CIZ regulates anabolic action of PTH on bone

我们分析了CIZ，BMP抑制因子，在PTH信号转导的参与。caPPR小鼠在成骨细胞和成牙本质细胞中表达组成型活性PTH/PTHrP受体（caPPR），并表现出骨体积增加。CIZKO小鼠还显示出增加的骨体积。我们将caPPR小鼠与CIZKO小鼠杂交，在我们的初步实验中，caPPR-CIZKO小鼠表现出进一步增加的骨体积。我们难以扩大caPPR-CIZKO小鼠的数量，因为caPPR小鼠很弱，并且因为CIZKO小鼠有精子发生缺陷。在细胞培养体系中，我们使用了成骨样细胞系MC-3 T3 E1细胞。为了分析cAMP应答元件（CRE）的转录活性，我们用pCre-Luc载体转染细胞并进行荧光素酶分析。当CIZ过表达时，caPPR诱导的CRE活性增加没有显示出变化。CIZ抑制BMP信号，据报道PTH增强BMP信号。因此，我们推测CIZ不直接抑制PTH诱导的骨增加，但CIZ通过抑制BMP信号传导影响PTH诱导的骨增加。

We analyzed the involvement of CIZ, a BMP-inhibitory factor, in PTH-signaling. The caPPR mice express constitutively active PTH/PTHrP receptor (caPPR) in osteoblasts and in odontoblasts, and exhibit increased bone volume. The CIZKO mice also show increased bone volume. We crossed caPPR mice with CIZKO and caPPR-CIZKO mice exhibited further increased bone volume in our preliminary experiments.We had difficulties in expanding the number of caPPR-CIZKO mice, because caPPR mice are weak and because CIZKO mice have defect in spermatogenesis as reported. However, we finally got 6-10 mice in each group of 4 genotypes x 2 sex.In cell culture system, we used MC-3T3E1 cells, a osteoblast-like cell line. In order to analyze the transcriptional activity of CRE (cAMP response element), we transfected cellswith pCre-Luc vector and performed luciferase assays. When CIZ was overexpressed, caPPR-induced increase of CRE-activity did not show changes. CIZ inhibits BMP signal and PTH are reported to enhance BMP signals. Therefore we speculate that CIZ does not directly inhibit PTH-induced bone increase but that CIZ affects PTH-induced bone increase by way of inhibiting BMP signaling.