SMER28 attenuates PI3K/mTOR signaling by direct inhibition of PI3K p110 delta

Abstract

SMER28 (Small molecule enhancer of Rapamycin 28) is an autophagy-inducing compound functioning by a hitherto unknown mechanism. Here we confirm its autophagy-inducing effect by assessing classical autophagy-related parameters. Interestingly, we also discovered several additional effects of SMER28, including growth retardation and reduced G1 to S phase progression. Most strikingly, SMER28 treatment led to a complete arrest of receptor tyrosine kinase signaling, and consequently growth factor-induced cell scattering and dorsal ruffle formation. This coincided with a dramatic reduction of phosphorylation patterns of PI3K downstream effectors. Consistently, SMER28 directly inhibited PI3Kδ and to a lesser extent p110γ. The biological relevance of our observations was underscored by interference of SMER28 with InlB-mediated host cell entry of Listeria monocytogenes, which requires signaling through the prominent receptor typrosine kinase c-Met. This effect was signaling-specific, since entry of unrelated, gram-negative Salmonella Typhimurium was not inhibited.

The autophagy inducer SMER28 attenuates microtubule dynamics mediating neuroprotection

“…Earlier reports have shown that the speed of MT assembly and of CLIP170 at MT plus ends is regulated by the phosphorylation of CLIP170 [9][10][11] . A recently posted report from our laboratory suggests that the molecular target of SMER28 might be class I PI3 kinases 79 . It is tempting to speculate, therefore, that SMER28 might speci cally interfere with a cellular kinase such as AKT or AMPK, involved in CLIP-170 phosphorylation 11,12,80 , and downstream of PI3Ks 81 .…”

Wirkstoffe an der Schnittstelle zwischen Autophagie und Cytoskelettdynamik

“…1). Dies führt zu einer Hemmung der Signalweiterleitung über die PI3K-AKT-mTORC1-Signalachse und hemmt Prozesse wie Zellzyklusregulation und Zellmigration, wobei gleichzeitig die resultierende Aktivierung der Kinase Ulk1 zu einer erhöhten Autophagierate führt [7]. Neben diesem direkten Effekt auf Klasse-I-PI3-Kinasen, besonders auf PI3Kδ, zeigten sich weitere indirekte Effekte.…”

“…SMER28 beeinfl usst indirekt das Cytoskelett und dessen dynamische Reorganisation: Aktin-gesteuerte Prozesse, wie die Bildung von Membranvorschüben bei Zellbewegungen, werden durch SMER28 signifi kant reduziert, was einen Einfl uss auf die RTK-induzierte Aufnahme von z. B. Listerien [7] oder auch Cytomegalie-Viren hat [6]. Neben dem Aktincytoskelett wirkt sich SMER28 außerdem auf Mikrotubuli aus: Über die Hemmung der AMPK inhibiert SMER28 die Phosphorylierung von cytoplasmic linker protein 170 (CLIP-170), einer Komponente des +TIP-Komplexes an den wachsenden Mikrotubuli-Enden.…”