The Proline-rich Homeodomain Protein Recruits Members of the Groucho/Transducin-like Enhancer of Split Protein Family to Co-repress Transcription in Hematopoietic Cells

Abstract

The proline-rich homeodomain protein (PRH/Hex) is important in the control of cell proliferation and differentiation and in the regulation of multiple processes in embryonic development. We have shown previously that PRH contains two domains that can independently bring about transcriptional repression. The PRH homeodomain represses transcription by binding to TATA box sequences, whereas the proline-rich N-terminal domain of PRH can repress transcription when attached to a heterologous DNA-binding domain. The Groucho/ transducin-like enhancer of split (TLE) family of proteins are transcriptional co-repressors that interact with a number of DNA-bound transcription factors and play multiple roles in development. Here we demonstrate that the proline-rich N-terminal domain of PRH binds to TLE1 in vitro and in yeast two-hybrid assays. We show that PRH and TLE proteins are co-expressed in hematopoietic cells and interact in co-immunoprecipitation assays. We demonstrate that TLE1 increases repression by PRH in transient transfection assays and that titration of endogenous TLE proteins by co-expression of Grg5, a natural trans-dominant negative protein, alleviates transcriptional repression by PRH. Finally, we show that a mutation in the PRH N-terminal domain that blocks the PRH-TLE1 interaction in vitro eliminates co-repression. We discuss these results in terms of the roles of PRH and TLE in cell differentiation and development.

PRH/HHex inhibits the migration of breast and prostate epithelial cells through direct transcriptional regulation of Endoglin

“…PRH N187A contains a mutation in the PRH homeodomain and is unable to bind DNA (4,27). PRH F32E contains a mutation that blocks the binding of PRH to co-repressor proteins belonging to the TLE family (3,27). Both of these mutated proteins show a significantly reduced ability to inhibit cell migration compared to wild type PRH (Fig.2B) although all three proteins are expressed at roughly equivalent levels (Fig.2C).…”

“…A rabbit polyclonal antibody was used to detect Endoglin (Abcam). PRH antibodies have been described previously (3,42). Lamin A/C and Tubulin antibodies were from Santa-Cruz.…”

“…PRH can activate or repress transcription of its target genes and it can also control gene expression at the posttranscriptional level via a protein-protein interaction with eIF4E (2)(3)(4)(5). In the mouse, retroviral expression of PRH leads to a T-cell leukaemia (6).…”

NKL homeobox genes in leukemia

“…107,108 For HHEX and TLX1, it has been shown that the interaction with TLE proteins is important in regulating downstream targets in hematopoietic lineages and in T-ALL. 52,109 Binding of TLE can result in repression of transcription of NKL targets, but it can also act as a competitive substrate for TLE proteins relieving other factors from TLE-mediated repression and activation of transcription. 110 For example, TLX1 expression enhances NOTCH1 signaling in a T-ALL cell line, partly by sequestering TLE from the Hairy/Enhancer of split 1 -TLE-mediated transcriptional repression complex.…”

Genomic and Expression Profiling of Benign & Malignant Nerve Sheath Tumors in Neurofibromatosis Patients

“…TLE1 is one of four TLE (Transducin-Like Enhancer of split) genes that encode human transcriptional repressors homologous to the Drosophila corepressor groucho (30); differential overexpression of TLE2, 3 and 4 has also been demonstrated in synovial sarcoma (1,3,25). TLE proteins are temporally expressed in embryogenesis where they are involved in developmental processes including neurogenesis, body patterning and hematopoesis (6,30,31,34). The repressive effect of Groucho and TLE1 is dependent on phosphorylation status and involves histone deacetylase (HDAC) activity (4,7,16,26,35).…”