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.
Surfactant protein D (SP-D) is a member of the collectin family that has an important role in maintaining pulmonary homeostasis. In this study, we demonstrated that SP-D inhibited the proliferation, ...migration and invasion of A549 human lung adenocarcinoma cells. We found that SP-D suppressed epidermal growth factor (EGF) signaling in A549 cells, H441 human lung adenocarcinoma cells and human EGF receptor (EGFR) stable expression CHO-K1 cells. A binding study using (125)I-EGF demonstrated that SP-D downregulated the binding of EGF to EGFR. A ligand blot indicated that SP-D bound to EGFR, and a lectin blot suggested that EGFR in A549 cells had both high-mannose type and complex type N-glycans. We purified the recombinant extracellular domain of EGFR (soluble EGFR=soluble EGFR (sEGFR)), and demonstrated that SP-D directly bound to sEGFR in a Ca(2+)-dependent manner. The binding of SP-D to sEGFR was suppressed by EDTA, mannose or N-glycopeptidase F treatment. Mass spectrometric analysis indicated that N-glycans in domain III of EGFR were of a high-mannose type. These data suggest that SP-D reduces EGF binding to EGFR through the interaction between the carbohydrate recognition domain of SP-D and N-glycans of EGFR, and downregulates EGF signaling. Our finding suggests the novel type of regulation system of EGF signaling involving lectin-to-carbohydrate interaction and downregulation of ligand binding.
Efferocytosis is believed to be a key regulator for lung inflammation in chronic obstructive pulmonary disease. In this study we pharmacologically inhibited efferocytosis with annexin V and attempted ...to determine its impact on the progression of pulmonary emphysema in mouse. We first demonstrated in vitro and in vivo efferocytosis experiments using annexin V, an inhibitor for phosphatidylserine-mediated efferocytosis. We then inhibited efferocytosis in porcine pancreatic elastase (PPE)-treated mice. PPE-treated mice were instilled annexin V intranasally starting from day 8 until day 20. Mean linear intercept (Lm) was measured, and cell apoptosis was assessed in lung specimen obtained on day 21. Cell profile, apoptosis, and mRNA expression of matrix metalloproteinases (MMPs) and growth factors were evaluated in bronchoalveolar lavage (BAL) cells on day 15. Annexin V attenuated macrophage efferocytosis both in vitro and in vivo. PPE-treated mice had a significant higher Lm, and annexin V further increased that by 32%. More number of macrophages was found in BAL fluid in this group. Interestingly, cell apoptosis was not increased by annexin V treatment both in lung specimens and BAL fluid, but macrophages from mice treated with both PPE and annexin V expressed higher MMP-2 mRNA levels and had a trend for higher MMP-12 mRNA expression. mRNA expression of keratinocyte growth factor tended to be downregulated. We showed that inhibited efferocytosis with annexin V worsened elastase-induced pulmonary emphysema in mice, which was, at least partly, attributed to a lack of phenotypic change in macrophages toward anti-inflammatory one.
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