L-plastin Ser5 phosphorylation is modulated by the PI3K/SGK pathway and promotes breast cancer cell invasiveness

• Published in: Cell communication and signaling 2021-02, Vol.19 (1), p.22-22, Article 22
• Main Authors: Machado, Raquel A C, Stojevski, Dunja, De Landtsheer, Sébastien, Lucarelli, Philippe, Baron, Alexandre, Sauter, Thomas, Schaffner-Reckinger, Elisabeth
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase; Actin; Actin-bundling; Breast cancer; Breast Neoplasms - metabolism; Breast Neoplasms - pathology; Cell adhesion & migration; Cell Line; Cell Movement; Cloning; Computer applications; Confocal microscopy; ERK/MAPK pathway; Extracellular matrix; Extracellular signal-regulated kinase; Female; Gelatin; Gelatinase B; Humans; Image processing; Invasiveness; Kinases; L-plastin; MAP kinase; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Metastases; Microfilament Proteins - genetics; Microfilament Proteins - metabolism; Models, Biological; Morbidity; Neoplasm Invasiveness; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; PI3K pathway; Plasmids; Protein Kinases - metabolism; Protein L; Proteins; Ribosomal protein S6 kinase; RSK; Serine - metabolism; SGK; Signal transduction
• ISSN: 1478-811X; 1478-811X
• DOI: 10.1186/s12964-021-00710-5

Metastasis is the predominant cause for cancer morbidity and mortality accounting for approximatively 90% of cancer deaths. The actin-bundling protein L-plastin has been proposed as a metastatic marker and phosphorylation on its residue Ser5 is known to increase its actin-bundling activity. We recently showed that activation of the ERK/MAPK signalling pathway leads to L-plastin Ser5 phosphorylation and that the downstream kinases RSK1 and RSK2 are able to directly phosphorylate Ser5. Here we investigate the involvement of the PI3K pathway in L-plastin Ser5 phosphorylation and the functional effect of this phosphorylation event in breast cancer cells. To unravel the signal transduction network upstream of L-plastin Ser5 phosphorylation, we performed computational modelling based on immunoblot analysis data, followed by experimental validation through inhibition/overexpression studies and in vitro kinase assays. To assess the functional impact of L-plastin expression/Ser5 phosphorylation in breast cancer cells, we either silenced L-plastin in cell lines initially expressing endogenous L-plastin or neoexpressed L-plastin wild type and phosphovariants in cell lines devoid of endogenous L-plastin. The established cell lines were used for cell biology experiments and confocal microscopy analysis. Our modelling approach revealed that, in addition to the ERK/MAPK pathway and depending on the cellular context, the PI3K pathway contributes to L-plastin Ser5 phosphorylation through its downstream kinase SGK3. The results of the transwell invasion/migration assays showed that shRNA-mediated knockdown of L-plastin in BT-20 or HCC38 cells significantly reduced cell invasion, whereas stable expression of the phosphomimetic L-plastin Ser5Glu variant led to increased migration and invasion of BT-549 and MDA-MB-231 cells. Finally, confocal image analysis combined with zymography experiments and gelatin degradation assays provided evidence that L-plastin Ser5 phosphorylation promotes L-plastin recruitment to invadopodia, MMP-9 activity and concomitant extracellular matrix degradation. Altogether, our results demonstrate that L-plastin Ser5 phosphorylation increases breast cancer cell invasiveness. Being a downstream molecule of both ERK/MAPK and PI3K/SGK pathways, L-plastin is proposed here as a potential target for therapeutic approaches that are aimed at blocking dysregulated signalling outcome of both pathways and, thus, at impairing cancer cell invasion and metastasis fo