Hepatocyte growth factor renders BRAF mutant human melanoma cell lines resistant to PLX4032 by downregulating the pro-apoptotic BH3-only proteins PUMA and BIM

Abstract

A large proportion of melanomas harbour the activating BRAF V600E mutation that renders these cells dependent on MAPK signalling for their survival. Although the highly specific and clinically approved BRAF V600E kinase inhibitor, PLX4032, induces apoptosis of melanoma cells bearing this mutation, the underlying molecular mechanisms are not fully understood. Here, we reveal that PLX4032-induced apoptosis depends on the induction of the pro-apoptotic BH3-only protein PUMA with a minor contribution of its relative BIM. Apoptosis could be significantly augmented when PLX4032 was combined with an inhibitor of the pro-survival protein BCL-XL, whereas neutralization of the pro-survival family member BCL-2 caused no additional cell death. Although the initial response to PLX4032 in melanoma patients is very potent, resistance to the drug eventually develops and relapse occurs. Several factors can cause melanoma cells to develop resistance to PLX4032; one of them is the activation of the receptor tyrosine kinase cMET on melanoma cells by its ligand, hepatocyte growth factor (HGF), provided by the tumour microenvironment or the cancer cells themselves. We found that HGF mediates resistance of cMET-expressing BRAF mutant melanoma cells to PLX4032-induced apoptosis through downregulation of PUMA and BIM rather than by increasing the expression of pro-survival BCL-2-like proteins. These results suggest that resistance to PLX4032 may be overcome by specifically increasing the levels of PUMA and BIM in melanoma cells through alternative signalling cascades or by blocking pro-survival BCL-2 family members with suitable BH3 mimetic compounds.

Hgf/Met activation mediates resistance to BRAF inhibition in murine anaplastic thyroid cancers

“…The tumor remnants con- Met amplification was the most prevalent defect associated with disease recurrence, and generated a de novo vulnerability to MET kinase inhibitors. Activation of MET has been shown to cause adaptive resistance to RAF kinase inhibition in melanoma cells and in 2 thyroid cancer cell lines (38,39,(48)(49)(50). There is also clinical evidence that MET overexpression can arise in melanomas (17) and colorectal cancers (51) resistant to RAF or RAF plus EGFR inhibition, respectively, although the dependency on MET for viability was only demonstrated in the latter.…”

BH3-Mimetic Drugs: Blazing the Trail for New Cancer Medicines

“…Combining BH3-mimetics with targeted therapies, such as inhibitors of oncogenic kinases may also be an attractive strategy for cancer therapy. Kinase inhibition increases expression of pro-apoptotic BH3-only proteins, such as BIM and PUMA, thereby inhibiting pro-survival BCL-2 proteins that are not targeted by the BH3-mimetics (Cragg et al, 2007(Cragg et al, , 2008Rohrbeck et al, 2016). Accordingly, combinations of MCL-1 inhibitors, such as S63845 and AMG 176 (and the related compound AM 8621), with inhibitors of EGFR, MEK, or B-RAF were shown to efficiently diminish the in vitro and even the in vivo growth of cell lines derived from NSCLC (Kotschy et al, 2016;Leverson et al, 2015b;Nangia et al, 2018;Song et al, 2005;Zhang et al, 2011), lung squamous cell carcinoma (Weeden et al, 2018), hepatocarcinoma, or glioblastoma (Karpel-Massler et al, 2017).…”

Role Played by Signalling Pathways in Overcoming BRAF Inhibitor Resistance in Melanoma

“…It causes a decrease in ERK activation in BRAF V600E melanoma cells, resulting in G1 phase cell cycle arrest, inducing cell death [ 29 , 30 , 31 ]. Vemurafenib has been shown to reduce the abundance of anti-apoptotic proteins [ 32 ] as well as increase that of the pro-apoptotic proteins PUMA (p53 upregulated modulator of apoptosis) and BIM (Bcl-2-like protein 11) [ 33 ]. This imbalance resulted in an increase in cytosolic Ca 2+ levels which induced endoplasmic reticulum (ER) stress-mediated apoptosis in BRAF V600E melanoma cells [ 32 ].…”