Keratin 8 phosphorylation regulates keratin reorganization and migration of epithelial tumor cells

Abstract

SummaryCell migration and invasion are largely dependent on the complex organization of the various cytoskeletal components. Whereas the role of actin filaments and microtubules in cell motility is well established, the role of intermediate filaments in this process is incompletely understood. Organization and structure of the keratin cytoskeleton, which consists of heteropolymers of at least one type 1 and one type 2 intermediate filament, are in part regulated by post-translational modifications. In particular, phosphorylation events influence the properties of the keratin network. Sphingosylphosphorylcholine (SPC) is a bioactive lipid with the exceptional ability to change the organization of the keratin cytoskeleton, leading to reorganization of keratin filaments, increased elasticity, and subsequently increased migration of epithelial tumor cells. Here we investigate the signaling pathways that mediate SPC-induced keratin reorganization and the role of keratin phosphorylation in this process. We establish that the MEK-ERK signaling cascade regulates both SPC-induced keratin phosphorylation and reorganization in human pancreatic and gastric cancer cells and identify Ser431 in keratin 8 as the crucial residue whose phosphorylation is required and sufficient to induce keratin reorganization and consequently enhanced migration of human epithelial tumor cells.

GABA(A) Receptor Pi (GABRP) Stimulates Basal-like Breast Cancer Cell Migration through Activation of Extracellular-regulated Kinase 1/2 (ERK1/2)

“…However, to our knowledge, GABAergic signaling has not previously been shown to regulate intermediate filament expression. In contrast, ERK1/2 is an established regulator of both cellular motility (33,39,40) and cytokeratin expression (34,41). GABA induces ERK1/2 activation in pancreatic (10) and renal cancers (21), hence we postulated that GABRP stimulates BLBC motility through ERK1/2 regulation of basal-like cytokeratin expression.…”

“…The cytoskeleton is comprised of a combination of intermediate filaments, actin microfilaments and microtubules and alterations in any of these elements can affect cellular motility (47,48). Specifically, cytokeratins have been implicated in the migratory potential of multiple cancer types, including breast (33,34,49). However, to our knowledge, GABAergic signaling has not previously been shown to regulate intermediate filament expression.…”

“…Like calcium signaling, ERK1/2 signaling is pro-migratory (33,39,40), and importantly, regulates cytokeratin expression in non-breast cancer cell lines (34,41). These findings, in combination with the observation that BLBC cells are sensitive to ERK1/2 inhibition (42, 43), led us to predict that in BLBC, GABRP may maintain basal-like cytokeratin expression through the ERK1/2 pathway.…”

“…5A. As intermediate filaments, the cytokeratins are critical components of the cytoskeleton and cancer cell motility (33,34). Moreover, KRT5, KRT6B, KRT14, and KRT17 are all well-described BLBC markers (reviewed in Ref.…”

Sphingolipids inhibit vimentin-dependent cell migration

“…Among the identified targets for SPC signalling are the intermediate filament proteins, keratins 8 and 18 (K8 and K18), with site-specific phosphorylation being a key mediator of the SPCinduced effects on keratin network reorganisation and cell motility (Beil et al, 2003;Busch et al, 2012;Fois et al, 2013;Park et al, 2011). Another member of the intermediate filament family, vimentin, has well established roles in migratory signalling and processes, often acting in concert with K8/K18 (Hyder et al, 2011;Ivaska et al, 2007;Pallari and Eriksson, 2006).…”