The role of the neuregulins in the nucleus

The neuregulins (NRGs) are ligands for receptor tyrosine kinases of the ErbB family. The NRG gene family consists of four members, NRG 1- 4 encoding different isoforms due to alternative splicing. NRG signalling has been implicated in normal development and in the pathology of many diseases. Using immunohistochemical staining of tissue arrays, we detected that NRG 1 a and 1 ~ localised to the cell nuclei of a range of normal and human cancer tissues. The ~3 isoform of NRG 1 localised to two subnuclear compartments: nucleoli and spliceosomes. We tagged NRG 1 ~3 with photoactivateable GFP and demonstrated that the fusion protein re-Iocalised from nucleoli to spliceosomes over a ninety minute period. Using wild type NRG 1 ~3 and its two mutants which localised exclusively to spliceosomes or to nuc1eoH, we explored the possible functions

of intranuclear NRG 1 ~3 in each of these compartments separately. We showed using an array capable of detecting 42 receptor tyrosine kinases that wild type NRG 1 and a mutant exclusively local ising to spliceosomes increased phosphorylation and/or expression of the ErbB4 and ErbB2 receptors. Using a transcriptomic analysis the same two constructs induced expression of messenger RNA of Heat Shock Protein 70B' and

we confirmed its increased expression at the protein level using western blot analysis.

This data supports the hypothesis that intranuclear NRGs could activate receptor signalling and alter gene expression when localised in spliceosomes.