Arachidonate initiated protein kinase C activation regulates HeLa cell spreading on a gelatin substrate by inducing F-actin formation and exocytotic upregulation of β1 Integrin

Release of arachidonic acid (AA) and subsequent formation of a lipoxygenase (LOX) metabolite(s) is an obligatory signal to induce spreading of HeLa cells on a gelatin substratum (Chun and Jacobson, 1992). This study characterizes signaling pathways that follow the LOX metabolite(s) formation. Levels of diacylglycerol (DG) increase upon attachment and before cell spreading on a gelatin substratum. DG production and cell spreading are insignificant when phospholipase A2 (PLA2) or LOX is blocked. In contrast, when cells in suspension where PLA2 activity is not stimulated are treated with exogenous AA, DG production is turned on, and inhibition of LOX turns it off. This indicates that the formation of a LOX metabolite(s) from AA released during cell attachment induces the production of DG. Consistent with the DG production is the activation of protein kinase C (PKC) which, as with AA and DG, occurs upon attachment and before cell spreading. Inhibition of AA release and subsequent DG production blocks both PKC activation and cell spreading. Cell spreading is also blocked by the inhibition of PKC with calphostin C or sphingosine. The inhibition of cell spreading induced by blocking AA release is reversed by the direct activation of PKC with phorbol ester. However, the inhibition of cell spreading induced by PKC inhibition is not reversed by exogenously applied AA. In addition, inhibition of PKC does not block AA release and DG production. The data indicate that there is a sequence of events triggered by HeLa cell attachment to a gelatin substratum that leads to the initiation of cell spreading: AA release, a LOX metabolite(s) formation, DG production, and PKC activation. The data also provide evidence indicating that HeLa cell spreading is a cyclic feedback amplification process centered on the production of AA, which is the first messenger produced in the sequence of messengers initiating cell spreading. Both DG and PKC activity that are increased during HeLa cell attachment to a gelatin substratum appear to be involved. DG not only activates PKC, which is essential for cell spreading, but is also hydrolyzed to AA. PKC, which is initially activated as consequence of AA production, also increases more AA production by activating PLA2.

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Filamin A is required for vimentin-mediated cell adhesion and spreading

AJP Cell Physiology ◽

10.1152/ajpcell.00323.2009 ◽

2010 ◽

Vol 298 (2) ◽

pp. C221-C236 ◽

Cited By ~ 60

Author(s):

Hugh Kim ◽

Fumihiko Nakamura ◽

Wilson Lee ◽

Yulia Shifrin ◽

Pamela Arora ◽

...

Keyword(s):

Protein Kinase C ◽

Cell Adhesion ◽

Protein Kinase ◽

Cell Spreading ◽

Intermediate Filament Protein ◽

Β1 Integrin ◽

Filamin A ◽

Integrin Activation ◽

Hek 293 ◽

Kinase C

Cell adhesion and spreading are regulated by complex interactions involving the cytoskeleton and extracellular matrix proteins. We examined the interaction of the intermediate filament protein vimentin with the actin cross-linking protein filamin A in regulation of spreading in HEK-293 and 3T3 cells. Filamin A and vimentin-expressing cells were well spread on collagen and exhibited numerous cell extensions enriched with filamin A and vimentin. By contrast, cells treated with small interfering RNA (siRNA) to knock down filamin A or vimentin were poorly spread; both of these cell populations exhibited >50% reductions of cell adhesion, cell surface β1 integrin expression, and β1 integrin activation. Knockdown of filamin A reduced vimentin phosphorylation and blocked recruitment of vimentin to cell extensions, whereas knockdown of filamin and/or vimentin inhibited the formation of cell extensions. Reduced vimentin phosphorylation, cell spreading, and β1 integrin surface expression, and activation were phenocopied in cells treated with the protein kinase C inhibitor bisindolylmaleimide; cell spreading was also reduced by siRNA knockdown of protein kinase C-ε. By immunoprecipitation of cell lysates and by pull-down assays using purified proteins, we found an association between filamin A and vimentin. Filamin A also associated with protein kinase C-ε, which was enriched in cell extensions. These data indicate that filamin A associates with vimentin and to protein kinase C-ε, thereby enabling vimentin phosphorylation, which is important for β1 integrin activation and cell spreading on collagen.

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