Sharing lead with businesses making roads (2-8)

'sharing' is the definition.
The answer and definition can be both to do with fundamental existence as well as being present participle verbs.
Perhaps you can see a link between them that I can't see?

'lead with businesses making roads' is the wordplay.
I cannot really see how this works, but
'lead' could be 'costar' (co-star is a kind of lead) and 'costar' is located in the answer.
'roads' could be 'ring' (ring road is a kind of road) and 'ring' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?