Given the task definition and input, reply with output. In this task, you are given a sentence. You are expected to recognize the name of gene or protein. Although there might be several correct answers, you need to write one of them.

In this study , we examined whether PPARgamma ligand regulates osteopontin gene expression in THP - 1 cells , a cell line derived from human monocytic leukemia cells which can differentiate to macrophage upon stimulation with phorbol ester PMA .
PPARgamma ligand