Identification of the retinoic acid-inducible Gprc5a as a new lung tumor suppressor gene.
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.
Tao
Qingguo
Q
Department of Thoracic/Head and Neck Medical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Fujimoto
Junya
J
Men
Taoyan
T
Ye
Xiaofeng
X
Deng
Jiong
J
Lacroix
Ludovic
L
Clifford
John L
JL
Mao
Li
L
Van Pelt
Carolyn S
CS
Lee
J Jack
JJ
Lotan
Dafna
D
Lotan
Reuben
R
D000230:Adenocarcinoma / Q000737:chemistry* / Q000473:pathology; D000818:Animals; D015152:Blotting, Northern; D002289:Carcinoma, Non-Small-Cell Lung / Q000737:chemistry; D018288:Carcinoma, Small Cell / Q000737:chemistry; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D004195:Disease Models, Animal; D053595:Embryonic Stem Cells; D005455:Fluorescent Antibody Technique; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D011905:Genes, ras; D020022:Genetic Predisposition to Disease; D006720:Homozygote; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008168:Lung / Q000737:chemistry*; D008175:Lung Neoplasms / Q000737:chemistry* / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics; D014411:Neoplastic Stem Cells / Q000737:chemistry*; D010641:Phenotype; D040081:Protein Array Analysis; D012333:RNA, Messenger / Q000032:analysis; D043562:Receptors, G-Protein-Coupled / Q000172:deficiency / Q000235:genetics* / Q000302:isolation & purification; D020545:Respiratory Mucosa / Q000473:pathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014410:Tumor Stem Cell Assay
C116760:GPRC5A protein, human; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled