Int. J. Dev. Biol. 57: 375 - 381 (2013)
doi: 10.1387/ijdb.130046jw
© UPV/EHU Press

The Dictyostelium prestalk inducer DIF-1 directs phosphorylation of a bZIP transcription factor

Yoko Yamada, Yuzuru Kubohara1, Haruhisa Kikuchi2, Yoshiteru Oshima2, Hong-Yu Wang, Susan Ross and Jeffrey G. Williams*

1 College of Life Sciences, Welcome Trust Biocentre, University of Dundee, UK, 2 Department of Molecular and Cellular Biology, Institute for Molecular and Cellular Regulation, Gunma University, Japan and 3Laboratory of Natural Product Chemistry, Tohoku University Graduate School of Pharmaceutical Sciences, Aoba-yama, Aoba-ku, Sendai, Japan

ABSTRACT DIF-1, a chlorinated hexaphenone produced by developing Dictyostelium cells, induces prestalk differentiation. DimB is a bZIP transcription factor that accumulates in the nucleus upon exposure to DIF-1, where it directly activates transcription of DIF-responsive genes. The signaling steps upstream of DimB and downstream of DIF-1 are entirely unknown. Analysis by mass spectrometry shows that incubation with DIF-1 rapidly stimulates phosphorylation at several sites in DimB. We characterize the most highly responsive site, S590, which is located very close to the C terminus. A point mutation in this site, S590A, does not inhibit DimB nuclear accumulation in response to DIF. However, this seems likely to reflect functional redundancy with other sites; because a panel of chemical variants on the structure of DIF-1 show a correlation between their potencies as inducers of DimB nuclear accumulation and their potencies as inducers of phosphorylation at S590. Furthermore, the S590A mutant is fully active in mutant rescue of a dimB null strain, arguing against an alternative role in transcriptional activation of target genes. We conclude that i) DIF-1 directs phosphorylation at S590, ii) although it is not essential for nuclear accumulation in response to DIF-1 correlative evidence, based upon a panel of DIF-1 related molecules, suggests that this modification may play a redundant role in the process. iii) We also present evidence that the kinase activity, which phosphorylates S590, is non-nuclear and that this signalling pathway is, in part at least, independent of the DIF-regulated STATc activation pathway.

Keywords:

Dictyostelium, DimB: DIF-1, activation, kinase

*Corresponding author e-mail: j.g.williams@dundee.ac.uk