Smads-RUNX2复合体在RUNX2介导的乳腺癌骨转移进程中的核心调控作用研究

Runt-related transcription factor 2 (RUNX2) plays a central role in bone metastasis of breast cancer. Smad proteins, key signaling molecules in TGF-β and BMPs signaling pathways, are recruited to RUNX2 regulatory complexes via a Smad interating domain sequence (SMID) which overlapped with the nuclear matrix targeting signal (NMTS) in RUNX2. Smads-RUNX2 complexes can regulate the location and transcription regulation activity of RUNX2. Both of the reports and our previous works indicate that Smad2/3-RUNX2 complex might promote bone metastasis drived by TGF-β signaling pathway in breast cancer; however, Smad1/5/8 might play an opposite role which can inhibit bone metastasis by binding to RUNX2 competitively with Samd2/3. In this study, we attempt to make clear the different roles and molecular mechanisms of Smad2/3-RUNX2 and Smad1/5/8-RUNX2 complexes of breast cancer cells in chemotaxis to the bone, growth in bone microenvironment, and osteolytic bone damage, which can elucidate the central regulatory role of Smads-RUNX2 in bone metastasis of breast cancer and explore the antagonistic effects on bone metastasis of Smad1/5/8-RUNX2 complex and Smad2/3-RUNX2 complex.

成骨特异性转录因子RUNX2是促进乳腺癌骨转移的关键转录因子。Smads可以与RUNX2蛋白核基质定位信号结构域(NMTS)上的SMID位点结合形成Smads-RUNX2复合体，调节RUNX2在染色体上的定位及转录调节活性。文献报道和本课题组前期研究结果提示Smad2/3-RUNX2可能介导TGF-β信号通路促进乳腺癌骨转移，而BMPs信号通路的关键转录因子Smad1/5/8可能与Smad2/3竞争性结合RUNX2抑制乳腺癌骨转移。本项目拟探讨Smad2/3-RUNX2和Smad1/5/8-RUNX2复合体在调控乳腺癌细胞向骨组织趋化、亲骨性生长和溶骨性骨损伤三个骨转移进程中的不同作用和机制，阐明Smads-RUNX2复合体在RUNX2介导的乳腺癌骨转移中的核心调控作用，并揭示Smad1/5/8-RUNX2复合体对Smad2/3-RUNX2复合体在骨转移进程中可能的拮抗作用及分子机制。

【背景】成骨特异性转录因子RUNX2是乳腺癌骨转移的关键转录因子。Smads可以与RUNX2蛋白上的SMID位点结合形成Smads-RUNX2复合体，调节RUNX2在染色体上的定位及转录活性。而Smads-RUNX2复合体在乳腺癌骨转移中的作用尚不清楚。.【目的】探讨Smad2/3-RUNX2和Smad1/5/8-RUNX2复合体在调控乳腺癌细胞向骨组织趋化、骨粘附和在骨微环境中克隆性增殖等骨转移进程中的不同作用和机制，阐明Smads-RUNX2复合体在RUNX2介导的乳腺癌骨转移中的核心调控作用。.【结果】临床病例研究表明，癌细胞表达的TGFB3和BMP7对RUNX2高表达乳腺癌骨转移作用相反；高表达RUNX2的细胞受TGF-βs刺激时RUNX2的SMID结构域与Smad2/3结合形成Smad2/3-RUNX2复合体，受BMPs刺激时RUNX2与Smad1/5/8结合形成Smad1/5/8-RUNX2复合体；TGF-βs诱导形成的Smad2/3-RUNX2复合体增强癌细胞向骨组织的趋化能力、减弱癌细胞与成骨细胞的粘附能力、并增强癌细胞在骨微环境中的克隆形成能力；BMPs诱导形成的Smad1/5/8-RUNX2复合体则减弱癌细胞向骨组织的趋化能力、促进癌细胞与成骨细胞粘附、并增强癌细胞在骨微环境中的克隆性增殖能力；RUNX2转录调控ITGA5的表达量，且ITGA5介导Smads-RUNX2在癌细胞的骨趋化和骨粘附作用；Smad1/5/8-RUNX2和Smad2/3-RUNX2在癌细胞向骨趋化和粘附于骨组织进程中相互拮抗，而在在骨微环境中定植和克隆性增殖进程中又相互协同促进。.【结论】乳腺癌细胞中TGF-βs诱导形成的Smad2/3-RUNX2复合体和BMPs诱导形成的Smad1/5/8-RUNX2复合体在乳腺癌骨转移过程中呈既相互拮抗，又相辅相成的作用：在原发灶，癌细胞和间质细胞分泌的TGF-βs发挥主要作用，Smad2/3-RUNX2复合体占优势地位，促进癌细胞向骨特异性趋化；癌细胞到达骨组织后，骨微环境中的BMPs发挥主要功能，Smad1/5/8-RUNX2复合体处于优势地位，促进癌细胞粘附于骨组织；粘附于骨的癌细胞在TGF-βs和BMPs的共同作用下，Smad2/3-RUNX2和Smad1/5/8-RUNX2复合体协同作用利于癌细胞定植并生长成为骨转移灶。