Structural basis for inositol pyrophosphate gating of the phosphate channel XPR1.

Precise regulation of intracellular phosphate (Pi) is critical for cellular function, with XPR1 serving as the sole Pi exporter in humans. The mechanism of Pi efflux, activated by inositol pyrophosphates (PP-IPs), has remained unclear. This study presents cryo-electron microscopy structures of XPR1 in multiple conformations, revealing a transmembrane pathway for Pi export and a dual-binding activation pattern by PP-IPs. A canonical binding site is located at the dimeric interface of SPX domains, and a second site, biased toward PP-IPs, is found between the transmembrane and SPX domains. By integrating structural studies with electrophysiological analyses, we characterize XPR1 as an IPs/PP-IPs-activated phosphate channel. The interplay among its TMDs, SPX domains, and IPs/PP-IPs orchestrates the conformational transition between its closed and open states.

Structural insights into the orthosteric inhibition of P2X receptors by non-ATP analog antagonists.

P2X receptors are extracellular ATP-gated ion channels that form homo- or heterotrimers and consist of seven subtypes. They are expressed in various tissues, including neuronal and nonneuronal cells, and play critical roles in physiological processes such as neurotransmission, inflammation, pain, and cancer. As a result, P2X receptors have attracted considerable interest as drug targets, and various competitive inhibitors have been developed. However, although several P2X receptor structures from different subtypes have been reported, the limited structural information of P2X receptors in complex with competitive antagonists hampers the understanding of orthosteric inhibition, hindering the further design and optimization of those antagonists for drug discovery. We determined the cryogenic electron microscopy (cryo-EM) structures of the mammalian P2X7 receptor in complex with two classical competitive antagonists of pyridoxal-5'-phosphate derivatives, pyridoxal-5'-phosphate-6-(2'-naphthylazo-6'-nitro-4',8'-disulfonate) (PPNDS) and pyridoxal phosphate-6-azophenyl-2',5'-disulfonic acid (PPADS), and performed structure-based mutational analysis by patch-clamp recording as well as molecular dynamics (MD) simulations. Our structures revealed the orthosteric site for PPADS/PPNDS, and structural comparison with the previously reported apo- and ATP-bound structures showed how PPADS/PPNDS binding inhibits the conformational changes associated with channel activation. In addition, structure-based mutational analysis identified key residues involved in the PPNDS sensitivity of P2X1 and P2X3, which are known to have higher affinity for PPADS/PPNDS than other P2X subtypes.

A shared mechanism for TNP-ATP recognition by members of the P2X receptor family.

P2X receptors (P2X1-7) are non-selective cation channels involved in many physiological activities such as synaptic transmission, immunological modulation, and cardiovascular function. These receptors share a conserved mechanism to sense extracellular ATP. TNP-ATP is an ATP derivative acting as a nonselective competitive P2X antagonist. Understanding how it occupies the orthosteric site in the absence of agonism may help reveal the key allostery during P2X gating. However, TNP-ATP/P2X complexes (TNP-ATP/human P2X3 (hP2X3) and TNP-ATP/chicken P2X7 (ckP2X7)) with distinct conformations and different mechanisms of action have been proposed. Whether these represent species and subtype variations or experimental differences remains unclear. Here, we show that a common mechanism of TNP-ATP recognition exists for the P2X family members by combining enhanced conformation sampling, engineered disulfide bond analysis, and covalent occupancy. In this model, the polar triphosphate moiety of TNP-ATP interacts with the orthosteric site, while its TNP-moiety is deeply embedded in the head and dorsal fin (DF) interface, creating a restrictive allostery in these two domains that results in a partly enlarged yet ion-impermeable pore. Similar results were obtained from multiple P2X subtypes of different species, including ckP2X7, hP2X3, rat P2X2 (rP2X2), and human P2X1 (hP2X1). Thus, TNP-ATP uses a common mechanism for P2X recognition and modulation by restricting the movements of the head and DF domains which are essential for P2X activation. This knowledge is applicable to the development of new P2X inhibitors.

Chronic cough relief by allosteric modulation of P2X3 without taste disturbance.

P2X receptors are cation channels that sense extracellular ATP. Many therapeutic candidates targeting P2X receptors have begun clinical trials or acquired approval for the treatment of refractory chronic cough (RCC) and other disorders. However, the present negative allosteric modulation of P2X receptors is primarily limited to the central pocket or the site below the left flipper domain. Here, we uncover a mechanism of allosteric regulation of P2X3 in the inner pocket of the head domain (IP-HD), and show that the antitussive effects of quercetin and PSFL2915 (our nM-affinity P2X3 inhibitor optimized based on quercetin) on male mice and guinea pigs were achieved by preventing allosteric changes of IP-HD in P2X3. While being therapeutically comparable to the newly licensed P2X3 RCC drug gefapixant, quercetin and PSFL2915 do not have an adverse effect on taste as gefapixant does. Thus, allosteric modulation of P2X3 via IP-HD may be a druggable strategy to alleviate RCC.

Significant difference of c-type lectin-like receptor 2 between colorectal cancer and polyp subgroups.

