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MAF mediates crosstalk between Ras-MAPK and mTOR signaling in NF1.

Brundage ME, Tandon P, Eaves DW, Williams JP, Miller SJ, Hennigan RH, Jegga A, Cripe TP, Ratner N - Oncogene (2014)

Bottom Line: Mutations in the neurofibromatosis type 1 (NF1) tumor suppressor gene are common in cancer and can cause resistance to therapy.RAD001 blocked MAF-mediated tumor growth, and MAF regulated the mTOR pathway through DEPTOR.MAPK inhibition with NF1 loss of function is predicted to show limited efficacy due to reactivation of mTOR signaling via MAF.

View Article: PubMed Central - PubMed

Affiliation: Division of Experimental Hematology and Cancer Biology, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.

ABSTRACT
Mutations in the neurofibromatosis type 1 (NF1) tumor suppressor gene are common in cancer and can cause resistance to therapy. Using transcriptome analysis we identified MAF as an NF1- regulated transcription factor and verified MAF regulation through RAS/MAPK/AP-1 signaling in malignant peripheral nerve sheath tumor (MPNST) cell lines. MAF was also downregulated in human MPNST. Acute re-expression of MAF promoted expression of glial differentiation markers in MPNST cells in vitro, decreased self-renewal of embryonic precursors and transiently affected tumor cell phenotypes in vitro by increasing MPNST cell death and reducing metabolic activity and anchorage-independent growth. Paradoxically, chronic MAF overexpression enhanced MPNST cell tumor growth in vivo, correlating with elevated pS6 in vitro and in vivo. RAD001 blocked MAF-mediated tumor growth, and MAF regulated the mTOR pathway through DEPTOR. MAPK inhibition with NF1 loss of function is predicted to show limited efficacy due to reactivation of mTOR signaling via MAF.

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MAF enhances tumor growth in a xenograft model, and enhances response to RAD001(A) Growth curve shows average tumor volumes from S462-TY cells infected with vector (pLVX) or inducible MAF and injected into the right flanks of Balb/c nude mice (n=8 – 10 per group). Doxycycline (Dox) was administered after cell implantation. (B) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections for MAF, pS6 and DEPTOR. Brown indicates DAB reaction product.(C) Four day MTS assay using S462TY MPNST cells, comparing control and doxycycline inducible MAF (iMAF) expression with exposure to RAD001 at 10 or 30nM, showing enhanced drug effect with MAF expression. (D) Waterfall plot of change in tumor volume of S462-TY xenografts during treatment with either vehicle control or 10 mg/kg RAD001 showing absence of significant response of this MPNST cell line to RAD001 in vivo. (E) Waterfall plot of significant (p = 0.05) change in tumor volume of S462-TY xenografts transduced with inducible MAF (MAF) when 10 mg/kg RAD001 is also present. (F) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections with anti-MAF and anti-pS6K. Reaction product is brown.
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Figure 7: MAF enhances tumor growth in a xenograft model, and enhances response to RAD001(A) Growth curve shows average tumor volumes from S462-TY cells infected with vector (pLVX) or inducible MAF and injected into the right flanks of Balb/c nude mice (n=8 – 10 per group). Doxycycline (Dox) was administered after cell implantation. (B) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections for MAF, pS6 and DEPTOR. Brown indicates DAB reaction product.(C) Four day MTS assay using S462TY MPNST cells, comparing control and doxycycline inducible MAF (iMAF) expression with exposure to RAD001 at 10 or 30nM, showing enhanced drug effect with MAF expression. (D) Waterfall plot of change in tumor volume of S462-TY xenografts during treatment with either vehicle control or 10 mg/kg RAD001 showing absence of significant response of this MPNST cell line to RAD001 in vivo. (E) Waterfall plot of significant (p = 0.05) change in tumor volume of S462-TY xenografts transduced with inducible MAF (MAF) when 10 mg/kg RAD001 is also present. (F) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections with anti-MAF and anti-pS6K. Reaction product is brown.

Mentions: To test whether MAF-induced increased TORC1 activity affects tumorigenesis in vivo, we injected BALB/cnu/nu mice with S462-TY cells transduced with doxycycline-inducible MAF or vector-control lentivirus. Tumors overexpressing MAF were larger than vector control tumors (Figure 7A), consistent with MAF regulating an escape mechanism, conferring a survival advantage. IHC analysis of tumor xenografts confirmed crosstalk to the mTOR pathway seen in vitro. P-S6 increased and DEPTOR decreased in MAF expressing tumors (Figure 7B). Levels of pS6 and DEPTOR varied throughout the tumors and were most pronounced in regions of densely packed growing tumor cells.


MAF mediates crosstalk between Ras-MAPK and mTOR signaling in NF1.

