Tend to run up banks of Seine (5)
I believe the answer is:
nurse
'tend to' is the definition.
(I've seen this before)
'run up banks of seine' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'banks of' means to remove the middle letters (the banks are the sides of the word).
'seine' with its middle removed is 'se'.
'run' written backwards gives 'nur'.
'nur'+'se'='NURSE'
(Other definitions for nurse that I've seen before include "Look after: entertain" , "Foster" , "Entangle" , "Medical worker" , "Tend - care for" .)