Elevated TRF2 in advanced breast cancers with short telomeres

Abstract

Introduction Telomere repeat binding factor 2 (TRF2) binds directly to telomeres and preserves the structural integrity of chromosome ends. In vitro models suggest that expression of TRF2 protein increases during mammary cancer progression. However, a recent study has reported that TRF2 mRNA levels tend to be lower in clinical specimens of malignant breast tissue. Here, we conduct the first large scale investigation to assess the levels and cellular localization of the TRF2 protein in normal, pre-malignant and malignant breast tissues. Methods Breast tissue arrays, containing normal, ductal carcinoma in situ (DCIS) and invasive carcinoma specimens, were used to assess the expression and localization of TRF2 protein. Telomere lengths were semi-quantitatively measured using a pantelomeric peptide nucleic acid probe. A mixed effects modeling approach was used to assess the relationship between TRF2 expression and telomeric signal scores across disease states or clinical staging. Results We demonstrate that TRF2 is exclusively nuclear with a trend towards lower expression with increased malignancy. More case-to-case variability of TRF2 immunostaining intensity was noted amongst the invasive carcinomas than the other disease groups. Invasive carcinomas also displayed variable telomere lengths while telomeres in normal mammary epithelium were generally longer. Statistical analyses revealed that increased TRF2 immunostaining intensity in invasive carcinomas is associated with shorter telomeres and shorter telomeres correlate with a higher TNM stage. All immortalized and cancer cell lines within the array displayed strong, nuclear TRF2 expression. Conclusion Our data indicate that elevated expression of TRF2 is not a frequent occurrence during the transformation of breast cancer cells in vivo, but higher levels of this telomere binding protein may be important for protecting advanced cancer cells with critically short telomeres. Our findings also reinforce the concept that serially propagated cancer cells, although tumor-derived, may not model all types of authentic tumors; especially those demonstrating genetic heterogeneity.

MST-312 Alters Telomere Dynamics, Gene Expression Profiles and Growth in Human Breast Cancer Cells

“…Rather, we observed a decrease in TRF2 protein level with prolonged treatment of MST-312. Increased TRF2 mRNA expression could be a feedback response to telomere dysfunction as a recent study has shown that a higher level of TRF2 observed in advanced cancer cells with critically short telomeres may be important for the protective function of telomeres [43]. While a gradual telomere shortening was observed in MCF-7 cells following telomerase inhibition, a decrease in telomere length was observed 5 days after treatment with telomerase inhibitor in MDA-MB-231 cells.…”

“…As TRF2 is essential for telomere protection, this rather early effect on telomere length could also be due to telomere deprotection due to a decrease in TRF2 expression in MDA-MB-231 cells. Studies performed in breast tissue arrays demonstrated a significant inverse relationship between a high expression of TRF2 protein and short telomeres within invasive breast carcinomas [43]. Since TRF2 inhibits telomerase and prevents activation of DNA damage response at the telomeres, the high level of TRF2 at short telomeres reflects the increased DNA repair capacity.…”

Mesenchymal stem cells in mammary adipose tissue stimulate progression of breast cancer resembling the basal-type

“…Tissue sections were processed according to a routine immunohistochemical staining procedure. 42 The Ki-67 primary antibody (1:50 dilution of H-300; Santa Cruz Biotechnologies) was applied to the tissue sections for overnight incubation at 4°C. Omission of the primary antibody was included as a negative control for each specimen.…”

Molecular targeting of TRF2 suppresses the growth and tumorigenesis of glioblastoma stem cells

“…First, by reducing the amount of TRF2 at telomeres, targeted depletion of TRF2 may activate DNA checkpoint and render cells vulnerable to apoptosis. Previous studies have shown that TRF2 is highly expressed in a range of tumors including breast cancers (Diehl et al, ), colorectal carcinomas (Dong et al, ) and epithelial cancers (Blanco et al, ). Our analysis of the TCGA database indicated that the gene encoding TRF2 ( Terf2 ) is not mutated or deleted in GBM patients.…”