CLDN18.1 attenuates malignancy and related signaling pathways of lung adenocarcinoma in vivo and in vitro

Int J Cancer. 2018 Dec 15;143(12):3169-3180. doi: 10.1002/ijc.31734. Epub 2018 Oct 16.

Abstract

Claudins are a family of transmembrane proteins integral to the structure and function of tight junctions (TJ). Disruption of TJ and alterations in claudin expression are important features of invasive and metastatic cancer cells. Expression of CLDN18.1, the lung-specific isoform of CLDN18, is markedly decreased in lung adenocarcinoma (LuAd). Furthermore, we recently observed that aged Cldn18 -/- mice have increased propensity to develop LuAd. We now demonstrate that CLDN18.1 expression correlates inversely with promoter methylation and with LuAd patient mortality. In addition, when restored in LuAd cells that have lost expression, CLDN18.1 markedly attenuates malignant properties including xenograft tumor growth in vivo as well as cell proliferation, migration, invasion and anchorage-independent colony formation in vitro. Based on high throughput analyses of Cldn18 -/- murine lung alveolar epithelial type II cells, as well as CLDN18.1-repleted human LuAd cells, we hypothesized and subsequently confirmed by Western analysis that CLDN18.1 inhibits insulin-like growth factor-1 receptor (IGF-1R) and AKT phosphorylation. Consistent with recent data in Cldn18 -/- knockout mice, expression of CLDN18.1 in human LuAd cells also decreased expression of transcriptional co-activator with PDZ-binding motif (TAZ) and Yes-associated protein (YAP) and their target genes, contributing to its tumor suppressor activity. Moreover, analysis of LuAd cells in which YAP and/or TAZ are silenced with siRNA suggests that inhibition of TAZ, and possibly YAP, is also involved in CLDN18.1-mediated AKT inactivation. Taken together, these data indicate a tumor suppressor role for CLDN18.1 in LuAd mediated by a regulatory network that encompasses YAP/TAZ, IGF-1R and AKT signaling.

Keywords: AKT; IGF-1 receptor; YAP/TAZ; lung alveolar epithelial type II cells; xenograft.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenocarcinoma of Lung / genetics
  • Adenocarcinoma of Lung / metabolism*
  • Adenocarcinoma of Lung / pathology
  • Animals
  • Blotting, Western
  • Cell Proliferation
  • Claudins / genetics
  • Claudins / physiology*
  • DNA Methylation
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Lung Neoplasms / genetics
  • Lung Neoplasms / metabolism*
  • Lung Neoplasms / pathology
  • Mice
  • Mice, Knockout
  • Neoplasm Invasiveness
  • Neoplasm Metastasis
  • Phosphorylation
  • Promoter Regions, Genetic
  • Proto-Oncogene Proteins c-akt / metabolism
  • Proto-Oncogene Proteins c-yes / metabolism
  • Receptor, IGF Type 1 / metabolism
  • Signal Transduction / physiology*
  • Trans-Activators
  • Transcription Factors

Substances

  • CLDN18 protein, human
  • Claudins
  • Intracellular Signaling Peptides and Proteins
  • Trans-Activators
  • Transcription Factors
  • WWTR1 protein, human
  • Receptor, IGF Type 1
  • Proto-Oncogene Proteins c-yes
  • YES1 protein, human
  • Proto-Oncogene Proteins c-akt