Kazanietz, M. | bioRxiv Science

bioRxiv2022

Mechanical strain stimulates COPII-dependent trafficking via Rac1

Secretory trafficking from the endoplasmic reticulum (ER) is subject to regulation by extrinsic and intrinsic factors. While much of the focus has been on biochemical triggers, little is known whether and how the ER is subject to regulation by mechanical signals. Here, we show that COPII-dependent ER-export is regulated by mechanical strain. Mechanotransduction to the ER was mediated via a previously unappreciated ER-localized pool of the small GTPase Rac1. Mechanistically, we show that Rac1 interacts with the small GTPase Sar1 to drive budding of COPII carriers and stimulate ER-to-Golgi transport. Altogether, we establish an unprecedented link between mechanical strain and export from the ER.

cell biology↗

bioRxiv2020

Mechanisms of protein kinase C epsilon down-regulation by transforming growth factor-beta in lung cancer cells

Protein kinase C epsilon (PKC{varepsilon}), a diacylglycerol (DAG)/phorbol ester-regulated PKC isoform, has been widely linked to oncogenesis and metastasis. PKC{varepsilon} plays important roles in the regulation of motility and invasiveness in non-small cell lung cancer (NSCLC). We previously reported that this kinase becomes prominently down-regulated upon TGF-{beta}-induced epithelial-to-mesenchymal transition (EMT), which leads to prominent phenotypic changes. While the phorbol ester PMA causes down-regulation of PKC, {delta} and {varepsilon} within hours, TGF-{beta} requires at least 4 days to reduce the expression levels of PKC{varepsilon} without affecting the expression of other PKCs, an effect that parallels the acquisition of a mesenchymal phenotype. Despite the prominent transcriptional component involved in EMT, we found that PKC{varepsilon} down-regulation does not involve changes in PKC{varepsilon} mRNA levels and was entirely independent of transcriptional activation of the PRKCE gene. Further mechanistic analysis revealed that the reduction in PKC{varepsilon} expression is dependent on proteasomal and endolysosomal pathways, but independent of autophagy processing mechanisms. Site-directed mutagenesis of Lys312 and Lys321 in PKC{varepsilon} prevented its down-regulation in response to either TGF-{beta} or the phorbol ester PMA. The shift in PKC{varepsilon} isozyme levels depending on cell plasticity underscores relevant functional consequences by modulating the expression of this oncogenic/metastatic kinase and highlights key roles of protein stability mechanisms in the control of PKC{varepsilon} phenotypic outcomes.

cell biology↗