Biology subjects

Chitsazan, A.

Publications and source records attributed to Chitsazan, A..

6 recordsLinked to original sources

bioRxiv2024

The RNA-binding protein HuR impairs adipose tissue anabolism in pancreatic cancer cachexia

BackgroundCachexia is defined by chronic loss of fat and muscle, is a frequent complication of pancreatic ductal adenocarcinoma (PDAC), and negatively impacts patient outcomes. Nutritional supplementation cannot fully reverse tissue wasting, and the mechanisms underlying this phenotype are unclear. This work aims to define the relative contributions of catabolism and anabolism to adipose wasting in PDAC-bearing mice. Human antigen R (HuR) is an RNA-binding protein recently shown to suppress adipogenesis. We hypothesize that fat wasting results from a loss of adipose anabolism driven by increased HuR activity in adipocytes of PDAC-bearing mice. MethodsAdult C57BL/6J mice received orthotopic PDAC cell (KrasG12D; p53R172H/+; Pdx1-cre) (PDAC) or PBS (sham) injections. Mice exhibiting moderate cachexia (9 days after injection) were fasted for 24h, or fasted 24h and refed 24h before euthanasia. A separate cohort of PDAC mice were treated with an established HuR inhibitor (KH-3, 100 mg/kg) and subjected to the fast/refeed paradigm. We analyzed body mass, gross fat pad mass, and adipose tissue mRNA expression. We quantified lipolytic rate as the normalized quantity of glycerol released from 3T3-L1 adipocytes in vitro, and gonadal fat pads (gWAT) ex vivo. Results3T3-L1 adipocytes treated with PDAC cell conditioned media (CM) had lower expression of lipolysis and lipogenesis genes than control cells, and did not display elevated lipolysis as measured by liberated glycerol. PDAC gWAT cultured ex vivo displayed decreased lipolysis compared to sham gWAT (-54.7%). PDAC and sham mice lost equivalent fat mass after a 24h fast, however, PDAC mice could not restore inguinal fat pads (iWAT) (-40.5%) or gWAT (-31.8%) mass after refeeding. RNAseq revealed 572 differentially expressed genes in gWAT from PDAC compared to sham mice. Downregulated genes (n=126) were associated with adipogenesis (adj p=0.05), and expression of adipogenesis master regulators Pparg and Cebpa were reduced in gWAT from PDAC mice. Immunohistochemistry revealed increased HuR staining in gWAT (+74.9%) and iWAT (+41.2%) from PDAC mice. Inhibiting HuR binding restored lipogenesis in refed animals with a concomitant increase in iWAT mass (+131.7%). ConclusionsOur work highlights deficient adipose anabolism as a driver of reduced lipid content in 3T3-L1 adipocytes treated with PDAC conditioned media and PDAC mice. The small molecule KH-3, which disrupts HuR binding, restored adipose anabolism in PDAC mice. This highlights HuR as a potentially targetable regulatory node for adipose anabolism in cancer cachexia.

cancer biology↗

bioRxiv2024

Unveiling the Power of PROTAC Valency: Navigating Cell Type-Specific Hook Effects

Targeted protein degradation (TPD) using bivalent proteolysis-targeting chimeras (PROTAC) technology has shown potential in expanding the "druggable" proteome. In their publication in Nature Chemical Biology, Imaide et al.1 posited that augmenting PROTAC valency could potentially lead to the formation of long-lived ternary complexes between PROTAC, the protein of interest (POI), and E3 ligase, thereby constraining the formation of potent binary complexes, as evidenced by a pronounced hook effect. The authors introduced SIM1, a trivalent von Hippel-Lindau (VHL)-based PROTAC, which exhibited a superior degradation profile in comparison to its parent molecule MZ1, towards bromo and extra terminal (BET) proteins, with a predilection for BRD2. The authors attributed this heightened degradation capability of SIM1 over bivalent MZ1 as supportive evidence for their hypothesis. While we concur with the notion that increasing valency and avidity could enhance the efficacy of a PROTAC, the claim that trivalent PROTACs unequivocally eliminate the hook effect is not entirely accurate. We propose that the presence or absence of a hook effect is influenced by numerous factors beyond PROTAC valency.

cancer biology↗

bioRxiv2023

Multiplex imaging of localized prostate tumors reveals changes in mast cell type composition and spatial organization of AR-positive cells in the tumor microenvironment

