Phosphoproteomic Screen Identifies Potential Therapeutic Targets in Melanoma

Abstract

Therapies directed against receptor tyrosine kinases are effective in many cancer subtypes, including lung and breast cancer. We used a phospho-proteomic platform to identify active receptor tyrosine kinases that might represent therapeutic targets in a panel of twenty-five melanoma cell strains. We detected activated receptors including TYRO3, AXL, MERTK, EPHB2, MET, IGF1R, EGFR, KIT, HER3, and HER4. Statistical analysis of receptor tyrosine kinase activation as well as ligand and receptor expression indicates that some receptors, such as FGFR3, may be activated via autocrine circuits. shRNA knockdown targeting three of the active kinases identified in the screen, AXL, HER3, and IGF1R, inhibited the proliferation of melanoma cells and knockdown of active AXL also reduced melanoma cell migration. The changes in cellular phenotype observed upon AXL knockdown appear to be modulated via the STAT3 signaling pathway, while the IGF1R-dependent alterations seem to be regulated by the AKT signaling pathway. Ultimately, this study identifies several novel targets for therapeutic intervention in melanoma.

MERTK receptor tyrosine kinase is a therapeutic target in melanoma

“…In agreement with a previous report demonstrating phosphorylation of TAM family receptors in several melanoma cell lines (16), the data presented here confirm that MERTK can be phosphorylated in melanoma cells and further show that MERTK is functionally important for several oncogenic signaling pathways and phenotypes. Specifically, we report here on MERTK-mediated signaling through the MAPK/ERK, PI3K/ AKT, and JAK/STAT signaling pathways.…”

“…Although MERTK expression has been previously demonstrated in several melanoma cell lines (16), its expression in melanoma tissues has not been previously reported. To investigate the pattern and expression levels of MERTK during nevusto-melanoma progression, 2 independent tissue microarrays…”

“…Additional signaling pathways that lead to antiinflammatory cytokine production as well as enhanced migration and invasion have been identified downstream of MERTK (11,14,15). A phosphoproteomic study identified MERTK and other TAM receptors as commonly activated RTKs in melanoma, however no studies have reported on the function of MERTK in melanoma (16). The role of other TAM receptors in melanoma has been described, suggesting that MERTK may also have a significant role in melanoma development and progression.…”

Combined inhibition of AXL, Lyn and p130Cas kinases block migration of triple negative breast cancer cells

“…9,10 AXL is frequently overexpressed in human cancers including lymphocytic leukemia, breast, colon, skin, thyroid and prostate cancer. [11][12][13][14][15][16][17] Down-regulation of AXL by siRNA attenuates the migration and invasion of breast, 18 ovarian, 19 hepatocellular carcinoma, 20 mesothelioma, 21 prostate 22 and pancreatic cancer. 23 Furthermore it has been shown that the inhibition of AXL results in the reduction of cancer progression and metastatic potential and induces apoptosis in cancer cells.…”

MERTK: upstream from BRAF

“…At least one study has shown that TAM and other tyrosine kinase receptors are activated in melanoma, 6 and two more have linked TYRO3, AXL and the TAM receptor ligand, growth arrest-specific 6 (GAS6), to melanoma tumorigenesis and invasiveness. 7,8 Collectively, these findings prompted Douglas Graham and colleagues to hypothesize that MERTK might also be a therapeutic target in melanoma.…”