Abstract
We have identified a novel c-Myc-responsive gene, named JPO1, by representational difference analysis. JPO1 responds to two inducible c-Myc systems and behaves as a direct c-Myc target gene. JPO1 mRNA expression is readily detectable in the thymus, small intestine, and colon, whereas expression is relatively low in spleen, bone marrow, and peripheral leukocytes. We cloned a full-length JPO1 cDNA that encodes a 47-kDa nuclear protein. To determine the role of JPO1 in Myc-mediated cellular phenotypes, stable Rat1a fibroblasts overexpressing JPO1 were tested and compared with transformed Rat1a-Myc cells. Although JPO1 has a diminished transforming activity as compared with c-Myc, JPO1 complements a transformation-defective Myc Box II mutant in the Rat1a transformation assay. This complementation provides evidence for a genetic link between c-Myc and JPO1. Similar to c-Myc, JPO1 overexpression enhances the clonogenicity of CB33 human lymphoblastoid cells in methylcellulose assays. These observations suggest that JPO1 participates in c-Myc-mediated transformation, supporting an emerging concept that c-Myc target genes constitute nodal points in a network of pathways that lead from c-Myc to various Myc-related phenotypes and ultimately to tumorigenesis.
Highlights
We have identified a novel c-Myc-responsive gene, named JPO1, by representational difference analysis
Initial work in our laboratory relied on representational difference analysis (RDA)1 to identify novel putative c-Myc target genes that could be involved in cellular transformation
Fulllength human JPO1 cDNA was cloned from a human spleen cDNA library using this EST as a probe
Summary
We have identified a novel c-Myc-responsive gene, named JPO1, by representational difference analysis. Cloning of Human JPO1—JPO1 was identified as a differentially expressed gene in an RDA of non-adherent Rat1a versus Rat1a-Myc fibroblasts [36]. The effect of cellular adherence on JPO1 transcript levels was examined by Northern blot analysis of mRNA collected from both adherent and non-adherent Rat1a and Rat1a-Myc cell lines (Fig. 2A).
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