Proteins for the basic helix-loop-helix transcription factor SCL

• Main Author: Bloor, A. J. C.
• Published: University of Cambridge 2003
• Subjects: 572.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596727

Members of the basic Helix-Loop-Helix (bHLH) family of transcription factors play critical roles in the control of development processes in species ranging from yeast to humans. The product of the <i>SCL</i> (Stem Cell Leukaemia) gene is a bHLH protein that was first identified by its ectopic expression in a case of childhood acute leukaemia and it has subsequently been characterised as a key player in the regulation of the development of blood and endothelium. The mechanism by which SCL functions are unclear, however it is likely that it regulates target genes by the formation of cell specific multiprotein complexes. A number of such complexes have been identified, however only in a small number of cell types. The aim of this project was to identify novel SCL partner proteins in order to better understand how it functions both normally and as an oncogene. Over 300 potential SCL interaction partners were identified in a yeast 2-hybrid screen of an embryonic cDNA library. Of these, the interaction between SCL and RFP (Ret Finger Protein) was characterised in the greatest detail. RFP is a ubiquitously expressed TRIM (Tripartite Motif) protein and little was previously known about its cellular function. RFP interacts with SCL in vitro and a stable complex of the two proteins was isolated in both COS cells and the haemopoietic progenitor cell line of 416B. RFP also interacts with a subset of other bHLH proteins via the bHLH domain but not with other classes of transcription factors and functions to repress their ability to transactivate reporter genes. The expression pattern of RFP was studied in a panel of haemopoietic cell lines. The subcellular location of RFP correlates with the lineage and development stage of the cell and also appears to be cell cycle regulated which suggests a number of novel mechanisms by which it could regulate SCL or other bHLH factors. Moreover, RFP is able to inhibit the ability of myogenic bHLH factors to convert multipotent fibroblasts into muscle indicating that its interaction with bHLH proteins is biologically significant.