The signals for starvation response are transduced through elevated [Ca2+]i in Dictyostelium cells.
The mechanism by which cells recognize starvation to allow subsequent cellular development was analyzed using Dictyostelium discoideum, with special emphasis on Ca2+ as a crucial signal transducer in intra- and intercellular communications. As was expected, the cytosolic Ca2+ concentration ([Ca2+]i) in aequorin-expressing cells (RHI76 derived from D. discoideum Ax-3) was temporarily increased, when 3-5 microM thapsigargin (Tg), a specific inhibitor of the Ca(2+)-ATPase, was added into the cells incubated in semistarvation medium (SS-medium: 1 vol of growth medium plus 7 vol either of 20 mM Na2/K-phosphate buffer (pH 6.2) or of Bonner's salt solution (BSS)). Essentially the same result was obtained by the application of 5 microM nigericin (Ng), an acid ionophore to cells under the semistarved condition. Here it is of interest to note that in the SS-medium Tg and Ng are capable of enhancing cell differentiation as exemplified well by the earlier acquisition of chemotactic response to cAMP, possibly inducing the starvation response through the [Ca2+]i increase. From Western blot analysis of phosphotyrosine (pTyr)-containing proteins using anti-pTyr antibody, it was found that the pTyr-phosphorylation levels of 97-, 80-, and 45-kDa proteins increase specifically in response to starvation. Interestingly, Tg and Ng induced such a change of the 80-kDa protein in the cells incubated in the SS-medium. Taken together these results strongly suggest that the temporal increase of [Ca2+]i may be a matter of importance for signal transduction coupled with starvation response.
Tanaka
Y
Y
Biological Institute, Graduate School of Science, Tohoku University, Sendai, Japan. yukki@biology.tohoku.ac.jp
Itakura
R
R
Amagai
A
A
Maeda
Y
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004023:Dictyostelium; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D009550:Nigericin / Q000494:pharmacology; D010766:Phosphorylation; D019000:Phosphotyrosine; D015398:Signal Transduction; D019284:Thapsigargin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007476:Ionophores; D019000:Phosphotyrosine; D019284:Thapsigargin; D009550:Nigericin; D002118:Calcium