Development of FRET Biosensor to Characterize CSK Subcellular Regulation.

C-terminal Src kinase (CSK) is the major inhibitory kinase for Src family kinases (SFKs) through the phosphorylation of their C-tail tyrosine sites, and it regulates various types of cellular activity in association with SFK function. As a cytoplasmic protein, CSK needs be recruited to the plasma membrane to regulate SFKs' activity. The regulatory mechanism behind CSK activity and its subcellular localization remains largely unclear. In this work, we developed a genetically encoded biosensor based on fluorescence resonance energy transfer (FRET) to visualize the CSK activity in live cells. The biosensor, with an optimized substrate peptide, confirmed the crucial Arg107 site in the CSK SH2 domain and displayed sensitivity and specificity to CSK activity, while showing minor responses to co-transfected Src and Fyn. FRET measurements showed that CSK had a relatively mild level of kinase activity in comparison to Src and Fyn in rat airway smooth muscle cells. The biosensor tagged with different submembrane-targeting signals detected CSK activity at both non-lipid raft and lipid raft microregions, while it showed a higher FRET level at non-lipid ones. Co-transfected receptor-type protein tyrosine phosphatase alpha (PTPα) had an inhibitory effect on the CSK FRET response. The biosensor did not detect obvious changes in CSK activity between metastatic cancer cells and normal ones. In conclusion, a novel FRET biosensor was generated to monitor CSK activity and demonstrated CSK activity existing in both non-lipid and lipid raft membrane microregions, being more present at non-lipid ones.

Discovery of a Covalent Inhibitor Selectively Targeting the Autophosphorylation Site of c-Src Kinase.

Nonreceptor tyrosine kinase c-Src plays a crucial role in cell signaling and contributes to tumor progression. However, the development of selective c-Src inhibitors turns out to be challenging. In our previous study, we performed posttranslational modification-inspired drug design (PTMI-DD) to provide a plausible way for designing selective kinase inhibitors. In this study, after identifying a unique pocket comprising a less conserved cysteine and an autophosphorylation site in c-Src as well as a promiscuous covalent inhibitor, chemical optimization was performed to obtain (R)-LW-Srci-8 with nearly 75-fold improved potency (IC50 = 35.83 ± 7.21 nM). Crystallographic studies revealed the critical C-F···C═O interactions that may contribute to tight binding. The kinact and Ki values validated the improved binding affinity and decreased warhead reactivity of (R)-LW-Srci-8 for c-Src. Notably, in vitro tyrosine kinase profiling and cellular activity-based protein profiling (ABPP) cooperatively indicated a specific inhibition of c-Src by (R)-LW-Srci-8. Intriguingly, (R)-LW-Srci-8 preferentially binds to inactive c-Src with unphosphorylated Y419 both in vitro and in cells, subsequently disrupting the autophosphorylation. Collectively, our study demonstrated the feasibility of developing selective kinase inhibitors by cotargeting a nucleophilic residue and a posttranslational modification site and providing a chemical probe for c-Src functional studies.

N- and s-substituted Pyrazolopyrimidines: A promising new class of potent c-Src kinase inhibitors with prominent antitumor activity.

In this work, readily achievable synthetic pathways were utilized for construction of a library of N/S analogues based on the pyrazolopyrimidine scaffold with terminal alkyl or aryl fragments. Subsequently, we evaluated the anticancer effects of these novel analogs against the proliferation of various cancer cell lines, including breast, colon, and liver lines. The results were striking, most of the tested molecules exhibited strong and selective cytotoxic activity against the MDA-MB-231 cancer cell line; IC50 1.13 µM. Structure-activity relationship (SAR) analysis revealed that N-substituted derivatives generally enhanced the cytotoxic effect, particularly with aliphatic side chains that facilitated favorable target interactions. We also investigated apoptosis, DNA fragmentation, invasion assay, and anti-migration effects, and discussed their underlying molecular mechanisms for the most active compound 7c. We demonstrated that 7c N-propyl analogue could inhibit MDA-MB-231 TNBC cell proliferation by inducing apoptosis through the regulation of vital proteins, namely c-Src, p53, and Bax. In addition, our results also revealed the potential of these compounds against tumor metastasis by downregulating the invasion and migration modes. Moreover, the in vitro inhibitory effect of active analogs against c-Src kinase was studied and proved that might be the main cause of their antiproliferative effect. Overall, these compelling results point towards the therapeutic potential of these derivatives, particularly those with N-substitution as promising candidates for the treatment of TNBC type of breast cancer.

