Acidic microenvironment plays a key role in human melanoma progression through a sustained exosome mediated transfer of clinically relevant metastatic molecules

Abstract

BackgroundMicroenvironment cues involved in melanoma progression are largely unknown. Melanoma is highly influenced in its aggressive phenotype by the changes it determinates in its microenvironment, such as pH decrease, in turn influencing cancer cell invasiveness, progression and tissue remodelling through an abundant secretion of exosomes, dictating cancer strategy to the whole host. A role of exosomes in driving melanoma progression under microenvironmental acidity was never described.MethodsWe studied four differently staged human melanoma lines, reflecting melanoma progression, under microenvironmental acidic pHs pressure ranging between pH 6.0–6.7. To estimate exosome secretion as a function of tumor stage and environmental pH, we applied a technique to generate native fluorescent exosomes characterized by vesicles integrity, size, density, markers expression, and quantifiable by direct FACS analysis.Functional roles of exosomes were tested in migration and invasion tests. Then we performed a comparative proteomic analysis of acid versus control exosomes to elucidate a specific signature involved in melanoma progression.ResultsWe found that metastatic melanoma secretes a higher exosome amount than primary melanoma, and that acidic pH increases exosome secretion when melanoma is in an intermediate stage, i.e. metastatic non-invasive.We were thus able to show that acidic pH influences the intercellular cross-talk mediated by exosomes. In fact when exposed to exosomes produced in an acidic medium, pH naïve melanoma cells acquire migratory and invasive capacities likely due to transfer of metastatic exosomal proteins, favoring cell motility and angiogenesis.A Prognoscan-based meta-analysis study of proteins enriched in acidic exosomes, identified 11 genes (HRAS, GANAB, CFL2, HSP90B1, HSP90AB1, GSN, HSPA1L, NRAS, HSPA5, TIMP3, HYOU1), significantly correlating with poor prognosis, whose high expression was in part confirmed in bioptic samples of lymph node metastases.ConclusionsA crucial step of melanoma progression does occur at melanoma intermediate –stage, when extracellular acidic pH induces an abundant release and intra-tumoral uptake of exosomes. Such exosomes are endowed with pro-invasive molecules of clinical relevance, which may provide a signature of melanoma advancement.Electronic supplementary materialThe online version of this article (10.1186/s13046-018-0915-z) contains supplementary material, which is available to authorized users.

MicroRNA Profiling of Exosomes Derived from Red Blood Cell Units: Implications in Transfusion-Related Immunomodulation

“…However, none of the 3 miRNAs could serve as a biomarker for predicting storage lesions and monitoring the quality of RBC units. Although mature RBCs can not generate new RNA molecules and exosomal RNA molecules are possibly degraded with the extending storage time, we can find increasing of these 3 miRNAs during storage and attribute this phenomenon to the changes in microenvironment of stored RBCs which were previously reported [32], leading to the changes in contents of exosomes [13,27,29,30]. However, high abundance of exosomal miR-451a may mark it as an important regulatory miRNA in the recipients.…”

“…However, the role and mechanisms of exosomes (RBCs-derived) in transfusion-related immunomodulation await clear elucidation. Secretion and contents of exosomes are regulated by different microenvironments [13,27,29,30]. The contents of exosomes (RBC-derived), stored in ACD-A solution, are still unknown.…”

Exosomes as a Source of Cancer Biomarkers: Advances in Electrochemical Biosensing of Exosomes

“…An acidic microenvironment promotes exosome secretion in intermediate melanomas (non‐invasive, metastatic) . When melanoma cells are exposed to exosomes produced in an acidic environment, they acquire migratory and invasive capacities, most probably due to an exchange of metastatic exosomal proteins . As a result, a meta‐analysis study identified 11 genes, which correlated with a poor prognosis .…”

“…When melanoma cells are exposed to exosomes produced in an acidic environment, they acquire migratory and invasive capacities, most probably due to an exchange of metastatic exosomal proteins . As a result, a meta‐analysis study identified 11 genes, which correlated with a poor prognosis . The release of exosomes from human tumour cell lines derived from colon, breast and prostate cancers, osteosarcoma and melanoma was significantly increased at pH 6.5 in comparison with the control pH 7.4 .…”

Tumor‐derived exosomes (TDEs): How to avoid the sting in the tail

“…The tumor microenvironment thus tends to become nutrient poor, hypoxic and acidic as the metabolic demands of the tumor exceed the ability of tissue perfusion to maintain local homeostasis. Notably, multiple physiologic changes associated with the tumor microenvironment can induce cell stress pathways and increase exosome secretion rates, including hypoxia, extracellular acidification, and several proinflammatory mechanisms . Many of these processes are also known to interact, and to increase tumor resistance to cancer therapeutics.…”