Identification of the retinoic acid-inducible Gprc5a as a new lung tumor suppressor gene

J Natl Cancer Inst. 2007 Nov 21;99(22):1668-82. doi: 10.1093/jnci/djm208. Epub 2007 Nov 13.


Background: Lung cancers develop via multiple genetic and epigenetic changes, including inactivation of tumor suppressor genes. We previously cloned human G protein-coupled receptor family C type 5A (GPRC5A), whose expression is suppressed in some human lung carcinoma cells, and its mouse homolog Gprc5a.

Methods: We generated Gprc5a knockout mice by homologous recombination and studied their phenotype by macroscopic observation and microscopic histologic analysis of embryos and lungs of 1- to 2-year-old mice. GPRC5A mRNA expression was analyzed by reverse transcription-polymerase chain reaction in surgical specimens of 18 human lung tumors and adjacent normal tissues and by analyzing previously published data from 186 lung tumor tissues of a variety of histologic types and 17 normal lung samples. Human embryonic kidney, human non-small-cell lung cancer, and mouse lung adenocarcinoma cells were transfected with a GPRC5A expression vector or a control vector, and colony formation in semisolid medium was assayed. Statistical tests were two-sided.

Results: Homozygous knockout mice developed many more lung tumors at 1-2 years of age (incidence: 76% adenomas and 17% adenocarcinomas) than heterozygous (11% adenomas) or wild-type (10% adenomas) mice. Human GPRC5A mRNA levels were lower in most (11 of 18 [61%]) human lung tumors than in adjacent normal tissues. The mean GPRC5A mRNA level in adenocarcinoma (n = 139), squamous cell carcinoma (n = 21), small-cell lung cancer (n = 6), and carcinoid (n = 20) tissues was 46.2% (P = .014), 7.5% (P<.001), 5.3% (P<.001), and 1.8% (P<.001), respectively, that in normal lung tissues (n = 17) GPRC5A transfection suppressed colony formation in semisolid medium of immortalized human embryonic kidney, human non-small-cell lung cancer, and mouse lung adenocarcinoma cells by 91%, 91%, and 68%, respectively, compared with vector controls (all P<.001).

Conclusions: Gprc5a functions as a tumor suppressor in mouse lung, and human GPRC5A may share this property. The Gprc5a-deficient mouse is a novel model to study lung carcinogenesis and chemoprevention.

Publication types

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

MeSH terms

  • Adenocarcinoma / chemistry*
  • Adenocarcinoma / pathology
  • Animals
  • Blotting, Northern
  • Carcinoma, Non-Small-Cell Lung / chemistry
  • Carcinoma, Small Cell / chemistry
  • Cell Line, Tumor
  • Cell Transformation, Neoplastic
  • Disease Models, Animal
  • Embryonic Stem Cells
  • Fluorescent Antibody Technique
  • Gene Expression Regulation, Neoplastic
  • Genes, Tumor Suppressor*
  • Genes, ras
  • Genetic Predisposition to Disease
  • Homozygote
  • Humans
  • Immunoblotting
  • Immunohistochemistry
  • In Situ Hybridization
  • Lung / chemistry*
  • Lung Neoplasms / chemistry*
  • Lung Neoplasms / pathology
  • Mice
  • Mice, Knockout
  • Mutation
  • Neoplasm Proteins / genetics
  • Neoplastic Stem Cells / chemistry*
  • Phenotype
  • Protein Array Analysis
  • RNA, Messenger / analysis
  • Receptors, G-Protein-Coupled / deficiency
  • Receptors, G-Protein-Coupled / genetics*
  • Receptors, G-Protein-Coupled / isolation & purification
  • Respiratory Mucosa / pathology*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transfection
  • Tumor Stem Cell Assay


  • GPRC5A protein, human
  • Neoplasm Proteins
  • RNA, Messenger
  • Receptors, G-Protein-Coupled