Oncogenic BRAF regulates beta-Trcp expression and NF-kappaB activity in human melanoma cells.
Mutational activation of BRAF is a frequent event in human malignant melanomas suggesting that BRAF-dependent signaling is conducive to melanoma cell growth and survival. Previously published work reported that melanoma cells exhibit constitutive anti-apoptotic nuclear factor kappaB (NF-kappaB) transcription factor activation triggered by proteolysis of its inhibitor IkappaB. IkappaB degradation is dependent upon its phosphorylation by the IkappaB kinase (IKK) complex and subsequent ubiquitination facilitated by beta-Trcp E3 ubiquitin ligase. Here, we report that melanocytes expressing a conditionally oncogenic form of BRAF(V600E) exhibit enhanced beta-Trcp expression, increased IKK activity and a concomitant increase in the rate of IkappaBalpha degradation. Conversely, inhibition of BRAF signaling using either a broad-spectrum Raf inhibitor (BAY 43-9006) or by selective knock-down of BRAF(V600E) expression by RNA interference in human melanoma cells leads to decreased IKK activity and beta-Trcp expression, stabilization of IkappaB, inhibition of NF-kappaB transcriptional activity and sensitization of these cells to apoptosis. Taken together, these data support a model in which mutational activation of BRAF in human melanomas contributes to constitutive induction of NF-kappaB activity and to increased survival of melanoma cells.
Liu
J
J
Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6046, USA.
Suresh Kumar
K G
KG
Yu
D
D
Molton
S A
SA
McMahon
M
M
Herlyn
M
M
Thomas-Tikhonenko
A
A
Fuchs
S Y
SY
D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D006868:Hydrolysis; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D048493:Proto-Oncogene Proteins B-raf / Q000502:physiology*; D034622:RNA Interference; D044844:beta-Transducin Repeat-Containing Proteins / Q000235:genetics*
D016328:NF-kappa B; D044844:beta-Transducin Repeat-Containing Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf