Bashir, S. | bioRxiv Science

bioRxiv2019

Bid as a novel interacting partner of IRE1 differentially regulating its RNAse activity

Unfolded protein response is a dynamic signalling pathway, which is involved in the maintenance of proteostasis and cellular homeostasis. IRE1, a transmembrane signalling protein represents the start point of a highly conserved UPR signalling cascade. IRE1 is endowed with kinase and endoribonuclease activities. The activation of the kinase domain of IRE1 by trans-autophosphorylation leads to the activation of its RNAse domain. RNAse domain performs atypical splicing of Xbp1 mRNA and degradation of mRNAs by an effector function known as Regulated IRE1 Dependent Decay (RIDD). The regulation of the distinctive nature of the IRE1 ribonuclease function is potentially mediated by a dynamic protein structure UPRosome that is an assembly of a huge number of proteins on IRE1. Here, we reported that Bid is a novel recruit to UPRosome, which directly interacts with the cytoplasmic domain of IRE1. Bid controls the auto-phosphorylation of IRE1 in a negative manner where Bid overexpression conditions displayed reduced phosphorylation levels of IRE1 and Bid knockdown cells showed slightly enhanced IRE1 phosphorylation. This effect was reciprocated with JNK, a downstream target of IRE1. Our Insilico analysis revealed that Bid binding to IRE1 dimer averts its structural flexibility and thereby preventing its trans-autophosphorylation activity. We found that the effect of Bid is specific to the IRE1 branch of UPR signalling and competitive in nature. The highlighting observation of the study was that Bid stimulated a differential activity of the IRE1 RNAse domain towards Xbp1 splicing and RIDD. These results together establish that Bid is a part of the UPRosome and modulates IRE1 in a way to differentially regulate its RNAse outputs.

cell biology↗

bioRxiv2019

Molecular Genetic Analysis of RB1 gene among Sudanese children with Retinoblastoma

BACKGROUNDRetinoblastoma (RB), the commonest early childhood intraocular tumor, is most often related to mutations in the RB1 gene with an incidence of 3% of all pediatric tumors. It has good prognosis if diagnosed early but it is life-threatening when diagnosed late.\n\nOBJECTIVETo study the Molecular Genetic Analysis of Retinoblastoma (RB) in Sudanese families.\n\nMETHODSThirty one (n=31) clinically and histopathologically diagnosed cases of RB attending Makkah Eye Complex (MEC) Orbit clinic (Khartoum, Sudan) were included in this Molecular Genetic RB Analysis. Fresh blood samples extracted from seven RB patients and 15 close families for DNA extraction and PCR were sent for Genetic Sequencing and In silico approach for \"Exon 18 mutations\" which is one of the highly mutated exons worldwide.\n\nRESULTSThe majority of patients (41.9%) were below five years old. Females were 58.1%, males were 41.9%. Leukocoria was the commonest sign at presentation (41.9%). RB Unilaterality were in (77.4%) while Bilaterality in 19.4%. Both eyes were equally affected 50% each. The age at diagnosis time ranged from 0.02 to five years. Consanguinity of parents was very high (85.7%), the 1st degree cousins were less (28.6%) while the 2nd degree was high (57.1%). The patients ethnic background and geographical area were from seven different tribes; all belong to the Western Sudan. The molecular genetic study showed that exon 18 was free of mutation among the seven patients + their three relatives. The Functional Analysis and (SNPs) prediction study of exon 18 from NCBI data base showed that the various computational approaches used (SIFT, PolyPhen-2, I-mutant and Project hope) identified 16 reported mutations worldwide, three of which (rs137853292, rs375645171 and rs772068738) are major nsSNPs (non-synonymous) which might contribute to native RB1 protein malfunction and ultimately causing carcinoma.\n\nCONCLUSIONRB mainly affected children under five years and both sexes are equally affected. Unilaterality was predominant. Consanguinity plays a role in inheritance and the majority of patients were from Western Sudan. The most commonly detected deleterious mutations worldwide in exon 18 were not found in the Sudanese studies samples. Further screening for the highly reported mutations in exons 8, 10 and 14 or Next Generation Sequencing (NGS) are recommended. In silico tools are useful in studying the functional analysis of SNPs.

molecular biology↗