Role of Smads and TAK1 in BMP-induced growth arrest and apoptosis

骨形态发生蛋白（BMPs）属于转化生长因子-β超家族，部分通过控制细胞增殖和凋亡细胞死亡参与各种器官的功能和形态发生调节。然而，BMP-2触发生长抑制和凋亡的机制仍有待阐明。我们以前发现，BMP-2诱导细胞周期停滞在G1期和HS-72小鼠杂交瘤细胞的凋亡细胞死亡。在这项研究中，我们发现BMP-2没有改变细胞周期蛋白D、细胞周期蛋白E、细胞周期蛋白依赖性激酶2（CDK 2）、CDK 4、p27^<KIP1>、p16^<INK4a>、p15^<INK4b>的表达，但增强了p21^&lt;CIP 1/WAF 1&gt;的表达。p21^&lt;CIP 1/WAF 1&gt;的积累导致p21^&lt;CIP 1/WAF 1&gt;与CDK 4的结合增加，并伴随引起CDK 4的体外视网膜母细胞瘤蛋白（Rb）激酶活性的显著降低。此外，人乳头瘤病毒16型E7（p21^&lt;CIP 1/WAF 1&gt;和Rb，rev的抑制剂）的异位表达， ...更多信息 BMP-2诱导的G1期阻滞。E6/E7的表达，而不增加p53水平，阻断Rb磷酸化和G1期阻滞的抑制，但没有减弱BMP处理的HS-72细胞的细胞死亡。综上所述，这些结果表明，p21^&lt;CIP 1/WAF 1&gt;抑制Rb磷酸化是BMP-2介导的G1期阻滞的原因，BMP-2诱导凋亡可能不依赖于Rb磷酸化不足。我们还证明，BMP-2激活了小鼠HS-72细胞中的p21^&lt;CIP 1/WAF 1&gt;启动子，启动子的29个碱基对（B）区域，在小鼠和人之间保守的，对BMP-2以及Smad 1、Smad 4和BMP I型受体的组成型活性突变体的表达有反应。此外，发现含有29-B区的寡核苷酸与HS-72核提取物中的Smad 1和Smad 4相关。提示BMP-2可能通过诱导Smad 4和Smad 1与HS-72细胞29-B区的间接结合而激活p21^&lt;CIP 1/WAF 1&gt;的转录。少

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor-β superfamily and participate in functional and morphogenetic regulation of various organs by, in part, controlling cell proliferation and apoptotic cell death . However, the mechanisms by which BMPs trigger growth inhibition and apoptosis remain to be elucidated.We have previously found that BMP-2 induces cell-cycle arrest in the G1 phase and apoptotic cell death of HS-72 mouse hybridoma cells. In this study, we showed that BMP-2 did not alter expression of cyclin D, cyclin E, cyclin-dependent kinase 2 (CDK2), CDK4, p27^<KIP1>, p16^<INK4a>, p15^<INK4b>, but enhanced expression of p21^<CIP1/WAF1>. Accumulation of p21^<CIP1/WAF1> resulted in increased binding of p21^<CIP1/WAF1> to CDK4 and concomitantly caused a profound decrease in the in vitro retinoblastoma protein (Rb) kinase activity of CDK4. Furthermore, the ectopic expression of human papilloma virus type-16 E7, an inhibitor of p21^<CIP1/WAF1> and Rb, rev … More erted G1-arrest induced by BMP-2. Expression of E6/E7, without increasing the p53 level, blocked inhibition of Rb phosphorylation and G1 arrest, but did not attenuate cell death in BMP-treated HS-72 cells. Taken together, these results suggest that inhibition of Rb phosphorylation by p21^<CIP1/WAF1> is responsible for BMP-2-mediated G1 arrest and that BMP-2-induction of apoptosis might be independent of Rb hypophosphorylation.We also demonstrated that BMP-2 activated the mouse p21^<CIP1/WAF1> promoter in HS-72 cells, and that a 29-base pair (b) region of the promoter, conserved between mice and humans, was responsive to BMP-2 as well as expression of Smad1, Smad4, and constitutively active mutants of BMP type I receptors. Furthermore, an oligoncleotide containing the 29-b region was found to be associated with Smad1 and Smad4 in the HS-72 nuclear extract. These results suggested that BMP-2 might activate p21^<CIP1/WAF1> transcription by inducing an indirect binding of Smad4 and Smad1 to the 29-b region in HS-72 cells. Less