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Spatial and Temporal Control of Murine Melanoma Initiation from Mutant Melanocyte Stem Cells
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Spatial and Temporal Control of Murine Melanoma Initiation from Mutant Melanocyte Stem Cells

Published on: June 7, 2019

Plexin B1 is repressed by oncogenic B-Raf signaling and functions as a tumor suppressor in melanoma cells

G M Argast1, C H Croy, K L Couts

  • 1Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA.

Oncogene
|June 2, 2009
PubMed

Insights

Human melanomas with B-Raf mutations downregulate plexin B1, a tumor suppressor. Loss of plexin B1 function promotes melanoma growth, while its restoration inhibits it, suggesting therapeutic potential.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cell Signaling

Background:

  • Human melanomas frequently harbor oncogenic B-Raf mutations, activating the B-Raf/MKK/ERK signaling pathway.
  • This pathway influences numerous cellular processes, but its specific targets in melanoma are not fully elucidated.

Purpose of the Study:

  • To identify cellular targets regulated by the B-Raf/MKK/ERK pathway in melanoma.
  • To investigate the role of plexin B1, a downstream target, in melanoma development and progression.

Main Methods:

  • Microarray screening to identify genes modulated by the B-Raf/MKK/ERK pathway.
  • In vitro assays (soft agar, spheroid formation) and in vivo xenograft models to assess plexin B1's tumor-suppressive function.
  • Analysis of plexin B1 expression and function in primary versus metastatic melanoma cells.

Main Results:

  • Genes upregulated by B-Raf/MKK/ERK signaling were associated with cell-cycle regulation, while downregulated genes included axon guidance molecules like plexin B1.
  • Plexin B1 exhibited tumor-suppressor activity in primary melanoma cells, inhibiting tumorigenesis and correlating with AKT inhibition.
  • Metastatic melanoma cells showed reduced or absent inhibitory response to plexin B1, indicating a bypass of tumor-suppressor mechanisms and altered migratory behavior.

Conclusions:

  • The B-Raf/MKK/ERK pathway promotes melanoma genesis by downregulating plexin B1, a key tumor suppressor in early-stage disease.
  • Plexin B1's tumor-suppressive function is dependent on its C-terminal domain and GTPase activating protein activity.
  • Alterations in plexin B1 response in metastatic cells highlight its complex role and potential escape mechanisms during melanoma progression.

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