Falkor, a novel cell growth regulator isolated by a functional genetic screen

Abstract

A novel cell growth regulator, named Falkor, was identified using a functional approach to mammalian gene cloning, the Genetic Supressor Elements (GSE) method. In this screen, expression of the C-terminal domain of Falkor conferred cells with resistance to cisplatin-induced growth arrest. Expression of the Cterminus of Falkor, but not of the full-length protein, enhanced cell growth both following genotoxic stress and under normal conditions suggesting a general role for this protein in cell growth control. This effect of the Cterminus fragment was abrogated by over-expression of the full-length Falkor, suggesting that the fragment counteracts the function of the full-length protein. Falkor is encoded by a 2-kb mRNA which is present at different levels in various tissues, and is localized in the nucleus of cells. The C-terminal domain of Falkor, isolated from the GSE library, has significant homology to a known human and rat cell growth regulator, SM-20, and to the C. elegans protein EGL-9, recently shown to modify the Hypoxia Inducible Factor-1a. The homology suggests that these proteins share a functional domain that is conserved among a family of growth regulation proteins.

Genomewide gain-of-function genetic screen identifies functionally active genes in mouse embryonic stem cells

“…Surprisingly, overexpression of a full-length IRF1-encoding cDNA induced cell death, opposite to the expected phenotype, whereas cells carrying the 5Ј truncated construct proliferated normally. Similarly, truncated transcripts whose functions strongly differ from the full-length genes were detected in gain-of-function screen studies previously published by other groups (23). As another example, constitutive expression of a Nanog cDNA with a truncated 3Ј UTR induced higher rates of proliferation than the full-length version.…”

Oxygen sensing in the hypoxic response pathway: regulation of the hypoxia-inducible transcription factor

“…The HIF prolyl hydroxylases have been reported to be regulated at the level of enzyme expression in response to growth factors (Moschella et al 1999;Lipscomb et al 2001;Erez et al 2002). The relevance of these findings to the regulation of HIF activity remains unclear.…”

HIF prolyl and asparaginyl hydroxylases in the biological response to intracellular O2 levels

“…Recent evidence suggests that both HIF-3α and the large subunit (Rpb1) of RNA polymerase II are also targeted for VHL-dependent ubiquitylation via prolyl hydroxylation (Kuznetsova et al, 2003;Maynard et al, 2003). Previous studies of PHD1 and PHD3 have implicated these gene products in the regulation of a variety of cellular growth, differentiation and apoptotic pathways, and it is possible that prolyl hydroxylation of non-HIF-α substrates is involved in such responses (Erez et al, 2002;Lipscomb et al, 2001;Madden et al, 1996;Seth et al, 2002;Wax et al, 1994). In addition, more effective database searching enabled by new structural insights suggests the existence of a much larger 2-OG oxygenase family than has been previously recognised (Elkins et al, 2003), raising the possibility that other members of this family function in oxygen-regulated pathways that involve protein hydroxylation.…”