Skin melanoma cells produce diverse gelsolin (GSN) isoforms, which play non-redundant roles in cells' proliferation and motility.

Abstract

Background: Skin melanoma is a malignant tumor that becomes increasingly difficult to treat when diagnosed late. Previously, we demonstrated that high levels of gelsolin (GSN) correlate with the advanced stages of cutaneous melanoma. GSN can be produced as various isoforms due to alternative splicing and differing start codon positions. To date, no studies have been conducted to determine whether GSN diverse isoforms are produced by melanoma cells in vivo and melanoma cell lines. Therefore, nothing is known about the role of specific GSN isoforms in skin melanoma biology.

Methods: We applied immunocytochemical staining to melanoma tissue samples to analyze the localization of GSN production within tumor samples. Additionally, we utilized bioinformatics analysis of transcript levels coding for selected GSN isoforms in publicly available gene transcript databases. To investigate the role of these GSN isoforms, we used the melanoma A375 cell line with GSN knockout to restore the production of only one GSN isoform at a time in these cells. We evaluated the modified cells' ability to migrate, spread, and regulate actin polymerization. We also tested the cells growing on laminin 1, a significant component of the basement membrane, and the melanoma microenvironment.

Results: We found that GSN expression produces three GSN isoforms in human melanoma cell lines: two cytosolic (B and C) and one secretory (A). Furthermore, we noted the presence of GSN both intracellularly and extracellularly in melanoma tumor samples, indicating that human melanoma cells produce diverse GSN isoforms in vivo. We discovered that cells producing GSN-A invade more efficiently, while cells producing GSN-C form the longest filipodia and migrate the best in 2D conditions. Both GSN-B and -C decrease the amount of filamentous actin. On the other hand, cells producing GSN-A and -B exhibit a lower proliferation rate. Finally, we observed that tumors formed by the clones expressing individual GSN isoforms do not grow in zebrafish embryos.

Conclusions: Overall, we demonstrate that GSN isoforms are produced as a mixture in melanoma cells and are not redundant in their function. Therefore, to support the well-being of melanoma cells, a mixture of GSN isoforms must be produced.