Surfactant protein D inhibits activation of non-small cell lung cancer-associated mutant EGFR and affects clinical outcomes of patients

Abstract

Tyrosine kinase inhibitor (TKI)-sensitive and TKI-resistant mutations of epidermal growth factor receptor (EGFR) are associated with lung adenocarcinoma. EGFR mutants were previously shown to exhibit ligand-independent activation. We have previously demonstrated that pulmonary surfactant protein D (SP-D, SFTPD) suppressed wild-type EGFR signaling by blocking ligand binding to EGFR. We herein demonstrate that SFTPD downregulates ligand-independent signaling in cells harboring EGFR mutations such as TKI-sensitive exon 19 deletion (Ex19del) and L858R mutation as well as TKI-resistant T790M mutation, subsequently suppressing cellular growth and motility. Lectin blotting and ligand blotting in lung cancer cell lines suggested that EGFR mutants express oligomannose-type N-glycans and interact with SFTPD directly. Cross-linking assay indicated that SFTPD inhibits ligand-independent dimerization of EGFR mutants. We also demonstrated that SFTPD reduced dimerization-independent phosphorylation of Ex19del and T790M EGFR mutants using point mutations that disrupted the asymmetric dimer interface. It was confirmed that SFTPD augmented the viability-suppressing effects of EGFR-TKIs. Furthermore, retrospective analysis of 121 patients with lung adenocarcinoma to examine associations between serum SFTPD levels and clinical outcome indicated that in TKI-treated patients with lung cancer harboring EGFR mutations, including Ex19del or L858R, high serum SFTPD levels correlated with a lower number of distant metastases and prolonged overall survival and progression-free survival. These findings suggest that SFTPD downregulates both TKI-sensitive and -resistant EGFR mutant signaling, and SFTPD level is correlated with clinical outcome. These findings illustrate the use of serum SFTPD level as a potential marker to estimate the efficacy of EGFR-TKIs.

MiR-629-3p-induced downregulation of SFTPC promotes cell proliferation and predicts poor survival in lung adenocarcinoma

“…For instance, Hasegawa et al [13] demonstrated that SFTPD suppressed the proliferation, migration and invasion of A549 cells by inhibiting the epidermal growth factor signaling. Umeda et al [15] reported that high serum SFTPD levels were associated with a lower number of distant metastases and better prognosis. Besides, recent studies also suggested that SFTPD could suppress the progression of pancreatic cancer by inducing epithelial-mesenchymal-transition (EMT) and apoptosis of pancreatic cancer cells [16,17].…”

“…Inversely, SFTPB and SFTPC are hydrophobic proteins with the capacity of mitigating surface tension in the lung [12]. Strikingly, it has been proposed that SFTPD expression was associated with tumour progression and survival of patients with lung cancer [13][14][15]. Furthermore, recent evidence also showed that SFTPD could suppress the progression of pancreatic cancer by inducing epithelial-mesenchymal-transition (EMT) and apoptosis of pancreatic cancer cells [16,17].…”

Surfactant protein A down-regulates epidermal growth factor receptor by mechanisms different from those of surfactant protein D

“…This study showed that SP-A down-regulates EGFR by mechanisms differing from those of SP-D. Our study indicated that through the interaction between CRD of SP-D and N-glycans of EGFR, SP-D suppresses EGF signaling by interfering with ligand binding to EGFR, EGFR dimerization, or EGFR autophosphorylation (11,26). In contrast, lectin activity of SP-A and N-glycans of EGFR were not involved in the interaction between SP-A and EGFR.…”

“…The SP-A concentrations used in this study are within the best estimates of the physiological ranges of the lung tissue. EGFR is expressed in the basolateral surface of the epithelial cells (26), whereas SP-A is secreted into the alveolar space. Therefore, we infer that a small amount of SP-A in serum or interstitial tissues might weakly regulate EGF signaling in normal alveolar epithelial cells.…”

Dexamethasone Treatment Increases the Intracellular Calcium Level Through TRPV6 in A549 Cells

“…Pulmonary surfactants are composed of four proteins (SFTPA1, SFTPB, SFTPC, and SFTPD) that are produced by type II alveolar epithelial cells such as A549 [6]. Surfactant proteins are reported to be involved in the regulation of the immune system, and in enhancing the absorption of surfactant phospholipids into the air-liquid interface and reducing the surface tension within the lungs [7,8]. Pulmonary surfactant level is widely used as a biomarker of lung cancer [9].…”