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Cancer Res. 2019 Jun 1;79(11):2892-2908. doi: 10.1158/0008-5472.CAN-18-3026. Epub 2019 May 2.

The Small GTPase ARF6 Activates PI3K in Melanoma to Induce a Prometastatic State.

Author information

1
Department of Medicine, Program in Molecular Medicine, University of Utah, Salt Lake City, Utah.
2
Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, Salt Lake City, Utah.
3
Department of Biomedical Informatics, School of Medicine, University of Utah, Salt Lake City, Utah.
4
Department of Pathology, University of Utah, Salt Lake City, Utah.
5
Huntsman Cancer Institute, University of Utah Health Sciences Center, Salt Lake City, Utah.
6
Department of Oncological Sciences, School of Medicine, University of Utah, Salt Lake City, Utah.
7
Department of Medical Oncology and Therapeutics, City of Hope Comprehensive Cancer Institute, Monrovia, California.
8
Department of Neurobiology and Anatomy, University of Utah, Salt Lake City, Utah.
9
Division of Cardiovascular Medicine, Department of Medicine, University of Utah, Salt Lake City, Utah.
10
Department of Human Genetics, University of Utah, Salt Lake City, Utah.
11
Department of Surgery, University of Utah Health Sciences Center, Salt Lake City, Utah.
12
Department of Pathology, University of Utah, Salt Lake City, Utah. allie.grossmann@path.utah.edu.
13
ARUP Laboratories, University of Utah, Salt Lake City, Utah.
#
Contributed equally

Abstract

Melanoma has an unusual capacity to spread in early-stage disease, prompting aggressive clinical intervention in very thin primary tumors. Despite these proactive efforts, patients with low-risk, low-stage disease can still develop metastasis, indicating the presence of permissive cues for distant spread. Here, we show that constitutive activation of the small GTPase ARF6 (ARF6Q67L) is sufficient to accelerate metastasis in mice with BRAFV600E/Cdkn2aNULL melanoma at a similar incidence and severity to Pten loss, a major driver of PI3K activation and melanoma metastasis. ARF6Q67L promoted spontaneous metastasis from significantly smaller primary tumors than PTENNULL, implying an enhanced ability of ARF6-GTP to drive distant spread. ARF6 activation increased lung colonization from circulating melanoma cells, suggesting that the prometastatic function of ARF6 extends to late steps in metastasis. Unexpectedly, ARF6Q67L tumors showed upregulation of Pik3r1 expression, which encodes the p85 regulatory subunit of PI3K. Tumor cells expressing ARF6Q67L displayed increased PI3K protein levels and activity, enhanced PI3K distribution to cellular protrusions, and increased AKT activation in invadopodia. ARF6 is necessary and sufficient for activation of both PI3K and AKT, and PI3K and AKT are necessary for ARF6-mediated invasion. We provide evidence for aberrant ARF6 activation in human melanoma samples, which is associated with reduced survival. Our work reveals a previously unknown ARF6-PI3K-AKT proinvasive pathway, it demonstrates a critical role for ARF6 in multiple steps of the metastatic cascade, and it illuminates how melanoma cells can acquire an early metastatic phenotype in patients. SIGNIFICANCE: These findings reveal a prometastatic role for ARF6 independent of tumor growth, which may help explain how melanoma spreads distantly from thin, early-stage primary tumors.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/11/2892/F1.large.jpg.

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