Department of Pathology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Lab Invest. 2012 Feb;92(2):200-13. doi: 10.1038/labinvest.2011.163. Epub 2011 Nov 7.
Endoplasmic reticulum protein 29 (ERp29) is an ER luminal protein that has a role in protein unfolding and secretion, but its role in cancer is unclear. Recently, we reported that overexpression of ERp29 significantly inhibited cell proliferation and prevented tumorigenesis in highly proliferative MDA-MB-231 breast cancer cells. Here, we show that ERp29-induced cancer cell growth arrest is modulated by the interplay between the concomitant phosphorylation of p38 and upregulation of the inhibitor of the interferon-induced, double-stranded RNA-activated protein kinase, p58(IPK). In this cell model, ERp29 overexpression significantly downregulates modulators of cell proliferation, namely urokinase plasminogen activator receptor, β(1)-integrin and epidermal growth factor receptor. Furthermore, ERp29 significantly (P<0.001) increases phosphorylation of p38 (p-p38) and reduces matrix metalloproteinase-9 secretion. The role of ERp29 in upregulating cyclin-dependent kinase inhibitors (p15 and p21) and in downregulating cyclin D(2) is demonstrated in slowly proliferating ERp29-overexpressing MDA-MB-231 cells, whereas the opposite response was observed in ERp29-knockdown MCF-7 cells. Pharmacological inhibition of p-p38 downregulates p15 and p21 and inhibits eIF2α phosphorylation, indicating a role for p-p38 in this process. Furthermore, p58(IPK) expression was increased in ERp29-overexpressing MDA-MB-231 cells and highly decreased in ERp29-knockdown MCF-7 cells. This upregulation of p58(IPK) by ERp29 suppresses the activation of p-p38/p-PERK/p-eIF2α by repressing eIF2α phosphorylation. In fact, reduction of p58(IPK) expression by RNA interference stimulated eIF2α phosphorylation. The repression of eIF2α phosphorylation by p58(IPK) prevents ERp29-transfected cells from undergoing ER-dependent apoptosis driven by the activation of ATF4/CHOP/caspase-3. Hence, the interplay between p38 phosphorylation and p58(IPK) upregulation has key roles in modulating ERp29-induced cell-growth arrest and survival.
内质网蛋白 29（ERp29）是一种内质网腔蛋白，在蛋白质展开和分泌中发挥作用，但它在癌症中的作用尚不清楚。最近，我们报道 ERp29 的过表达显著抑制了高度增殖的 MDA-MB-231 乳腺癌细胞的增殖并阻止了肿瘤的发生。在这里，我们表明 ERp29 诱导的癌细胞生长停滞是通过 p38 的伴随磷酸化和干扰素诱导的双链 RNA 激活蛋白激酶的抑制剂 p58(IPK)的上调之间的相互作用来调节的。在这个细胞模型中，ERp29 的过表达显著下调了细胞增殖调节剂，即尿激酶型纤溶酶原激活物受体、β(1)-整联蛋白和表皮生长因子受体。此外，ERp29 显著（P<0.001）增加了 p38 的磷酸化（p-p38）并减少了基质金属蛋白酶-9 的分泌。在增殖缓慢的 ERp29 过表达 MDA-MB-231 细胞中证明了 ERp29 上调细胞周期蛋白依赖性激酶抑制剂（p15 和 p21）和下调细胞周期蛋白 D(2)的作用，而在 ERp29 敲低 MCF-7 细胞中观察到相反的反应。p-p38 的药理学抑制下调了 p15 和 p21 并抑制了 eIF2α 的磷酸化，表明 p-p38 在这个过程中起作用。此外，在 ERp29 过表达的 MDA-MB-231 细胞中 p58(IPK)的表达增加，而在 ERp29 敲低的 MCF-7 细胞中则高度降低。ERp29 通过抑制 eIF2α 的磷酸化而上调 p58(IPK)，从而抑制 p-p38/p-PERK/p-eIF2α 的激活。事实上，通过 RNA 干扰降低 p58(IPK)的表达刺激了 eIF2α 的磷酸化。p58(IPK)对 eIF2α 磷酸化的抑制阻止了由 ATF4/CHOP/caspase-3 激活驱动的 ERp29 转染细胞发生 ER 依赖性细胞凋亡。因此，p38 磷酸化和 p58(IPK)上调之间的相互作用在调节 ERp29 诱导的细胞生长停滞和存活方面起着关键作用。
