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Novel functions of ribosomal protein S6 in growth and differentiation of Dictyostelium cells
Author(s) -
Ishii Kazutaka,
Nakao Yusaku,
Amagai Aiko,
Maeda Yasuo
Publication year - 2009
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1111/j.1440-169x.2009.01115.x
Subject(s) - ribosomal protein s6 , biology , cytokinesis , microbiology and biotechnology , cell division , p70 s6 kinase 1 , cell , pi3k/akt/mtor pathway , genetics , signal transduction
We have previously shown that in Dictyostelium cells a 32 kDa protein is rapidly and completely dephosphorylated in response to starvation that is essential for the initiation of differentiation (Akiyama & Maeda 1992). In the present work, this phosphoprotein was identified as a homologue (Dd‐RPS6) of ribosomal protein S6 (RPS6) that is an essential member for protein synthesis. As expected, Dd‐RPS6 seems to be absolutely required for cell survival, because we failed to obtain antisense‐RNA mediated cells as well as Dd‐rps6 ‐null cells by homologous recombination in spite of many trials. In many kinds of cell lines, RPS6 is known to be located in the nucleus and cytosol, but Dd‐RPS6 is predominantly located in the cell cortex with cytoskeletons, and in the contractile ring of just‐dividing cells. In this connection, the overexpression of Dd‐RPS6 greatly impairs cytokinesis during axenic shake‐cultures in growth medium, resulting in the formation of multinucleate cells. Much severe impairment of cytokinesis was observed when Dd‐RPS6‐overexpressing cells (Dd‐RPS6 OE cells) were incubated on a living Escherichia coli lawn. The initiation of differentiation triggered by starvation was also delayed in Dd‐RPS6 OE cells. In addition, Dd‐RPS6 OE cells exhibit defective differentiation into prespore cells and spores during late development. Thus, it is likely that the proper expression of Dd‐RPS6 may be of importance for the normal progression of late differentiation as well as for the initiation of differentiation.