Identification of highly conserved genes: SNZ and SNO in the marine spongeSuberites domuncula: their gene structure and promoter activity in mammalian cells

Recently, we reported that cells from the sponge Suberites domuncula respon d to ethylene with an increase in intracellular Ca2+ level [Ca2+](i), and w ith an upregulation of the expression of (at least) two genes, a Ca2+/calmo dulin-dependent protein kinase and the potential ethylene-responsive gene, termed SDSNZERR (A. Krasko, H.C. Schroder, S. Perovic, R. Steffen, M. Kruse , W. Reichert, I.M. Muller, W.E.G. Muller, J. Biol. Chem. 274 (1999)). Here , we describe for the first time that also mammalian (3T3) cells respond to ethylene, generated by ethephon, with an immediate and transient, strong i ncrease in [Ca2+]i. Next, the promoter for the sponge SDSNZERR gene was iso lated from S. domuncula. It was found that the SDSNZERR gene is positioned adjacent to the SAZ-related gene (SNZ-proximal open reading frame) (SDSNO) and linked, as in Saccharomyces cerevisiae, in a head-to-head manner. Until now, neither homologues nor orthologues of these two genes have been ident ified in higher metazoan phyla. The full-length genes share a bidirectional promoter. 3T3 cells were transfected with this promoter; the activity of t he SDSNZERR promoter was strong and twice as high as that of the SV40 promo ter, while the SDSNO promoter was less active. Surprisingly, the activity o f the SDSNZERR promoter could not be modulated by ethylene or salicylic aci d while it is strongly upregulated, by 4-fold, under serum-starved conditio ns. It is concluded that the modulation of the level of [Ca2+](i) by ethyle ne in mammalian cells is not correlated with an upregulation of the ethylen e-responsive gene SDSNZERR. The data indicate that in mammalian cells, the activity of the SDSNZERR promoter is associated with the repression of seru m-mediated growth arrest. (C) 2001 Elsevier Science B.V. All rights reserve d.