The stiffness and collagen control differentiation of osteoclasts with an altered expression of c-Src in podosome.

Osteoclasts are hematopoietic cells attached to the bones containing type I collagen-deposited hydroxyapatite during bone resorption. Two major elements determine the stiffness of bones: regular calcified bone (bone that is resorbable by osteoclasts) and un-calcified osteoid bone (bone that is un-resorbable by osteoclasts). The osteolytic cytokine RANKL promotes osteoclast differentiation; however, the roles of the physical interactions of osteoclasts with calcified and un-calcified bone at the sealing zones and the subsequent cellular signaling remain unclear. In this study, we investigated podosomes, actin-rich adhesion structures (actin-ring) in the sealing zone that participates in sensing hard stiffness with collagen in the physical environment during osteoclast differentiation. RANKL-induced osteoclast differentiation induction was promoted when Raw264.7 cells were cultured on collagen-coated plastic dishes but not on non-coated plastic dishes, which was associated with the increased expression of podosome-related genes and Src. In contrast, when cells were cultured on collagen gel, expression of podosome-related genes and Src were not upregulated. The induction of podosome-related genes and Src requires hard stiffness with RGD-containing substratum and integrin-mediated F-actin polymerization. These results indicate that osteoclasts sense both the RGD sequence and stiffness of calcified collagen through their podosome components regulating osteoclast differentiation via the c-Src pathway.

Secretion of Sphinganine by Drug-Induced Cancer Cells and Modified Mimetic Sphinganine (MMS) as c-Src Kinase Inhibitor.

BACKGROUND: Cancer cells exhibit selective metabolic reprogramming to promote proliferation, invasiveness, and metastasis. Sphingolipids such as sphingosine and sphinganine have been reported to modulate cell death processes in cancer cells. However, the potential of extracellular sphinganine and its mimetic compounds as inducers of cancer cell death has not been thoroughly investigated. METHODS: We obtained extracellular conditioned medium from HCT-116 cells treated with the previously reported anticancer composition, goat urine DMSO fraction (GUDF). The extracellular metabolites were purified using a novel and in-house developed vertical tube gel electrophoresis (VTGE) technique and identified through LC-HRMS. Extracellular metabolites such as sphinganine, sphingosine, C16 sphinganine, and phytosphingosine were screened for their inhibitory role against intracellular kinases using molecular docking. Molecular dynamics (MD) simulations were performed to study the inhibitory potential of a novel designed modified mimetic sphinganine (MMS) (Pubchem CID: 162625115) upon c-Src kinase. Furthermore, inhibitory potential and ADME profile of MMS was compared with luteolin, a known c-Src kinase inhibitor. RESULTS: Data showed accumulation of sphinganine and other sphingolipids such as C16 sphinganine, phytosphingosine, and ceramide (d18:1/14:0) in the extracellular compartment of GUDF-treated HCT-116 cells. Molecular docking projected c-Src kinase as an inhibitory target of sphinganine. MD simulations projected MMS with strong (-7.1 kcal/mol) and specific (MET341, ASP404) binding to the inhibitory pocket of c-Src kinase. The projected MMS showed comparable inhibitory role and acceptable ADME profile over known inhibitors. CONCLUSION: In summary, our findings highlight the significance of extracellular sphinganine and other sphingolipids, including C16 sphinganine, phytosphingosine, and ceramide (d18:1/14:0), in the context of drug-induced cell death in HCT-116 cancer cells. Furthermore, we demonstrated the importance of extracellular sphinganine and its modified mimetic sphinganine (MMS) as a potential inhibitor of c-Src kinase. These findings suggest that MMS holds promise for future applications in targeted and combinatorial anticancer therapy.

CSK may be a potential prognostic biomarker reflecting the immune status of gastric cancer.

