Abstract C82: The role of the neuregulin family in the nucleus

Abstract

Abstract The neuregulin family consists of four members, NRG1- 4 each of which plays an important role in several normal physiological processes including tumorigenesis. We have focused on the 3 isoform of NRG1 which was found to localise to two subnuclear compartments: nucleoli and spliceosomes. We hypothesised that such localisation may have specific functions in modifying cell behaviour. Methods: To examine whether nuclear accumulation of NRG1 occurs in other physiological conditions besides in ductal carcinomas of the breast, we immunohistochemically stained a range of normal and cancer tissues with antibodies to NRG1α or NRG1β. Second, Based on the previous observation that NRG1 3 localisation could change from the nucleolar pattern to the speckle pattern or vice versa, we monitored the trafficking of photoactivatable green fluorescent protein (PAGFP) tagged NRG1β3 in live cells using confocal fluorescence microscopy. We also explored the expression patterns of ErbB3 when co-expressed with NRG1β3 by immunofluorescence microscopy. To test the hypothesis whether nuclear targeting of NRG1β3 could be involved in stimulating cell mitogenesis we performed a Bromodeoxyuridine (BrdU) assay on cells transfected with NRG1β3 constructs. Results: Nuclear expression of NRG1α and NRG1β was found in normal skin, adrenal and thyroid tissues and in various cancers. In general, NRG1α has a higher frequency of nuclear expression than NRG1β. By monitoring the PAGFP tagged NRG1β3 in live cells we observed that NRG1β3 moved from nucleoli to spliceosomes. As a cognate receptor of NRG1, ErbB3 was not colocalised with NRG1β3 in the nucleus. With respect to possible functions of intranuclear NRG1, the BrdU assay results showed that wildtype NRG1β3 and the mutant which lost the ability to target to nucleoli had no obvious effect on DNA synthesis. Conclusion: Detection of nuclear expression of NRG1 in a range of normal and cancer tissues using immunohistochemical staining provides a physiological basis for further studies at the molecular level. The receptor-independent nuclear localisation of NRG1β3 suggests it may be participating in a novel-signalling pathway. Moreover, its association with nucleoli and spliceosomes, two nuclear compartments involved in ribosome synthesis and RNA splicing supports the hypothesis that nuclear NRG may have highly specific functions in defined nuclear compartments. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C82.