Estrogen-dependent Transcription of the NEL-like 2 (NELL2) Gene and Its Role in Protection from Cell Death

Abstract

NELL2 (neural tissue-specific epidermal growth factor-like repeat domain-containing protein) is a secreted glycoprotein that is predominantly expressed in neural tissues. We reported previously that NELL2 mRNA abundance in brain is increased by estrogen (E2) treatment and that NELL2 is involved in the E2-dependent organization of a sexually dimorphic nucleus in the preoptic area. In this study we cloned the mouse NELL2 promoter and found it to contain two half-E2 response elements. Electrophoretic mobility shift assays and promoter assays showed that E2 and its receptors (ER␣ and ER␤) stimulated NELL2 transcription by binding to the two half-E2 response elements. Hippocampal neuroprogenitor HiB5 cells expressing recombinant NELL2 showed increased cell survival under cell death-inducing conditions. Blockade of endogenous synthesis of NELL2 in HiB5 cells abolished the cell survival effect of E2 and resulted in a decrease in phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2). These data suggest that the NELL2 gene is trans-activated by E2 and contributes to mediating the survival promoting effects of E2 via intracellular signaling pathway of ERK.A gene encoding neural epidermal growth factor (EGF) 4 -like protein (NEL) was first identified in the chick embryo (1). A subsequent study reported two mammalian homologs of the chick NEL gene, NEL-like 1 (NELL1) and NEL-like 2 (NELL2), isolated from a human fetal brain cDNA library (2). NELL2 has a greater sequence similarity to chicken NEL than NELL1 and is strongly expressed in mammalian brain in an apparent neuronspecific manner (3-5). NELL2 is a secreted, N-glycosylated protein (3). A large fraction of NELL2 is secreted into culture medium from transfected COS7 and HiB5 cells (3, 6) and from in ovo-transfected chicken spinal cord cells (7). The released NELL2 promotes proliferation and differentiation of neural cells (7) and increases survival of in vitro cultured primary cortical and hippocampal neurons (8).NELL2 is also involved in promoting the neuronal survival required for the formation of a sexually dimorphic nucleus of the preoptic area (SDN-POA) in male rats (6). The volume of the SDN-POA in male rats is much larger than females (for review, see Ref. 9). This has been known to result from the actions of estrogen (E2) on cells of the male SDN-POA (9). E2 exerts multiple effects on developmental processes taking place in the mammalian central nervous system, such as neurogenesis, survival, and differentiation of different neuronal populations (for review, see Ref. 10). A prominent function of E2 in the nervous system is to protect neurons from cell death (for review, see Ref. 11). E2 produced locally by aromatization of circulating testosterone promotes survival of the SDN-POA in neonatal male rats, whereas this effect is not observed in females because fetoneonatal E2 binding protein blocks E2 action in the female brain (12-14). Because blockade of NELL2 synthesis in the neonatal male rat brain resulted in a decreased size of SDN-POA (6),...

Regulation of the Female Rat Estrous Cycle by a Neural Cell-Specific Epidermal Growth Factor-like Repeat Domain Containing Protein, NELL2

“…Western blot analysis revealed that NELL2 expression was significantly increased by E2 in the POA of OVX female rats (Figs. 2A and 2B), which concurs with our previous finding of positive E2 action on NELL2 expression (Choi et al, 2010). Real-time PCR analysis also revealed that E2 increased KiSS1 mRNA levels in the POA (Fig.…”

“…This finding is consistent with the results of our previous studies showing that E2 activates NELL2 transcription (Choi et al, 2010) and that NELL2 is expressed in the ERα expressing hypothalamic cells (Choi et al, 2010;Jeong et al, 2008a).…”

“…The results of our previous reports suggested that NELL2 is important in the regulation of E2-dependent differentiation of the hypothalamus (Choi et al, 2001), and plays an important role in regulation of GnRH release by acting on glutamatergic neurons (Ha et al, 2008). Moreover, it is involved in the development of the sexually dimorphic nucleus of the male rat POA (Jeong et al, 2008a) by mediating the survival-promoting effect of E2 on neuronal cells (Choi et al, 2010). This suggests that NELL2 is involved in maintaining the normalcy of male sexual behavior.…”

“…Therefore, the feedback action of E2 on GnRH-releasing neurons may be conveyed by ERα-expressing neurons (Dorling et al, 2003). Our studies revealed that one such candidate neuron is the NELL2 expressing neuron (Choi et al, 2010;Ha et al, 2008).…”

“…Promoter assays using the 5′ flanking region of the NELL2 gene further revealed that E2 and its receptors (ERα and ERβ) directly regulate transcription of the NELL2 gene (Choi et al, 2010). We also identified that NELL2 is specifically expressed in hypothalamic cells expressing ERα and is involved in E2-dependent hypothalamic sexual differentiation (Jeong et al, 2008a) and reproductive maturation (Ha et al, 2008), while GnRH neurons do not express ERα, a major feedback regulator for the GnRH neural apparatus (Herbison and Theodosis, 1992).…”