OBJECTIVE: C-terminal Src kinase (CSK), a sarcoma (Src) homologous family kinase, is one of the most important negative regulators. It acts as a tumor suppressor by inhibiting the activity of Src family tyrosine kinases. Paradoxically, CSK is highly expressed in a variety of common tumors. Therefore, we report the expression profile of CSK in pan-cancer patients, focusing on the prognostic value, immune infiltration pattern, and biological function of CSK in gastric cancer. MATERIALS AND METHODS: We used the TCGA database to analyze CSK expression, clinical relevance, prognostic significance, assessment of the tumor immune microenvironment, and GO and Kegg enrichment analysis based on co-expressed genes using a bioinformatics approach. RESULTS: CSK is a protective factor in gastric cancer, and its expression correlates with the level of immune cell infiltration and immune checkpoint molecules. CONCLUSIONS: Our findings suggest that CSK is an independent prognostic factor in gastric cancer and may predict molecular targeting and immunotherapy and provide ideas for its therapeutic strategy.

Explanatory review on pyrimidine/fused pyrimidine derivatives as anticancer agents targeting Src kinase.

The pyrimidine and fused pyrimidine ring systems play vital roles to inhibit the c-Src kinase. The Src kinase is made of different domains but the kinase domain is responsible for inhibition of Src kinase. In which the kinase domain is the main domain that is made of several amino acids. The Src kinase is inhibited by its inhibitors when it is activated by phosphorylation. Although dysregulation of Src kinase caused cancer in the late nineteenth century, medicinal chemists have not explored it extensively; therefore it is still regarded as a cult pathway. There are numerous FDA-approved drugs on the market, yet novel anticancer drugs are still in demand. Existing medications have adverse effects and drug resistance owing to rapid protein mutation. In this review, we discussed the activation process of Src kinase, chemistry of pyrimidine ring and its different synthetic routes, as well as the recent development in c-Src kinase inhibitors containing pyrimidine and their biological activity, SAR, and selectivity. The c-Src binding pocket has been predicted in detail to discover the vital amino acids which will interact with inhibitors. The potent derivatives were docked to discover the binding pattern. The derivative 2 established three hydrogen bonds with the amino acid residues Thr341 and Gln278 and had the greatest binding energy of -13.0 kcal/mol. The top docked molecules were further studied for ADMET studies. The derivative 1, 2, and 43 did not show any violation of Lipinski's rule. All derivatives used for the prediction of toxicity showed toxicity.

Design, synthesis of novel chromene-based scaffolds targeting hepatocellular carcinoma: Cell cycle arrest, cytotoxic effect against resistant cancer cells, apoptosis induction, and c-Src inhibition.

New chromene derivatives were synthesized based on 4-(3,4-dimethoxy)-4H-chromene scaffold. All target compounds exhibited cytotoxic activity against HepG2 cells (IC50 = 2.40-141.22 µM). Chromens 5 and 9 showed superior cytotoxicity over staurosporine (IC50 = 18.27 µM) and vinblastine (IC50 = 5.20 µM). c-Src kinase inhibition assay of compounds 5 and 9 displayed the dominant c-Src inhibitory activity of 5 (IC50 = 0.184 µM) over 9 (IC50 = 0.288 µM). The safety of the most potent compound 5 against normal WI-38 cells was confirmed via its IC50 of 115.75 µM comparable with 5-FU (IC50 = 16.28 µM). Moreover, the promising chromene 5 displayed potent cytotoxicity against resistant HepG2 cells with IC50 of 26.03 µM comparable with 5-FU (IC50 = 42.68 µM). The most active chromene 5 arrested the HepG2 cell cycle at the S phase and induced a 29-fold increase in the total number of apoptotic cells indicating pre-G1 apoptosis. The ability of compound 5 to induce apoptosis was supported via elevation of caspase-3, caspase-7, caspase-9 and proapoptotic Bax protein levels in addition to downregulation of the antiapoptotic Bcl2 protein. Molecular docking studies of compound 5 showed good binding interaction pattern inside c-Src kinase enzyme active site.

Oxidative Stress Participates in Age-Related Cataract Formation by Disrupting Connection between Lens Epithelial Cells through c-Src/VEGF Pathway.

