They are held responsible in the same way as the news websites will be - if they remove the article fast enough, and publish an article that's equally visible retracting their previous statement, within of 24h, there won't be any punishment.

News organizations could post a bond on each article. Then they could lose money if they lie. For the main context of a story, for factual inaccuracies, for spelling mistakes, it could be contextual with different types of bonds. The question is how to verify, since these 'fact-checker' websites are a 'who guards the guards' problem.

I'd guess that in many jurisdictions, some libel law could be used to slap them if the story names individuals or (some places) corporate entities.

This probably would require the mentioned parties to sue, though - so no luck if it is a fake news story portraying someone in a positive light.