Take context from the input text and decide on the accurate relationship between 'Turkish Airlines' and 'Istanbul' from the options provided.
Options: chief executive officer, creator, parent organization, headquarters location

Partnerships with airlines including Lufthansa and Poland’s LOT remain key even as Turkish Airlines builds its Istanbul base into a global hub with an eye to the success of Gulf operators Dubai-Emirates, Qatar Airways Ltd. and Abu Dhabi’s Etihad Airways PJCS, Kotil said.
headquarters location