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See detailL-plastin Ser5 phosphorylation is modulated by the PI3K/SGK pathway and promotes breast cancer cell invasiveness
Machado, Raquel A.C.; Stojevski, Dunja; de Landtsheer, Sébastien UL et al

in Cell Communication and Signaling (2021), 19(22), 1-22

Background: Metastasis is the predominant cause for cancer morbidity and mortality accounting for approxima‑ tively 90% of cancer deaths. The actin‑bundling protein L‑plastin has been proposed as a ... [more ▼]

Background: Metastasis is the predominant cause for cancer morbidity and mortality accounting for approxima‑ tively 90% of cancer deaths. The actin‑bundling protein L‑plastin has been proposed as a metastatic marker and phos‑ phorylation 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. Methods: 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 inhi‑ bition/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. Results: 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. Conclusion: 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 formation. [less ▲]

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See detailThe actin-bundling protein L-plastin—A double-edged sword: Beneficial for the immune response, maleficent in cancer
Schaffner-Reckinger, Elisabeth UL; Machado, Raquel A.C.

in INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY (2020)

The dynamic organization of the actin cytoskeleton into bundles and networks is orchestrated by a large variety of actin-binding proteins. Among them, the actinbundling protein L-plastin is normally ... [more ▼]

The dynamic organization of the actin cytoskeleton into bundles and networks is orchestrated by a large variety of actin-binding proteins. Among them, the actinbundling protein L-plastin is normally expressed in hematopoietic cells, where it is involved in the immune response. However, L-plastin is also often ectopically expressed in malignant cancer cells of non-hematopoietic origin and is even considered as a marker for cancer progression. Post-translational modification modulates L-plastin activity. In particular, L-plastin Ser5 phosphorylation has been shown to be important for the immune response in leukocytes as well as for invasion and metastasis formation of carcinoma cells. [less ▲]

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