Abstract
Fascin 1 (FSCN1) is a cytoskeleton-associated protein recognized to function primarily in the regulation of cytoskeleton structure and formation of plasma membrane protrusions. Here we report a novel nuclear function for Fascin 1. Biochemical studies and genome wide localization using ChIP-seq identified phosphorylated Fascin 1 (pFascin) in complexes associated with transcription and that it co-localizes with histone H3 Lys4 trimethylation (H3K4me3) on chromatin. Gene expression profiling identified genes affected by Fascin 1 including SLC3A2, a gene encoding for a plasma membrane transporter that regulates intracellular amino acid levels. RbBP5, a subunit of the H3K4 histone methyltransferase (HMT) complex was found to interact with Fascin 1 supporting its role in H3K4me3 establishment at target genes. Moreover, we show that changes to SLC3A2 levels affect amino acid-mediated mTORC1 activation. These results reveal that Fascin 1 has a yet undiscovered nuclear function as an epigenetic modulator of genes essential for amino acid metabolism.
Highlights
A molecule reported earlier to interfere with cancer metastasis[10], was found to target Fascin in part via inhibition of its ability to bind actin[11]
A reblot of the same nitrocellulose membrane showed that our phosphorylated Fascin (pFascin) antibody was specific to pFascin as the higher molecular weight band disappeared in both C1 and C5 clones (Figure S2)
We identified pFascin to be primarily localized to the nucleus in several cell types
Summary
Two selected representative genes, DDIT3 (DNA-damage-inducible transcript 3) and SLC3A2 (a plasma membrane transporter that regulates intracellular amino acid levels), formerly shown to be implicated in mediating cancer progression[23,24], showed striking decrease in mRNA levels upon Fascin knockdown (Fig. 4C). To confirm that Fascin-mediated gene transcription is a result of a direct action of Fascin at the chromatin level, we immunoprecipitated chromatin from control and Fascin-knockdown cells using a pFascin specific antibody coupled with high-throughput sequencing (ChIP-seq) to map the regions possibly bound by pFascin. This finding confirms that the pFascin-SLC3A2 regulatory axis is functional and supports the idea that pFascin modulation of gene expression has relevance to cell metabolism
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