Journal of Stem Cell Research & Therapy

Abstract

Transactivating Target Gene Expression by Recombinant SALL4B: A Pluripotent Stem Cell Marker

Mengru Yuan, Yun Wang, Zhihua Ren, Wei Dai and Yongping Jiang

SALL4 is an important transcription factor that supports the expansion of hematopoietic stem cells. SALL4 expression is also deregulated in several types of leukemia. Recent studies reveal that SALL4B, a major isoform of SALL4, is heavily modified by post-translational mechanisms and these modifications are critical for their stability, subcellular localization, and transcriptional activities. Given the importance of SALL4B in supporting stem cell selfrenewal and expansion, we optimized a large scale expression and purification process to obtain SALL4B using the baculovirus expression vector system. Recombinant TAT-SALL4B was efficiently purified by nickel affinity chromatography under native conditions. Immuno-blotting confirmed that recombinant SALL4B was highly expressed and purified. As the first step to test the biological activity of purified TAT-SALL4B, we investigated whether TATSALL4B, directly supplemented to the culture medium, was capable of entering into cells through the protein transduction process. Fluorescent microscopy revealed that recombinant TAT-SALL4B specifically localized to the nucleus in a concentration- and time-dependent manner. Reporter gene assays showed that purified TAT-SALL4B protein activated OCT4 gene promoter, indicating that recombinant SALL4B was transcriptionally active in vivo. Combined, our results suggest that TAT-SALL4B may provide a promising factor for supporting ex vivo expansion of hematopoietic stem cells.