Direct interaction of natural and synthetic catechins with signal transducer activator of transcription 1 affects both its phosphorylation and activity

Abstract

Our previous studies showed that (À)-epigallocatechin-3-gallate (EGCG) inhibits signal transducer activator of transcription 1 (STAT1) activation. Since EGCG may be a promising lead compound for new anti-STAT1 drug design, 15 synthetic catechins, characterized by the (À)-gallocatechin-3-gallate stereochemistry, were studied in the human mammary MDA-MB-231 cell line to identify the minimal structural features that preserve the anti-STAT1 activity. We demonstrate that the presence of three hydroxyl groups of B ring and one hydroxyl group in D ring is essential to preserve their inhibitory action. Moreover, a possible molecular target of these compounds in the STAT1 pathway was investigated. Our results demonstrate a direct interaction between STAT1 protein and catechins displaying anti-STAT1 activity. In particular, surface plasmon resonance (SPR) analysis and molecular modeling indicate the presence of two putative binding sites (a and b) with different affinity. Based on docking data, site-directed mutagenesis was performed, and interaction of the most active catechins with STAT1 was studied with SPR to test whether Gln518 on site a and His568 on site b could be important for the catechin-STAT1 interaction. Data indicate that site b has higher affinity for catechins than site a as the highest affinity constant disappears in the H568A-STAT1 mutant. Furthermore, Janus kinase 2 (JAK2) kinase assay data suggest that the contemporary presence in vitro of STAT1 and catechins inhibits JAK2-elicited STAT1 phosphorylation. The very tight catechin-STAT1 interaction prevents STAT1 phosphorylation and represents a novel, specific and efficient molecular mechanism for the inhibition of STAT1 activation. Structured digital abstract• Jak2 phosphorylates STAT1 by protein kinase assay (View interaction)

Opposite Structural Effects of Epigallocatechin-3-gallate and Dopamine Binding to α-Synuclein

“…S-11). In conclusion, these and previously published results point to EGCG as a generic binder [34][35][36][37][38][39][40][41][42] and modulator 41,42 of protein structure.…”

Persistence of STAT-1 inhibition and induction of cytokine resistance in pancreatic β cells treated with St John's wort and its component hyperforin

“…The former is responsible for STAT-1 dimer formation with subsequent nuclear transfer and DNA binding [7] and the latter for improvement of its transcriptional efficiency. [19] We have hypothesized that intracellular availability of HPF after pre-exposure of b cells to either SJW extract or HPF itself may favour its direct and probably prolonged interaction with STAT-1 phosphorylation sites, making them unavailable for cytokine signals, [28] similarly to what has been reported for other plant extracts, like natural and synthetic catechins tightly interacting with STAT-1 [29] or the flavonoids myricetin and delphinidin. [23] As STAT-1 phosphorylation is an early event, already occurring 10-20 min after cytokine treatment, [28] yet long lasting, [14] it is more difficult to explain why SJW extract and in particular HPF may counteract STAT-1 DNA binding when added after cytokine treatment, at time intervals ranging from 15 to 90 min, although with a progressively decreasing efficiency.…”

In Vitro and In Silico Studies of the Molecular Interactions of Epigallocatechin-3-O-gallate (EGCG) with Proteins That Explain the Health Benefits of Green Tea

“…Menegazzi et al demonstrated that EGCG and ECG bound to the signal transduction activator of transcription 1 (STAT1) with Kd = 23 nM in breast cancer cells [ 77 ]. Previous studies showed that EGCG inhibited STAT1 activation.…”