Brundage ME, Tandon P, Eaves DW, Williams JP, Miller SJ, Hennigan RH, Jegga A, Cripe TP, Ratner N - Oncogene (2014)

MAF enhances tumor growth in a xenograft model, and enhances response to RAD001(A) Growth curve shows average tumor volumes from S462-TY cells infected with vector (pLVX) or inducible MAF and injected into the right flanks of Balb/c nude mice (n=8 – 10 per group). Doxycycline (Dox) was administered after cell implantation. (B) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections for MAF, pS6 and DEPTOR. Brown indicates DAB reaction product.(C) Four day MTS assay using S462TY MPNST cells, comparing control and doxycycline inducible MAF (iMAF) expression with exposure to RAD001 at 10 or 30nM, showing enhanced drug effect with MAF expression. (D) Waterfall plot of change in tumor volume of S462-TY xenografts during treatment with either vehicle control or 10 mg/kg RAD001 showing absence of significant response of this MPNST cell line to RAD001 in vivo. (E) Waterfall plot of significant (p = 0.05) change in tumor volume of S462-TY xenografts transduced with inducible MAF (MAF) when 10 mg/kg RAD001 is also present. (F) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections with anti-MAF and anti-pS6K. Reaction product is brown.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4127377&req=5

Figure 7: MAF enhances tumor growth in a xenograft model, and enhances response to RAD001(A) Growth curve shows average tumor volumes from S462-TY cells infected with vector (pLVX) or inducible MAF and injected into the right flanks of Balb/c nude mice (n=8 – 10 per group). Doxycycline (Dox) was administered after cell implantation. (B) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections for MAF, pS6 and DEPTOR. Brown indicates DAB reaction product.(C) Four day MTS assay using S462TY MPNST cells, comparing control and doxycycline inducible MAF (iMAF) expression with exposure to RAD001 at 10 or 30nM, showing enhanced drug effect with MAF expression. (D) Waterfall plot of change in tumor volume of S462-TY xenografts during treatment with either vehicle control or 10 mg/kg RAD001 showing absence of significant response of this MPNST cell line to RAD001 in vivo. (E) Waterfall plot of significant (p = 0.05) change in tumor volume of S462-TY xenografts transduced with inducible MAF (MAF) when 10 mg/kg RAD001 is also present. (F) Immunohistochemical staining of pLVX vector control and MAF expressing tumor paraffin sections with anti-MAF and anti-pS6K. Reaction product is brown.
Mentions: To test whether MAF-induced increased TORC1 activity affects tumorigenesis in vivo, we injected BALB/cnu/nu mice with S462-TY cells transduced with doxycycline-inducible MAF or vector-control lentivirus. Tumors overexpressing MAF were larger than vector control tumors (Figure 7A), consistent with MAF regulating an escape mechanism, conferring a survival advantage. IHC analysis of tumor xenografts confirmed crosstalk to the mTOR pathway seen in vitro. P-S6 increased and DEPTOR decreased in MAF expressing tumors (Figure 7B). Levels of pS6 and DEPTOR varied throughout the tumors and were most pronounced in regions of densely packed growing tumor cells.

Bottom Line: Mutations in the neurofibromatosis type 1 (NF1) tumor suppressor gene are common in cancer and can cause resistance to therapy.RAD001 blocked MAF-mediated tumor growth, and MAF regulated the mTOR pathway through DEPTOR.MAPK inhibition with NF1 loss of function is predicted to show limited efficacy due to reactivation of mTOR signaling via MAF.

View Article: PubMed Central - PubMed

Affiliation: Division of Experimental Hematology and Cancer Biology, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.

ABSTRACT
Mutations in the neurofibromatosis type 1 (NF1) tumor suppressor gene are common in cancer and can cause resistance to therapy. Using transcriptome analysis we identified MAF as an NF1- regulated transcription factor and verified MAF regulation through RAS/MAPK/AP-1 signaling in malignant peripheral nerve sheath tumor (MPNST) cell lines. MAF was also downregulated in human MPNST. Acute re-expression of MAF promoted expression of glial differentiation markers in MPNST cells in vitro, decreased self-renewal of embryonic precursors and transiently affected tumor cell phenotypes in vitro by increasing MPNST cell death and reducing metabolic activity and anchorage-independent growth. Paradoxically, chronic MAF overexpression enhanced MPNST cell tumor growth in vivo, correlating with elevated pS6 in vitro and in vivo. RAD001 blocked MAF-mediated tumor growth, and MAF regulated the mTOR pathway through DEPTOR. MAPK inhibition with NF1 loss of function is predicted to show limited efficacy due to reactivation of mTOR signaling via MAF.

Show MeSH
Related in: MedlinePlus