I have a similar question. Is it possible to update the status of a discussion (to resolved) OR close a discussion using REST apis? Did not see that option in the documentation.
The "resolved" property controls this. A question is either "open", "assumed_answered" or "resolved" if you set the field to resolved you also should set the field "answer" to the correct response, e.g. "https://jivedemo-smarterpath.jiveon.com/api/core/v3/messages/2055"
Simply get the json for the content/discussion you want to change, and post it back with an updated subject field