hTERT Downregulation Attenuates Resistance to DOX, Impairs FAK-Mediated Adhesion, and Leads to Autophagy Induction in Breast Cancer Cells

Abstract

Telomerase is known to contribute to telomere maintenance and to provide cancer cell immortality. However, numerous reports are showing that the function of the enzyme goes far beyond chromosome ends. The study aimed to explore how telomerase downregulation in MCF7 and MDA-MB-231 breast cancer cells affects their ability to survive. Consequently, sensitivity to drug resistance, proliferation, and adhesion were assessed. The lentiviral-mediated human telomerase reverse transcriptase (hTERT) downregulation efficiency was performed at gene expression and protein level using qPCR and Western blot, respectively. Telomerase activity was evaluated using the Telomeric Repeat Amplification Protocol (TRAP) assay. The study revealed that hTERT downregulation led to an increased sensitivity of breast cancer cells to doxorubicin which was demonstrated in MTT and clonogenic assays. During a long-term doubling time assessment, a decreased population doubling level was observed. Interestingly, it did not dramatically affect cell cycle distribution. hTERT downregulation was accompanied by an alteration in β1-integrin- and by focal adhesion kinase (FAK)-driven pathways together with the reduction of target proteins phosphorylation, i.e., paxillin and c-Src. Additionally, autophagy activation was observed in MDA-MB-231 cells manifested by alternations in Atg5, Beclin 1, LC3II/I ratio, and p62. These results provide new evidence supporting the possible therapeutic potential of telomerase downregulation leading to induction of autophagy and cancer cells elimination.

Favipiravir, an antiviral drug, in combination with tamoxifen exerts synergistic effect in tamoxifen-resistant breast cancer cells via hTERT inhibition

“…A known resistance mechanism focuses on hTERT overexpression 16 , 17 . hTERT promotes cancer cell proliferation, angiogenesis, migration, and metastasis 39 , 40 .…”

“…Elevated levels of telomerase have been reported in 85% of human carcinomas and 90% of breast cancers 13 – 15 . hTERT has been found to be overexpressed in resistant cancer cells 16 , 17 . Cell immortality correlates with the maintenance of telomere length and the restoration of hTERT activity.…”

Doxorubicin and Cisplatin Modulate miR-21, miR-106, miR-126, miR-155 and miR-199 Levels in MCF7, MDA-MB-231 and SK-BR-3 Cells That Makes Them Potential Elements of the DNA-Damaging Drug Treatment Response Monitoring in Breast Cancer Cells—A Preliminary Study

“…Cell survival was determined using MTT assay by assessing the sensitivity of cells subjected to drugs, i.e., doxorubicin or cisplatin, as previously described [ 28 ]. Drugs selection was based on common use in breast cancer [ 29 ].…”

The Role of Telomerase in Breast Cancer’s Response to Therapy

“…Importantly, one of the most characteristic features of the vast majority of adenocarcinomas, including breast cancer, is the restoration of the telomerase expression (specifically the key catalytic telomerase subunit hTERT) and activity that provide tumor cell immortality. Telomerase is also postulated to modulate cancer cells’ responses to drugs as well as their metastatic potential via affecting adhesion pathways [ 13 ]. For these reasons, telomerase seems to be a good therapeutic target in breast cancer.…”