Plant steroid hormones, brassinosteroids (BRs), are perceived by a cell surface receptor kinase, BRI1, but how BR binding leads to regulation of gene expression in the nucleus is unknown. Here we describe the identification of BZR1 as a nuclear component of the BR signal transduction pathway. A dominant mutation bzr1-1D suppresses BR-deficient and BR-insensitive (bri1) phenotypes and enhances feedback inhibition of BR biosynthesis. BZR1 protein accumulates in the nucleus of elongating cells of dark-grown hypocotyls and is stabilized by BR signaling and the bzr1-1D mutation. Our results demonstrate that BZR1 is a positive regulator of the BR signaling pathway that mediates both downstream BR responses and feedback regulation of BR biosynthesis.

Brassinosteroids (BRs) are a class of steroid hormones essential for normal growth and development in plants. BR signaling involves the cell-surface receptor BRI1, the glycogen synthase kinase-3-like kinase BIN2 as a negative regulator, and nuclear proteins BZR1 and BZR2͞BES1 as positive regulators. The interactions among these components remain unclear. Here we report that BRs induce dephosphorylation and accumulation of BZR1 protein. Experiments using a proteasome inhibitor, MG132, suggest that phosphorylation of BZR1 increases its degradation by the proteasome machinery. BIN2 directly interacts with BZR1 in yeast two-hybrid assays, phosphorylates BZR1 in vitro, and negatively regulates BZR1 protein accumulation in vivo. These results strongly suggest that BIN2 phosphorylates BZR1 and targets it for degradation and that BR signaling causes BZR1 dephosphorylation and accumulation by inhibiting BIN2 activity. B rassinosteroids (BRs) are a class of steroid hormones that play important roles in plant growth and development (1-3). Deficiency in BR biosynthesis or signaling causes dramatic growth defects that include dwarfism, reduced apical dominance and fertility, delayed flowering and senescence, and photomorphogenesis in the dark (4-6). BRs are perceived by a cell-surface receptor kinase and transduced via an undefined signal transduction pathway, leading to changes in gene expression and growth (7,8). BR signaling thus resembles the nongenomic steroid actions observed in some animal systems (9), but differs from the well-studied genomic steroid actions mediated by the nuclear receptors in animals (10).Extensive genetic screens for recessive BR-insensitive Arabidopsis mutants have identified only one gene, brassinosteroid insensitive 1 (BRI1), that is essential for BR response. BRI1 encodes a leucine-rich-repeat receptor kinase localized to the plasma membrane (11-13). Molecular biochemical studies have shown that BRI1 functions as the BR receptor. BRI1 perceives BRs through its extracellular domain and transduces the signal by phosphorylating downstream signaling proteins that have yet to be identified (7).Studies of the semidominant dwarf mutant brassinosteroid insensitive 2 (bin2) have led to the identification of a potential downstream component that negatively regulates BR response. BIN2 encodes a member of the glycogen synthase kinase-3 (GSK3)-like kinases (14, 15). The increased kinase activity by the semidominant bin2-1 mutation and the phenotypes of transgenic plants with altered BIN2 expression levels indicate that BIN2 is a negative regulator for BR response and cell elongation (16). In animals, GSK3-like kinases play key roles as negative regulators in a variety of signaling pathways (17). Extracellular signals, such as insulin or growth factors, inhibit GSK3 kinases, allowing dephosphorylation of the substrates and activation of downstream responses (18,19). As a negative regulator of BR response, BIN2 might function in a manner similar to the animal GSK3 kinases. BIN2 may phosphorylate and inactiva...

Parkin is a RING-between-RING E3 ligase that functions in the covalent attachment of ubiquitin to specific substrates, and mutations in Parkin are linked to Parkinson’s disease, cancer and mycobacterial infection. The RING-between-RING family of E3 ligases are suggested to function with a canonical RING domain and a catalytic cysteine residue usually restricted to HECT E3 ligases, thus termed ‘RING/HECT hybrid’ enzymes. Here we present the 1.58 Å structure of Parkin-R0RBR, revealing the fold architecture for the four RING domains, and several unpredicted interfaces. Examination of the Parkin active site suggests a catalytic network consisting of C431 and H433. In cells, mutation of C431 eliminates Parkin-catalysed degradation of mitochondria, and capture of an ubiquitin oxyester confirms C431 as Parkin’s cellular active site. Our data confirm that Parkin is a RING/HECT hybrid, and provide the first crystal structure of an RING-between-RING E3 ligase at atomic resolution, providing insight into this disease-related protein.

Background COVID-19 is a viral respiratory disease caused by the severe acute respiratory syndrome-Coronavirus type 2 (SARS-CoV-2). Patients with this disease may be more prone to venous or arterial thrombosis because of the activation of many factors involved in it, including inflammation, platelet activation and endothelial dysfunction. Interferon gamma inducible protein-10 (IP-10), monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein 1-alpha (MIP1α) are cytokines related to thrombosis. Therefore, this study focused on these three indicators in COVID-19, with the hope to find biomarkers that are associated with patients’ outcome. Methods This is a retrospective single-center study involving 74 severe and critically ill COVID-19 patients recruited from the ICU department of the Tongji Hospital in Wuhan, China. The patients were divided into two groups: severe patients and critically ill patients. The serum IP-10, MCP-1 and MIP1α level in both groups was detected using the enzyme-linked immunosorbent assay (ELISA) kit. The clinical symptoms, laboratory test results, and the outcome of COVID-19 patients were retrospectively analyzed. Results The serum IP-10 and MCP-1 level in critically ill patients was significantly higher than that in severe patients (P < 0.001). However, no statistical difference in MIP1α between the two groups was found. The analysis of dynamic changes showed that these indicators remarkably increased in patients with poor prognosis. Since the selected patients were severe or critically ill, no significant difference was observed between survival and death. Conclusions IP-10 and MCP-1 are biomarkers associated with the severity of COVID-19 disease and can be related to the risk of death in COVID-19 patients.