Smad7 sensitizes A549 lung cancer cells to cisplatin-induced apoptosis through heme oxygenase-1 inhibition

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Abstract

Smad7, an inhibitory Smad, acts as a key regulator forming autoinhibitory feedback loop in transforming growth factor-beta (TGF-β) signaling. However, a growing body of evidences suggests that Smad7 is capable of apoptotic function. In the present study, we have demonstrated a proapoptotic function of Smad7 as a negative regulator of survival protein heme oxygenase-1 (HO-1). The HO-1 protein level was elevated in cisplatin-resistant A549 human lung cancer cells and blockade of HO-1 activation sensitized the cells to apoptosis. Interestingly, overexpression of Smad7 decreased HO-1 gene expression and its enzymatic activity. Notably, Smad7 reduced Akt activity and infection with adenovirus expressing a constitutively active form of the Akt reversed the inhibitory effects of Smad7 to HO-1, indicating a negative action mechanism of Smad7 to Akt-HO-1-linked survival pathway. Consistently, Smad7 sensitized A549 cells to cisplatin-induced apoptosis and these effects were dependent on HO-1 and Akt inhibition. Based on these findings, we suggest that targeting Smad7 may be an efficient strategy for overcoming drug-resistance in cancer therapy.

Highlights

► We examine the proapoptotic effect of Smad7 to cisplatin resistance cancer cells. ► Smad7 shows strong Akt inhibition activity. ► Smad7 shows strong HO-1 inhibition activity.

Introduction

Heme oxygenase-1 (HO-1) is a microsomal enzyme, catalyzing the breakdown of heme into equimolar amounts of carbon monoxide (CO), biliverdin, and free iron using molecular oxygen and reducing equivalents from NADPH:cytochrome P450 reductase [1], [2]. HO-1 contributes to the cellular homeostasis and defense reaction against oxidative injury through the antioxidant activities of biliverdin and its metabolite, bilirubin, as well as the cytoprotective action of CO. Therefore, the expression of HO-1 must be tightly controlled in normal cells. A growing body of evidences indicates, however, that HO-1 is elevated in a variety of human cancers, including breast, liver, lung, pancreas, and prostate cancers [3], [4], [5], [6]. Indeed, HO-1 activation may play a role in carcinogenesis and can potently influence the growth and metastasis of tumors.

Smad7 is an inhibitory Smad, which forms autoinhibitory feedback loop in transforming growth factor-beta (TGF-β) signaling [7]. However, growing body of evidences indicate that Smad7 may be involved in another signaling pathway [8], [9] and have another cellular functions [10], [11], [12]. For example, Smad7 increases sensitization of cells to apoptosis through nuclear factor-kappa B inhibition and c-Jun N-terminal kinase activation. In view of these observations, we sought to gain further insight into the role of Smad7 in cell death. In the present study, we found that Smad7 represent a pro-apoptotic function that promotes sensitivity to cisplatin in cancer cells by suppressing the expression of survival protein HO-1.

Section snippets

Materials

Cisplain was purchased from Sigma Chemical Co. (St. Louis, MI). The N-acetyl-Asp-Glu-Val-Asp-ρ-nitroanlide (Ac-DEVD-pNA) was purchased from Enzyme Systems Products (Dublin, CA). Zinc protoporphyrin IX was purchased from Sigma Chemical Co. (St. Louis, MI).

Cell culture and generation of stable cell lines

A549 human lung carcinoma cells were obtained from American Type Culture Collection (Manassas, VA). The cells were cultured in RPMI1640 medium supplemented with 2 mM l-glutamine, 10% heat-inactivated fetal bovine serum, 100 U/mL penicillin, and

HO-1 decreases sensitivity to cisplatin-induced apoptosis

Heme oxygenase-1 (HO-1) is considered as an enzyme facilitating cell survival and tumor progression [3], [4], [5], [6]. First, we analyzed the expression level of HO-1 in BEAS2B, A549, and NCI-H322 cells. Highly elevated HO-1 protein expression was detected in A549 lung cancer cells compared with BEAS2B lung epithelial cells and NCI-H322 lung cancer cells (Fig. 1A). To determine relationship between HO-1 level and cell death, we treated the anticancer agent cisplatin and assayed the caspase

Acknowledgments

This study was supported by a grant from the National R&D Program for Cancer Control, Ministry for Health and Welfare, Republic of Korea (1020420).

References (19)

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