| Summary: | 碩士 === 國立陽明大學 === 生命科學暨基因體科學研究所 === 98 === Neuromedin U (NMU) is a versatile neuropeptide that controls smooth muscle contraction, blood pressure, calcium transpotation, food intake, immune regulation, tumor formation and ovarian development. Two endogenous receptors, NMUR1 and NMUR2, have been found to belong to the seven-transmembrane G protein-coupled receptor family. Of interest, we recently identified a novel NMUR2 splice variant, named NMUR2S, and demonstrated its co-existence with NMUR1 and NMUR2 in diverse cancer cells. Using sequence prediction in combination with cell surface ELISA and immunocytochemistry, we characterized the NMUR2S protein has only six transmembrane domains with an extracellular C-terminal orientation. According to the theory that GPCRs mediate their signals through receptor dimerization, we therefore hypothesized that NMUR2S may play a role in modulating the NMU signaling through heterodimerizing with NMUR1 and/or NMUR2. Pull-down assays in combination with fluorescent resonance energy transfer were performed to analyze the dimerization relationship among NMUR1, NMUR2 and NMUR2S. Following the reporter gene assay and radio-ligand binding, we demonstrated NMUR2S is capable of dampening either the NMUR1 or NMUR2 signaling through receptor heterodimerization. To further demonstrate such a signal regulation is existed endogenously, a breast cancer cell T-47D, which co-expresses NMUR1, NMUR2 and NMUR2S, was used. The c-fos induction assay confirmed the restoration of the NMU signaling after depletion of NMUR2 and NMUR2S expression in T-47D cells. Future works will focus on analyzing the downstream factors and molecular mechanisms of the NMU signaling in tumorigenesis.
In addition, recent studies have shown that NMU-knockout mice have early onset of vaginal opening and that NMU is able to suppress the FSH and LH secretion of rat antierior pituitary cells. However, we found that the NMU and the two types of NMUR genes are co-expressed in the ovary in our current studies. The ovarian NMU expression is tightly regulated by gonadotropins in a rat superovulatory model and the mouse ovarian array. Therefore, we hypothesized that the local signaling of NMU may regulate the ovarian development. We currently have characterized the expression profiles of NMU and two NMURs in different ovarian compartments. Further, we also found that the NMU expression in the granulosa and theca cells was rapidly increased in a short-term activation of cAMP/PKA pathway but dramatically decreased to the basal level after a prolong activation. Future works will be focused on exploring the mechanism that controls the NMU mRNA degradation and the downstream effectors that mediate the NMU signaling in the ovarian development.
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