PURPOSE: To observe the effects of oxidative stress on vascular endothelial growth factor (VEGF) and connections of lens epithelial cells. METHODS: Human lens epithelium of patients with age-related cataract (ARC), both SRA01/04 cells and whole mice lens stimulated by H2O2 were employed. VEGF in human aqueous humor of ARC-patients and the supernatant of SRA01/04 cells was determined by ELISA. The expressions of VEFG in human lens epithelium were detected by immunofluorescence staining. Multiple linear regression analysis and spearman rank-order correlation were used to determine the associations between VEGF and parameters of ARC individuals. In H2O2-induced SRA01/04 cells, Catalase (CAT), PP1 (inhibitor of c-Src kinase) and Avastin (VEGF antibody) were used to inhibit the effects of H2O2, activation of c-Src kinase and VEGF, which were detected by Western blot. The alterations of ZO-1 and N-cadherin were tested by immunofluorescence staining and Western blot. In H2O2-induced whole lens, the changes of opacification area in different treatment of inhibitors were observed. RESULTS: The secretion of VEGF in aqueous humor and expression of VEGF in the lens epithelium of ARC patients increased significantly with age. In H2O2-induced SRA01/04 cells, the VEGF in the supernatant was increased with the culture duration and the dose of H2O2. The expressions of p-Src418 and VEGF were also up-regulated, whereas the expressions of ZO-1 and N-cadherin were down-regulated. CAT effectively prevented these changes induced by H2O2, while PP1 inhibited not only p-Src418 but also up-regulation of VEGF, Avastin partially inhibited VEGF up-regulation. Both PP1 and Avastin prevented down-regulation of ZO-1 and N-cadherin, respectively, but Avastin combined with PP1 had no significant synergistic effects. In H2O2-induced cataract, CAT prevented development of opacification area effectively, and PP1 and Avastin did partially. CONCLUSIONS: Oxidative stress disrupts connections of lens epithelial cells by activating c-Src/VEGF, inhibiting which may prevent cataract.

Selective and Potent PROTAC Degraders of c-Src Kinase.

Using dasatinib linked to E3 ligase ligands, we identified a potent and selective dual Csk/c-Src PROTAC degrader. We then replaced dasatinib, the c-Src-directed ligand, with a conformation-selective analogue that stabilizes the αC-helix-out conformation of c-Src. Using the αC-helix-out ligand, we identified a PROTAC that is potent and selective for c-Src. We demonstrated a high degree of catalysis with our c-Src PROTACs. Using our c-Src PROTACs, we identified pharmacological advantages of c-Src degradation compared to inhibition with respect to cancer cell proliferation.

Protocol to characterize extracellular c-Src tyrosine kinase function through substrate interaction and phosphorylation.

Cellular Src tyrosine kinase (c-Src) exists in the secretomes of several human cancers (extracellular, e-Src). Phosphoproteomics has demonstrated the existence of 114 potential extracellular e-Src substrates in addition to Tissue Inhibitor of Metalloproteinases 2. Here, we present a protocol to characterize secreted tyrosine-phosphorylated substrates as a result of c-Src expression and secretion. We describe steps for collecting cell secretomes and extracts, performing antibody treatment and Ni-NTA pull-down, and detecting protein-protein interaction and substrate Y-phosphorylation. This protocol is adaptable for studies examining the function of other extracellular kinases. For complete details on the use and execution of this protocol, please refer to Backe et al. (2023)1 and Sánchez-Pozo et al. (2018).2.

An allosteric switch between the activation loop and a c-terminal palindromic phospho-motif controls c-Src function.

Autophosphorylation controls the transition between discrete functional and conformational states in protein kinases, yet the structural and molecular determinants underlying this fundamental process remain unclear. Here we show that c-terminal Tyr 530 is a de facto c-Src autophosphorylation site with slow time-resolution kinetics and a strong intermolecular component. On the contrary, activation-loop Tyr 419 undergoes faster kinetics and a cis-to-trans phosphorylation switch that controls c-terminal Tyr 530 autophosphorylation, enzyme specificity, and strikingly, c-Src non-catalytic function as a substrate. In line with this, we visualize by X-ray crystallography a snapshot of Tyr 530 intermolecular autophosphorylation. In an asymmetric arrangement of both catalytic domains, a c-terminal palindromic phospho-motif flanking Tyr 530 on the substrate molecule engages the G-loop of the active kinase adopting a position ready for entry into the catalytic cleft. Perturbation of the phospho-motif accounts for c-Src dysfunction as indicated by viral and colorectal cancer (CRC)-associated c-terminal deleted variants. We show that c-terminal residues 531 to 536 are required for c-Src Tyr 530 autophosphorylation, and such a detrimental effect is caused by the substrate molecule inhibiting allosterically the active kinase. Our work reveals a crosstalk between the activation and c-terminal segments that control the allosteric interplay between substrate- and enzyme-acting kinases during autophosphorylation.

