Acquired or intrinsic resistance to apoptotic and necroptotic stimuli is considered a major hindrance of therapeutic success in
malignant melanoma.
Inhibitor of apoptosis proteins (IAPs) are important regulators of apoptotic and necroptotic cell death mediated by numerous cell death signalling platforms. In this report we investigated the impact of IAPs for cell death regulation in
malignant melanoma. Suppression of IAPs strongly sensitized a panel of
melanoma cells to death
ligand-induced cell death, which, surprisingly, was largely mediated by apoptosis, as it was completely rescued by addition of
caspase inhibitors. Interestingly, the absence of necroptosis signalling correlated with a lack of receptor-interacting
protein kinase-3 (RIPK3)
mRNA and
protein expression in all cell lines, whereas primary melanocytes and cultured
nevus cells strongly expressed RIPK3. Reconstitution of RIPK3, but not a RIPK3-kinase dead mutant in a set of
melanoma cell lines overcame
CD95L/IAP antagonist-induced necroptosis resistance independent of autocrine tumour
necrosis factor secretion. Using specific inhibitors, functional studies revealed that RIPK3-mediated mixed-lineage
kinase domain-like
protein (MLKL) phosphorylation and necroptosis induction critically required receptor-interacting
protein kinase-1 signalling. Furthermore, the inhibitor of mutant BRAF
Dabrafenib, but not
Vemurafenib, inhibited necroptosis in
melanoma cells whenever RIPK3 is present. Our data suggest that loss of RIPK3 in
melanoma and selective inhibition of the RIPK3/MLKL axis by BRAF inhibitor
Dabrafenib, but not
Vemurafenib, is critical to protect from necroptosis. Strategies that allow RIPK3 expression may allow unmasking the necroptotic signalling machinery in
melanoma and points to reactivation of this pathway as a treatment option for metastatic
melanoma.