribosomes in cells. When ectopically overexpressed, β-deletion protein competed for binding to telomerase RNA (hTR/TERC), thereby inhibiting endogenous telomerase activity. Overexpressed β-deletion protein localized to the nucleus and mitochondria and protected breast cancer cells from cisplatin-induced apoptosis. Our results reveal that a major hTERT splice variant can confer a growth advantage to cancer cells independent of telomere maintenance, suggesting that hTERT makes multiple contributions to cancer pathophysiology. Cancer Res; 73(9); 2817–28. ©2013 AACR.