Thrombin-Induced COX-2 Expression and PGE2 Synthesis in Human Tracheal Smooth Muscle Cells: Role of PKCδ/Pyk2-Dependent AP-1 Pathway Modulation.

In this study, we confirmed that thrombin significantly increases the production of COX-2 and PGE2 in human tracheal smooth muscle cells (HTSMCs), leading to inflammation in the airways and lungs. These molecules are well-known contributors to various inflammatory diseases. Here, we investigated in detail the involved signaling pathways using specific inhibitors and small interfering RNAs (siRNAs). Our results demonstrated that inhibitors targeting proteins such as protein kinase C (PKC)δ, proline-rich tyrosine kinase 2 (Pyk2), c-Src, epidermal growth factor receptor (EGFR), phosphatidylinositol 3-kinase (PI3K), or activator protein-1 (AP-1) effectively reduced thrombin-induced COX-2 and PGE2 production. Additionally, transfection with siRNAs against PKCδ, Pyk2, c-Src, EGFR, protein kinase B (Akt), or c-Jun mitigated these responses. Furthermore, our observations revealed that thrombin stimulated the phosphorylation of key components of the signaling cascade, including PKCδ, Pyk2, c-Src, EGFR, Akt, and c-Jun. Thrombin activated COX-2 promoter activity through AP-1 activation, a process that was disrupted by a point-mutated AP-1 site within the COX-2 promoter. Finally, resveratrol (one of the most researched natural polyphenols) was found to effectively inhibit thrombin-induced COX-2 expression and PGE2 release in HTSMCs through blocking the activation of Pyk2, c-Src, EGFR, Akt, and c-Jun. In summary, our findings demonstrate that thrombin-induced COX-2 and PGE2 generation involves a PKCδ/Pyk2/c-Src/EGFR/PI3K/Akt-dependent AP-1 activation pathway. This study also suggests the potential use of resveratrol as an intervention for managing airway inflammation.

STAP-2 negatively regulates BCR-mediated B cell activation by recruiting tyrosine-protein kinase CSK to LYN.

Although signal-transducing adaptor protein-2 (STAP-2) acts in certain immune responses, its role in B cell receptor (BCR)-mediated signals remains unknown. In this study, we have revealed that BCR-mediated signals, cytokine production and antibody production were increased in STAP-2 knockout (KO) mice compared with wild-type (WT) mice. Phosphorylation of tyrosine-protein kinase LYN Y508 was reduced in STAP-2 KO B cells after BCR stimulation. Mechanistic analysis revealed that STAP-2 directly binds to LYN, dependently of STAP-2 Y250 phosphorylation by LYN. Furthermore, phosphorylation of STAP-2 enhanced interactions between LYN and tyrosine-protein kinase CSK, resulting in enhanced CSK-mediated LYN Y508 phosphorylation. These results suggest that STAP-2 is crucial for controlling BCR-mediated signals and antibody production by enhanced CSK-mediated feedback regulation of LYN.

Endothelial VEGFR2-PLCγ signaling regulates vascular permeability and antitumor immunity through eNOS/Src.

Endothelial phospholipase Cγ (PLCγ) is essential for vascular development; however, its role in healthy, mature, or pathological vessels is unexplored. Here, we show that PLCγ was prominently expressed in vessels of several human cancer forms, notably in renal cell carcinoma (RCC). High PLCγ expression in clear cell RCC correlated with angiogenic activity and poor prognosis, while low expression correlated with immune cell activation. PLCγ was induced downstream of vascular endothelial growth factor receptor 2 (VEGFR2) phosphosite Y1173 (pY1173). Heterozygous Vegfr2Y1173F/+ mice or mice lacking endothelial PLCγ (Plcg1iECKO) exhibited a stabilized endothelial barrier and diminished vascular leakage. Barrier stabilization was accompanied by decreased expression of immunosuppressive cytokines, reduced infiltration of B cells, helper T cells and regulatory T cells, and improved response to chemo- and immunotherapy. Mechanistically, pY1173/PLCγ signaling induced Ca2+/protein kinase C-dependent activation of endothelial nitric oxide synthase (eNOS), required for tyrosine nitration and activation of Src. Src-induced phosphorylation of VE-cadherin at Y685 was accompanied by disintegration of endothelial junctions. This pY1173/PLCγ/eNOS/Src pathway was detected in both healthy and tumor vessels in Vegfr2Y1173F/+ mice, which displayed decreased activation of PLCγ and eNOS and suppressed vascular leakage. Thus, we believe that we have identified a clinically relevant endothelial PLCγ pathway downstream of VEGFR2 pY1173, which destabilizes the endothelial barrier and results in loss of antitumor immunity.

