Background In our previous study,we found that DAZAP2 was the most significantly down regulated gene whendifferential screening of complementary DNA(cDNA)chips were used to analyze mRNA isolated from bone marrowmononuclear cells from newly diagnosed multiple myeloma(MM)patients without anticancer treatment.In this study,weobserved DAZAP2 mRNA and protein expression in the mononuclear cells from MM bone marrow and investigated itsrole in the pathogenesis of MM.Methods The full-length cDNA of DAZAP2 was cloned and sequenced from mononuclear cells from human bonemarrow.The nucleotide and amino acid sequences of DAZAP2 were analyzed using the ClustalW program.Adendrogram was constructed by multiple sequence alignment using ClustalW and amino acid sequence identity/similaritywas derived based on comparisons attained using the MegAlign software.The recombinant pEGFP expression vectorwas constructed and the confocal microscopy was used for the localization of the DAZAP2 protein in transfected COS7cells.The expression of DAZAP2 mRNA was detected by semi-quantitative reverse transcription polymerase chainreaction (RT-PCR) and the expression level of DAZAP2 protein was detected by Western blotting analysis in MMsamples.Results DAZAP2 proteins of vertebrates is highly conserved in evolution.It contains a proline-rich region,severalpotential SH2 and SH3 domain-binding motifs and a possible protein kinase C (PKC) phosphorylation site.We showedby confocal microscopy that the DAZAP2 protein predominantly resides in the cytoplasm with a discrete pattern ofpunctuated distribution.The expression of DAZAP2 was not detected in 24 of 36 MM samples by semi-quantitativeRT-PCR.In contrast,DAZAP2 expression was detected in all 30 normal controls.The expression level of DAZAP2protein was assayed by Western blotting analysis,showing a robust down-regulation in MM patients (P<0.001) thatmatched with the results of the RT-PCR.Conclusions DAZAP2 is downregulated in MM samples and it may be a signal molecule in MM cells.DAZAP2 isinvolved in the pathogenesis of MM and could be used as a genetic marker for MM.Chin Med J 2007;120(19):1659-1665 Background In our previous study, we found that DAZAP2 was the most significantly down regulated gene whendifferential screening of complementary DNA (cDNA) chips were used to analyze mRNA isolated from bone marrowmononuclear cells from newly diagnosed multiple myeloma (MM) patients without anticancer treatment. this study, weobserved DAZAP2 mRNA and protein expression in the mononuclear cells from MM bone marrow and investigated its roles in the pathogenesis of MM. Methods The full-length cDNA of DAZAP2 was cloned and sequenced from mononuclear cells from human bone marrow. The nucleotide and amino acid Sequences of DAZAP2 were analyzed using the ClustalW program. Adendrogram was constructed by multiple sequence alignment using ClustalW and amino acid sequence identity / similarity was derived based on comparisons attained using the MegAlign software. Recombinant pEGFP expression vector was constructed and the confocal microscopy was used for the localization of the DAZAP2 protein in transfected COS7 cells. The expression of DAZAP2 mRNA was detected by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) and the expression level of DAZAP2 protein was detected by Western blotting analysis in MMsamples.Results DAZAP2 proteins of vertebrates are highly conserved in evolution. It contains a proline-rich region, several potential SH2 and SH3 domain-binding motifs and a possible protein kinase C (PKC) phosphorylation site. We showed by confocal microscopy that the DAZAP2 protein predominantly resides in the cytoplasm with a discrete pattern of unpunctuated distribution. The expression of DAZAP2 was not detected in 24 of 36 MM samples by semiquantitative RT-PCR.In contrast, DAZAP2 expression was detected in all 30 normal controls. The expression level of DAZAP2protein was assayed by Western blotting analysis, showing a robust down-regulation in MM patients (P <0.001) thatmatched with the results of the RT-PCR. Confc DAZAP2 is downregulated in MM samples and it may be a signal molecule in MM cells. DAZAP2 is involved in the pathogenesis of MM and could be used as a genetic marker for MM. Chin Med J 2007; 120 (19): 1659-1665