Inhibition of Proliferation by PERK Regulates Mammary Acinar Morphogenesis and Tumor Formation

Abstract

Endoplasmic reticulum (ER) stress signaling can be mediated by the ER kinase PERK, which phosphorylates its substrate eIF2α. This in turn, results in translational repression and the activation of downstream programs that can limit cell growth through cell cycle arrest and/or apoptosis. These responses can also be initiated by perturbations in cell adhesion. Thus, we hypothesized that adhesion-dependent regulation of PERK signaling might determine cell fate. We tested this hypothesis in a model of mammary acini development, a morphogenetic process regulated in part by adhesion signaling. Here we report a novel role for PERK in limiting MCF10A mammary epithelial cell proliferation during acinar morphogenesis in 3D Matrigel culture as well as in preventing mammary tumor formation in vivo. We show that loss of adhesion to a suitable substratum induces PERK-dependent phosphorylation of eIF2α and selective upregulation of ATF4 and GADD153. Further, inhibition of endogenous PERK signaling during acinar morphogenesis, using two dominant-negative PERK mutants (PERK-ΔC or PERK-K618A), does not affect apoptosis but results instead in hyper-proliferative and enlarged lumen-filled acini, devoid of proper architecture. This phenotype correlated with an adhesion-dependent increase in translation initiation, Ki67 staining and upregulation of Laminin-5, ErbB1 and ErbB2 expression. More importantly, the MCF10A cells expressing PERKΔC, but not a vector control, were tumorigenic in vivo upon orthotopic implantation in denuded mouse mammary fat pads. Our results reveal that the PERK pathway is responsive to adhesion-regulated signals and that it is essential for proper acinar morphogenesis and in preventing mammary tumor formation. The possibility that deficiencies in PERK signaling could lead to hyperproliferation of the mammary epithelium and increase the likelihood of tumor formation, is of significance to the understanding of breast cancer.

Overexpression of endoplasmic reticulum protein 29 regulates mesenchymal–epithelial transition and suppresses xenograft tumor growth of invasive breast cancer cells

“…15,[35][36][37] In this study, we show that ERp29 is a novel regulator in modulating cell growth arrest and phenotypic changes associated with MET in proliferative/invasive breast cancer cells. Importantly, we show that ERp29 is a potential tumor suppressor in breast cancer progression.…”

“…[12][13][14] These effects have been evidenced by the fact that the PERK pathway inhibits hyperproliferation of tumor cells and tumor formation. 15 Endoplasmic reticulum protein 29 (ERp29), a novel reticuloplasmin, was first cloned from rat liver and enamel cells. 16,17 Structurally, it has an ER-retrieval signal of the Cterminal tetrapeptide (KEEL) targeting the ER lumen, but lacks the classical chaperone, disulfide-editing, calcium-buffer, and stress-response properties.…”

PKCζ regulates cell polarisation and proliferation restriction during mammary acinus formation

“…7B). After the initial rounds of cell growth during early acinus maturation, a crucial restriction of cell proliferation occurs (Petersen et al, 1992;Sequeira et al, 2007). Triggered activation of ErbB2 in acini lead to re-initiation of proliferation, filling of their lumenal space and the formation of multi-acinar structures (Muthuswamy et al, 2001).…”

Impaired tissue growth is mediated by checkpoint kinase 1 (CHK1) in the integrated stress response

“…In the mammary epithelium, PERK limits growth during acinar morphogenesis and dominant-negative PERK constructs are tumorigenic in breast-cancer-derived cells, suggesting that PERK negatively regulates growth of this tissue (Sequeira et al, 2007). However, solid tumours deficient in PERK grow poorly in hypoxic conditions, revealing a role for the ISR in enabling tissues to match cell proliferation with oxygen and nutrient supply (Bi et al, 2005).…”