To tease us up can be sweet! (5)
I believe the answer is:
sugar
'be sweet' is the definition.
(thesaurus)
'to tease us up' is the wordplay.
'to tease' becomes 'rag' ('rag' can be a synonym of 'tease').
'up' says the letters should be written backwards (in down clue: letters go upwards).
'rag'+'us'='ragus'
'ragus' reversed gives 'SUGAR'.
'can' acts as a link.
(Other definitions for sugar that I've seen before include "Sucrose" , "Sweeten" , "Damn" , "Plantation product" , "e.g. Glucose" .)