Biology subjects

Coonrod, S. A.

Publications and source records attributed to Coonrod, S. A..

3 recordsLinked to original sources

bioRxiv2022

CRISPRa screen identifies a role for c-KIT signaling in tamoxifen resistance, potentially through upregulation of ABC transporters

Resistance to endocrine therapy is a common problem in patients with estrogen receptor alpha (ER) positive breast cancer. In this study, we took a non-biased genome-wide approach to identify novel mechanisms of endocrine resistance using a clustered regularly interspaced short palindromic repeats (CRISPR) activating (CRISPRa) screen. Results from the screen identified 109 candidate resistance-associated genes, with several of these genes, such as EGFR and SRC, having been previously associated with endocrine resistance. One candidate gene that has not been previously associated with endocrine resistance is the tyrosine kinase receptor, c-KIT. We further tested for associations between c-KIT and endocrine resistance and found that c-KIT overexpressing cells proliferate more rapidly in the presence of tamoxifen compared to control cell lines. To gain deeper insight into the potential role of c-KIT signaling in tamoxifen resistance, we next performed precision nuclear run-on and sequencing (PRO-seq) analysis of c-KIT overexpressing cells to identify downstream factors that may mediate the c-KIT response. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the overexpressed genes found that the only class of factors that was significantly induced by c-KIT was the ATP-binding cassette (ABC) transporters; specifically, ABCA1, ABCA4, and ABCG1. Interestingly, overexpression of two of these ABC transporters, ABCA1 and ABCG1, significantly correlated with worse prognosis in ER+ breast cancer patients following endocrine therapy. We then tested for potential therapeutic effects of c-KIT inhibition on endocrine resistance and found that the c-KIT inhibitor Gleevec appears to synergize with tamoxifen to suppress MCF-7-S cell growth. Together, our findings support the hypothesis that c-KIT signaling promotes endocrine resistance via the induction of ABC transporter activity. Additionally, our studies suggest that inhibition of c-KIT signaling may represent a novel strategy for preventing or overcoming endocrine resistance in ER+ patients.

cancer biology↗

bioRxiv2022

GDNF-RET signaling and EGR1 form a positive feedback loop that promotes tamoxifen resistance via cyclin D1

BackgroundRearranged during transfection (RET) tyrosine kinase signaling has been previously implicated in endocrine resistant breast cancer, however the mechanism by which this signaling cascade promotes resistance is currently not well described. We recently reported that glial-cell derived neurotrophic factor (GDNF)-RET signaling appears to promote a positive feedback loop with the transcription factor early growth response 1 (EGR1). Here we investigate the mechanism behind this feedback loop and test the hypothesis that GDNF-RET signaling forms a regulatory loop with EGR1 to upregulate cyclin D1 (CCND1) transcription, leading to cell cycle progression and tamoxifen resistance. MethodsTo gain a better understanding of the GDNF-RET-EGR1 resistance mechanism, we studied the GDNF-EGR1 positive feedback loop and the role of GDNF and EGR1 in endocrine resistance by modulating their transcription levels using CRISPR-dCAS9 in tamoxifen sensitive (TamS) and tamoxifen resistant (TamR) MCF-7 cells. Additionally, we performed kinetic studies using recombinant GDNF (rGDNF) treatment of TamS cells. Statistical significance for qPCR and chromatin immunoprecipitation (ChIP)-qPCR was determined using a students t-test. ResultsGDNF-RET signaling formed a positive feedback loop with EGR1 and also downregulated estrogen receptor 1 (ESR1) transcription. Upregulation of GDNF and EGR1 promoted tamoxifen resistance in TamS cells and downregulation of GDNF promoted tamoxifen sensitivity in TamR cells. Additionally, we show that rGDNF treatment activated GDNF-RET signaling in TamS cells, leading to recruitment of p-ELK-1 to the EGR1 promoter, upregulation of EGR1 mRNA and protein, binding of EGR1 to the GDNF and CCND1 promoters, increased GDNF protein expression, and subsequent upregulation of CCND1 mRNA levels. ConclusionOutcomes from these studies support the hypotheses that GDNF-RET signaling forms a positive feedback loop with the transcription factor EGR1, and that GDNF-RET-EGR1 signaling promotes endocrine resistance via signaling to cyclin D1. Inhibition of components of this signaling pathway could lead to therapeutic insights into the treatment of endocrine resistant breast cancer.

molecular biology↗

bioRxiv2022

Disrupted development and altered hormone signaling in male Padi2/Padi4 double knockout mice

BackgroundPeptidylarginine deiminase enzymes (PADs) convert arginine residues to citrulline in a process called citrullination or deimination. Recently, two PADs, PAD2 and PAD4, have been linked to hormone signaling in vitro and the goal of this study was to test for links between PAD2/PAD4 and hormone signaling in vivo. MethodsPreliminary analysis of Padi2 and Padi4 single knockout (SKO) mice did not find any overt reproductive defects and we predicted that this was likely due to genetic compensation. To test this hypothesis, we created a Padi2/Padi4 double knockout (DKO) mouse model and tested these mice along with wild-type FVB/NJ (WT) and both strains of SKO mice for a range of reproductive defects. ResultsControlled breeding trials found that male DKO mice appeared to take longer to have their first litter than WT controls. This tendency was maintained when these mice were mated to either DKO and WT females. Additionally, unsexed 2-day old DKO pups and male DKO weanlings both weighed significantly less than their WT counterparts, took significantly longer than WT males to reach puberty, and had consistently lower serum testosterone levels. Furthermore, 90-day old adult DKO males had smaller testes than WT males with increased rates of germ cell apoptosis. ConclusionsThe Padi2/Padi4 DKO mouse model provides a new tool for investigating PAD function and outcomes from our studies provide the first in vivo evidence linking PADs with hormone signaling.

molecular biology↗