Relevance of BRAF Subcellular Localization and Its Interaction with KRAS and KIT Mutations in Skin Melanoma.

Marius-Alexandru Beleaua,Cornelia Braicu,Ioan Jung,Doina Milutin,Simona Gurzu

doi:10.3390/ijms222111918

Abstract

Although skin melanoma (SKM) represents only one-quarter of newly diagnosed skin malignant tumors, it presents a high mortality rate. Hence, new prognostic and therapeutic tools need to be developed. This study focused on investigating the prognostic value of the subcellular expression of BRAF, KRAS, and KIT in SKM in correlation with their gene-encoding interactions. In silico analysis of the abovementioned gene interactions, along with their mRNA expression, was conducted, and the results were validated at the protein level using immunohistochemical (IHC) stains. For IHC expression, the encoded protein expressions were checked on 96 consecutive SKMs and 30 nevi. The UALCAN database showed no prognostic value for the mRNA expression level of KRAS and BRAF and demonstrated a longer survival for patients with low mRNA expression of KIT in SKMs. IHC examinations of SKMs confirmed the UALCAN data and showed that KIT expression was inversely correlated with ulceration, Breslow index, mitotic rate, and pT stage. KRAS expression was also found to be inversely correlated with ulceration and perineural invasion. When the subcellular expression of BRAF protein was recorded (nuclear vs. cytoplasmatic vs. mixed nucleus + cytoplasm), a direct correlation was emphasized between nuclear positivity and lymphovascular or perineural invasion. The independent prognostic value was demonstrated for mixed expression of the BRAF protein in SKM. BRAF cytoplasmic predominance, in association with KIT’s IHC positivity, was more frequently observed in early-stage nonulcerated SKMs, which displayed a low mitotic rate and a late death event. The present study firstly verified the possible prognostic value of BRAF subcellular localization in SKMs. A low mRNA expression or IHC cytoplasmic positivity for KIT and BRAF might be used as a positive prognostic parameter of SKM. SKM’s BRAF nuclear positivity needs to be evaluated in further studies as a possible indicator of perineural and lymphovascular invasion.

Highlights

Skin melanoma (SKM) has an incidence of approximately 1.7% of the globally diagnosed new cases of malignancies compared to non-melanoma cancers of the skin, which represent 6.2%
The molecular analysis performed in the 14 studies focused on SKMs, which is available on cBioPortal, refers to mutation, amplification, and deletion of the abovementioned genes [11]
We examined the correlation between gene expression profile and survival rate of patients with SKMs using the UALCAN database, which was accessed on 2 May 2021 [12]

Summary

Introduction

Skin melanoma (SKM) has an incidence of approximately 1.7% of the globally diagnosed new cases of malignancies compared to non-melanoma cancers of the skin, which represent 6.2% Despite this discrepancy, SKM has the highest mortality of all skin malignancies, with a slightly higher prevalence in males [1]. The most frequently encountered mutation (52%) involves the BRAF (B-Raf proto-oncogene, serine/threonine kinase) gene, being represented by the V600 amino-acid residue. It is followed by the RAS (RAS-type GTPase family) family of proto-oncogenes (NRAS, KRAS, and HRAS) and NF1 (neurofibromin 1) [3,4]. Triple wild-type SKMs, which do not harbor BRAF, RAS, or NF1 mutations, represent about 14.69% of all SKMs [3,4]

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