Transcriptional Regulation of the SHP-1, a Candidate Tumor Suppressor Gene in Hematological Malignancies.

The SH2-Containing Protein-Tyrosine Phosphatase-1 (SHP-1) is a hematopoietic cell specific protein-tyrosine phosphatase and a candidate tumor suppressor. It has been shown that expression of SHP-1 is repressed in HTLV-1 transformed lymphocyte cell lines, Adult T-cell Leukemia and other hematological malignancies. However, the mechanisms that regulate SHP-1 expression remain unclear. We previously identified that the −120 to +157 of the SHP-1 P2 promoter (core promoter) exhibits similar levels of activity as the wild type promoter. Here we report the involvement of NF-kB and Oct-1 in the transcriptional regulation of the SHP-1 P2 promoter. To elucidate the mechanisms by which SHP-1 promoter is regulated, in vitro DNase I footprinting experiments were performed. Incubation of nuclear extracts from Jurkat cells with the SHP-1 P2 promoter probes revealed two DNase I protected regions between −100 and −90 and between −80 and −55 in the SHP-1 P2 promoter. Elk-1, Ik-1, NF-kB and Oct-1 were identified through database search as likely candidate factors binding to these regions. Electrophoretic Mobility Shift Assay (EMSA) was carried out using a double strand DNA probe that covers the previous DNase I footprinting area (−120 to −19) and Jurkat nuclear extract. Transcription factors NF-kB and Oct-1 were confirmed as binding to the SHP-1 P2 promoter through antibody supershift, probe competition, and/or site directed mutagenesis. Results from in vivo Chromatin Immunoprecipitation (ChIP) assay with anti-NF-kB and anti-Oct-1 antibody also strongly suggested that Oct-1 and NF-kB bound the SHP-1 P2 promoter in Jurkat cells. In transient transfection experiments using luciferase as a reporter, mutations at Oct-1 binding sites and NF-kB binding sites showed significant reduction in SHP-1 promoter activity compared to wild type core promoter, further indicating the involvement of these factors in the SHP-1 P2 promoter transcription regulation. In summary, this is the first report demonstrating that Oct-1 and NF-kB are involved in the regulation of SHP-1 P2 promoter. Modulation of these transcription factors could provide new targets for treatment of hematological malignancies.