CircKIF4A combines EIF4A3 to stabilize SDC1 expression to activate c-src/FAK and promotes TNBC progression.

Triple-negative breast cancer (TNBC) is recognized for its poor prognosis and limited options for treatment. Circular RNA KIF4A (circKIF4A) was documented to be abnormally overexpressed in TNBC and was correlated with a poor survival rate. The objective of this study is to further examine the functional role of circKIF4A and its underlying mechanism. CircKIF4A was significantly upregulated in TNBC and the knockdown of circKIF4A suppressed TNBC cell proliferation, migration, and invasion. CircKIF4A was directly bound to EIF4A3, which interacted with SDC1. Knockdown of circKIF4A reduced interaction between EIF4A3 and SDC1 as well as SDC1 mRNA stability. SDC1 activated the c-src/FAK signaling pathways and finally promoted TNBC progression. circKIF4A induced TNBC progress in the in vivo mouse model via SDC1. CircKIF4A interacts with EIF4A3 to stabilize SDC1 mRNA, which activates the c-src/FAK signaling pathways and promotes TNBC progression. This may provide a potential therapy for TNBC treatment.

Morphine-induced mechanical hypersensitivity in mice requires δ receptors, ß-arrestin2, and c-Src activity.

Morphine diminishes pain, but its long-term use is compromised by tolerance and hyperalgesia. Studies implicate δ receptors, ß-arrestin2 and Src kinase in tolerance. We examined whether these proteins are also involved in morphine-induced hypersensitivity (MIH). A common pathway for tolerance and hypersensitivity may provide a single target to guide improved analgesic approaches. We examined mechanical sensitivity using automated von Frey in wild-type (WT) and transgenic male and female C57Bl/6 mice before and after hind paw inflammation by complete Freund's adjuvant (CFA). CFA-evoked hypersensitivity ceased on day 7 in WT but persisted for the 15-day testing period in µ-/- . Recovery was delayed until day 13 in δ-/- . We explored the expression of opioid genes in the spinal cord using quantitative RT-PCR. Restoration to basal sensitivity in WT occurred with increased δ expression. By contrast, κ expression was reduced, while µ remained unchanged. Daily morphine reduced hypersensitivity in WT on day 3 compared to controls; however, hypersensitivity recurred on day 9 and beyond. By contrast, WT had no recurrence of hypersensitivity in the absence of daily morphine. We used ß-arrestin2-/- , δ-/- and Src inhibition by dasatinib in WT to establish whether these approaches, which diminish tolerance, also attenuate MIH. While none of these approaches affected CFA-evoked inflammation or acute hypersensitivity, all caused sustained morphine anti-hypersensitivity, abolishing MIH. Like morphine tolerance, MIH in this model requires δ receptors, ß-arrestin2 and Src activity. Our findings suggest that MIH is caused by a tolerance-induced reduction in endogenous opioid signalling. KEY POINTS: Morphine is effective for treating severe acute pain, but tolerance and hypersensitivity often develop during its use in treating chronic pain. It is unclear whether these detrimental effects share similar mechanisms; if so, it might be possible to develop a single approach to minimise both phenomena. Mice deficient in µ receptors, δ receptors or ß-arrestin2 and wild type mice treated with the Src inhibitor dasatinib exhibit negligible morphine tolerance. We show that these same approaches also prevent the development of morphine-induced hypersensitivity during persistent inflammation. This knowledge identifies strategies, such as the use of Src inhibitors, which may mitigate tolerance and morphine induced hyperalgesia.

Identifying bioactive phytoconstituents as C-terminal Src kinase inhibitors: a virtual screening and molecular simulation approach.

