Molecular Evolution of Apoptotic Pathways: Cloning of Key Domains from Sponges (Bcl-2 Homology Domains and Death Domains) and Their Phylogenetic Relationships

Abstract

Cells from metazoan organisms are eliminated in a variety of physiological and pathophysiological processes by apoptosis. In this report, we describe the cloning and characterization of molecules from the marine sponges Geodia cydonium and Suberites domuncula, whose domains show a high similarity to those that are found in molecules of the vertebrate Bcl-2 superfamily and of the death receptors. The Bcl-2 proteins contain up to four Bcl-2 homology regions (BH). Two Bcl-2-related molecules have been identified from sponges that are provided with two of those regions, BH1 and BH2, and are termed Bcl-2 homology proteins (BHP). The G. cydonium molecule, BHP1_GC, has a putative size of 28,164, while the related sequence from S. domuncula, BHP1_SD, has a M(r) of 24,187. Phylogenetic analyses of the entire two sponge BHPs revealed a high similarity to members of the mammalian Bcl-2 superfamilies and to the Caenorhabditis elegans Ced-9. When the two domains, BH1 and BH2, are analyzed separately, again the highest similarity was found to the members of the Bcl-2 superfamily, but a clearly lower relationship to the C. elegans BH1 and BH2 domains in Ced-9. In unrooted phylogenetic trees the sponge BH1 and BH2 are grouped among the mammalian sequences and are only distantly related to the C. elegans BH domains. The analysis of the gene structure of the G. cydonium BHP showed that the single intron present is located within the BH2 domain at the same position as in C. elegans and rat Bcl-x(L). In addition, a sponge molecule comprising two death domains has been characterized from G. cydonium. The two death domains of the potential proapoptotic molecule GC_DD2, M(r) 24,970, share a high similarity with the Fas-FADD/MORT1 domains. A death domain-containing molecule has not been identified in the C. elegans genome. The phylogenetic analysis revealed that the sponge domain originated from an ankyrin building block from which the mammalian Fas-FADD/MORT1 evolved. It is suggested that the apoptotic pathways that involve members of the Bcl-2 superfamily and of the death receptors are already present in the lowest metazoan phylum, the Porifera.

Living with death: the evolution of the mitochondrial pathway of apoptosis in animals

“…70 GCBHP2 expression is upregulated in sponge cells exposed to low Apical and initiator caspase homologs, pro-and antiapoptotic Bcl-2 family members. Caspase-dependent cell death observed in allograft rejection [67][68][69][70][71][72] (but not high) levels of tributyltin or heat shock, and GCBHP2 appears to have an antiapoptotic role. Mammalian cells transfected with GCBHP2 were somewhat resistant to serum starvation and tributylin-induced apoptosis.…”

Sponge Bcl-2 homologous protein (BHP2-GC) confers distinct stress resistance to human HEK-293 cells

“…Until recent discoveries 1,2 it was assumed that the physiological cell death is restricted to multicellular organisms, which have separate germ and somatic cells. 3 Originally it was suggested to divide the physiological cell death into two processes: (a)`programmed cell death', describing the developmentally regulated elimination of specific cells during embryogenesis, 4 and (b)`apoptotis', describing morphological changes of dying cells.…”

“…24 The first cDNAs encoding putative Bcl-2 homologous proteins from animals evolutionary older than the triploblastic Metazoa have been identified from the sponges G. cydonium and S. domuncula. 1 They are characterized by BH1 and BH2 domains and one transmembrane segment. It was the aim of the present study to elucidate the function of the putative Bcl-2 homologous proteins in sponges.…”

“…Like the previous sponge Bcl-2's the new molecule, termed GCBHP2 (deduced polypeptide BHP2_GC), comprises the BH1 and the BH2 domains as well as the transmembrane segment. 1 Exposure of sponge cells to the organic derivative of the heavy metal tin, tributyltin [TBT] and heat shock causes an increased expression of GCBHP2. TBT also causes an [Ca 2+ ] i overload, cytoskeletal damage and mitochondrial failure (see 25 ); and it was already earlier found that TBT induces apoptosis in sponges 26 and also in vertebrate cells.…”

Discovery and molecular characterization of a Bcl-2–regulated cell death pathway in schistosomes

“…However, further characterization of these proteins is required to fully establish their function(s). Multi-BH-domain Bcl-2 proteins have also been described in the most ancient metazoans, sponges (phylum Porifera) (14)(15)(16), but their functions are only poorly characterized.…”