Prolyl isomerase Pin1 promotes survival in EGFR-mutant lung adenocarcinoma cells with an epithelial–mesenchymal transition phenotype

Abstract

The secondary epidermal growth factor receptor (EGFR) T790M mutation is the most prominent mechanism that confers resistance to first-or second-generation EGFR tyrosine kinase inhibitors (TKIs) in lung cancer treatment. Although third-generation EGFR TKIs can suppress the kinase activity of T790M-positive EGFR, they still cannot eradicate EGFR-mutated cancer cells. We previously reported that a subpopulation of EGFR-mutant lung adenocarcinomas depends on enhanced autophagy, instead of EGFR, for survival, and in this study we explore another mechanism that contributes to TKI resistance. We demonstrate here that an EGFR-mutant lung adenocarcinoma cell line, H1975 (L858R+T790M), has a subset of cells that exhibits an epithelial-mesenchymal transition (EMT) phenotype and can thrive in the presence of third-generation EGFR TKIs. These cells depend on not only autophagy but also on the isomerase Pin1 for survival in vitro, unlike their parental cells. The Pin1 protein was expressed in an EGFR-mutant lung cancer tissue that has undergone partial EMT and acquired resistance to EGFR TKIs, but not its primary tumor. These findings suggest that inhibition of Pin1 activity can be a novel strategy in lung cancer treatment. Lung adenocarcinomas with an activating mutation in the epidermal growth factor receptor (EGFR) gene depend on EGFR signaling for survival and proliferation. Although most EGFR-mutant lung cancers initially respond to EGFR tyrosine kinase inhibitors (TKIs), such as gefitinib, erlotinib, or afatinib, disease progression almost inevitably develops, on average, 1 year after the initiation of TKI therapy. The most common mechanism of acquired resistance is the secondary EGFR T790M mutation, which is found in 50-60% of resistant tumors. 1 To overcome T790M-mediated resistance, third-generation EGFR TKIs, including CO-1686 (also known rociletinib) and AZD9291, have been developed. 2,3 These drugs have potent activity against both the common EGFR mutations (inframe deletions in exon 19 and the L858R mutation in exon 21) and the T790M mutation. Recent early-phase clinical trial data demonstrated a response rate of 60% in patients with T790M-positive tumors. 4,5 Although this response rate was much higher than that of patients with T790M-negative tumors (21-29%), acquired resistance to these agents has emerged even in T790M-positive tumors. 4,5 We previously reported that two EGFR-mutated lung adenocarcinoma cell lines, HCC827 and HCC4006, have subpopulations of cells that display an epithelial-mesenchymal transition (EMT) phenotype and depend on enhanced autophagy, but not on EGFR activity, for survival. 6 We surmise that these EGFR-mutant cells devoid of EGFR dependency lie at the root of TKI resistance.Protein phosphorylation is a fundamental mode of intracellular signaling in many cellular processes such as proliferation and differentiation. The peptidyl-prolyl isomerase Pin1 has been identified as a regulator that catalyzes cis-trans isomerization of phosphorylated Ser/Thr-Pro motifs in a subset of phosphoryla...

Epithelial‐to‐mesenchymal transition and its role in EGFR‐mutant lung adenocarcinoma and idiopathic pulmonary fibrosis

“…We searched for other mechanism(s) that these EGFR ‐mutant cells devoid of EGFR dependency rely on, and found that the mesenchymal EGFR ‐mutant cells depend on enhanced autophagy for survival (Fig. c) . Although it has been reported that AXL kinase plays a key role in the survival of mesenchymal EGFR ‐mutant cells, we did not find evidence suggesting that such cells derived from HCC827 or HCC4006 cells are addicted to the kinase for survival …”

“…In the three TKI‐resistant cells, E‐cadherin (a representative epithelial marker) and TTF‐1 were markedly reduced, while expression levels of vimentin, ZEB1 (an EMT‐inducing transcription factor), and CD44 standard form (CD44s) were elevated compared with the parental cells (Fig. b), indicating that they exhibited a mesenchymal phenotype and consequently lost features of alveolar epithelia . Considering that EGFR ‐mutant cells that have completed EMT readily emerge, and the parental cells contain a minor subpopulation (<2%) of cells that express CD44s, it is likely that TKI treatment selects for these mesenchymal cells among the parental cells .…”

“…a), and Pin1 protein was expressed only in mesenchymal EGFR ‐mutant lung cancer tissue that had acquired resistance to EGFR TKIs (Fig. b), suggesting that a minor subset of patients with acquired resistance can derive some benefit from Pin1 inhibition.…”

“…Interestingly, most of the cells that can thrive in the presence of EGFR TKIs are spindle shaped (Fig. a) . In vitro models like this roughly reflect the clinical course of EGFR ‐mutant lung adenocarcinomas treated with TKIs.…”

Understanding the role of PIN1 in hepatocellular carcinoma

“…Consistently, PIN1 silencing suppresses protein expression and promoter activity of EMT regulator SNAIL, leading to increased expression of its downstream effector E-cadherin in tamoxifen-resistant breast cancer cells[96]. In epidermal growth factor receptor (EGFR) Thr 790 Met mutant lung cancer tissues, PIN1 expression is also positively correlated with the mesenchymal markers vimentin and Zeb1[97]. PIN1 expression enhances the survival of EGFR-mutant lung adenocarcinoma cells with an EMT phenotype.…”