Overexpression of Yin Yang 1 in bone marrow-derived human multiple myeloma and its clinical significance.

Multiple myeloma (MM) patients initially respond to conventional therapy, however, many develop resistance and have recurrences. We have reported in other tumors that the transcription factor Yin Yang 1 (YY1) is a resistant factor and, thus, we hypothesized that YY1 may be over-expressed in MM. Significantly, higher expression (staining intensity and cell frequency) of YY1 in MM cell lines and in bone marrow-derived (BM) MM from 22 MM patients was observed as compared to expression in normal BM. Higher nuclear YY1 staining was associated with disease progression. Bioinformatic analyses of mRNA in data sets corroborated the above findings and showed significant overexpression of YY1 in MM compared to normal tissues and other hematopoietic disorders. The role of YY1 expression in the regulation of drug resistance was exemplified in a drug-resistant MM cell line transfected with YY1 siRNA and which was shown to be sensitized to bortezomib-induced apoptosis. These findings highlight the potential prognostic significance of YY1 expression level in MM patients and as a therapeutic target.