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Activated mutant NRas(Q61K) drives aberrant melanocyte signaling, survival, and invasiveness via a Rac1-dependent mechanism.

Li A, Ma Y, Jin M, Mason S, Mort RL, Blyth K, Larue L, Sansom OJ, Machesky LM - J. Invest. Dermatol. (2012)

Bottom Line: The Ras oncogene also activates signaling via the related Rho GTPase Rac1, which can mediate growth, survival, and motility signaling.We tested the effects of activated NRas(Q61K) on the proliferation, motility, and invasiveness of melanoblasts and melanocytes in the developing mouse and ex vivo explant culture as well as in a melanoma transplant model.We also show that genetic deletion or pharmacological inhibition of Rac1 in NRas(Q61K) induced melanoma suppresses tumor growth, lymph node spread, and tumor cell invasiveness, suggesting a potential value for Rac1 as a therapeutic target for activated NRas-driven tumor growth and invasiveness.

View Article: PubMed Central - PubMed

Affiliation: The Beatson Institute for Cancer Research, Garscube Estate, Glasgow, UK.

ABSTRACT
Around a fifth of melanomas exhibit an activating mutation in the oncogene NRas that confers constitutive signaling to proliferation and promotes tumor initiation. NRas signals downstream of the major melanocyte tyrosine kinase receptor c-kit and activated NRas results in increased signaling via the extracellular signal-regulated kinase (ERK)/MAPK/ERK kinase/mitogen-activated protein kinase (MAPK) pathways to enhance proliferation. The Ras oncogene also activates signaling via the related Rho GTPase Rac1, which can mediate growth, survival, and motility signaling. We tested the effects of activated NRas(Q61K) on the proliferation, motility, and invasiveness of melanoblasts and melanocytes in the developing mouse and ex vivo explant culture as well as in a melanoma transplant model. We find an important role for Rac1 downstream of NRas(Q61K) in mediating dermal melanocyte survival in vivo in mouse, but surprisingly NRas(Q61K) does not appear to affect melanoblast motility or proliferation during mouse embryogenesis. We also show that genetic deletion or pharmacological inhibition of Rac1 in NRas(Q61K) induced melanoma suppresses tumor growth, lymph node spread, and tumor cell invasiveness, suggesting a potential value for Rac1 as a therapeutic target for activated NRas-driven tumor growth and invasiveness.

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Expression of NRasQ61K does not affect melanoblast migration in epidermis. All experiments show embryo skin explants or embryos. (a) Combined Z-stack confocal images of melanoblasts from Z/EG NRas and Z/EG Rac1 f/f NRas embryo skin. Long (⩾cell body width) and short (⩽cell body width) protrusions, are shown with white and yellow arrows, respectively. (b) Three hour tracks of melanoblasts. Black tracks migrated faster and red slower than average of control (Ctr). (c) Live imaging of cell protrusion (yellow arrow) dynamics. (d) Live imaging of melanoblast in GFP-Lifeact NRas Ctr or GFP-Lifeact Rac1 f/f NRas skin. Yellow arrows indicate protrusions. (e) Migration speed. (f) Persistence. (g) Number of long/short protrusions per melanoblast. (h) Proportion of melanoblasts with long/short protrusions. (i) Lifetime of growing protrusions. (j) Frequency of protrusion formation. (k) Photos and (l) quantification of melanoblasts in E15.5 DCT∷LacZ embryos. Melanoblasts are indicated with black arrows. Black dotted lines represent epi/dermal junction. Error bars indicate mean±SEM. **P<0.01, by t-test. Bars (a, c)=10 μm and (k) 20 μm.
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fig4: Expression of NRasQ61K does not affect melanoblast migration in epidermis. All experiments show embryo skin explants or embryos. (a) Combined Z-stack confocal images of melanoblasts from Z/EG NRas and Z/EG Rac1 f/f NRas embryo skin. Long (⩾cell body width) and short (⩽cell body width) protrusions, are shown with white and yellow arrows, respectively. (b) Three hour tracks of melanoblasts. Black tracks migrated faster and red slower than average of control (Ctr). (c) Live imaging of cell protrusion (yellow arrow) dynamics. (d) Live imaging of melanoblast in GFP-Lifeact NRas Ctr or GFP-Lifeact Rac1 f/f NRas skin. Yellow arrows indicate protrusions. (e) Migration speed. (f) Persistence. (g) Number of long/short protrusions per melanoblast. (h) Proportion of melanoblasts with long/short protrusions. (i) Lifetime of growing protrusions. (j) Frequency of protrusion formation. (k) Photos and (l) quantification of melanoblasts in E15.5 DCT∷LacZ embryos. Melanoblasts are indicated with black arrows. Black dotted lines represent epi/dermal junction. Error bars indicate mean±SEM. **P<0.01, by t-test. Bars (a, c)=10 μm and (k) 20 μm.

Mentions: The transition from anagen to telogen leads to apoptosis of most follicular melanocytes (Sharov et al., 2005). In the telogen phase of the first hair follicle cycle (P21), only the permanent part of the hair follicles remained in dorsal skin taken from control mice (Supplementary Figure S4A online). Most of follicular melanocytes remained in the dermis even after the hair follicles in Tyr∷NRasQ61K mouse degenerated (Figure 3f and Supplementary Figure S4B online, arrows). Which, however, failed to be maintained when Rac1 was deleted (Figure 4f, Supplementary Figure S4C online). Thus, NRasQ61K protects dermal melanocytes from being cleared from the skin in a Rac1-dependent manner.


