Biology subjects

Nicchitta, C. V.

Publications and source records attributed to Nicchitta, C. V..

5 recordsLinked to original sources

bioRxiv2025

Compartmentalization of mRNA and Translation by Desmosomes

Subcellular compartmentalization enables cells to concentrate and locally regulate functions. Here we find that translational machinery is compartmentalized to the cell cortex in epidermal cells. Furthermore, we observed broad enrichment of transcripts at the cortex, establishing a novel axis of mRNA organization in these cells. Mechanistically, we identified the desmosomal protein, desmoplakin, to be essential for cortical recruitment of both ribosomes and mRNAs, through distinct mechanisms. While mRNA localization is usually proposed to promote local translation, we found that most cortical transcripts were translationally repressed. These findings reveal spatial and transcript-dependent features of the cortical translatome. One mediator of this regulation is the RNA-induced Silencing Complex (RISC) which is also cortically enriched in a desmoplakin-dependent manner. Under homeostatic conditions, cortical RISC associates with transcripts for cell adhesion and the cytoskeleton. Upon wounding RISC is delocalized from the cortex and its associated transcripts become translationally upregulated. Together our data demonstrate a desmosome-dependent cortical compartmentalization of translation that dynamically responds to barrier perturbations, including wounding.

cell biology↗

bioRxiv2021

Selective recruitment of endoplasmic reticulum-targeted and cytosolic mRNAs into membrane-associated stress granules

Stress granules (SGs) are membraneless organelles composed of mRNAs and RNA binding proteins which undergo assembly in response to stress-induced inactivation of translation initiation. The biochemical criteria for mRNA recruitment into SGs are largely unknown. In general, SG recruitment is limited to a subpopulation of a given mRNA species and RNA-seq analyses of purified SGs revealed that signal sequence-encoding (i.e. endoplasmic reticulum (ER)-targeted) transcripts are significantly under-represented, consistent with prior reports that ER-localized mRNAs are excluded from SGs. Using translational profiling, cell fractionation, and single molecule mRNA imaging, we examined SG biogenesis during the unfolded protein response (UPR) and report that UPR-elicited SG formation is gene selective. Combined immunofluorescence-smFISH studies demonstrated that UPR-induced mRNA granules co-localized with SG protein markers and were in close physical proximity to or directly associated with the ER membrane. mRNA recruitment into ER-associated SGs required stress-induced translational inhibition, though translational inhibition was not solely predictive of mRNA accumulation in SGs. SG formation in response to UPR activation or arsenite addition was blocked by the transcriptional inhibitors actinomycin D or triptolide, suggesting a functional link between gene transcriptional state and SG biogenesis. These data demonstrate that ER-targeted mRNAs can be recruited into SGs and identify the ER as a subcellular site of SG assembly. On the basis of the transcriptional inhibitor studies, we propose that newly transcribed mRNAs undergoing nuclear export during conditions of suppressed translation initiation are key substrates for SG biogenesis.

cell biology↗

bioRxiv2021

Cooperative regulation of coupled oncoprotein translation and stability in triple-negative breast cancer by EGFR and CDK12

Evidence has long suggested that epidermal growth factor receptor (EGFR) may play a prominent role in triple-negative breast cancer (TNBC) pathogenesis, but clinical trials of EGFR inhibitors have yielded disappointing results. Using a candidate drug screen, we discovered that inhibition of CDK12 dramatically sensitizes diverse models of TNBC to EGFR blockade. Instead of functioning through CDK12s well-established roles proximal to transcription, this combination therapy drives cell death through the 4E-BP1-dependent suppression of the translation and consequent stability of driver oncoproteins, including MYC. A genome-wide CRISPR/Cas9 screen identified the CCR4-NOT complex as a major determinant of sensitivity to the combination therapy whose loss renders 4E-BP1 unresponsive to drug-induced dephosphorylation, rescuing MYC translational suppression and stability. The central roles of CCR4-NOT and 4E-BP1 in response to the combination therapy were further underscored by the observation of CNOT1 loss and rescue of 4E-BP1 phosphorylation in TNBC cells that naturally evolved therapy resistance. Thus, pharmacological inhibition of CDK12 reveals a long proposed EGFR dependence in TNBC that functions through the cooperative regulation of translation-coupled oncoprotein stability.

cancer biology↗

bioRxiv2020

Quantitative proteomics links the LRRC59 interactome to mRNA translation on the ER membrane

Protein synthesis on the endoplasmic reticulum (ER) requires the dynamic coordination of resident membrane proteins and cytoplasmic translation factors. While ER membrane proteins functioning in ribosome association, mRNA anchoring, and protein translocation, have been identified, little is known regarding the higher order organization of ER-localized translation. Here we utilized proximity proteomics to identify neighboring protein networks for the ribosome interactors SEC61{beta}, RPN1, SEC62, and LRRC59. Whereas the SEC61{beta} and RPN1 BioID reporters revealed translocon-associated networks, the SEC62 and LRRC59 reporters identified divergent interactome networks of previously unexplored functions. Notably, the SEC62 interactome is enriched in redox-linked proteins and ER luminal chaperones, whereas the LRRC59 interactome is enriched in SRP pathway components, translation factors, and ER-localized RNA-binding proteins. Analysis of the LRRC59 interactome by native immunoprecipitation identified similar protein and functional enrichments. Combined, these data reveal a functional domain organization for the ER and suggest a key role for LRRC59 in the organization of mRNA translation on the ER. SummaryHannigan et al. characterize the protein interactomes of four ER ribosome-binding proteins, providing evidence that ER-bound ribosomes reside in distinct molecular environments. Their data link SEC62 to ER redox regulation and chaperone trafficking, and suggest a role for LRRC59 in SRP-coupled protein synthesis.

cell biology↗

bioRxiv2018

Meta-organization of Translation Centers Revealed by Proximity Mapping of Endoplasmic Reticulum Ribosome Interactors

The endoplasmic reticulum (ER) is a nexus for mRNA localization and translation; the molecular organization of these processes remains however largely undefined. To gain insight into mechanisms supporting a diverse ER translational landscape, we utilized BioID labeling to study the protein neighborhoods of the Sec61 translocon, specifically Sec61{beta}, an established ribosome interactor, and ER proteins (Ribophorin I, LRRC59, and Sec62) previously implicated in ribosome association. Divergent protein interactomes enriched for distinct GO functions were identified for the four reporters, within a cohort of shared interactors. Efficient BioID tagging of ribosomes was only observed for the Sec61{beta} and LRRC59 reporters. RNA-seq analyses of the Sec61{beta}- and LRRC59-labeled ribosomes revealed divergent enrichments in mRNAs and identified a transcriptome-wide role for the ER in proteome expression. These data provide evidence for a mesoscale organization of the ER and suggest that such organization provides a mechanism for the diversity of translation on the ER.

cell biology↗