Tyrosine-protein kinase CSK otherwise known as C-terminal Src kinase (CSK), is involved in multiple pathways and processes, including regulating cell growth, differentiation, migration, and immune responses. Altered expression of CSK has been associated with various complexities, including cancer, CD45 deficiency, Osteopetrosis and lupus erythematosus. Important auxiliary roles of CSK in cancer progression make it a crucial target in developing novel anticancer therapy. Thus, CSK inhibitors are of concern as potent immuno-oncology agents. In this perspective, phytochemicals can be a significant source for unraveling novel CSK inhibitors. In this study, we carried out a systematic structure-based virtual screening of bioactive phytoconstituents against CSK to identify its potential inhibitors. After a multi-step screening process, two hits (Shinpterocarpin and Justicidin B) were selected based on their druglike properties and binding affinity towards CSK. The selected hits were further analyzed for their stability and interaction via all-atom molecular dynamics (MD) simulations. The selected hits indicated their potential as selective binding partners of CSK, which can further be used for therapeutic development against CSK-associated malignancies.Communicated by Ramaswamy H. Sarma.

SHP-1 tyrosine phosphatase binding to c-Src kinase phosphor-dependent conformations: A comparative structural framework.

SHP-1 is a cytosolic tyrosine phosphatase that is primarily expressed in hematopoietic cells. It acts as a negative regulator of numerous signaling pathways and controls multiple cellular functions involved in cancer pathogenesis. This study describes the binding preferences of SHP-1 (pY536) to c-Srcopen (pY416) and c-Srcclose (pY527) through in silico approaches. Molecular dynamics simulation analysis revealed more conformational changes in c-Srcclose upon binding to SHP-1, as compared to its active/open conformation that is stabilized by the cooperative binding of the C-SH2 domain and C-terminal tail of SHP-1 to c-Src SH2 and KD. In contrast, c-Srcclose and SHP-1 interaction is mediated by PTP domain-specific WPD-loop (WPDXGXP) and Q-loop (QTXXQYXF) binding to c-Srcclose C-terminal tail residues. The dynamic correlation analysis demonstrated a positive correlation for SHP-1 PTP with KD, SH3, and the C-terminal tail of c-Srcclose. In the case of the c-Srcopen-SHP-1 complex, SH3 and SH2 domains of c-Srcopen were correlated to C-SH2 and the C-terminal tail of SHP-1. Our findings reveal that SHP1-dependent c-Src activation through dephosphorylation relies on the conformational shift in the inhibitory C-terminal tail that may ease the recruitment of the N-SH2 domain to phosphotyrosine residue, resulting in the relieving of the PTP domain. Collectively, this study delineates the intermolecular interaction paradigm and underlying conformational readjustments in SHP-1 due to binding with the c-Src active and inactive state. This study will largely help in devising novel therapeutic strategies for targeting cancer development.

Phosphorylation of mammalian mitochondrial EF-Tu by Fyn and c-Src kinases.

Src Family Kinases (SFKs) are tyrosine kinases known to regulate glucose and fatty acid metabolism as well as oxidative phosphorylation (OXPHOS) in mammalian mitochondria. We and others discovered the association of the SFK kinases Fyn and c-Src with mitochondrial translation components. This translational system is responsible for the synthesis of 13 mitochondrial (mt)-encoded subunits of the OXPHOS complexes and is, thus, essential for energy generation. Mitochondrial ribosomal proteins and various translation elongation factors including Tu (EF-Tumt) have been identified as possible Fyn and c-Src kinase targets. However, the phosphorylation of specific residues in EF-Tumt by these kinases and their roles in the regulation of protein synthesis are yet to be explored. In this study, we report the association of EF-Tumt with cSrc kinase and mapping of phosphorylated Tyr (pTyr) residues by these kinases. We determined that a specific Tyr residue in EF-Tumt at position 266 (EF-Tumt-Y266), located in a highly conserved c-Src consensus motif is one of the major phosphorylation sites. The potential role of EF-Tumt-Y266 phosphorylation in regulation of mitochondrial translation investigated by site-directed mutagenesis. Its phosphomimetic to Glu residue (EF-Tumt-E266) inhibited ternary complex (EF-Tumt•GTP•aatRNA) formation and translation in vitro. Our findings along with data mining analysis of the c-Src knock out (KO) mice proteome suggest that the SFKs have possible roles for regulation of mitochondrial protein synthesis and oxidative energy metabolism in animals.