SEMAPHORINS and their receptors: focus on the crosstalk between melanoma and hypoxia

Hypoxia, a condition of oxygen deprivation, is considered a hallmark of tumor microenvironment regulating several pathways and promoting cancer progression and resistance to therapy. Semaphorins, a family of about 20 secreted, transmembrane and GPI-linked glycoproteins, and their cognate receptors (plexins and neuropilins) play a pivotal role in the crosstalk between cancer and stromal cells present in the tumor microenvironment. Many studies reported that some semaphorins are involved in the development of a permissive tumor niche, guiding cell-cell communication and, consequently, the development and progression, as well as the response to therapy, of different cancer histotypes, including melanoma. In this review we will summarize the state of art of semaphorins regulation by hypoxic condition in cancer with different origin. We will also describe evidence about the ability of semaphorins to affect the expression and activity of transcription factors activated by hypoxia, such as hypoxia-inducible factor-1. Finally, we will focus our attention on findings reporting the role of semaphorins in melanocytes transformation, melanoma progression and response to therapy. Further studies are necessary to understand the mechanisms through which semaphorins induce their effect and to shed light on the possibility to use semaphorins or their cognate receptors as prognostic markers and/or therapeutic targets in melanoma or other malignancies.