mTOR-dependent upregulation of xCT blocks melanin synthesis and promotes tumorigenesis

Area of Science:

• Oncology
• Dermatology
• Molecular Biology

Background:

• Tuberous Sclerosis Complex (TSC) arises from TSC1/TSC2 loss, activating the mTOR pathway.
• TSC manifests as skin lesions and organ tumors, with underlying molecular causes often unclear.
• The role of the Xc- cystine/glutamate antiporter (xCT) in TSC pathogenesis is largely unexplored.

Purpose of the Study:

• To investigate the role of xCT in TSC pathogenesis.
• To elucidate the molecular mechanisms linking mTOR signaling, melanin synthesis, and tumorigenesis in TSC.
• To evaluate xCT as a potential therapeutic target for TSC.

Main Methods:

• Analysis of xCT expression in Tsc2-/- or Pten-/- cells, Tsc1 knockout mouse tissues, and human TSC kidney tumors.
• Investigating the transcriptional regulation of xCT by the mTOR-Oct1 signaling cascade.
• Assessing the impact of xCT disruption on cell proliferation, melanin synthesis, and tumorigenesis in vitro and in vivo.
• Evaluating the efficacy of mTOR and xCT inhibitors, alone and in combination.

Main Results:

• xCT was found to be elevated in various TSC models and human tumors.
• mTOR-mediated Oct1 signaling was identified as a key regulator of xCT transcription.
• Increased xCT levels altered melanin composition and promoted proliferation and tumorigenesis.
• Inhibition of mTOR or xCT, particularly in combination, effectively suppressed tumor growth in mTOR-hyperactive cells.

Conclusions:

• Oncogenic mTOR activation of xCT represents a critical link between aberrant melanin synthesis and tumorigenesis in TSC.
• xCT is a novel therapeutic target for TSC.
• Targeting xCT may offer a new strategy for treating TSC and other mTOR-related diseases.