Unexpected roles of aDictyosteliumhomologue of eukaryotic EF-2 in growth and differentiation

Abstract

EF-2 is believed to be indispensable for polypeptide chain elongation in protein synthesis and therefore for cell proliferation. Surprisingly, we could isolate ef2 null cells from Dictyostelium discoideum that exhibited almost normal growth and protein synthesis, which suggests that there is another molecule capable of compensating for EF-2 function. The knock-out of Dictyostelium EF-2 (Dd-EF2H; 101 kDa phosphoprotein)impairs cytokinesis, resulting in formation of multinucleate cells. The initiation of differentiation, including the acquisition of aggregation competence, was delayed in Dd-ef2 null cells compared with that in wild-type. By contrast, Dd-ef2 overexpression enhanced the progression of differentiation, thus indicating a positive involvement of Dd-EF2H in growth/differentiation transition.

Novel functions of ribosomal protein S6 in growth and differentiation of Dictyostelium cells

“…2004, 2008). We have shown that a Dictystelium homologue (Dd‐EF‐2A; 101 kDa) of the polypeptide chain elongation 2 (EF‐2) is in a dephosphorylated state, coupling with the initial differentiation of starved Ax‐2 cells from the GDT‐point (Akiyama & Maeda 1992; Watanabe et al. 2003).…”

“…2003). More importantly, the initiation of differentiation, including the acquisition of aggregation‐competence, is delayed in Dd‐ef‐2a null cells compared with that in parental Ax‐2 cells, while Dd‐ef‐2a overexpression enhances the progression of differentiation, thus resulting in a positive involvement of Dd‐EF‐2A in GDT (Watanabe et al. 2003).…”

“…2003). Although EF‐2 is believed to be indispensable for polypeptide chain elongation and therefore for cell proliferation, the knock‐out of Dd‐ef‐2a by homologous recombination is not very effective on growth and protein synthesis (Watanabe et al. 2003).…”

Unique Behavior and Function of the Mitochondrial Ribosomal Protein S4 (RPS4) in Early Dictyostelium Development

“…Recently, we have revealed that the 101 kDa protein is a Dictyostelium homologue of elongation factor 2 (EF-2) (Watanabe et al, 2003). In this connection, it has been demonstrated in animal cells that the activity of EF-2 in translation is regulated by its phosphorylation levels, and that the dephosphorylated state is generally the active form (Ryazanov et al, 1988).…”

“…We have also demonstrated that the phosphorylation levels of 90 kDa and 101 kDa proteins are specifically reduced during early cellular differentiation from the PS-point (Akiyama and Maeda, 1992). The 90 kDa and 101 kDa phosphoproteins were identified as homologues of GRP94 (glucose-regulated protein 94; the endoplasmic reticulum HSP90) in D. discoideum (Dd-GRP94) (Morita et al ., 2000) and a Dictyostelium homologue of EF-2 (Watanabe et al ., 2003) respectively. As previously presented , the dia3 gene, which encodes a mitochondrial protein cluster including ribosomal protein S4 (RPS4), is expressed specifically during the GDT of Ax-2 cells: its overexpression enhances the progress of cell differentiation, while its partial inativation by means of homologous recombination greatly impairs differentiation and morphogenesis after starvation (Inazu et al ., 1999).…”