Localisation of Neuregulin 1-β3 to different sub-nuclear structures alters gene expression

Abstract

Neuregulins are growth factors that signal via the ErbB3 and ErbB4 receptors. Here we show using immunohistochemistry that they are often expressed in the nucleus of a range of tumour types including soft tissue and breast. The Neuregulin 1 type I-β3 (NRG1-β3) isoform localises to two sub-nuclear compartments in animal cells, nucleoli and spliceosomes. We used NRG1-β3 tagged with photoactivatable GFP and demonstrated that this re-localised from nucleoli to spliceosomes over 90 min. Tyrosine kinase activity was not required for retaining the NRG1-β3 within the nucleus. Mutation of the lysines 14 and 16 or 15 and 16 together prevented nucleolar uptake while four positively charged residues were identified which were required for spliceosome uptake. Molecular modelling suggests that three of these may form a binding site. We showed using a kinome array that NRG1-β3 and a mutant exclusively localising to spliceosomes increased phosphorylation and/or expression of the HER4 and HER2 receptors. Using a transcriptomic analysis the same two constructs induced expression of several messenger RNAs and we confirmed the increased expression at the protein level of the most highly induced, Heat Shock Protein 70B′. These results suggest that Neuregulin activates receptor signalling in spliceosomes leading to altered gene expression.