Insulin-like growth factor-1 receptor induces immunosuppression in lung cancer by upregulating B7–H4 expression through the MEK/ERK signaling pathway

Highlights

• IGF1R is associated with CD8⁺ T cell inhibition in lung cancer.

• IGF1R upregulates B7–H4 expression.

• IGF1R downstream MEK/ERK activation contributes to the B7–H4 upregulation.

• B7–H4 knockdown inhibits IGF1R-overexpression tumor growth and reverse the tumor infiltrated CD8⁺ T cell inhibition.

Abstract

The Insulin-like growth factor-1/Insulin-like growth factor-1 receptor (IGF1/IGF1R) axis contributes to immunosuppression during tumor progression; however, the underlying mechanism remains unclear. In the present study, we found that IGF1 stimulation or IGF1R overexpression (IGF1R-OE) could upregulate the expression of B7–H4, while IGF1R inhibition downregulated B7–H4 in both A549 and SPC-A-1 lung cancer cell lines. IGF1R-OE conferred the inhibition of CD8⁺ T cells by cancer cells in vitro, and induction of B7–H4 expression was mediated by the activation of the MEK/ERK1/2 signaling pathway. The in vitro findings were further confirmed in vivo using a Lewis lung cancer mouse model. IGF1R-OE promoted tumor growth and inhibited tumor infiltration by CD8⁺ T cells in the mouse model. However, this effect was suppressed when B7–H4 was knocked down in IGF1R-OE cells. Our findings suggest that IGF1R could induce immunosuppression in lung cancer by upregulating the expression of B7–H4 through the MEK/ERK pathway. B7–H4 may therefore be a potential therapeutic target for lung cancer immunotherapy.

Introduction

The IGF axis, which is composed of ligands (IGF-1, IGF-2), IGF receptors (IGF1R, IGF2R), and six IGF binding proteins (IGFBPs 1–6), has a pivotal role in tumor progression [1]. IGF1R activation results in the activation of the PI3K/Akt and MEK/ERK signaling pathways [2]. IGF signaling can promote immunosuppressive and anti-inflammatory responses that facilitate tumor growth [[3], [4], [5]]. By disrupting PI3K/Akt signaling, which is downstream of IGF1R, tumor cells are sensitized toward cytotoxicity by antigen-specific CTL both in vitro and in vivo [6]. Activation of MEK/ERK, the other IGF1R downstream signaling pathway, is associated with reduced tumor-infiltrated lymphocytes (TILs) [7]. Taken together, these findings suggest that IGF1R signaling activation might affect the tumor immunity by regulating TILs. However, the exact molecular mechanism by which IGF1R regulates the tumor immune microenvironment remains largely unknown.

Immune checkpoints are the T-cell regulatory molecules that regulate the activation and effector functions of TILs through costimulatory and coinhibitory signals [8,9]. Tumor cells can deploy co-inhibitory molecules to escape immune surveillance and resist the cytotoxic effect of host T cells [10]. Among these molecules, B7–H4 (VTCN1), which is expressed by tumor cells and a variety of immune cells, is known to inhibit T cell function [11,12]. B7–H4 expression is regulated by lipopolysaccharides (LPS), phytohemagglutinin (PHA), phorbol 12-myristate 13-acetate (PMA), and inflammatory cytokines such as IL-6, IL-10, IL-2, IFN-α, IFN-γ, and TNF-α [[13], [14], [15], [16], [17], [18]]. B7–H4 inhibits T cell activation and proliferation through binding with unknown receptor on T cells [12]. The B7–H4 antibody blockade can reverse the inhibition of tumor-specific T-cells in vivo [[19], [20], [21]]. Increasing numbers of studies have shown that B7–H4 is highly expressed in different tumor types [22], and its expression levels correlate with clinical tumor progression and pathological characteristics [21,[23], [24], [25], [26]]. Blocking with a B7–H4 antibody synergizes with anti-PD-1 in suppression of tumor growth [12,20]. B7–H4 is therefore a promising immunotherapeutic target [23,26,27]. However, the exact signaling pathways that regulate B7–H4 expression remain largely unclear [22]. The association between B7–H4 and IGF1R has not previously been reported.

In the present study, we found that IGF1R was associated with increased B7–H4 expression, and decreased CD8, IFN-γ, and Granzyme B (GzmB) expression in lung cancer by analyzing the Cancer Genome Atlas (TCGA) datasets and performing immunohistochemistry (IHC). IGF1R expression in lung cancer cells mediated CD8⁺ T cell inhibition through B7–H4 in vitro. The MEK/ERK1/2 pathway was involved in IGF1R-induced B7–H4 upregulation. B7–H4 knockdown could inhibit IGF1R-overexpression-induced tumor growth and restore tumor infiltrated CD8⁺ T cells in vivo. These findings demonstrate that IGF1R contributes to tumor immunosuppression through upregulating B7–H4 in lung cancer. B7–H4 might therefore be an immunotherapeutic target for lung cancers overexpressing IGF1R.