By design, the dependencies are used only for visualization. There are no specific fields to be updated when successors or predecessors are changed. The dependency described is implemented in the child-parent relation. For example, when the child start or end is changed, the same is propagated to the parent.
With dependencies, if there is a specific case that should propagated through items, it should be implemented additionally. You can get the DataSource with the dataSource field. And then use the HierarchicalDataSource API in order to get changed items and update other items' fields programmatically.