Biology subjects

Haimovich, G.

Publications and source records attributed to Haimovich, G..

6 recordsLinked to original sources

bioRxiv2026

A massively parallel reporter screen defines the syntax of SECReTE, a secretion-enhancing cis regulatory targeting element, in mammalian cells

Messenger RNA (mRNA) localization to specific subcellular regions is crucial for proper protein translation and localization. Potential means to localize mRNAs include cis-acting or structural motifs embedded within the sequence. We previously identified a secretion-enhancing cis regulatory targeting element (SECReTE) enriched in mRNAs encoding secreted proteins from prokaryotes, eukaryotes, and viruses, found to enhance both protein synthesis and secretion by localizing mRNAs to the endoplasmic reticulum (ER) membrane. Defined as at least 10 consecutive NNY triplets (where N is any nucleotide and Y is a pyrimidine), this highly degenerate motif can be specified by approximately ~10^15 different sequence combinations. Yet, some combinations may prove more efficient than others in regulating mRNA localization and protein secretion. To better understand SECReTE syntax and to identify robust combinations, we designed and synthesized a library of ~5 x 10^4 variants and inserted them into the 3' untranslated region (3'UTR) of two reporter genes, green fluorescent protein (GFP) and immunoglobulin light chain. We expressed each variant in Chinese hamster ovary cells and assayed their activity using parallel assays to measure the effect of each variant upon mRNA partitioning between the ER and cytoplasm, and protein secretion. Our results reveal that ER-associated mRNAs are enriched with SECReTE elements of a defined syntax. Notably, RRY repeats (where R is purine) were superior to NNY repeats. Variants conferring a high mRNA ER localization score consistently enhanced protein secretion, confirming the mechanistic relationship between mRNA targeting to the ER and secretion efficiency. The correlation between variant performances across both reporters suggests a shared regulatory mechanism. Additional analysis identified a novel secretion-promoting cis element, called "split NNS" (where S is G or C). This work refines the syntactic definition of mRNA localization motifs that regulate protein secretion in both natural and heterologous expression systems.

cell biology↗

bioRxiv2024

Complementation of a human disease phenotype in vitro by intercellular mRNA transfer

There is growing evidence that full-length mRNAs undergo intercellular transfer through long, thin cytoplasmic connections called tunneling nanotubes (TNTs), but whether transferred mRNAs are translated and effect cellular changes post-transfer is unknown. Using multiple lines of evidence, we show that transferred mRNAs undergo translation and can fully complement the phenotype of genetic mutations in vitro. For example, the human peroxisome biogenesis disorder, Zellweger Syndrome, results from mutations in genes like PEX5 and PEX6. We demonstrate that the co-culture of patient-derived PEX6 mutant fibroblasts or PEX5 knock-out cells with wild-type cells leads to de novo peroxisome biogenesis. Complementation occurs by TNT-mediated mRNA transfer and translation in acceptor cells and not by peroxisome transfer. We provide additional examples of genetic complementation via transfer of mRNAs encoding the HSF1 transcription factor or CRE recombinase. Our study provides evidence for the physiological significance of mRNA transfer and suggests a new approach for mRNA therapeutics. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=128 SRC="FIGDIR/small/622258v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@fe4563org.highwire.dtl.DTLVardef@17d6d3forg.highwire.dtl.DTLVardef@18f47f7org.highwire.dtl.DTLVardef@1bdae08_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2021

Global analysis of human-to-mouse intercellular RNA transfer in cell culture

Full-length mRNAs can transfer between adjacent mammalian cells via direct cell-to-cell connections called tunneling nanotubes (TNTs). However, the extent of mRNA transfer at the transcriptome-wide level (the transferome) is unknown. Here, we analyzed whole transcriptome mRNA and lncRNA transfer between heterogeneous human-mouse cell populations in in vitro co-culture using RNA-sequencing. Our data indicate that mRNA transfer is non-selective, prevalent across the human transcriptome, and that the amount of transfer to mouse embryonic fibroblasts (MEFs) strongly correlates with the endogenous level of gene expression in donor human breast cancer cells (MCF7). These results were validated by both quantitative RT-PCR and in situ hybridization, and analysis shows that typically <1% of endogenous mRNAs and lncRNAs undergo transfer. Non-selective expression-dependent RNA transfer was further validated using synthetic RNA reporters. Notably, significant differential changes in the native MEF transcriptome were observed in response to co-culture, including the upregulation of multiple cancer and cancer-associated fibroblast-related genes and pathways. Together, these results lead us to suggest that TNT-mediated RNA transfer could be a phenomenon of physiological importance under both normal and pathogenic conditions. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=183 SRC="FIGDIR/small/470233v2_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@13a7176org.highwire.dtl.DTLVardef@1ef1c75org.highwire.dtl.DTLVardef@1355eeforg.highwire.dtl.DTLVardef@ebc275_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2021

