Regulation of mTOR and S6K1 activation by the nPKC isoforms, PKCε and PKCδ, in adult cardiac muscle cells

Abstract

SUMMARYActivation of both mTOR and its downstream target, S6K1 (p70 S6 kinase) have been implicated to affect cardiac hypertrophy. Our earlier work, in a feline model of 1-48 h pressure overload, demonstrated that mTOR/S6K1 activation occurred primarily through a PKC/c-Raf pathway. To further delineate the role of specific PKC isoforms on mTOR/S6K1 activation, we utilized primary cultures of adult feline cardiomyocytes in vitro and stimulated with endothelin-1 (ET-1), phenylephrine (PE), TPA, or insulin. All agonist treatments resulted in S2248 phosphorylation of mTOR and T389 and S421/T424 phosphorylation of S6K1, however only ET-1 and TPA-stimulated mTOR/S6K1 activation was abolished with infection of a dominant negative adenoviral c-Raf (DNRaf) construct. Expression of DN-PKC ε blocked ET-1-stimulated mTOR S2448 and S6K1 S421/ T424 and T389 phosphorylation but had no effect on insulin-stimulated S6K1 phosphorylation. Expression of DN-PKC δ or pretreatment of cardiomyocytes with rottlerin, a PKC δ specific inhibitor, blocked both ET-1 and insulin stimulated mTOR S2448 and S6K1 T389 phosphorylation. However, treatment with Gö6976, a specific classical PKC (cPKC) inhibitor did not affect mTOR/S6K1 activation. These data indicate that: (i) PKC ε is required for ET-1-stimulated T421/S424 phosphorylation of S6K1, (ii) both PKC ε and PKC δ are required for ET-1-stimulated mTOR S2448 and S6K1 T389 phosphorylation, (iii) PKC δ is also required for insulin-stimulated mTOR S2448 and S6K1 T389 phosphorylation. Together, these data delineate both distinct and combinatorial roles of specific PKC isoforms on mTOR and S6K1 activation in adult cardiac myocytes following hypertrophic stimulation.

Antitumoral Activity of Rapamycin Mediated Through Inhibition of HIF-1alpha and VEGF in Hepatocellular Carcinoma

“…CsAinduced VEGF overexpression is attributed to protein kinase C (PKC) and SP1 activity. Importantly, PKC involves in Akt and mTOR activation [24][25][26], which are key components of survival signaling pathways. Thus, RAPA and CsA might antagonize one another when used in combination.…”

Frontier of Epilepsy Research - mTOR signaling pathway

“…It also hypophosphorylates 4E-BP1 by increasing PP2A activity, which results in the inhibition of protein translation in PI3K/AKT/mTORindependent manner . PKCε is required for ET-1-stimulated phosphorylation of S6K1 at Thr389, Thr421 and Ser424, and mTOR at Ser 2448 (Moschella et al, 2007). PKCδ are required for ET-1-and insulin-stimulated phosphorylation of mTOR at Ser2448 and S6K1 at Thr389 (Moschella et al, 2007).…”

“…PKCε is required for ET-1-stimulated phosphorylation of S6K1 at Thr389, Thr421 and Ser424, and mTOR at Ser 2448 (Moschella et al, 2007). PKCδ are required for ET-1-and insulin-stimulated phosphorylation of mTOR at Ser2448 and S6K1 at Thr389 (Moschella et al, 2007). PKCζ phosphorylates PKCδ, and this process is rapamycin sensitive, and it also activates mTOR via MAPK activation (Ziegler et al, 1999;Leseux et al, 2008).…”

Developmental regulation of p70 S6 kinase by a G protein-coupled receptor dynamically modelized in primary cells

“…Even more, in mitotic cells, paclitaxel, a chemotherapeutic agent which destabilizes microtubules, has been shown to stimulate phosphorylation of p70S6K on T421/S424, concurrently with catalytic inactivation of the enzyme [17], indicating that phosphorylation of this region of p70S6K may even be linked to enzyme inactivation. In addition, in response to G protein-coupled receptors (GPCR), agonists recognizing the thyroid-stimulating hormone receptor [18], the prostaglandin F2a receptor [19], the endothelin receptor [20], or the a1-adrenergic receptor [21] respectively, epistatic elements such as PI3K may not be activated [18,19], or may even be inhibited [21], despite activation of p70S6K.…”