Steroid Receptor RNA Activator, a Long Noncoding RNA, Activates p38, Facilitates Epithelial-Mesenchymal Transformation, and Mediates Experimental Melanoma Metastasis

Abstract

Melanoma metastasis signals dismal prognosis even with current checkpoint inhibitors. Long noncoding RNAs (lncRNAs) regulate dynamic metastasis in several cancers, including melanoma. We became interested in a lncRNA, steroid receptor RNA activator (SRA), because it is the first lncRNA also encoding a conserved protein, SRAP, and it regulates progression of prostate and breast cancers. We investigated how SRA mediates melanoma proliferation, migration, invasion, epithelial-mesenchymal transformation (EMT), and metastasis by RNA interference. The expression of SRAP was measured in melanoma tissue and in human and mouse B16 melanoma cells by immunofluorescence and PCR. The results showed that SRA knockdown decreased B16 cell and A375 cell proliferation and inhibited B16 cell migration significantly. Transwell analysis revealed that CCL21mediated invasion was abolished in SRA-deficient B16 cells. In parallel, p38 dephosphorylation and reciprocal phosphorylation of B-Raf and mitogen-activated protein kinase kinase 1/2 were present in B16eSRA inhibited cells. The induction of EMT markers, b-catenin and N-cadherin, by CCL21 was reduced in B16eSRA inhibited cells, suggesting that SRA promotes the EMT process. In vivo experimental metastasis showed that B16eSRA inhibited cells formed significantly fewer tumor nodules in the lungs grossly and microscopically. In summary, our results showed that SRA expression is increased in melanoma tissue and that SRA mediates p38 activation, cell invasion, and proliferation and regulates EMT and distant metastasis.

Targeting steroid receptor RNA activator (SRA), a long non-coding RNA, enhances melanogenesis through activation of TRP1 and inhibition of p38 phosphorylation

“…We attempted to identify the common pathways that are involved in both melanogenesis or carcinogenesis and SRA signaling. The literatures search revealed that p38 MAPK [ 14 , 21 ] and Notch-1 [ 20 , 22 ] are indeed involved in both pathophysiological processes. Hence, we measured the activation of p38 and the cleavage of Notch1 by western blotting after inhibiting SRA.…”

“…We attempted to identify the common pathways that are involved in both melanogenesis or carcinogenesis and SRA signaling. The literatures search revealed that p38 MAPK [14,21] and Notch-1 [20,22] are indeed involved in both https://doi.org/10.1371/journal.pone.0237577.g002…”

“…We then investigated how other novel lncRNAs might be involved in melanogenesis and melanoma progression. We have previously found that steroid receptor RNA activator (SRA) is consistently upregulated in several melanoma cell lines, including B16 cells, and SRA has a functional role in melanoma progression [14]. A PUBMED search with the keywords "steroid receptor RNA activator" returned only 102 results as of May 2020.…”

The role of long non-coding RNAs in human carcinoma

“…Inhibition of SRA could significantly reduce melanoma development, which was mediated by p38 activation. 41 The therapy of melanoma is still pool, these studies provided new ways to improve the prognosis of melanoma.…”

Regulation of melanoma malignancy by the RP11-705C15.3/miR-145-5p/NRAS/MAPK signaling axis

“…Current knowledge about lncRNAs shows that they are involved in the pathogenesis of various diseases, particular for cancers [8,9]. In melanoma, several lncRNAs were recently reported to be associated with the initiation and progression of melanoma, such as SPRY4-IT1, Llme23, OVAAL, SRA, and LINC00520 [10][11][12][13][14]. In our previous reports, we also identified three oncogenic lncRNAs in melanoma: PVT1, ILF3-AS1, and MHENCR [15][16][17].…”