RNA-controlled nucleocytoplasmic shuttling of mRNA decay factors regulates mRNA synthesis and initiates a novel mRNA decay pathway

mRNA level is controlled by factors that mediate both mRNA synthesis and decay, including the exonuclease Xrn1 - a major mRNA synthesis and decay factor. Here we show that nucleocytoplasmic shuttling of Xrn1 and of some of its associated mRNA decay factors plays a key role in determining both mRNA synthesis and decay. Shuttling is regulated by RNA-controlled binding of the karyopherin Kap120 to two nuclear localization sequences (NLSs) in Xrn1. The decaying RNA binds and masks NLS1, establishing a link between mRNA decay and Xrn1 shuttling. Mutations in the two NLSs, which prevent Xrn1 import, compromise transcription and, unexpectedly, also the cytoplasmic decay of [~]50% of the cellular mRNAs - comparably to Xrn1 deletion. These findings uncover a cytoplasmic mRNA decay pathway that begins in the nucleus. Interestingly, Xrn1 shuttling is required for proper adaptation to environmental changes, in particular to ever changing environmental fluctuations.

molecular biology↗

bioRxiv2020

Identification and enrichment of SECReTE cis-acting RNA elements in the Coronaviridae and other (+) single-strand RNA viruses

cis-acting RNA motifs play a major role in regulating many aspects of RNA biology including posttranscriptional processing, nuclear export, RNA localization, translation and degradation. Here we analyzed the genomes of SARS-CoV-2 and other single-strand RNA (ssRNA) viruses for the presence of a unique cis RNA element called SECReTE. This motif consists of 10 or more consecutive triplet nucleotide repeats where a pyrimidine nucleotide (C or U) in present every third base, and which we identified in mRNAs encoding secreted proteins in bacteria, yeast, and humans. This motif facilitates mRNA localization to the endoplasmic reticulum (ER), along with the enhanced translation and secretion of translated protein. We now examined for SECReTE presence in Group IV and V RNA viruses, the former including the Coronaviridae, like SARS-CoV-2 and other positive (+)ssRNA viruses, and the latter consisting of negative (-) ssRNA viruses. Interestingly, the SARS-CoV-2 genome contains 40 SECReTE motifs at an abundance of ~1.3 SECReTEs/kilobase (kb). Moreover, all ssRNA viruses we examined contain multiple copies of this motif and appears in (+)ssRNA viruses as non-random in occurrence and independent of genome length. Importantly, (+)ssRNA viruses (e.g. Coronaviruses and Hepaciviruses), which utilize ER membranes to create double membrane vesicles to serve as viral replication centers (VRCs), contain more SECReTE motifs per kb as compared to (-)ssRNA viruses (e.g. Rabies, Mumps, and Influenza), that replicate in the nucleus or the cytoplasm, or other (+)ssRNA viruses (e.g. Enteroviruses and Flaviviruses) which employ different organellar membranes. As predicted by our earlier work, SECReTE sequences are mostly found in membranal or ER-associated/secreted proteins. Thus, we propose that SECReTE motifs could be important for the efficient translation and secretion of secreted viral proteins, as well as for VRC formation. Future studies of SECReTE function and identification of SECReTE-binding proteins could provide new drug targets to treat COVID-19 and other (+)ssRNA related diseases.

bioinformatics↗

bioRxiv2017

Intercellular mRNA Trafficking Via Membrane Nanotubes In Mammalian Cells

RNAs have been shown to undergo transfer between mammalian cells, though the mechanism behind this phenomenon and its overall importance to cell physiology is not well understood. Numerous publications have suggested that RNAs (microRNAs and incomplete mRNAs) undergo transfer via extracellular vesicles (e.g. exosomes). However, in contrast to a diffusion-based transfer mechanism, we find that full-length mRNAs undergo direct cell-cell transfer via cytoplasmic extensions, called membrane nanotubes (mNTs), which connect donor and acceptor cells. By employing a simple co-culture experimental model and using single-molecule imaging, we provide quantitative data showing that mRNAs are transferred between cells in contact. Examples of mRNAs that undergo transfer include those encoding GFP, mouse {beta}-actin, and human Cyclin D1, BRCA1, MT2A, and HER2. We show that intercellular mRNA transfer occurs in all co-culture models tested (e.g. between primary cells, immortalized cells, and in co-cultures of immortalized human and murine cells). Rapid mRNA transfer is dependent upon actin, but independent of de novo protein synthesis, and is modulated by stress conditions and gene expression levels. Hence, this work supports the hypothesis that full-length mRNAs undergo transfer between cells through a refined structural connection. Importantly, unlike the transfer of miRNA or RNA fragments, this process of communication transfers genetic information that could potentially alter the acceptor cell proteome. This phenomenon may prove important for the proper development and functioning of tissues, as well as host-parasite or symbiotic interactions.\n\nSignificanceMessenger RNA (mRNA) molecules convey genetic information within cells, beginning from genes in the nucleus to ribosomes in the cell body, where they are translated into proteins. Here, we show a novel mode of transferring genetic information from one cell to another. Contrary to previous publications suggesting that mRNAs transfer via extracellular vesicles, we provide visual and quantitative data showing that mRNAs transfer via membrane nanotubes and direct cell-to-cell contact. We predict that this process has a major role in regulating local cellular environments with respect to tissue development and maintenance, cellular responses to stress, interactions with parasites, tissue transplants, and the tumor microenvironment.\n\nAuthor contributionsG.H., A.R. and R.H.S. conceived the research and designed the experiments; C.M.E. performed and analyzed the experiments with WM983b+/-GFP, including transwell and exosomes; M.C.D. and E.E. performed and analyzed the WM983b/NIH393 co-culture experiments; G.H. performed and analyzed all other experiments; and G.H., J.E.G, A.R. and R.H.S. wrote the paper.

cell biology↗