Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 977R225A, Berkeley, CA 94720, USA.
J Cell Sci. 2011 Jan 1;124(Pt 1):123-32. doi: 10.1242/jcs.073197.
Functional differentiation is orchestrated by precise growth-regulatory controls conveyed by the tissue microenvironment. Cues from laminin 111 (LN1) lower transcription and suppress mammary epithelial cell growth in culture, but how LN1 induces quiescence is unknown. Recent literature points to involvement of nuclear β-actin in transcriptional regulation. Here, we show that quiescence induced by growth factor withdrawal, or LN1 addition, rapidly decreases nuclear β-actin. LN1, but not other extracellular matrix (ECM) molecules, decreases the levels of nuclear β-actin and destabilizes RNA polymerase (RNA Pol) II and III binding to transcription sites, leading to a dramatic drop in transcription and DNA synthesis. Constitutive overexpression of globular β-actin in the nucleus reverses the effect of LN1 on transcription and RNA Pol II association and prevents the cells from becoming quiescent in the presence of LN1. The physiological relevance of our findings was verified by identifying a clear spatial separation of LN1 and β-actin in developing mammary end buds. These data indicate a novel role for nuclear β-actin in growth arrest of epithelial cells and underscore the importance of the integrity of the basement membrane in homeostasis.
功能分化是由组织微环境传递的精确生长调控控制协调的。层粘连蛋白 111（LN1）的信号降低了培养中的乳腺上皮细胞的转录和增殖，但 LN1 如何诱导静止状态尚不清楚。最近的文献指出核 β-肌动蛋白参与转录调控。在这里，我们表明，生长因子撤出或 LN1 加所诱导的静止状态会迅速降低核 β-肌动蛋白的水平。LN1，但不是其他细胞外基质（ECM）分子，降低了核 β-肌动蛋白的水平并使 RNA 聚合酶（RNA Pol）II 和 III 与转录位点的结合不稳定，导致转录和 DNA 合成急剧下降。核中球状 β-肌动蛋白的组成性过表达逆转了 LN1 对转录和 RNA Pol II 结合的影响，并防止细胞在 LN1 存在的情况下进入静止状态。通过鉴定发育中的乳腺末端芽中 LN1 和 β-肌动蛋白的明显空间分离，验证了我们发现的生理相关性。这些数据表明核 β-肌动蛋白在上皮细胞生长停滞中的新作用，并强调了基底层完整性在维持体内平衡中的重要性。
