In what way are literature and superstructure related?
The relationship you mention can be established through a Marxist approach to literary criticism. Superstructure and base are the two pillars of the Marxist view of society. The base involves economic relations between labor and capital and includes the actors: employers and workers. The superstructure comprises culture in every form, politics, religion, the legal system, and ideology.
Thus, a Marxist approach to literary criticism will take the above items into account in order to show how a literary work expresses these concerns at a given time. By looking at the lives of the different social classes and at the economic development of their members in particular and of the country or area in general, the Marxist approach will draw conclusions regarding the success or failure of social mobility.
Moreover, from the Marxist point of view, literary creation is the combined product of both the writer's personal inspiration and the way in which he/she is affected by the ruling system or regime.
Writers such as Jean-Paul Sartre intentionally described society along the lines of Marxism, but in fact practically any work of literature can be analyzed in the light of the Marxist approach. Bearing in mind the components of the superstructure, you may find striking facts and thoughts in many authors that were in no way supporters of Marx, or that wrote before his time. An outstanding example of this is Henry Fielding's Tom Jones, first published in 1749.