The conformation change and tumor suppressor role of Merlin are both independent of Serine 518 phosphorylation.

Merlin functions as a tumor suppressor and suppresses malignant activity of cancer cells through multiple mechanisms. However, whether Serine 518 phosphorylation regulates the conformation of Merlin as well as the open-closed conformational changes affect Merlin's tumor inhibitory activity remain controversial. In this study, we used different mutants to mimic related conformational states of Merlin and investigated its physiological functions. Our results showed that the phosphorylation at Serine 518 has no influence on Merlin's conformation, subcellular localization, or cell proliferation inhibitory activity. As a fully closed conformational state, the A585W mutant loses the ability to recruit Lats2 to the cell membrane, but it does not affect its subcellular distribution or cell proliferation inhibitory activity. As a fully open conformational state, mimicking the conformation of Merlin isoform II, the ΔEL mutant has the same physiological function as the wild type Merlin isoform I. Collectively, we provide for the first time in vivo evidence that the function of Merlin, as a tumor suppressor is independent of its conformational change.

Tetramerization of SATB1 is essential for regulating of gene expression.

Special AT-rich sequence-binding protein 1 (SATB1) functions as a 'genome organizer' in tumorigenesis. Our previous report showed that SATB1 forms a tetramer through its N-terminal ubiquitin like domain rather than the proposed PDZ domain. In the present study, we aim to illustrate whether this oligomerization is critical to its function as a global repressor of gene expression in vivo. Luciferase and GST pull-down assays demonstrated that disrupting SATB1's tetramerization not only affects the activities of promoters but also influences the recruitment of interaction partners. Furthermore, we developed stable cell lines that overexpressed either the SATB1 tetramer or STAB1 dimer (KWN-AAA) and monitored global gene expression. Gene expression profiling revealed that over 1000 genes were significantly upregulated or downregulated upon the overexpression of SATB1 or the SATB1 (KWN-AAA) mutant. These data implied that SATB1 might regulate gene expression through its different oligomerization state. In conclusion, we inferred that the oligomerization of SATB1 is pivotal to its function of different biological processes.

GZR18, a novel long-acting GLP-1 analog, demonstrated positive in vitro and in vivo pharmacokinetic and pharmacodynamic characteristics in animal models.

GZR18 is a novel analog of glucagon-like peptide-1 (GLP-1). This study evaluates the pharmacology, pharmacokinetics, and efficacy of GZR18, and its potential for the treatment of Type 2 diabetes mellitus (T2DM). In vitro pharmacology and activity of GZR18 were characterized by a binding assay of GZR18 using human serum albumin (HSA), an activation assay in human GLP-1 receptor-expressing cell lines, and its effect on glucose-stimulated insulin secretion (GSIS) in primary mice islets. Pharmacokinetic profiling was performed in Sprague Dawley rats and cynomolgus monkeys, and efficacy evaluated using GZR18 single or repeated doses in db/db mice. GZR18 showed similar binding affinity for HSA and GLP-1 receptor compared with semaglutide and liraglutide. GZR18 increased GSIS, which was confirmed by dynamic islet perifusion and fluorescence imaging using PKZnR-5 for real-time detection. In cynomolgus monkeys, the average GZR18 maximal concentration was 527 nmol L-1, the terminal half-life (T1/2) was 61.3 h, and the time to maximum concentration was 14 h. Single-dose GZR18 lowered blood glucose levels and reduced body weight over 72 h in db/db mice. GZR18 successive administration (every three days for 33 days, i.e. 11 doses) lowered nonfasting and fasting blood glucose levels (p < 0.05 versus control) and glycated hemoglobin, following the 11th dose. Food and water consumption in db/db mice was lowered following repeated doses of GZR18 (p < 0.05 versus control), without a reduction in body weight. These results demonstrate the potential of GZR18 as a long-acting GLP-1 analog for the treatment of T2DM.

Angiomotin binding-induced activation of Merlin/NF2 in the Hippo pathway.

The tumor suppressor Merlin/NF2 functions upstream of the core Hippo pathway kinases Lats1/2 and Mst1/2, as well as the nuclear E3 ubiquitin ligase CRL4(DCAF1). Numerous mutations of Merlin have been identified in Neurofibromatosis type 2 and other cancer patients. Despite more than two decades of research, the upstream regulator of Merlin in the Hippo pathway remains unknown. Here we show by high-resolution crystal structures that the Lats1/2-binding site on the Merlin FERM domain is physically blocked by Merlin's auto-inhibitory tail. Angiomotin binding releases the auto-inhibition and promotes Merlin's binding to Lats1/2. Phosphorylation of Ser518 outside the Merlin's auto-inhibitory tail does not obviously alter Merlin's conformation, but instead prevents angiomotin from binding and thus inhibits Hippo pathway kinase activation. Cancer-causing mutations clustered in the angiomotin-binding domain impair angiomotin-mediated Merlin activation. Our findings reveal that angiomotin and Merlin respectively interface cortical actin filaments and core kinases in Hippo signaling, and allow construction of a complete Hippo signaling pathway.