Recruited by SOX15 to FOXK1 promoters where it acts as a transcriptional coactivator of FOXK1. Interacts with SOX15; the interaction recruits FHL3 to FOXK1 promoters where it acts as a transcriptional coactivator of FOXK1. Expressed in myogenic progenitor cells (at protein level) (PubMed:17363903). Expressed in skeletal striated muscle and the heart (PubMed:10906474, PubMed:17363903). Expressed to a lesser extent, in lung, and kidney (PubMed:10906474). Expressed in skin and skeletal muscles such as the masseter, tongue, tibialis anterior and plantar muscles (PubMed:10049693). Expressed ubiquitously at low levels during embryonic development.