Full length TrkB potentiates estrogen receptor alpha mediated transcription suggesting convergence of susceptibility pathways in schizophrenia Jenny Wong a,b,c , Heng Giap Woon a,b , Cynthia Shannon Weickert a,b,d, ⁎ a Schizophrenia Research Institute, Sydney, Australia b Schizophrenia Research Laboratory, Neuroscience Research Australia, Randwick NSW 2031, Australia c School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney NSW 2052, Australia d School of Psychiatry, Faculty of Medicine, University of New South Wales, Sydney NSW 2052, Australia abstract article info Article history: Received 7 April 2010 Revised 3 August 2010 Accepted 5 August 2010 Available online 27 August 2010 Keywords: Estrogen receptor alpha TrkB BDNF Schizophrenia Estrogen In this study, we determined if estrogen receptor alpha (ERα) can interact with the full length tropomyosin receptor kinase B (TrkB-TK+), both of which are implicated in schizophrenia pathogenesis. Using neuronal (SHSY5Y) and non-neuronal (CHOK1) cell-lines, we showed that TrkB-TK+ can increase transcription at estrogen response elements (EREs) with and without exogenous estrogen treatment. In the presence of estrogen, TrkB-TK+ further potentiated the effect of estrogen stimulation on ERα-mediated transcription. This synergistic effect of TrkB-TK+ on ERα-mediated transcription was not due to direct effects of TrkB-TK+ in the nucleus, but occurred through cytoplasmic signaling of TrkB-TK+ via the MAPK/ERK pathway to phosphorylate ERα, leading to an induction in ERα-mediated transcription. When we examined the PI3K/ AKT pathway, we found that PI3K/AKT activity constitutively inhibited baseline transcription at EREs. Furthermore, we showed that signaling via PI3K/AKT inhibited TrkB-TK+-dependent transcriptional potentiation at EREs. Our findings suggest that TrkB-TK+-linked second messenger signaling pathways can reciprocally regulate ERα-mediated transcription at EREs. Considering that both ERα and TrkB-TK+ expression are reduced in schizophrenia, our findings suggest that dysfunction in TrkB-TK+ signaling may occur upstream of, or in conjunction with a dysfunction in ERα, and that transcriptional regulation by ERα may be decreased by reductions in TrkB-TK+. © 2010 Elsevier Inc. All rights reserved. Introduction Schizophrenia is a disabling mental illness of unknown cause. The symptoms of schizophrenia (including hallucinations, delusions and cognitive impairments) typically present during adolescence and both genders are afflicted, although with a slight male bias (3 males:2 females) (McGrath et al., 2008). However, women with schizophrenia display symptom exacerbation at times of low estrogen: during post- partum and menopause (Grigoriadis and Seeman, 2002; Riecher- Rossler and Seeman, 2002; Seeman, 1997) and schizophrenic symptoms can be ameliorated with estrogen treatment (Kulkarni et al., 1996, 2001, 2002, 2008; Seeman, 1986). In our previous study, we showed that estrogen signaling may be disrupted in schizophrenia (Weickert et al., 2008). Using genetic association analysis, we found that a “risk” polymorphism in intron 1 (PvuII) of the estrogen receptor alpha (ERα) gene occurred more frequently in patients with schizophrenia and was related to decreased ERα mRNA levels in the prefrontal cortex (Weickert et al., 2008). In addition, when we examined the mRNA expression of the wild-type ERα mRNA and ERα splice variants, we found decreased frequency of wild-type ERα mRNA in patients with schizophrenia relative to controls (Weickert et al., 2008). These independent lines of evidence would suggest a disruption in normal sex steroid signaling in schizophrenia, in particular, estrogen signaling. However, mounting evidence suggests that schizophrenia does not arise from a disruption of a single gene or pathway, but may result from alterations of multiple genes and pathways which interact to regulate normal brain development, function, and cognition. In support of this, we have recently shown functional convergence between two schizophrenia susceptibility pathways, estrogen/ERα and neuregulin/ErbB4 (Wong and Weickert, 2009). Considering that estrogen is an upstream regulator of several important genes and pathways vital for brain development and function, we predicted that ERα may also converge with other schizophrenia susceptibility genes/pathways. Another estrogen re- ceptor, ERβ, also plays an important role in mediating the effects of estrogen, however, information regarding the role of ERβ in schizophrenia pathogenesis is limited. Hence, we focused our current study on ERα. Molecular and Cellular Neuroscience 46 (2011) 67–78 ⁎ Corresponding author. University of New South Wales, Department of Psychiatry, Neuroscience Research Australia, Hospital Road, Randwick, Sydney, New South Wales, 2031, Australia. Fax: +61 2 9399 1005(office). E-mail address: c.weickert@neura.edu.au (C.S. Weickert). 1044-7431/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.mcn.2010.08.007 Contents lists available at ScienceDirect Molecular and Cellular Neuroscience journal homepage: www.elsevier.com/locate/ymcne