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Rapamycin-induced miR-21 promotes mitochondrial homeostasis and adaptation in mTORC1 activated cells
Hilaire C Lam1, Heng-Jia Liu1, Christian V Baglini1
1Department of Medicine, Pulmonary and Critical Care Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
Abstract:
mTORC1 hyperactivation drives the multi-organ hamartomatous disease tuberous sclerosis complex (TSC). Rapamycin inhibits mTORC1, inducing partial tumor responses; however, the tumors regrow following treatment cessation. We discovered that the oncogenic miRNA, miR-21, is increased in Tsc2-deficient cells and, surprisingly, further increased by rapamycin. To determine the impact of miR-21 in TSC, we inhibited miR-21 in vitro. miR-21 inhibition significantly repressed the tumorigenic potential of Tsc2-deficient cells and increased apoptosis sensitivity. Tsc2-deficient cells' clonogenic and anchorage independent growth were reduced by ∼50% (p<0.01) and ∼75% (p<0.0001), respectively, and combined rapamycin treatment decreased soft agar growth by ∼90% (p<0.0001). miR-21 inhibition also increased sensitivity to apoptosis. Through a network biology-driven integration of RNAseq data, we discovered that miR-21 promotes mitochondrial adaptation and homeostasis in Tsc2-deficient cells. miR-21 inhibition reduced mitochondrial polarization and function in Tsc2-deficient cells, with and without co-treatment with rapamycin. Importantly, miR-21 inhibition limited Tsc2-deficient tumor growth in vivo, reducing tumor size by approximately 3-fold (p<0.0001). When combined with rapamcyin, miR-21 inhibition showed even more striking efficacy, both during treatment and after treatment cessation, with a 4-fold increase in median survival following rapamycin cessation (p=0.0008). We conclude that miR-21 promotes mTORC1-driven tumorigenesis via a mechanism that involves the mitochondria, and that miR-21 is a potential therapeutic target for TSC-associated hamartomas and other mTORC1-driven tumors, with the potential for synergistic efficacy when combined with rapalogs.
Insights
Inhibition of miR-21, an oncogenic microRNA, suppresses tuberous sclerosis complex (TSC) tumor growth and enhances apoptosis. Combining miR-21 inhibition with rapamycin offers synergistic therapeutic benefits for TSC and other mTORC1-driven tumors.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Tuberous sclerosis complex (TSC) is a genetic disorder characterized by hamartomatous growths driven by mTORC1 hyperactivation.
- Rapamycin, an mTORC1 inhibitor, shows partial efficacy but leads to tumor regrowth upon cessation.
- The role of microRNA-21 (miR-21) in TSC pathogenesis and its interaction with rapamycin therapy remain incompletely understood.
Purpose of the Study:
- To investigate the impact of miR-21 inhibition on the tumorigenic potential of Tsc2-deficient cells, the genetic basis of TSC.
- To explore the mechanistic role of miR-21 in mitochondrial function within the context of TSC.
- To evaluate the therapeutic efficacy of miR-21 inhibition, alone and in combination with rapamycin, for TSC-associated tumors.
Main Methods:
- In vitro inhibition of miR-21 in Tsc2-deficient cells to assess effects on proliferation, clonogenicity, and apoptosis.
- RNA sequencing and network biology approaches to elucidate miR-21's role in mitochondrial adaptation.
- In vivo studies using Tsc2-deficient mouse models to evaluate tumor growth inhibition and survival outcomes with miR-21 inhibition and rapamycin treatment.
Main Results:
- miR-21 inhibition significantly reduced Tsc2-deficient cell proliferation, clonogenic growth, and anchorage-independent growth.
- miR-21 inhibition increased apoptosis sensitivity and impaired mitochondrial function and polarization in Tsc2-deficient cells.
- In vivo, miR-21 inhibition markedly reduced tumor size, and combination therapy with rapamycin demonstrated superior efficacy and prolonged survival, even after treatment cessation.
Conclusions:
- miR-21 promotes mTORC1-driven tumorigenesis in TSC through a mechanism involving mitochondrial adaptation.
- miR-21 inhibition represents a promising therapeutic strategy for TSC-associated hamartomas.
- Combination therapy with miR-21 inhibitors and rapalogs may offer synergistic benefits for treating TSC and other mTORC1-driven malignancies.