The YSK1 kinase (red) is brought to the Golgi by GM130 (green).

The Golgi apparatus holds more than the key to protein secretion. On page 1009, Preisinger et al. show that the Golgi harbors signaling platforms from which kinases orchestrate cell migration.

The authors find that the Golgi is home to two kinases, YSK1 and MST4. By binding to the Golgi matrix protein GM130, the kinases are autophosphorylated and thus activated. Mutants that prevented Golgi localization of activated YSK1 disrupted the normal perinuclear Golgi pattern. Some YSK1 substrates may therefore maintain Golgi structure.

Other substrates are needed for migration, even when the Golgi structure remains intact. The authors identified 14–3-3ζ as one YSK1 substrate whose phosphorylation was required for wound-induced cell migration. Overexpression of MST4, in contrast, blocked migration without altering Golgi structure. Migration could therefore be regulated by competition between the kinases for GM130 binding, although the upstream signals that regulate their Golgi association are unknown.

14–3-3 proteins regulate membrane protein assembly and could thus influence which proteins are secreted to the plasma membrane, including integrins, which are known to interact with 14–3-3 proteins. Other kinase substrates might alter Golgi polarity to direct secretion to specific plasma membrane domains. Golgi polarity was indeed lost in YSK1 mutants. Both effects would be instrumental in migration.

On the flip side, changes at the Golgi could affect kinase signaling. The authors hypothesize that intensified protein secretion, for example, might remove GM130 to other interacting proteins (such as p115 or Rabs) and thus block kinase signaling. More kinase substrates need to be found to determine what effects this might have. ▪