Phosphatase and Tensin Homologue on Chromosome 10 (PTEN) Directs Prostaglandin E2-mediated Fibroblast Responses via Regulation of E Prostanoid 2 Receptor Expression

Abstract

Prostaglandin E 2 (PGE 2 ) is an arachidonic acid metabolite that counters transforming growth factor-␤-induced fibroblast activation via E prostanoid 2 (EP2) receptor binding. Phosphatase and tensin homologue on chromosome 10 (PTEN) is a lipid phosphatase that, by antagonizing the phosphoinositol 3-kinase (PI3K) pathway, also inhibits fibroblast activation. Here, we show that PTEN directly regulates PGE 2 inhibition of fibroblast activation by augmenting EP2 receptor expression. The increase in collagen production and ␣-smooth muscle actin expression observed in fibroblasts in which PTEN is deficient was resistant to the usual suppressive effects of PGE 2 . This was due to marked down-regulation of EP2, a G s protein-coupled receptor (GPCR) that mediates the inhibitory actions of this prostanoid via cAMP. pten ؊/؊ or PTEN-inhibited fibroblasts in which the PI3K pathway was blocked demonstrated a restoration of EP2 receptor expression, due to augmented gene transcription and mRNA instability. Importantly, restoration of the balance between PI3K and PTEN reestablished the inhibitory effect of PGE 2 on fibroblast activation. No such influence of PTEN was observed on alternative E prostanoid GPCRs. Moreover, our studies identified a positive feedback loop in which cAMP signaling enhanced EP2 receptor expression, independent of PTEN. Therefore, our findings indicate that PTEN regulates the antifibrotic effects of PGE 2 by a specific and permissive effect on EP2 receptor expression. Further, our data imply that cAMP signaling circumvents EP2 down-regulation in pten-deficient cells to restore EP2 receptor expression. This is the first description, to our knowledge, of PI3K/PTEN balance directing GPCR expression, and provides a novel mechanism for cellular effects of PTEN.Prostaglandin E 2 (PGE 2 ) 2 is a cyclooxygenase-derived metabolite of arachidonic acid that influences a spectrum of important biological processes including pain, inflammation, and fibrosis. PGE 2 effects may be cell-specific; for example, PGE 2 promotes migration of epithelial cells (1, 2), but it inhibits migration of fibroblasts (3, 4). These seemingly paradoxical actions of PGE 2 reflect the distinct responses resulting from ligation of a diverse repertoire of E prostanoid (EP) receptors on the cell surface. The four G protein-coupled (GPCR) EP receptors, termed EP1-4, signal by mobilizing intracellular calcium (EP1), increasing intracellular cAMP (EP2 and 4), or decreasing intracellular cAMP (EP3) (5). We have shown previously that PGE 2 is capable, in lung fibroblasts, of tempering the profibrotic, activating effects induced by TGF-␤ (e.g. ␣-smooth muscle actin (␣-SMA) and collagen I expression) (6) as well as the migratory effects of fibroblast growth factor (3). These effects are mediated by intracellular cAMP subsequent to binding of EP2, the most abundant of the fibroblast EP receptors.Phosphatase and tensin homologue on chromosome 10 (PTEN) is a dual specificity lipid and protein phosphatase, but its primary action involves dephosphorylat...

A Cyclooxygenase-2/Prostaglandin E2 Pathway Augments Activation-Induced Cytosine Deaminase Expression within Replicating Human B Cells

“…Nevertheless, we consider it pertinent that COX-2, mPGES-1, and EP2 are each subject to a feed-forward process by PGE 2 in other cell lineages. Thus, PGE 2 synthesized from inducible COX-2 and mPGES-1 initiates signals that further increase mRNA/protein levels of COX-2, mPGES-1, and EP2 (48)(49)(50)(51)(52). In support of such a feed-forward process in B cells is preliminary evidence that pulsing cultures with PGE 2 does augment COX-2 and EP2 mRNA and/or protein.…”

“…Third, EP2 and EP4, two PKA-activating receptors for PGE 2 (45), are expressed on activated B cells and reported to function in augmenting IgG and IgE synthesis (46,47). Finally, studies in nonlymphoid cells show that the COX-2 pathway is subject to significant positive feedback control; COX-2-driven PGE 2 can promote the further upregulation of COX-2 (48-50), downstream PGE 2 synthase (51), and EP2 (52). Thus, the progressive increase in AID within cycling B cells might reflect the influences of an increasingly functional COX-2/PGE 2 pathway during B cell clonal expansion.…”

Prostaglandin E2 Inhibits α-Smooth Muscle Actin Transcription during Myofibroblast Differentiation via Distinct Mechanisms of Modulation of Serum Response Factor and Myocardin-related Transcription Factor-A

“…Our group previously established that PGE 2 prevents expression of contractile genes such as ␣-SMA in lung fibroblasts (18,19). Recently, we have also demonstrated that PGE 2 can reverse already established myofibroblast differentiation induced in lung fibroblasts by TGF-␤1 as well as endothelin-1 (20).…”

International Union of Basic and Clinical Pharmacology. LXXXIII: Classification of Prostanoid Receptors, Updating 15 Years of Progress

“…EP 2 receptors are G s -coupled and mediate increases in cAMP (Regan et al, 1994b). A positive feedback loop whereby cAMP signaling enhances EP 2 receptor expression has been suggested (Sagana et al, 2009). Changes in cAMP levels produce pleiotropic effects by activating cAMP-binding proteins.…”