Li Jiarong, Sun Huayan, Feltri M Laura, Mercurio Arthur M
Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605, United States.
Hunter James Kelly Research Institute, Departments of Biochemistry and Neurology, School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, United States.
Dev Biol. 2015 Nov 15;407(2):313-20. doi: 10.1016/j.ydbio.2015.09.015. Epub 2015 Sep 30.
The integrin α6β4 (referred to as β4) is expressed in epithelial cells where it functions as a laminin receptor. Although in vitro studies have implicated β4 in the biology of mammary epithelial cells, its contribution to mammary gland development has not been settled. To address this problem, we generated and analyzed itgb4(flox/flox)MMTV-Cre(-) and itgb4(flox/flox)MMTV-Cre(+) mice. The salient features of embryonic mammary tissue from itgb4(flox/flox)MMTV-Cre(+) mice were significantly smaller mammary buds and increased apoptosis in the surrounding mesenchyme. Also, compared to control glands, the itgb4-deleted mammary buds lacked expression of the progenitor cell marker CK14 and they were unable to generate mammary glands upon transplantation into cleared fat pads of recipient mice. Analysis of mammary glands at puberty and during pregnancy revealed that itgb4-diminished mammary tissue was unable to elongate and undergo branching morphogenesis. Micro-dissection of epithelial cells in the mammary bud and of the surrounding mesenchyme revealed that loss of β4 resulted in a significant decrease in the expression of parathyroid hormone related protein (PTHrP) in epithelial cells and of target genes of the PTHrP receptor in mesenchymal cells. Given that the phenotype of the itgb4-deleted mammary tissue mimicked that of the PTHrP knockout, we hypothesized that β4 contributes to mammary gland development by sustaining PTHrP expression and enabling PTHrP signaling. Indeed, the inability of itgb4-deleted mammary buds to elongate was rescued by exogenous PTHrP. These data implicate a critical role for the β4 integrin in mammary gland development and provide a mechanism for this role.
整合素α6β4（简称为β4）在上皮细胞中表达，在其中作为层粘连蛋白受体发挥作用。尽管体外研究表明β4参与乳腺上皮细胞的生物学过程，但其对乳腺发育的贡献尚未明确。为了解决这个问题，我们构建并分析了itgb4(flox/flox)MMTV-Cre(-)和itgb4(flox/flox)MMTV-Cre(+)小鼠。itgb4(flox/flox)MMTV-Cre(+)小鼠胚胎乳腺组织的显著特征是乳腺芽明显较小，周围间充质中的细胞凋亡增加。此外，与对照腺体相比，缺失itgb4的乳腺芽缺乏祖细胞标志物CK14的表达，并且在移植到受体小鼠的清除脂肪垫后无法形成乳腺。对青春期和孕期乳腺的分析表明，itgb4减少的乳腺组织无法伸长并进行分支形态发生。对乳腺芽中的上皮细胞和周围间充质进行显微解剖发现，β4的缺失导致上皮细胞中甲状旁腺激素相关蛋白（PTHrP）的表达以及间充质细胞中PTHrP受体靶基因的表达显著降低。鉴于缺失itgb4的乳腺组织的表型与PTHrP基因敲除小鼠的表型相似，我们推测β4通过维持PTHrP表达和实现PTHrP信号传导来促进乳腺发育。事实上，外源性PTHrP挽救了缺失itgb4的乳腺芽无法伸长的缺陷。这些数据表明β4整合素在乳腺发育中起关键作用，并提供了其发挥作用的机制。
