SMi Source Lesson Oncology Treatment: Temsirolimus

  • SMi Source lesson Oncology Treatment: Temsirolimus has the following microlearning topics

  • 1. Temsirolimus Signal Transduction

  • Lesson Oncology Treatment: Temsirolimus teaches these concepts

  • Temsirolimus, Temsirolimus Signal Transduction, Growth Factor Receptor Activation

    Temsirolimus, Temsirolimus Signal Transduction, Growth Factor Receptor Signaling in Tumorigenesis

    Temsirolimus, Temsirolimus Signal Transduction, Activation of Ras

    Temsirolimus, Temsirolimus Signal Transduction, Akt Signaling Activation of mTOR and Proliferation

    Temsirolimus, Temsirolimus Signal Transduction, Akt Signaling and Cell Survival

    Temsirolimus, Temsirolimus Signal Transduction, VEGF Production in Angiogenesis

  • Lesson Oncology Treatment: Temsirolimus addresses these key points

  • Growth factor binding to tyrosine kinase receptors leads to receptor dimerization and transphosphorylation.

    Tyrosine kinase growth factor receptors

    • Activate PI3 kinase through Ras or independently of Ras

    PI3 kinase

    • Catalyzes the conversion of the lipid phosphatidyl inositol bisphosphate to phosphatidyl inositol trisphosphate


    • Interacts with the pleckstrin homology domain of Akt to recruit Akt to the plasma membrane


    • Activated through phosphorylation by PDK1
    • Signals cascades resulting in tumor cell proliferation and survival

    Phosphorylated tyrosine kinase receptor

    • Able to interact with the Src homology 2 domain or SH2 domain of the adapter proteins Shc and Grb2
    • Grb2 recruits Sos to the plasma membrane
    • Sos activates the small G protein Ras 
    • GTP bound Ras is activated and interacts with a variety of effectors


    • Phosphorylates and inhibits protein TSC


    • Serine/threonine kinase inhibited by the drug rapamycin
    • Phosphorylates the initiation factor 4EBP1 
    • Phosphorylates and activates p70 S6 kinase also known as S6 kinase
    • Activation regulated by cell stress, amino acid, and ATP availability and hypoxia


    • Binds to and inhibits eLF4E
    • Phosphorylation releases eLF4E allowing for initiation of translation


    • Phosphorylated by Akt inhibiting pro-apoptotic ability
    • Binds to and inhibits the anti-apoptotic actions of Bcl-2 and Bcl-XL
      • These proteins prevent the release of cytochrome C release from the mitochondria
    • Inhibition promotes cell survival

    One of the early events in apoptotic cell death includes the loss of mitochondrial membrane integrity followed by the release of cytochrome C.


    • Regulates expression of VEGF
    • Hydroxylated by a family of oxygen-dependent prolyl hydroxylases under conditions of normoxia
    • Ubiquitination targets it for degradation
    • When levels are low cannot act as a transcription factor for VEGF production

    As tumor cells grow:

    • Supply of oxygen cannot keep up and becomes hypoxic
    • HIF-1 levels accumulate, and HIF-1 enters the nucleus
    • HIF-1-mediated expression of VEGF occurs, leading to the accumulation and release of VEGF
    • Increased vascular supply leads to additional tumor growth

    Recent studies have shown that signaling through the PI3 kinase-mTOR pathway inhibits the accumulation of HIF-1 and hypoxia-induced HIF-1-dependent gene transcription.

  • Lesson Oncology Treatment: Temsirolimus is built from these main references. Log into SMi Source for a complete list and details.

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    G. Song, G. Ouyang, S. Bao. The Activation of Akt/PKB Signaling Pathway and Cell Survival. J. Cell. Mol. Med. 9(1):59-71, 2005.

    M.J. Cross, J. Dixelius, T. Matsumoto, L. Claesson-Welsh. VEGF-Receptor Signal Transduction. TRENDS in Biochemical Sciences. 28(9):488-494, 2003.

    J.A. Forsythe et al. Activation of Vascular Endothelial Growth Factor Gene Transcription by Hypoxi-Inducible Factor 1. Mol Cell Biol. 16:4604-4613, 1996.

    R.H. Wenger. Cellular Adaptation to Hypoxia: O2-Sensing Protein Hydroxylases, Hypoxia-Inducible Transcription Factors, and O2-Regulated Gene Expression. FASEB J. 16:1151-1162, 2002.

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    O. Lliopaulos, A.P. Levy, C. Jiang, et al. Negative Regulation of Hypoxia Inducible Genes by the von Hippel Lindau Protein. Proc Nat Acad Sci USA. 93:10595-10599, 1996.

    M. Ohh, C.W. Park, M. Ivan et al. Ubiquitination of Hypoxia-Inducible Factor Requires Direct Binding to the Beta-Domain of the von Hippel-Lindau Protein. Nat Cell Biol. 2:423-427, 2000.

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    K. Kondo, W.G. Kaelin, Jr. The von Hippel-Lindau Tumor Suppressor Gene. Exp Cell Res. 264:117-125, 2001.

    C.C. Hudson, M. Liu, G.G. Chiang, D.M. Otterness, D.C. Loomis, F. Kaper, A.J. Giaccia, R.T. Abraham. Regulation of Hypoxia-Inducible Factor 1 Expression and Function by the Mammalian Target of Rapamycin. Molecular and Cellular Biology. 22(20):7004-7014.