Mapping spatial interactions of cancer, immune and stromal cells present novel opportunities for patient stratification and for advancing immunotherapy. While single-cell studies revealed significant molecular heterogeneity in prostate tumors, there is currently no understanding of how immune cell heterogeneity impacts spatial coordination between tumor and stromal cells in localized tumors. Here, we used cyclic immunofluorescent imaging on whole-tissue sections to uncover novel spatial associations between cancer and stromal cells in low- and high-grade prostate tumors and tumor-adjacent normal tissues. Our results provide a spatial map of 699,461 single-cells that show epigenetic and molecular differences in distinct clinical grades. We report unique populations of mast cells that differentially express CD44, CD90 and Granzyme B (GZMB) and demonstrate GZMB+ mast cells are spatially associated with M2 macrophages in prostate tumors. Finally, we uncover recurrent neighborhoods that are primarily driven by androgen receptor positive (AR+) stromal cells and identify transcriptional networks active in AR+ prostate stroma.

cancer biology↗

bioRxiv2021

Single-cell analysis of localized low- and high-grade prostate cancers

Approximately, 30% of early-stage localized prostate cancer cases reoccur within 5 to 10 years [1, 2]. However, identifying precise molecular subtypes attributable to specific stages of prostate cancer has proven difficult due to high heterogeneity within localized tumors [3-5]. Bulk assays represent a population average, which is a result of the heterogeneity that exists at the individual prostate cancer cell level [6]. Here, we sequenced the accessible chromatin regions of 14,424 single-cells collected from 18 fresh-frozen prostate tumors using sci-ATAC-seq [7, 8]. We observed that shared chromatin features among low-grade prostate cancer epithelial cells were lost in high-grade tumors. Despite this loss, all high-grade tumors exhibited an enrichment for FOXA1, HOXB13 and CDX2 transcription factor binding sites within their accessible chromatin regions, indicating a shared trans-regulatory program. Single-cell analysis of the differentially accessible regions in high- versus low-grade prostate tumors identified two unique genes encoding neuronal adhesion molecules, NRXN1 and NLGN1. We found that NRXN1 and NLGN1 are expressed in the epithelial luminal, basal and neuroendocrine cells, as well as the immune, endothelial and neuronal cell types in all prostate tumors. Overall, these results provide a deeper understanding of the active gene regulatory networks in low- and high-grade prostate tumors at a striking resolution and provide critical insights for molecular stratification of the disease.

cancer biology↗

bioRxiv2019

STAT pathway activation limits the Ascl1-mediated chromatin remodeling required for neural regeneration from Muller glia in adult mouse retina.

Muller glia can serve as a source for retinal regeneration in some non-mammalian vertebrates. Recently we found that this process can be induced in mouse Muller glia after injury, by combining transgenic expression of the proneural transcription factor Ascl1 and the HDAC inhibitor TSA. However, new neurons are only generated from a subset of Muller glia in this model, and identifying factors that limit Ascl1-mediated MG reprogramming could potentially make this process more efficient, and potentially useful clinically. One factor that limits neurogenesis in some non-mammalian vertebrates is the STAT pathway activation that occurs in Muller glia in response to injury. In this report, we tested whether injury induced STAT activation hampers the ability of Ascl1 to reprogram Muller glia into retinal neurons. Using a STAT inhibitor, in combination with our previously described reprogramming paradigm, we found a large increase in the ability of Muller glia to generate neurons, similar to those we described previously. Single-cell RNA-seq showed that the progenitor-like cells derived from Ascl1-expressing Muller glia have a higher level of STAT signaling than those that become neurons. Using Ascl1 ChIP-seq and DNase-seq, we found that developmentally inappropriate Ascl1 binding sites (that were unique to the overexpression context) had enrichment for the STAT binding motif. This study provides evidence that STAT pathway activation reduces the efficiency of Ascl1-mediated reprogramming in Muller glia, potentially by directing Ascl1 to inappropriate targets.

developmental biology↗

bioRxiv2018

Different genetic mechanisms mediate spontaneous versus UVR-induced malignant melanoma

Genetic variation conferring resistance and susceptibility to carcinogen-induced tumorigenesis is frequently studied in mice. We have now turned this to melanoma using the collaborative cross (CC), a resource of mouse strains designed to discover genes for complex diseases. We studied melanoma-prone transgenic progeny across seventy CC genetic backgrounds. We mapped a strong quantitative trait locus for rapid onset spontaneous melanoma onset to Prkdc, a gene involved in detection and repair of DNA damage. In contrast, rapid onset UVR-induced melanoma was linked to the ribosomal subunit gene Rrp15. Ribosome biogenesis was upregulated in skin shortly after UVR exposure, Mechanistically, variation in the \"usual suspects\" by which UVR may exacerbate melanoma, defective DNA repair, melanocyte proliferation, or inflammatory cell infiltration, did not explain melanoma susceptibility or resistance across the CC. Instead, events occurring soon after exposure, such as dysregulation of ribosome function, which alters many aspects of cellular metabolism, may be important.

cancer biology↗