[Truncated abstract] It is becoming increasingly obvious that cell signalling pathways are more complicated than we originally perceived. Research is revealing that, not only is there a multitude of new proteins involved in signalling cascades, but also that previously identified proteins may have additional, alternate roles in intracellular trafficking. Gonadotropin-releasing hormone (GnRH) in conjunction with its receptor (GnRHR), the primary regulator of reproduction in all species, is no exception. In the past few years it has become readily accepted that the classic linear GnRHR-Gαq/11 signalling pathway is not universal and that this receptor is involved in a far greater range of cellular activities than was previously considered. In particular, it is widely accepted that continuous administration of GnRH analogs results in an inhibition of growth of a number of reproductive-derived tumours and that this may, in part, be mediated by direct activation of GnRHs expressed on these cells. However, it is not fully understood how the GnRHR mediates these growth effects or whether such effects are unique to reproductive-derived cancer cells. Research within this thesis aimed to determine how the presence or absence of this receptor in different cell types might affect the ability of GnRH to directly mediate growth effects. We demonstrate that continuous treatment with a GnRH agonist (GnRHA) induces an anti-proliferative effect in a gonadotropederived cell line (LβT2) and also in HEK293 cells stably expressing either the rat or human GnRHR. The anti-proliferative effect was time- and dose-dependent and was specifically mediated via the GnRHR, as co-treatment of the GnRHRexpressing cell lines with a GnRH antagonist blocked the growth suppressive effect induced by GnRHA treatment. Cell cycle analysis revealed that the GnRHA treated HEK/GnRHR cell lines induced an accumulation of cells in the G2/M phase while a G0/G1 arrest was observed in LβT2 cells. Previous identification by our group of a potential interaction between the GnRHR and the transcription factor E2F4, an integral cell cycle regulatory protein, prompted further investigation as to the nature of this interaction. Bioluminescence energy transfer (BRET) was utilised to demonstrate that the GnRHR also interacts with E2F5, another member of the E2F family of cell cycle proteins that shares a high level of homology to E2F4. In addition, it was determined that the interaction between human GnRHR and E2F4, detected using BRET, was influenced by cell density.