Novel role for tumor suppressor gene, liver kinase B1, in epithelial–mesenchymal transition leading to chronic lung allograft dysfunction

Abstract

Epithelial-mesenchymal transition (EMT) has been implicated to play a role in chronic lung allograft dysfunction (CLAD). Liver kinase B1 (LKB1), a tumor suppressor gene, can regulate EMT. However, its role in CLAD development following lung transplantation remains unknown. Using qRT-PCR, biopsies from lung transplant recipients with bronchiolitis obliterans syndrome (BOS) demonstrated significant downregulation of LKB1 (p = .0001), compared to stable biopsies. To determine the role of LKB1 in EMT development, we analyzed EMT in human bronchial epithelial cell line BEAS-2B.Knockdown of LKB1 by siRNA significantly dysregulated mesenchymal markers expression in BEAS-2B cells. Following incubation of human primary bronchial epithelial cell or BEAS-2B cells with exosomes isolated from BOS or stable lung transplant recipients, LKB1 expression was inhibited when incubated with BOS-exosome. Incubation with BOS-exosomes also decreased LKB1 expression and induced EMT markers in air-liquid interface culture method. Our results provide novel evidence that exosomes released from transplanted lungs undergoing chronic rejection are associated with inactivated tumor suppressor gene LKB1 and this loss induces EMT leading to the pathogenesis of CLAD following human lung transplantation. K E Y W O R D S basic (laboratory) research/science, biomarker, bronchiolitis obliterans (BOS), lung (allograft) function/dysfunction, molecular biology 1 | INTRODUC TI ON Lung transplantation (LTx) is a therapeutic option for patients with advanced lung diseases. Long-term survival after LTx is limited by chronic lung allograft dysfunction (CLAD). CLAD commonly manifests as bronchiolitis obliterans syndrome (BOS), defined by a sustained reduction in the forced expiratory volume in first second of expiration. 1 BOS occurs in 50% of recipients within 5 years post-LTx

Is downregulation of liver kinase B1 the major factor driving epithelial-to-mesenchymal transition?

“…have been investigated in recent studies. 2 Exosomes are small vesicles that are induced after lung injury and can contain human leukocyte and lung self-antigens, major histocompatibility complex class II molecules, adhesion and costimulatory molecules, transcription factors, and 20S-proteasome. 2 Rahman et al demonstrate that exosomes released from transplanted lungs undergoing chronic rejection also contained inactivated LKB1, and this loss may subsequently stimulate EMT and contribute to the development and progression of CLAD.…”

“…Rahman and colleagues demonstrate that LKB1 was significantly downregulated in patients with BOS. 2 Further in vitro analyses of EMT in human bronchial epithelial cells showed dysregulated expression of mesenchymal markers in case of knockdown of LKB1.…”

“…1 In this issue, Rahman and colleagues highlight the possible role of serine-threonine kinase 11, also known as liver kinase B1 (LKB1), in the process of EMT in CLAD after lung transplantation. 2 LKB1 is a protein kinase that activates several downstream kinases by phosphorylating adenosine monophosphate-activated protein kinase (AMPK), and hereby regulates cell growth, cell polarity, cell metabolism, and autophagy. 2 LKB1 functions as a tumor suppressor gene and inhibits EMT, tissue fibrosis, and malignant transformation by activation of AMPK.…”

“…2 LKB1 functions as a tumor suppressor gene and inhibits EMT, tissue fibrosis, and malignant transformation by activation of AMPK. 2 A clear role has been established for the LKB1-AMPK pathway in cancer, in which it suppresses EMT during tumor progression. However, its role in chronic respiratory diseases or the development of CLAD after lung transplantation is less clear.…”

“…Similarly, after incubation of bronchial epithelial cells with exosomes isolated from BOS patients, LKB1 expression was inhibited and EMT markers were upregulated. 2 In future research, it would be important to assess if these findings can be reproduced in primary human bronchial epithelial cells obtained from lung transplant recipients exposed to classical immunosuppressants.…”