BACKGROUND: Platelets play a key role in tumor progression and metastasis. C-type lectin-like receptor 2 (CLEC-2) is the receptor expressed on platelets and the marker of platelet activation. OBJECTIVE: This study aims to determine whether soluble CLEC-2 levels differ between patients with benign colorectal polyps and those with colorectal cancer (CRC). METHODS: We measured plasma soluble CLEC-2 by enzyme-linked immunosorbent assay in 150 patients with colorectal polyps, 150 CRC patients without metastasis, 150 CRC liver metastasis, and 150 control subjects. RESULTS: The CRC patients had higher soluble CLEC-2 levels than patients with colorectal polyps (p< 0.001). Moreover, CRC patients with liver metastases displayed higher CLEC-2 levels than those in CRC patients without metastases (p< 0.001). In the CRC patients, CLEC-2 levels were correlated with lymph node metastasis and advanced stage. In the patients with polyps, there was a significant difference in CLEC-2 levels among patients with hyperplastic polyp, sessile serrated adenoma, and traditional serrated adenoma (p< 0.001). The ROC curve analysis revealed CLEC-2 had an optimal sensitivity of 77.3% and specificity of 94.6% for the screening of CRC, and sensitivity of 71.0% and specificity of 76.7% for the differential diagnosis of colorectal polyps and CRC. CONCLUSIONS: CRC patients have higher CLEC-2 levels than patients with colorectal polyps and healthy controls. Moreover, there is a significant difference in CLEC-2 levels among polyp subtypes. Further research is warranted.

Platelet Volume Is Reduced In Metastasing Breast Cancer: Blood Profiles Reveal Significant Shifts.

BACKGROUND: Platelets play a crucial role in breast cancer (BC) progression and metastases. Mean platelet volume (MPV) is an indicator of platelet activation. The aim of the present study was to assess whether there is a difference in MPV between patients with metastatic BC with liver metastases and those with BC without liver metastases. METHODS: Between January 2014 and December 2017, 211 metastatic BC patients with synchronous liver metastases and 215 BC patients without metastases were retrospectively analyzed. Patients' clinicopathological characteristics data were collected. RESULTS: MPV levels were reduced in patients with liver metastases compared with those in patients without liver metastases. There were significant differences in MPV levels according to liver metastases status both in premenopausal and in postmenopausal non-TNBC or non-HER2+ patients. Moreover, in postmenopausal HER2+ or TNBC patients, MPV levels were lower in patients with liver metastases compared with those in patients without liver metastases. In the group with non-liver metastasis, platelet distribution width was significantly associated with tumor N stage. In addition, the prevalence of BC liver metastases decreased as MPV quartiles increased. After adjusting for other risk factors, the odds ratios for liver metastases according to MPV quartiles were 1.000, 0.267 (0.134-0.530), 0.072 (0.034-0.152), and 0.137 (0.066-0.281), respectively. CONCLUSION: MPV is reduced in BC patients with liver metastases compared with that in BC patients without metastases. Moreover, MPV is independently associated with the presence of liver metastases.

Decreased platelet distribution width predicts a worse prognosis in patients undergoing surgical resection for hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is the sixth most common malignant tumor and second most common cause of tumor-related deaths worldwide. Activated platelets play a prominent role in tumor. Platelet distribution width (PDW) indicates platelets activation and is altered in malignancies. The aim of this study was to explore the prognostic value of PDW for overall survival (OS) in HCC patients. METHODS: We retrospectively reviewed 273 HCC patients at a single institution from 2010 to 2014. The relationship between PDW and clinicopathological characteristics was analyzed. Kaplan-Meier curves and multivariate Cox regression analyses were used to evaluate the relationship of PDW with OS. RESULTS: Low PDW levels were observed in 127 (46.5%) out of 273 patients. A significant correlation was found between PDW and liver cirrhosis. Median follow-up was 36 months, survival curves revealed that the patients with increased PDW had significantly shorter survival time than those with normal PDW (p= 0.001). Cox regression analysis demonstrated that PDW was an independent prognostic factor for overall survival (hazard ratio, 2.464; 95% confidence interval [CI], 1.402-4.330, p= 0.001). CONCLUSION: PDW is significantly associated with OS in HCC. This result suggests activated platelet may affect clinical outcome and warrant continued investigation.

Increased ileal bile acid binding protein and galectin-9 are associated with mild cognitive impairment and Alzheimer's disease.

Enterocyte damage and subsequent microbial translocation drive neuroinflammation in the pathogenesis of Alzheimer's disease (AD). Human ileal bile acid binding protein (I-BABP) and intestinal fatty acid binding proteins (I-FABP) are the indicators of enterocyte damage. Lipopolysaccharide-binding protein (LBP) is an indirect marker of microbial translocation. The activation of peripheral innate immune cells plays a crucial role in modulating AD progression. Galectin-9 is a versatile immunomodulatory molecule. The purpose of this study was to determine I-FABP, I-BABP, LBP, and galectin-9 levels in MCI and AD and investigate the relationship between I-FABP, I-BABP, LBP and galectin-9. In this study, I-FABP, I-BABP, LBP, and galectin-9 levels were measured using ELISA assay in 115 AD patients, 115 MCI patients, and 115 non-demented control subjects. Increased I-BABP and galectin-9 were observed in MCI and AD patients. Furthermore, AD patients had higher I-BABP and galectin-9 levels compared with MCI patients. However, I-FABP and LBP in three groups had no difference. I-BABP levels were positively correlated with galectin-9, after adjusting confounding factors (r = 0.409, p < 0.001). In addition, multivariate analysis revealed that increased I-BABP and galectin-9 levels were significantly associated with reduced mini-mental state examination (MMSE) score. In conclusion, galectin-9 is correlated with I-BABP after adjusting confounding covariates. Moreover, increased I-BABP and galectin-9 in MCI and AD are significant factors for reduced MMSE score. Further studies are needed.