Get entries filtered by author's category
You probably have to query twice, first get all the users and then get all news entries
published by any of these users using the authorId parameter on your criteria model.

{% set userRegion = currentUser.region.first() %}
{% set regionUsersIds = craft.users.relatedTo(userRegion).limit(null).ids() %}

{% set regionNews = craft.entries.section('news').authorId(regionUsersIds) %}