Mechanism of action of STAMP - a new comodulator of glucocorticoid receptors

STAMP是一种转录辅因子，在糖皮质激素受体调节的基因诱导和抑制中增强p160共激活因子SRC-1和TIF2的活性。在早期对GR、共激活因子TIF2和STAMP三元复合体的研究中，我们发现每个蛋白质的不同区域可以选择性地改变三个参数(Amax、EC50和PAA)，以诱导完整细胞中瞬时转染的报告基因的GR(AwDisi和Simons，2012，Mol Cell Endocrinol，355,121-134)。然而，STAMP也被描述为具有多谷氨酰化活性的酪氨酸微管蛋白连接酶样家族成员(TTLL5)。此外，我们之前报道了STAMP对几种细胞类型的生长的激素非依赖性活性(他等人，2010，BMC癌症，10,128)。该项目目前的目标是确定邮票的整个动物活动。 为了达到这一目的，人们在同质遗传背景下制备了STAMP KO小鼠。含有中断的Stamp基因，导致蛋白质中间翻译提前终止的小鼠，被制备出来。纯合子靶向突变(Stamptm/tm)雌性看起来正常。雄性Stamptm/tm似乎也很正常，只是他们几乎总是不育。这种男性不育症似乎是由于精子形成的严重缺陷造成的，这些缺陷导致尾巴卷曲和头部脱落的频率很高，以及剩余完整精子的活力下降。这些异常与精子尾部轴丝的破坏有关，伴随着一个微管蛋白双重体的丢失和微管蛋白多谷氨酰化的显著降低。其他结构中的轴丝似乎没有受到影响，尽管Stamp是TTLL家族中唯一有效地通过添加多谷氨酰化所需的第一个谷氨酰基来修饰α-微管蛋白的成员。与Stamptm/tm相比，wt雄性精子发育器官没有明显变化，尽管睾丸中wt stamp基因的水平是其他任何器官的20倍。男性生育能力的这种缺陷与之前被认为对精子功能重要的24个基因中的任何一个都没有关系。因此，STAMP似乎参与了精子成熟和运动的独特途径，这可能与男性生育能力有关。 综上所述，我们使用STAMP KO小鼠来确定KO动物的表型缺陷。对GR/TIF2/STAMP三元复合体作用的详细研究表明，GR调节诱导的三个参数(EC50、PAA和Amax)不是协同调节的。相反，这三种蛋白质的不同蛋白质表面可以选择性地调节单个参数，这表明可能存在药物可以改变一个、两个或所有三个参数的活性。这些综合的发现有助于我们在分子水平上定义类固醇激素的作用，并了解它们在人类生理学中的作用。

STAMP is a transcriptional cofactor that augments the activity of the p160 coactivators SRC-1 and TIF2 in glucocorticoid receptor-regulated gene induction and repression. In earlier studies of the ternary complex of GR, the coactivator TIF2, and STAMP, we found that different regions of each protein can selectively alter none, some, or all three parameters (Amax, EC50, and PAA) for GR induction of a transiently transfected reporter gene in intact cells (Awasthi and Simons, 2012, Mol Cell Endocrinol, 355, 121-134). However, STAMP has also been described by others as a tyrosine tubulin ligase-like family member (TTLL5) with polyglutamylation activity. Furthermore, we previously reported steroid-independent activity of STAMP regarding the growth of several cell types (He et al., 2010, BMC Cancer, 10, 128). The current aim of this project is to determine the whole animal activity of STAMP. This aim has been pursued by preparing the STAMP KO mice in a homogeneous genetic background. Mice containing a disrupted Stamp gene, resulting in premature termination of translation in the middle of the protein, were prepared. Homozygous targeted mutant (Stamptm/tm) females appear normal. Stamptm/tm males also seem normal except that they are almost always sterile. This male infertility appears to result from severe defects in sperm formation that cause a high frequency of coiling of the tails and detachment of the heads along with decreased motility in the remaining intact sperm. These abnormalities are associated with disruption of sperm tail axonemes that is accompanied by the loss of one tubulin doublet in conjunction with substantial reduction in α-tubulin polyglutamylation. The axonemes in other structures appear unaffected despite the fact that Stamp is the only member of the TTLL family that efficiently modifies a-tubulin by adding the first glutamyl group needed for polyglutamylation. There is no obvious change in the organs for sperm development of wt vs. Stamptm/tm males despite the levels of wt STAMP mRNA in the testes being 20-fold higher than in any other organ examined. This defect in male fertility is unrelated to any of the 24 genes previously identified as important for sperm function. Thus, STAMP appears to participate in a unique pathway of sperm maturation and motility that may be relevant for male fertility. In summary, we have used STAMP KO mice to determine the phenotypic defects of KO animals. Detailed studies of the action of the ternary complex of GR/TIF2/STAMP have established that the three parameters of GR-regulated induction (EC50, PAA, and Amax) are not coordinately regulated. Instead, different protein surfaces of the three proteins can selectively modulate individual parameters, which indicates that pharmaceuticals may exist that can alter the activities of one, two, or all three parameters. These combined findings contribute to our long-term goal of defining the action of steroid hormones at a molecular level and of understanding their role in human physiology.