The Anchoring Protein RACK1 Links Protein Kinase Cε to Integrin β Chains

Abstract

Integrin affinity is modulated by intracellular signaling cascades, in a process known as "inside-out" signaling, leading to changes in cell adhesion and motility. Protein kinase C (PKC) plays a critical role in integrinmediated events; however, the mechanism that links PKC to integrins remains unclear. Here, we report that PKC⑀ positively regulates integrin-dependent adhesion, spreading, and motility of human glioma cells. PKC⑀ activation was associated with increased focal adhesion and lamellipodia formation as well as clustering of select integrins, and it is required for phorbol 12-myristate 13-acetate-induced adhesion and motility. We provide novel evidence that the scaffolding protein RACK1 mediates the interaction between integrin ␤ chain and activated PKC⑀. Both depletion of RACK1 by antisense strategy and overexpression of a truncated form of RACK1 which lacks the integrin binding region resulted in decreased PKC⑀-induced adhesion and migration, suggesting that RACK1 links PKC⑀ to integrin ␤ chains. Altogether, these results provide a novel mechanistic link between PKC activation and integrin-mediated adhesion and motility.

Eicosanoid Activation of Protein Kinase C ϵ

“…PKC⑀ and MARCKS label are concentrated near the distal edge of lamellipodia, a closely adherent region where a particularly large number of actin filaments are anchored. Thus, MARCKS and PKC⑀ are indeed associated with the growth cone adhesive area, an observation that is consistent with earlier reports on different biological systems (19,20). Interestingly, MARCKS and PKC⑀ are only minimally associated with the growth cone actin cytoskeleton even though they are known to be able to bind to actin (18,25,36,73).…”

“…In neuroblastoma and pheochromocytoma cells, the ⑀ isoform in particular has been implicated in phenomena related to neurite outgrowth (13)(14)(15)(16). PKC⑀ can localize to adhesion sites, where it is involved reportedly in the regulation of cell spreading (17)(18)(19)(20)(21)(22). This raises the question of its activation.…”

Phosphorylation of claudin-4 by PKCε regulates tight junction barrier function in ovarian cancer cells

“…PKCε contribution to cell motility has been linked to β1 integrin by regulating its trafficking [48]. It is also known to be associated with β1 integrin through RACK1 and F-actin in mediating cell adhesion and mobility [49,50]. Our results suggest that PKCε's role in metastasis may be related to its ability to impair the barrier function (and cell adhesion) through phosphorylation of TJ proteins such as claudin-4.…”

Protein kinase Cε makes the life and death decision

“…PKCε transgenic mice developed highly metastatic SCCs [56,57]. PKCε positively regulated integrin-mediated cell invasion and motility in glioma cells through interaction with the scaffolding protein Receptor for Activated C Kinase-1 (RACK1) which targeted PKCε to integrin β chains, leading to integrin clustering, focal adhesion formation, and increased adhesion and migration [58]. PKCε has been associated with aggressive, invasive and motile phenotype in breast cancer and human head and neck squamous cell carcinoma (HNSCC) [59,60].…”