The contribution and therapeutic implications of IGHMBP2 mutations on IGHMBP2 biochemical activity and ABT1 association.

Mutations within immunoglobulin mu DNA binding protein (IGHMBP2), an RNA-DNA helicase, result in SMA with respiratory distress type I (SMARD1) and Charcot Marie Tooth type 2S (CMT2S). The underlying biochemical mechanism of IGHMBP2 is unknown as well as the functional significance of IGHMBP2 mutations in disease severity. Here we report the biochemical mechanisms of IGHMBP2 disease-causing mutations D565N and H924Y, and their potential impact on therapeutic strategies. The IGHMBP2-D565N mutation has been identified in SMARD1 patients, while the IGHMBP2-H924Y mutation has been identified in CMT2S patients. For the first time, we demonstrate a correlation between the altered IGHMBP2 biochemical activity associated with the D565N and H924Y mutations and disease severity and pathology in patients and our Ighmbp2 mouse models. We show that IGHMBP2 mutations that alter the association with activator of basal transcription (ABT1) impact the ATPase and helicase activities of IGHMBP2 and the association with the 47S pre-rRNA 5' external transcribed spacer. We demonstrate that the D565N mutation impairs IGHMBP2 ATPase and helicase activities consistent with disease pathology. The H924Y mutation alters IGHMBP2 activity to a lesser extent while maintaining association with ABT1. In the context of the compound heterozygous patient, we demonstrate that the total biochemical activity associated with IGHMBP2-D565N and IGHMBP2-H924Y proteins is improved over IGHMBP2-D565N alone. Importantly, we demonstrate that the efficacy of therapeutic applications may vary based on the underlying IGHMBP2 mutations and the relative biochemical activity of the mutant IGHMBP2 protein.

Identification of Potential Insulinotropic Cytotoxins from Indian Cobra Snake Venom Using High-Resolution Mass Spectrometry and Analyzing Their Possible Interactions with Potassium Channel Receptors by In Silico Studies.

Snake venoms are a potential source of bioactive peptides, which have multiple therapeutic properties in treating diseases such as diabetes, cancer, and neurological disorders. Among bioactive peptides, cytotoxins (CTXs) and neurotoxins are low molecular weight proteins belonging to the three-finger-fold toxins (3FTxs) family composed of two ß sheets that are stabilized by four to five conserved disulfide bonds containing 58-72 amino acid residues. These are highly abundant in snake venom and are predicted to have insulinotropic activities. In this study, the CTXs were purified from Indian cobra snake venom using preparative HPLC and characterized using high-resolution mass spectrometry (HRMS) TOF-MS/MS. Further SDS-PAGE analysis confirmed the presence of low molecular weight cytotoxic proteins. The CTXs in fractions A and B exhibited dose-dependent insulinotropic activity from 0.001 to 10 µM using rat pancreatic beta-cell lines (RIN-5F) in the ELISA. Nateglinide and repaglinide are synthetic small-molecule drugs that control sugar levels in the blood in type 2 diabetes, which were used as a positive control in ELISA. Concluded that purified CTXs have insulinotropic activity, and there is a scope to use these proteins as small molecules to stimulate insulinotropic activities. At this stage, the focus is on the efficiency of the cytotoxins to induce insulin. Additional work is ongoing on animal models to see the extent of the beneficial effects and efficiency to cure diabetes using streptozotocin-induced models.

ABT1 modifies SMARD1 pathology via interactions with IGHMBP2 and stimulation of ATPase and helicase activity.

SMA with respiratory distress type 1 (SMARD1) and Charcot-Marie-Tooth type 2S (CMT2S) are results of mutations in immunoglobulin mu DNA binding protein 2 (IGHMBP2). IGHMBP2 is a UPF1-like helicase with proposed roles in several cellular processes, including translation. This study examines activator of basal transcription 1 (ABT1), a modifier of SMARD1-nmd disease pathology. Microscale thermophoresis and dynamic light scattering demonstrate that IGHMBP2 and ABT1 proteins directly interact with high affinity. The association of ABT1 with IGHMBP2 significantly increases the ATPase and helicase activity as well as the processivity of IGHMBP2. The IGHMBP2/ABT1 complex interacts with the 47S pre-rRNA 5' external transcribed spacer and U3 small nucleolar RNA (snoRNA), suggesting that the IGHMBP2/ABT1 complex is important for pre-rRNA processing. Intracerebroventricular injection of scAAV9-Abt1 decreases FVB-Ighmbp2nmd/nmd disease pathology, significantly increases lifespan, and substantially decreases neuromuscular junction denervation. To our knowledge, ABT1 is the first disease-modifying gene identified for SMARD1. We provide a mechanism proposing that ABT1 decreases disease pathology in FVB-Ighmbp2nmd/nmd mutants by optimizing IGHMBP2 biochemical activity (ATPase and helicase activity). Our studies provide insight into SMARD1 pathogenesis, suggesting that ABT1 modifies IGHMBP2 activity as a means to regulate pre-rRNA processing.

Syd/JIP3 controls tissue size by regulating Diap1 protein turnover downstream of Yorkie/YAP.

How organisms control organ size is not fully understood. We found that Syd/JIP3 is required for proper wing size in Drosophila. JIP3 mutations are associated with organ size defects in mammals. The underlying mechanisms are not well understood. We discovered that Syd/JIP3 inhibition results in a downregulation of the inhibitor of apoptosis protein 1 (Diap1) in the Drosophila wing. Correspondingly, Syd/JIP3 deficient tissues exhibit ectopic cell death and yield smaller wings. Syd/JIP3 inhibition generated similar effects in mammalian cells, indicating a conserved mechanism. We found that Yorkie/YAP stimulates Syd/JIP3 in Drosophila and mammalian cells. Notably, Syd/JIP3 is required for the full effect of Yorkie-mediated tissue growth. Thus Syd/JIP3 regulation of Diap1 functions downstream of Yorkie/YAP to control growth. This study provides mechanistic insights into the recent and perplexing link between JIP3 mutations and organ size defects in mammals, including in humans where de novo JIP3 variants are associated with microcephaly.