Activated mutant NRas(Q61K) drives aberrant melanocyte signaling, survival, and invasiveness via a Rac1-dependent mechanism.

Li A, Ma Y, Jin M, Mason S, Mort RL, Blyth K, Larue L, Sansom OJ, Machesky LM - J. Invest. Dermatol. (2012)

Expression of NRasQ61K does not affect melanoblast migration in epidermis. All experiments show embryo skin explants or embryos. (a) Combined Z-stack confocal images of melanoblasts from Z/EG NRas and Z/EG Rac1 f/f NRas embryo skin. Long (⩾cell body width) and short (⩽cell body width) protrusions, are shown with white and yellow arrows, respectively. (b) Three hour tracks of melanoblasts. Black tracks migrated faster and red slower than average of control (Ctr). (c) Live imaging of cell protrusion (yellow arrow) dynamics. (d) Live imaging of melanoblast in GFP-Lifeact NRas Ctr or GFP-Lifeact Rac1 f/f NRas skin. Yellow arrows indicate protrusions. (e) Migration speed. (f) Persistence. (g) Number of long/short protrusions per melanoblast. (h) Proportion of melanoblasts with long/short protrusions. (i) Lifetime of growing protrusions. (j) Frequency of protrusion formation. (k) Photos and (l) quantification of melanoblasts in E15.5 DCT∷LacZ embryos. Melanoblasts are indicated with black arrows. Black dotted lines represent epi/dermal junction. Error bars indicate mean±SEM. **P<0.01, by t-test. Bars (a, c)=10 μm and (k) 20 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig4: Expression of NRasQ61K does not affect melanoblast migration in epidermis. All experiments show embryo skin explants or embryos. (a) Combined Z-stack confocal images of melanoblasts from Z/EG NRas and Z/EG Rac1 f/f NRas embryo skin. Long (⩾cell body width) and short (⩽cell body width) protrusions, are shown with white and yellow arrows, respectively. (b) Three hour tracks of melanoblasts. Black tracks migrated faster and red slower than average of control (Ctr). (c) Live imaging of cell protrusion (yellow arrow) dynamics. (d) Live imaging of melanoblast in GFP-Lifeact NRas Ctr or GFP-Lifeact Rac1 f/f NRas skin. Yellow arrows indicate protrusions. (e) Migration speed. (f) Persistence. (g) Number of long/short protrusions per melanoblast. (h) Proportion of melanoblasts with long/short protrusions. (i) Lifetime of growing protrusions. (j) Frequency of protrusion formation. (k) Photos and (l) quantification of melanoblasts in E15.5 DCT∷LacZ embryos. Melanoblasts are indicated with black arrows. Black dotted lines represent epi/dermal junction. Error bars indicate mean±SEM. **P<0.01, by t-test. Bars (a, c)=10 μm and (k) 20 μm.
Mentions: The transition from anagen to telogen leads to apoptosis of most follicular melanocytes (Sharov et al., 2005). In the telogen phase of the first hair follicle cycle (P21), only the permanent part of the hair follicles remained in dorsal skin taken from control mice (Supplementary Figure S4A online). Most of follicular melanocytes remained in the dermis even after the hair follicles in Tyr∷NRasQ61K mouse degenerated (Figure 3f and Supplementary Figure S4B online, arrows). Which, however, failed to be maintained when Rac1 was deleted (Figure 4f, Supplementary Figure S4C online). Thus, NRasQ61K protects dermal melanocytes from being cleared from the skin in a Rac1-dependent manner.

Bottom Line: The Ras oncogene also activates signaling via the related Rho GTPase Rac1, which can mediate growth, survival, and motility signaling.We tested the effects of activated NRas(Q61K) on the proliferation, motility, and invasiveness of melanoblasts and melanocytes in the developing mouse and ex vivo explant culture as well as in a melanoma transplant model.We also show that genetic deletion or pharmacological inhibition of Rac1 in NRas(Q61K) induced melanoma suppresses tumor growth, lymph node spread, and tumor cell invasiveness, suggesting a potential value for Rac1 as a therapeutic target for activated NRas-driven tumor growth and invasiveness.

View Article: PubMed Central - PubMed

Affiliation: The Beatson Institute for Cancer Research, Garscube Estate, Glasgow, UK.

ABSTRACT
Around a fifth of melanomas exhibit an activating mutation in the oncogene NRas that confers constitutive signaling to proliferation and promotes tumor initiation. NRas signals downstream of the major melanocyte tyrosine kinase receptor c-kit and activated NRas results in increased signaling via the extracellular signal-regulated kinase (ERK)/MAPK/ERK kinase/mitogen-activated protein kinase (MAPK) pathways to enhance proliferation. The Ras oncogene also activates signaling via the related Rho GTPase Rac1, which can mediate growth, survival, and motility signaling. We tested the effects of activated NRas(Q61K) on the proliferation, motility, and invasiveness of melanoblasts and melanocytes in the developing mouse and ex vivo explant culture as well as in a melanoma transplant model. We find an important role for Rac1 downstream of NRas(Q61K) in mediating dermal melanocyte survival in vivo in mouse, but surprisingly NRas(Q61K) does not appear to affect melanoblast motility or proliferation during mouse embryogenesis. We also show that genetic deletion or pharmacological inhibition of Rac1 in NRas(Q61K) induced melanoma suppresses tumor growth, lymph node spread, and tumor cell invasiveness, suggesting a potential value for Rac1 as a therapeutic target for activated NRas-driven tumor growth and invasiveness.

Show MeSH
Related in: MedlinePlus