Biology subjects

Ku, G.

Publications and source records attributed to Ku, G..

3 recordsLinked to original sources

bioRxiv2024

CLCC1 promotes hepatic neutral lipid flux and nuclear pore complex assembly

Imbalances in lipid storage and secretion lead to the accumulation of hepatocyte lipid droplets (LDs) (i.e., hepatic steatosis). Our understanding of the mechanisms that govern the channeling of hepatocyte neutral lipids towards cytosolic LDs or secreted lipoproteins remains incomplete. Here, we performed a series of CRISPR-Cas9 screens under different metabolic states to uncover mechanisms of hepatic neutral lipid flux. Clustering of chemical-genetic interactions identified CLIC-like chloride channel 1 (CLCC1) as a critical regulator of neutral lipid storage and secretion. Loss of CLCC1 resulted in the buildup of large LDs in hepatoma cells and knockout in mice caused liver steatosis. Remarkably, the LDs are in the lumen of the ER and exhibit properties of lipoproteins, indicating a profound shift in neutral lipid flux. Finally, remote homology searches identified a domain in CLCC1 that is homologous to yeast Brl1p and Brr6p, factors that promote the fusion of the inner and outer nuclear envelopes during nuclear pore complex assembly. Loss of CLCC1 lead to extensive nuclear membrane herniations, consistent with impaired nuclear pore complex assembly. Thus, we identify CLCC1 as the human Brl1p/Brr6p homolog and propose that CLCC1-mediated membrane remodeling promotes hepatic neutral lipid flux and nuclear pore complex assembly.

cell biology↗

bioRxiv2024

An shRNA screen in primary human beta cells identifies the serotonin 1F receptor as a negative regulator of survival during transplant

Islet transplantation can cure type 1 diabetes, but peri-transplant beta cell death limits this procedure to those with low insulin requirements. Improving human beta cell survival or proliferation may make islet transplantation a possibility for more type 1 patients. To identify novel regulators of beta cell survival and proliferation, we conducted a pooled small hairpin RNA (shRNA) screen in primary human beta cells transplanted into immunocompromised mice. shRNAs targeting several cyclin dependent kinase inhibitors were enriched after transplant. Here, we focused on the Gi/o-coupled GPCR, serotonin 1F receptor (HTR1F, 5-HT1F) which our screen identified as a negative regulator of beta cell numbers after transplant. In vitro, 5-HT1F knockdown induced human beta cell proliferation but only when combined with harmine and exendin-4. In vivo, knockdown of 5-HT1F reduced beta cell death during transplant. To demonstrate the feasibility of targeting 5-HT1F in islet transplant, we identified and validated a small molecule 5-HT1F antagonist. This antagonist increased glucose stimulated insulin secretion from primary human islets and cAMP accumulation in primary human beta cells. Finally, the 5-HT1F antagonist improved glycemia in marginal mass, human islet transplants into immunocompromised mice. We identify 5-HT1F as a novel druggable target to improve human beta cell survival in the setting of islet transplantation. One Sentence SummarySerotonin 1F receptor (5-HT1F) negatively regulates insulin secretion and beta cell survival during transplant.

cell biology↗

bioRxiv2017

The transcriptionally permissive chromatin state of ES cells is acutely tuned totranslational output

A permissive chromatin environment coupled to hypertranscription is critical to drive the rapid proliferation of Embryonic Stem (ES) cells and peri-implantation embryos. We carried out a genome-wide screen to systematically dissect the regulation of the euchromatic state of ES cells. The results reveal that activity of cellular growth pathways, prominently protein synthesis, perpetuates the euchromatic state and hypertranscription of ES cells. Acute, mild inhibition of translation results in rapid depletion of euchromatic marks in ES cells and blastocysts, concurrent with delocalization of RNA polymerase II and reduction in nascent transcription. Remarkably, reduced translational output leads to rewiring of open chromatin within 3 hours, including decreased accessibility at a subset of active developmental enhancers and increased accessibility at histone genes and transposable elements. Using a proteome-scale analysis, we show that several euchromatin regulators are unstable proteins and thus continuously depend on a high translational output. We propose that this mechanistic interdependence of euchromatin, transcription and translation sets the pace of proliferation at peri-implantation and may be employed generally by stem/progenitor cells.

molecular biology↗