Italian city supporting Church element that shines (6)
I believe the answer is:
chrome
'element that shines' is the definition.
(chrome is a shiny metal)
'italian city supporting church' is the wordplay.
'italian city' becomes 'rome' (city in Italy).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'church' becomes 'ch' (common abbreviation).
'rome' put after 'ch' is 'CHROME'.
(Other definitions for chrome that I've seen before include "Metallic plate" , "Plate (for bathroom fixtures etc)" , "Feature of bath taps" , "used to make plate" , "Metal plating - type of yellow" .)