A back-door insight into the modulation of Src kinase activity by the polyamine spermidine

Abstract

Src is a protein tyrosine kinase commonly activated downstream of transmembrane receptors and plays key roles in cell growth, migration and survival signaling pathways. In conventional dendritic cells (cDCs), Src is involved in the activation of the non-enzymatic functions of indoleamine 2,3-dioxygenase 1 (IDO1), an immunoregulatory molecule endowed with both catalytic activity and signal transducing properties. Prompted by the discovery that the metabolite spermidine confers a tolerogenic phenotype on cDCs that is dependent on both the expression of IDO1 and the activity of Src kinase, we here investigated the spermidine mode of action. We found that spermidine directly binds Src in a previously unknown allosteric site located on the backside of the SH2 domain and thus acts as a positive allosteric modulator of the enzyme. Besides confirming that Src phosphorylates IDO1, here we showed that spermidine promotes the protein-protein interaction of Src with IDO1. Overall, this study may pave the way toward the design of allosteric modulators able to switch on/off the Src-mediated pathways, including those involving the immunoregulatory protein IDO1.

Epacadostat stabilizes the apo-form of IDO1 and signals a pro-tumorigenic pathway in human ovarian cancer cells

“…IDO1 is the prototype of a dynamic protein, as it acquires mutually exclusive conformations endowed with distinct functions, namely the enzymatic and the non-enzymatic forms ( 12 ). The phosphorylation of specific tyrosine residues in the ITIMs is the critical event to trigger the IDO1 non-enzymatic function ( 6 , 10 ). Once phosphorylated, IDO1 interacts with different molecular partners, including the phosphatase SHP-2 ( 14 , 18 ).…”

“…While holo-IDO1 has a metabolic function related to its catalytic activity, apo-IDO1 has a transducer activity mediated by its interaction with SH2containing proteins, as the Src homology 2 domain phosphatases (SHPs), the phosphoinositide 3-kinase (PI3K), and the suppressor of cytokine signaling 3 (SOCS3) (7)(8)(9). Like an ordinary transducing molecule, IDO1 contains two immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in the small domain of the protein that can be tyrosine-phosphorylated by the Src kinase and become docking sites for the interaction with downstream SH2-containing proteins (10). The first evidence supporting a potential nonenzymatic activity has been recently described also for IDO2, a paralogue of IDO1 protein, in the human lung adenocarcinoma cell line A549, suggesting a shared 'moonlighting' feature by tryptophan-degrading enzymes (11).…”

Advanced age and female sex protect cerebral arteries from mitochondrial depolarization and apoptosis during acute oxidative stress

“…To further characterize the role of Src kinases in mediating cell death, we activated Src kinases with spermidine (Rossini et al., 2023 ). Spermidine (100 μM; 50 min) evoked minimal (<10%) SMC death in young and old males (Figure 6b ) and females (Figure 6c ).…”

“…The polyamine spermidine (100 μM; Cat. #AC132740050, Fisher) was utilized to activate Src kinases (Rossini et al., 2023 ). Controls include respective vehicles added to PSS without the pharmacological agent.…”

Membrane Localization and Phosphorylation of Indoleamine 2,3-Dioxygenase 2 (IDO2) in A549 Human Lung Adenocarcinoma Cells: First Steps in Exploring Its Signaling Function

“…Although the precise subcellular localization of human IDO2 is still to be defined and the function of its ITIM motifs is still unknown, it could be speculated that the IDO2's proximity to the plasma membrane is functional to a signaling activity and ITIMs act as connection points to recruit adaptor proteins containing SH2 domains, as it occurs in IDO1. Indeed, it has been previously demonstrated that SH2-containing tyrosine phosphatases (SHPs) and SOCS3 can bind IDO1's phosphorylated ITIM1 and ITIM2, respectively [41,42], and that Src kinase is involved in activating IDO1 signaling in DCs [43]. If analog mechanisms also operate in the IDO2 molecule, this is something that should be thoroughly investigated.…”