Biology subjects

Gaspar, C. J.

Publications and source records attributed to Gaspar, C. J..

3 recordsLinked to original sources

bioRxiv2023

A nonenzymatic dependency on inositol-requiring enzyme 1 controls cancer cell cycle progression and tumor growth

Endoplasmic-reticulum resident inositol-requiring enzyme 1 (IRE1) supports protein homeostasis via a cytoplasmic kinase-RNase module. Known cancer dependency on IRE1 entails its enzymatic activation of the transcription factor XBP1s and of RNA decay. We discovered that some cancer cells require IRE1 but not its enzymatic activity. IRE1 knockdown, but not enzymatic inhibition or XBP1 disruption, increased DNA damage and chromosome instability while engaging the TP53 pathway and cyclin-dependent kinase inhibitors and attenuating cell cycle progression. IRE1 depletion downregulated factors involved in chromosome replication and segregation and in chromatin remodeling. Immunoelectron microscopy indicated that endogenous IRE1 can localize to the nuclear envelope. Thus, cancer cells can require IRE1 either enzymatically or nonenzymatically, with significant implications for IRE1s biological role and therapeutic targeting.

cancer biology↗

bioRxiv2022

Xport-A functions as a chaperone by stabilizing the first 5 transmembrane domains of Rhodopsin-1

Rhodopsin-1 (Rh1), the main photo-sensitive protein of Drosophila, is a seven transmembrane domain protein, which is inserted co-translationally in the endoplasmic reticulum (ER) membrane. Maturation of Rh1 occurs in the ER, where various chaperones interact with Rh1 to aid in its folding and subsequent transport in the secretory pathway. Xport-A has been shown to be a chaperone/ transport factor for Rh1, but the exact molecular mechanism for Xport-A activity upon Rh1 is not known. Here, based on computational predictions, we propose a model where Xport-A functions as a chaperone in the biosynthesis of Rh1 by stabilizing the first 5 transmembrane domains of Rh1, but not the full length Rh1 protein.

cell biology↗

bioRxiv2021

EMC is required for biogenesis and membrane insertion of Xport-A, an essential chaperone of rhodopsin-1 and the TRP channel

Insertion of hydrophobic transmembrane domains (TMDs) into the endoplasmic reticulum (ER) lipid bilayer is an essential step during eukaryotic membrane protein biogenesis. The ER membrane complex (EMC) functions as an insertase for TMDs of low hydrophobicity and is required for the biogenesis of a subset of tail-anchored (TA) and polytopic membrane proteins, including rhodopsin-1 (Rh1) and the TRP channel. To better understand the physiological implications of membrane protein biogenesis dependent on the EMC, we performed a bioinformatic analysis to predict TA proteins present in the Drosophila proteome. From 254 predicted TA proteins, subsequent genetic screening in Drosophila larval eye discs led to the identification of 2 proteins that require EMC for their biogenesis: farinelli (fan) and Xport-A. Fan is required for sperm individualization and male fertility in Drosophila and we now show that EMC is also required for these important biological processes. Interestingly, Xport-A is essential for the biogenesis of both Rh1 and TRP, raising the possibility that disruption of Rh1 and TRP biogenesis in EMC loss of function mutations is secondary to the Xport-A defect. We show that EMC is required for Xport-A TMD membrane insertion and increasing the hydrophobicity of Xport-A TMD rendered its membrane insertion to become EMC-independent. Moreover, these EMC-independent Xport-A mutants rescued Rh1 and TRP biogenesis in EMC mutants. Our data establish that EMC can impact the biogenesis of polytopic membrane proteins indirectly, by controlling the biogenesis and membrane insertion of an essential protein co-factor.

cell biology↗