Create a new role "UserSecurity". Then in the "Row Filters" tab for your role, add filters for each table.
Partner dimension :
Partner[PartnerName] = LOOKUPVALUE(User[PartnerAccess], User[Username], USERNAME())
Region dimension :
Region[RegionName] = LOOKUPVALUE(User[RegionAccess], User[Username], USERNAME())
The fact table :
CALCULATE(
TRUE,
FILTER(
ALL(Partner),
Partner[PartnerName] = LOOKUPVALUE(User[PartnerAccess], User[Username], USERNAME())
),
FILTER(
ALL(Region),
Region[RegionName] = LOOKUPVALUE(User[RegionAccess], User[Username], USERNAME())
)
)