What different roles do lumacaftor and ivacaftor play in Orkambi's action on the CFTR protein?

In Orkambi, lumacaftor corrects F508del-CFTR processing and trafficking, increasing functional protein at the cell surface, while ivacaftor potentiates CFTR channel opening to increase chloride transport; together they increase F508del-CFTR quantity and function, although their exact mechanisms are unknown.