IFN-γ inhibits human airway smooth muscle cell proliferation by modulating the E2F-1/Rb pathway

Abstract

Elucidating the factors that inhibit the increase in airway smooth muscle (ASM) mass may be of therapeutic benefit in asthma. Here, we investigated whether interferon-γ (IFN-γ), a potent inducer of growth arrest in various cell types, regulates mitogen-induced ASM cell proliferation. IFN-γ (1–100 U/ml) was found to markedly decrease both DNA synthesis and ASM cell number induced by the mitogens epidermal growth factor (EGF) and thrombin. Interestingly, IFN-γ had no effect on mitogen-induced activation of three major mitogenic signaling pathways, phosphatidylinositol 3-kinase, p70S6k, or mitogen-activated protein kinases. Mitogen-induced expression of cell cycle regulator cyclin D1 was increased by IFN-γ, whereas no effect was observed on degradation of p27Kip1. Expression array analysis of 23 cell cycle-related genes showed that IFN-γ inhibited EGF-induced increases in E2F-1 expression, whereas induction of c- myc, cyclin D2, Egr-1, and mdm2 were unaffected. Induction of E2F-1 protein and Rb hyperphosphorylation after mitogen stimulation was also suppressed by IFN-γ. In addition, IFN-γ decreased activation of cdk2 and expression of cyclin E, upstream signaling molecules responsible for Rb hyperphosphorylation in the late G1 phase. IFN-γ also increased levels of IFI 16 protein, whose mouse homolog p202 has been associated with growth inhibition. Together, our data indicate that IFN-γ is an effective inhibitor of ASM cell proliferation by blocking transition from G1-to-S phase by acting at two different levels: modulation of cdk2/cyclin E activation and inhibition of E2F-1 gene expression.

Heterogeneous cross-talk of E2F family members is crucially involved in growth modulatory effects of interferon-γ and EGF

“…Interferon-γ-induced antiproliferative effects have been shown to be associated with inhibition of E2F1 expression and reduction of E2F binding to its DNA sequence. 20,21 In agreement with these findings we observed a decrease in transcript levels of E2F1 and E2F2 in HTB-77 and T47D cells following interferon-γ treatment. However, of special note is that our data indicate that the anti-proliferative effect of interferon-γ in ovarian cancer cells is strongly related to an increase in the two inhibitory transcription factors E2F4 and E2F5.…”

Silencing of Sodium–Hydrogen Exchanger 1 Attenuates the Proliferation, Hypertrophy, and Migration of Pulmonary Artery Smooth Muscle Cells via E2F1

“…Bindra and colleagues (40) reported that E2Fs may be linked to the transcriptional response to hypoxia. Previous studies demonstrated the involvement of E2F1 in cell proliferation (13)(14)(15)(16). Tammali and colleagues (13) found that the inhibition of high glucose-induced and TNF-a-induced rat aorta vascular smooth muscle cell proliferation by aldose reductase was accompanied by the decreased expression of E2F1.…”

“…Grouwels and colleagues (14) found that the overexpression of E2F1 by an adenovirus E2F1 promoter increased the proliferation of primary b-cells isolated from the pancreas of rats. Amrani and colleaues (15) reported that interferon-g inhibited the proliferation of airway smooth muscle cells by inhibiting the expression of the E2F1 gene. Goukassian and colleagues (16) reported that the overexpression of E2F1 negated the inhibitory effects of a potent repressor of cellular proliferation, PCA-4230, on the proliferation of human vascular smooth muscle cells.…”

“…E2F1, one member of the family and a downstream factor of cell-cycle modulators and a nuclear transcription factor, plays an important role in governing nuclear transcription factors that regulate the synthesis of DNA (12). Reports indicate that E2F1 is involved in regulating the proliferation of different cells (13)(14)(15)(16). We previously determined that p27, a cyclin-dependent kinase inhibitor and an upstream factor of E2F1, plays a critical role in inhibiting the proliferation of PASMCs and the pulmonary hypertension induced by hypoxia (17)(18)(19).…”

Neutrophil elastase inhibition of cell cycle progression in airway epithelial cells in vitro is mediated by p27kip1

“…Most of the information about the regulation of p27 expression is from cancer models and smooth muscle cells, with only limited information about its regulation in airway epithelium. Interferon-␥ inhibits bronchial epithelial and airway smooth muscle proliferation by upregulating p27 expression, decreasing cyclin E and CDK2 activity, and thus decreasing retinoblastoma protein phosphorylation (3,48). In a balloon angioplasty model, vascular smooth muscle growth arrest is regulated by Sp1-mediated transcriptional upregulation of p27 (4).…”