Head and Neck Neoplasms ; pathology ; Humans ; Male ; Middle Aged ; Plasmacytoma ; pathology

Objective To investigate the impact of pair box 3 (PAX3) gene mutations on transcriptional ac‐tivity of target gene microphthalmia -associated transcription factor (MITF) and the role it plays in the pathogene‐sis of Waardenburg syndrome type I .Methods The 293T cells were transient transfected with wild type (WT ) PAX3 and mutant type (M T ) H80D ,H186fsX5 plasmids .We observed and analysed the regulation effects of WT/MT PAX3 on the transcriptional activities of MITF and the influence of the two mutants on WT PAX3 function u‐sing luciferase activity assays ,detect DNA binding capacity of WT/MT PAX3 to MITF gene promoter using a bioti‐nylated double - stranded oligonucleotide probe containing PAX3 binding motif ATTAAT to precipitate PAX3 , H80D and H186fsX5 respectively .Results H80D mutant was partially functional and was able to transactivate the MITF promoter in part ,but it was dramatically reduced as compared with WT PAX 3(P<0 .01) .H186fsX5 mu‐tant was loss -of -function and failed to transactivate the MITF promoter as compared with WT PAX 3 (P<0 .01) . None of them showed dominant -negative effect on WT PAX3(P>0 .05) .WT PAX3 and H80D mutant were able to bind specifically to the ATTAAT motif on the MITF promoter ,whereas H186fsX5 PAX3 lost the DNA -binding ability .Conclusion The mutations H80D and H186fsX5 made down-regulation of MITF transcription and decrease syn‐thesis of melanin ,which resulted in haploinsufficiency of PAX3 protein and caused mild phenotypes of WS1 .