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mTORC1 promotes survival through translational control of Mcl-1

John R Mills1, Yoshitaka Hippo, Francis Robert

  • 1Department of Biochemistry, McGill University, Montreal, QC, Canada H3G 1Y6.

Proceedings of the National Academy of Sciences of the United States of America
|July 31, 2008
PubMed

Insights

Loss of TSC2 activates mTORC1, promoting lymphoma. Blocking mTORC1 with rapamycin induces apoptosis by reducing Mcl-1 levels, suggesting Mcl-1 modulation predicts response to mTORC1 inhibitors in cancer.

Area of Science:

  • Molecular Biology
  • Oncology
  • Biochemistry

Background:

  • The phosphatidylinositol 3-kinase (PI3K)/AKT pathway is frequently activated in cancers, contributing to chemotherapeutic resistance.
  • Inhibiting mTORC1, a downstream target of PI3K/AKT, may enhance chemosensitivity, but the underlying mechanisms and genetic factors are not fully understood.

Purpose of the Study:

  • To investigate the role of TSC2 loss in cancer development and its impact on the PI3K/AKT/mTORC1 pathway.
  • To identify genetic determinants of sensitivity to mTORC1 inhibitors like rapamycin.

Main Methods:

  • Utilized the E mu-myc murine lymphoma model to study the effects of TSC2 deficiency.
  • Administered rapamycin to Tsc2(+/-)E mu-Myc mice to assess tumor apoptosis and molecular responses.
  • Analyzed the expression and translational regulation of survival factors, including myeloid cell leukemia sequence 1 (Mcl-1).

Main Results:

  • Loss of TSC2 led to mTORC1 activation, accelerated oncogenesis, and a defective apoptotic program, despite reduced AKT phosphorylation.
  • Tumors from Tsc2(+/-)E mu-Myc mice exhibited rapid apoptosis upon mTORC1 inhibition with rapamycin.
  • Myeloid cell leukemia sequence 1 (Mcl-1) was identified as a key, translationally regulated determinant of mTORC1-dependent cell survival.

Conclusions:

  • TSC2 deficiency drives oncogenesis via mTORC1 activation and impaired apoptosis, creating sensitivity to mTORC1 blockade.
  • Mcl-1 is a critical mediator of mTORC1-driven survival, and its modulation by rapamycin is crucial for therapeutic response.
  • Rapamycin's efficacy in this model is linked to its ability to decrease Mcl-1 expression, highlighting Mcl-1 as a predictive biomarker for mTORC1 inhibitor therapy.

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