PRH/Hhex Controls Cell Survival through Coordinate Transcriptional Regulation of Vascular Endothelial Growth Factor Signaling

Abstract

The proline-rich homeodomain protein (PRH) plays multiple roles in the control of gene expression during embryonic development and in the adult. Vascular endothelial growth factor (VEGF) is a mitogen that stimulates cell proliferation and survival via cell surface receptors including VEGFR-1 and VEGFR-2. VEGF signaling is of critical importance in angiogenesis and hematopoiesis and is elevated in many tumors. Here we show that PRH binds directly to the promoter regions of the Vegf, Vegfr-1, and Vegfr-2 genes and that in each case PRH represses transcription. We demonstrate that overexpression or knockdown of PRH directly impinges on the survival of both leukemic and tumor cells and that the modulation of VEGF and VEGF receptor signaling by PRH mediates these effects. Our findings demonstrate that PRH is a key regulator of the VEGF signaling pathway and describe a mechanism whereby PRH plays an important role in tumorigenesis and leukemogenesis.

A previously unrecognized promoter of LMO2 forms part of a transcriptional regulatory circuit mediating LMO2 expression in a subset of T-acute lymphoblastic leukaemia patients

“…Having established that there is indeed a direct link, we next asked whether HHEX/PRH was important for the growth of human T-ALL cells. Using vectors previously established to produce effective knockdown of HHEX/PRH (Noy et al, 2010) we now show that following expression of short hairpin RNA against HHEX/PRH in the LMO2-expressing nontranslocated cell line Molt4, cells were unable to grow, whereas cells transfected with a control vector could expand as expected (Figure 7g). Taken together, these results not only support the existence of a highly connected LMO2, FLI1, ERG triad in T-ALL but also demonstrate that HHEX is a direct target of this triad with a likely role in human T-ALL (Figure 7h).…”

“…A total of 5 Â 10 6 Molt4 cells were electroporated using 10 mg green fluorescent protein short hairpin RNA (control) or 5 mg PRH49 and 5 mg PRH51 short hairpin RNA plasmids in combination previously as described (Noy et al, 2010). Cells were selected with 1 mg/ml puromycin and viable cells were counted daily for 14 days.…”

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

“…PRH can control cell proliferation via the posttranscriptional regulation of cyclin D mRNA transport (2). In addition, our previous work has shown that in leukaemic cells, PRH directly represses multiple genes that encode proteins involved in VEGF signalling including Vegfa and Vegfr-1 (31). In these cells VEGF acts as an autocrine growth factor and the transcriptional regulation of these VEGF signalling genes by PRH controls cell survival.…”

“…In these cells VEGF acts as an autocrine growth factor and the transcriptional regulation of these VEGF signalling genes by PRH controls cell survival. The extent to which these modes of cell survival control operate in other cell types is not known, although in breast cancer MCF-7 cells, PRH regulates the transcription of Vegf receptor genes and a PRH knockdown increases cell growth (31). In endothelial cells PRH over-expression also controls VEGF signalling genes and alters cell migration and invasion (24).…”

“…Presumably, the promoter distal PRH binding sites are responsible for Endoglin transcription activation by PRH. Alternatively, the presence of chromatin/chromatin associated factors may be important for activation of the Endoglin promoter by PRH just as they are for repression by PRH at the Vegfr-1 promoter (31).…”