Required for the formation of cilia. Plays an indirect role in sonic hedgehog signaling, cilia being required for all activity of the hedgehog pathway (By similarity). Together with RAB23 and KIF17, it is required for the localization of specific G protein-coupled receptors, such as dopamime receptor DRD1, to primary cilia (PubMed:26182404). Has pro-apoptotic function via its interaction with HIP1, leading to recruit caspase-8 (CASP8) and trigger apoptosis. Has the ability to bind DNA sequence motif 5'-AAAGACATG-3' present in the promoter of caspase genes such as CASP1, CASP8 and CASP10, suggesting that it may act as a transcription regulator; however the relevance of such function remains unclear. {ECO:0000250, ECO:0000269|PubMed:11788820, ECO:0000269|PubMed:17107665, ECO:0000269|PubMed:17623017, ECO:0000269|PubMed:26182404}. This is the function of IFT57 (intraflagellar transport 57, Ensembl gene identifier ENSG00000114446).