Aberrant activation of the mammalian target of rapamycin complex 1 (mTORC1) plays a critical role in tumorigenesis. However, the precise underlying mechanism is still not fully understood. Although accumulating evidence suggests that mTORC1 signaling is regulated by microRNAs (miRNAs), whether miRNAs are involved in the tumorigenesis mediated by mTORC1 dysregulation remains largely unclear. In our study, the comparison between tuberous sclerosis complex 1 (Tsc1) -/-or Tsc2-/-mouse embryonic fibroblasts (MEFs) and the control cells revealed the involvement of microRNA-125b-5p (miR-125b-5p) in the tumorigenesis driven by mTORC1 activation. Our study also showed that loss of TSC1 or TSC2 led to significant downregulation of miR-125b-5p and upregulation of signal transducer and activator of transcription 3 (STAT3) via mTORC1 activation. Overexpression of miR-125b-5p inhibited the proliferation of the cells with hyperactivated mTORC1 both in vitro and in vivo. Furthermore, we demonstrated that STAT3 is a direct target of miR-125b-5p. Depletion of STAT3 mimicked the effect of ectopic expression of miR-125b-5p, and reintroduction of STAT3 rescued the compromised cell proliferation driven by miR-125b-5p overexpression in Tsc1-/-or Tsc2-/-MEFs. We conclude that the miR-125b-5p/STAT3 pathway plays a crucial role in hyperactivated mTORC1-mediated tumorigenesis and miR-125b-5p is a potential therapeutic target.
Tuberous sclerosis complex (TSC) is an autosomal dominant disease characterized by the benign tumor formation in multiple organs. The main etiology of TSC is the loss‐of‐function mutation of TSC1 or TSC2 gene, which leads to aberrant activation of mammalian target of rapamycin complex 1 (mTORC1). In this research, we found a significant increase of 6‐phosphofructo‐2‐kinase/fructose‐2,6‐biphosphatase 3 (PFKFB3) expression in Tsc1−/− and Tsc2−/− mouse embryonic fibroblasts (MEFs) compared with the control cells. Inhibition of mTORC1 led to a dramatic decrease of PFKFB3 expression, indicating PFKFB3 regulation by mTORC1. Moreover, suppression of mTORC1 inhibited the expression of PFKFB3 in rat uterine leiomyoma‐derived Tsc2‐null ELT3 cells and human tumor cells. Furthermore, we identified hypoxia‐inducible factor 1α (HIF‐1α) as a mediator transmitting the signal from mTORC1 to PFKFB3. Depletion of PFKFB3 inhibited proliferation and tumorigenicity of Tsc1‐ or Tsc2‐deficient cells. In addition, combination of rapamycin with PFK15, a PFKFB3 inhibitor, exerts a stronger inhibitory effect on cell proliferation of Tsc1‐ or Tsc2‐null MEFs than treatment with single drug. We conclude that loss of TSC1 or TSC2 led to upregulated expression of PFKFB3 through activation of mTORC1/HIF‐1α signaling pathway and co‐administration of rapamycin and PFK15 may be a promising strategy for the treatment of TSC tumors as well as other hyperactivated mTORC1‐related tumors.
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