OBJECTIVEActivation and overexpression of pleomorphic adenoma (PLAG1) gene due to t(3;8)(p21;q12) translocation are associated with the development of human pleomorphic adenomas of the salivary glands. This study was conducted to generate ubiquitously-expressed or tissue-specific expressed PLAG1 transgenic mice and to elucidate the role of PLAG1 gene in tumorigenesis in vivo.

METHODSHuman PLAG1 cDNA was cloned from salivary gland tumor or placenta tissues by RT-PCR. Ubiquitous expression vector pCMV-EGFP/PLAG1 driven by CMV promoter and tissue-specific expression vector pMMTV-PLAG1 driven by MMTV LTR were constructed. NIH3T3 cells transiently transfected with pCMV-EGFP/PLAG1 showed high expression of PLAG1 in nucleus. Transgenes were microinjected into pronucleus of zygotes to generate transgenic mice.

RESULTSIt was found that the human PLAG1 cDNA cloned from several salivary gland tumor and normal placenta tissues consistently showed a variation of a single nucleotide at the same position when compared with the human PLAG1 cDNA sequence in Genbank (Accession No. U65002), which led to T458P at protein level. It might be a single nucleotide polymorphism (SNP)locus. Fused EGFP/PLAG1 protein was found to be localized in the nucleus of NIH3T3 cells transiently transfected with pCMV-EGFP/ PLAG1. Several pCMV-EGFP/PLAG1 and pMMTV-PLAG1 transgenic mouse lines were obtained respectively. As might be expected, pMMTV-PLAG1 transgenic mice spontaneously developed salivary gland tumors in three independent lines, among which, line 42 showed tumorigenic phenotype in 100% of transgenic mice within three months after birth.

CONCLUSIONOverexpression of PLAG1 gene plays a crucial role in tumorigenesis of salivary gland tumors.