Pretty sure its Islami Jamhoori Ittehad (urdu for Islamic Democratic Alliance) and the IJI pretty much supports PTI in concept, rather than the other way round. The IJI itself had been a supporter of PML-N, Imran too was in theory supporting PML-N during his anti-Musharraf days, until PML-N showed their true colors, Imran split from there after he told Sharif not to contest in the elections but he did under Benazir's push, we all know of Chaudhary Nisaar's links with the military establishment, they too span back to the IJI.
The only known and provable association might be when pretty much every party was united for the single aim of ousting Musharraf. Also recently in the Peshawar Dharna some of these parties came in protest of the Drones...
The Karachi and Multan Dharna, saw these people back off after they realized that only PTI is getting credit for it not them.