Targeting the PTTG1 oncogene impairs proliferation and invasiveness of melanoma cells sensitive or with acquired resistance to the BRAF inhibitor dabrafenib

Abstract

The pituitary tumor transforming gene 1 (PTTG1) is implicated in tumor growth, metastasis and drug resistance. Here, we investigated the involvement of PTTG1 in melanoma cell proliferation, invasiveness and response to the BRAF inhibitor (BRAFi) dabrafenib. We also preliminary assessed the potential value of circulating PTTG1 protein to monitor melanoma patient response to BRAFi or to dabrafenib plus trametinib. Dabrafenib-resistant cell lines (A375R and SK-Mel28R) were more invasive than their drug-sensitive counterparts (A375 and SK-Mel28), but expressed comparable PTTG1 levels. Dabrafenib abrogated PTTG1 expression and impaired invasion of the extracellular matrix (ECM) in A375 and SK-Mel28 cells. In contrast, it affected neither PTTG1 expression in A375R and SK-Mel28R cells, nor ECM invasion in the latter cells, while further stimulated A375R cell invasiveness. Assessment of proliferation and ECM invasion in control and PTTG1-silenced A375 and SK-Mel28 cells, exposed or not to dabrafenib, demonstrated that the inhibitory effects of this drug were, at least in part, dependent on its ability to down-regulate PTTG1 expression. PTTG1-silencing also impaired proliferation and invasiveness of A375R and SK-Mel28R cells, and counteracted dabrafenib-induced stimulation of ECM invasion in A375R cells. Further experiments performed in A375R cells indicated that PTTG1-silencing impaired cell invasiveness through inhibition of MMP-9 and that PTTG1 expression and ECM invasion could be also reduced by the CDK4/6 inhibitor LEE011. PTTG1 targeting might, therefore, represent a useful strategy to impair proliferation and metastasis of melanomas resistant to BRAFi. Circulating PTTG1 also appeared to deserve further investigation as biomarker to monitor patient response to targeted therapy.

Role of VEGFR‐1 in melanoma acquired resistance to the BRAF inhibitor vemurafenib

“…Consistently, enforced expression of VEGFR‐1, by stable gene transfection in receptor‐negative melanoma cells, markedly reduces sensitivity to vemurafenib. This finding is particularly relevant since we observed an increase in VEGF‐A secretion by resistant cells, as also reported for melanoma resistant to the BRAFi dabrafenib . Moreover, VEGFR‐1 is efficiently stimulated by its exclusive ligand PlGF that can be released by the tumour itself or by cells of the tumour microenvironment.…”

“…, by stable gene transfection in receptor-negative melanoma cells, markedly reduces sensitivity to vemurafenib. This finding is particularly relevant since we observed an increase in VEGF-A secretion by resistant cells, as also reported for melanoma resistant to the BRAFi dabrafenib [21][22][23]. Moreover, VEGFR-1 is efficiently stimulated by its exclusive ligand PlGF that can be released by the tumour itself or by cells of the tumour microenvironment.BRAF mutations can control processes such as invasion and metastasis, since BRAF down-modulation reduces MAPK and MMP-2 activities, and the invasive ability in a melanoma model 38.…”

“…19,20 In this regard, the onset of treatment resistance to the BRAFi dabrafenib is associated with restored VEGF-A production by melanoma cells. [21][22][23] Moreover, by paradoxically activating the MAPK pathway in BRAF wild-type macrophages, BRAFi may induce the production of VEGF-A, which directly stimulates macrophage survival, tumour immune evasion and ultimately melanoma growth. 20,24,25 Conversely, treatment of susceptible BRAF mutated melanoma with BRAFi results in reduced tumour vascularity and increased T cell infiltration in melanoma that was attributed to loss or reduced VEGF-A expression and secretion.…”

Molecular markers of prognosis in canine cortisol‐secreting adrenocortical tumours

“…PTTG1 is also a prognostic marker in human ACCs, as well as in other tumour types in humans and dogs . Several drugs have been shown to inhibit PTTG1 expression, including BRAF, HDAC, Hsp90 and STAT3 inhibitors, which could be interesting options to target PTTG1 in canine ACTs.…”

Joint action of miR‐126 and MAPK/PI3K inhibitors against metastatic melanoma

“…The malignant human melanoma cell line A375M was kindly provided by R. Giavazzi (Istituto Mario Negri, Bergamo, Italy). The human melanoma cell lines A375 and SK‐Mel28 and the sublines A375‐R and SK‐Mel28‐R with acquired resistance to dabrafenib, and the early passage cell lines obtained from bioptic samples (reported as Pt1, Pt2, Pt3, Pt4) were obtained from S. D'Atri (IDI IRCCS, Rome, Italy) (Caporali et al ., , ). All biological materials were obtained with the informed written consent of patients and the study was conducted according to the Declaration of Helsinki Principles.…”