Platelet-derived Growth Factor-induced Stabilization of Cyclooxygenase 2 mRNA in Rat Smooth Muscle Cells Requires the c-Src Family of Protein-tyrosine Kinases

Abstract

Cyclooxygenases (COXs) are crucial rate-limiting enzymes required for the biosynthesis of prostaglandins. COX-2 is an inducible isoform of this enzyme, which is believed to play important roles in the development of atherosclerotic vascular disease. We found that COX-2 expression rapidly increases in response to various signaling events, including activation of the platelet-derived growth factor (PDGF) pathway. Activation of PDGF receptor (PDGFR) in rat aortic vascular smooth muscle cells leads to c-Src-dependent stabilization of COX-2 mRNA requiring an AU-rich region within the 3-untranslated region of this transcript. This regulation correlates with tyrosine phosphorylation of the RNA-associated protein, CUG-binding protein 2 (CUGBP2), which appears to enhance its interaction with COX-2 mRNA. Site-directed mutagenesis of putative tyrosine phosphorylation sites in CUGBP2 identified tyrosine 39 as a c-Src target, and a CUGBP2 with a mutated tyrosine 39 displayed an attenuated ability to bind COX-2 mRNA. We further show that silencing of CUGBP2 with specific small interference RNAs significantly reduces PDGF-dependent induction of COX-2 at both mRNA and protein levels. Furthermore, forced expression of CUGBP2 or constitutively active c-Src leads to stabilization of co-expressed COX-2 mRNA. Finally, in vitro RNA decay assay demonstrates that CUGBP2 is functionally required for the stabilization of COX-2 mRNA. Therefore, our data suggest that tyrosine phosphorylation of CUGBP2 is an important underlying mechanism for the ability of PDGFR/c-Src signaling to control the stability of COX-2 mRNA.

Cigarette smoke extract induces COX-2 expression via a PKCα/c-Src/EGFR, PDGFR/PI3K/Akt/NF-κB pathway and p300 in tracheal smooth muscle cells

“…In this regard, CSE shares the same mechanism as GPCRs for lysophosphatidic acid, bradykinin, and endothelin (13), which promotes the association of Src with proline-rich tyrosine kinase 2, and subsequently the Src/proline-rich tyrosine kinase 2 complex activates the growth factor receptors, such as EGFR and PDGFR (3). Our results were also consistent with the reports showing that activation of EGFR and PDGFR lead to COX-2 expression in various cell types (17,56,57). Gö6976 has been shown to enhance agonist-induced tyrosine phosphorylation of the EGFR, possibly through inhibition of PTP, since a PTP inhibitor, sodium orthovanadate, mimicked the effects of Gö6976 (49).…”

“…Recent studies have suggested that numerous components of the PI3K pathway play a crucial role in the expression and activation of inflammatory mediators, inflammatory cell recruitment, immune cell function, airway remodeling, and corticosteroid insensitivity in chronic inflammatory diseases (23). Moreover, several studies have indicated that the expression of COX-2 and synthesis of PGE 2 induced by the proinflammatory mediators are mediated by the activation of PKCs, c-Src, EGFR, PDGFR, or PI3K/Akt in various cell types (24,56,57).…”

Growth Factor Regulation of Prostaglandin-Endoperoxide Synthase 2 (Ptgs2) Expression in Colonic Mesenchymal Stem Cells

“…61). Intriguingly, the Src family of kinases has recently also been implicated in the stabilization of Ptgs2 mRNA downstream of signaling by platelet-derived growth factor (42). There must also be more than one target of kinase activity.…”

“…5) identified multiple mRNA-binding proteins that were preferentially expressed in cMSCs compared with bmMSCs. One of these was CUGbp2, a protein known to stabilize Ptgs2 mRNA (40,41) and whose activity can be regulated by phosphorylation downstream of growth factors (42). We evaluated this gene at both the mRNA and protein level in the context of ERK inhibition and found that although CUGbp2 mRNA was not significantly altered by either serum starvation or by ERK inhibition (Fig.…”

CELF2 (CUGBP, Elav-like family member 2)

“…In our earlier studies we have demonstrated that CELF2 can interact with HuR, a key inducer of RNA stability and translation, and competitively inhibit HuR function (Sureban et al, 2007). Recently, platelet derived growth factor was shown to enhance CELF2 binding to COX-2 mRNA through increased phosphorylation of a tyrosine residue at position 39 in the protein (Xu et al, 2007). These data suggest that posttranscriptional control mechanisms are in place to modulate the CELF2 function as a regulator of stability and translation of AU-rich transcripts.…”