Arachidonic Acid Stimulates Cell Adhesion through a Novel p38 MAPK-RhoA Signaling Pathway That Involves Heat Shock Protein 27

Laboratory of Molecular Carcinogenesis, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2009; 284(31):20936-45. DOI: 10.1074/jbc.M109.020271
Source: PubMed


Rho GTPases are critical components of cellular signal transduction pathways. Both hyperactivity and overexpression of these proteins have been observed in human cancers and have been implicated as important factors in metastasis. We previously showed that dietary n-6 fatty acids increase cancer cell adhesion to extracellular matrix proteins, such as type IV collagen. Here we report that in MDA-MB-435 human melanoma cells, arachidonic acid activates RhoA, and inhibition of RhoA signaling with either C3 exoenzyme or dominant negative Rho blocked arachidonic acid-induced cell adhesion. Inhibition of the Rho kinase (ROCK) with either small molecule inhibitors or ROCK II-specific small interfering RNA (siRNA) blocked the fatty acid-induced adhesion. However, unlike other systems, inhibition of ROCK did not block the activation of p38 mitogen-activated protein kinase (MAPK); instead, Rho activation depended on p38 MAPK activity and the presence of heat shock protein 27 (HSP27), which is phosphorylated downstream of p38 after arachidonic acid treatment. HSP27 associated with p115RhoGEF in fatty acid-treated cells, and this association was blocked when p38 was inhibited. Furthermore, siRNA knockdown of HSP27 blocked the fatty acid-stimulated Rho activity. Expression of dominant negative p115-RhoGEF or p115RhoGEF-specific siRNA inhibited both RhoA activation and adhesion on type IV collagen, whereas a constitutively active p115RhoGEF restored the arachidonic acid stimulation in cells in which the p38 MAPK had been inhibited. These data suggest that n-6 dietary fatty acids stimulate a set of interactions that regulates cell adhesion through RhoA and ROCK II via a p38 MAPK-dependent association of HSP27 and p115RhoGEF.

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Available from: John D Roberts, Feb 11, 2015
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    • "Whereas ACSL4 orthologs activate LC-PUFAs (the eicosanoid precursors), it is unclear whether loss of Acsl4a produces changes in eicosanoid signaling. Consistent with Acsl4a inhibiting MAPKs, LC-PUFAs and eicosanoid metabolites have been shown to regulate MAPK activity (Alexander et al., 2001; Denys et al., 2002; Garcia et al., 2009; Holzer et al., 2011; Rao et al., 2007; Schley et al., 2007; Xue et al., 2006; Zeyda et al., 2003); however, the mechanism(s) of MAPK regulation remains unclear. It was recently reported that membrane FA saturation levels impact JNK activity through c-Src activation (Holzer et al., 2011). "
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    • "p38 MAPK is usually found primarily in the cytoplasm, but its location in cells after activation is not welldefined . Since activated p38 MAPK can activate MAPKAP kinase 2, which in turn can phosphorylate Hsp27, a protein that interacts with cytoskeletal components (Landry and Huot 1995; Hino and Hosoya 2003) and lead to activation of RhoA in these cells (Garcia et al. 2009), we examined the MDA-MB-435 cells for possible association of p38 with cytoskeletal proteins after arachidonic acid treatment. Concommitant with a striking increase in the number of vinculin-containing focal adhesions at the periphery of Fig. 6. "
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