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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 expression increases with Schwann cell differentiation and MAF over-expression reduces formation of Schwann cell precursors(A & B) RT-PCR analysis of mouse Schwann cell precursors and mature Schwann cells showing mRNA expression relative to Gapdh and normalized to mature Schwann cells for Sox9 or Schwann cell precursors for Maf. Immunohistochemical staining of each cell type is displayed below the RT-PCR panels for Sox9 or Maf protein expression. Note partial nuclear localization (DAPI, blue) of MAF (red) in unmerged and merged higher confocal images at right. (C) mCherry tagged MAF infected Schwann cell precursors show reduced sphere forming potential in a self-renewal assay compared to mCherry infected control cells. Maf expression in 4° spheres was verified by RT-PCR (right). (D) Model showing that Maf expression increases as cells differentiate, while Sox9 expression decreases.
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Figure 4: MAF expression increases with Schwann cell differentiation and MAF over-expression reduces formation of Schwann cell precursors(A & B) RT-PCR analysis of mouse Schwann cell precursors and mature Schwann cells showing mRNA expression relative to Gapdh and normalized to mature Schwann cells for Sox9 or Schwann cell precursors for Maf. Immunohistochemical staining of each cell type is displayed below the RT-PCR panels for Sox9 or Maf protein expression. Note partial nuclear localization (DAPI, blue) of MAF (red) in unmerged and merged higher confocal images at right. (C) mCherry tagged MAF infected Schwann cell precursors show reduced sphere forming potential in a self-renewal assay compared to mCherry infected control cells. Maf expression in 4° spheres was verified by RT-PCR (right). (D) Model showing that Maf expression increases as cells differentiate, while Sox9 expression decreases.

Mentions: To determine if MAF expression is relevant to normal glial differentiation, we monitored expression levels in mouse Schwann cell precursors derived from mouse embryonic E12.5 dorsal root ganglia and in mature Schwann cells. RT-PCR and immunohistochemical analysis revealed high SOX9 expression in Schwann cell precursors normalized to Schwann cells (Figure 4A), and low MAF expression in Schwann cell precursors compared to Schwann cells (Figure 4B). Confocal imaging showed that MAF is present in Schwann cell cytoplasm and nuclei (Figure 4B). To determine if low MAF expression contributes to the precursor state, we transduced mouse Schwann cell precursors at clonal density with lenti-MAF. We observed a decrease in Schwann cell precursor self-renewal, which was maintained for up to three serial replatings (Figure 4C). The reciprocal expression pattern of SOX9 and MAF compared to mature Schwann cells, together with MAF’s ability to decrease precursor self-renewal, is consistent with the idea that low MAF expression in SC precursors sustains them in a progenitor state (Figure 4D).


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 expression increases with Schwann cell differentiation and MAF over-expression reduces formation of Schwann cell precursors(A & B) RT-PCR analysis of mouse Schwann cell precursors and mature Schwann cells showing mRNA expression relative to Gapdh and normalized to mature Schwann cells for Sox9 or Schwann cell precursors for Maf. Immunohistochemical staining of each cell type is displayed below the RT-PCR panels for Sox9 or Maf protein expression. Note partial nuclear localization (DAPI, blue) of MAF (red) in unmerged and merged higher confocal images at right. (C) mCherry tagged MAF infected Schwann cell precursors show reduced sphere forming potential in a self-renewal assay compared to mCherry infected control cells. Maf expression in 4° spheres was verified by RT-PCR (right). (D) Model showing that Maf expression increases as cells differentiate, while Sox9 expression decreases.
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Related In: Results  -  Collection

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Figure 4: MAF expression increases with Schwann cell differentiation and MAF over-expression reduces formation of Schwann cell precursors(A & B) RT-PCR analysis of mouse Schwann cell precursors and mature Schwann cells showing mRNA expression relative to Gapdh and normalized to mature Schwann cells for Sox9 or Schwann cell precursors for Maf. Immunohistochemical staining of each cell type is displayed below the RT-PCR panels for Sox9 or Maf protein expression. Note partial nuclear localization (DAPI, blue) of MAF (red) in unmerged and merged higher confocal images at right. (C) mCherry tagged MAF infected Schwann cell precursors show reduced sphere forming potential in a self-renewal assay compared to mCherry infected control cells. Maf expression in 4° spheres was verified by RT-PCR (right). (D) Model showing that Maf expression increases as cells differentiate, while Sox9 expression decreases.
Mentions: To determine if MAF expression is relevant to normal glial differentiation, we monitored expression levels in mouse Schwann cell precursors derived from mouse embryonic E12.5 dorsal root ganglia and in mature Schwann cells. RT-PCR and immunohistochemical analysis revealed high SOX9 expression in Schwann cell precursors normalized to Schwann cells (Figure 4A), and low MAF expression in Schwann cell precursors compared to Schwann cells (Figure 4B). Confocal imaging showed that MAF is present in Schwann cell cytoplasm and nuclei (Figure 4B). To determine if low MAF expression contributes to the precursor state, we transduced mouse Schwann cell precursors at clonal density with lenti-MAF. We observed a decrease in Schwann cell precursor self-renewal, which was maintained for up to three serial replatings (Figure 4C). The reciprocal expression pattern of SOX9 and MAF compared to mature Schwann cells, together with MAF’s ability to decrease precursor self-renewal, is consistent with the idea that low MAF expression in SC precursors sustains them in a progenitor state (Figure 4D).

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