Transient recruitment of the hnRNP K protein to inducibly transcribed gene loci

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Abstract
The heterogeneous nuclear ribonucleoprotein K protein is an RNA‐ and DNA‐binding protein implicated in the regulation of multiple processes that comprise gene expression. We used chromatin immunoprecipitation (ChIP) assays to explore K protein interactions with serum‐inducible, constitutively expressed and untranscribed gene loci in vivo. In the rat HTC‐IR hepatoma cell line, serum treatment induced transient increases in the mRNA levels of two immediate‐early genes, egr‐1 and c‐myc. ChIP analysis showed that the induction of egr‐1 and c‐myc genes was associated with a transient recruitment of K protein to multiple sites within each of these loci, including the promoter and transcribed regions. In contrast, recruitment of K protein to the constitutively transcribed β‐actin locus and to randomly chosen non‐transcribed loci was far weaker. In rat mesangial cells, c‐myc was constitutively expressed while egr‐1 remained serum responsive. In these cells, ChIP analysis showed serum‐induced recruitment to the inducible egr‐1 but not to the c‐myc locus. Pre‐treatment with the transcription inhibitor actinomycin D blocked the inducible but not the constitutive binding of K protein to these loci. Taken together, the results of this study suggest that the transient recruitment of K protein to serum‐responsive loci depends on the inducible transcription of these immediate‐early genes.