Required for the formation of cilia. Plays an indirect role in sonic hedgehog signaling, cilia being required for all activity of the hedgehog pathway. 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 (By similarity). Component of the IFT complex B, at least composed of IFT20, IFT22, HSPB11/IFT25, IFT27, IFT46, IFT52, TRAF3IP1/IFT54, IFT57, IFT74, IFT80, IFT81, and IFT88 (By similarity). Interacts with IFT20 (By similarity). Interacts with IFT88 (By similarity). Interacts with IFT80, IFT-81, IFT74, IFT172, TTC30B and KIF17 (By similarity). Interacts with BLOC1S2 (By similarity). Interacts with RYBP (By similarity). Interacts with HOMER1; the interaction possibly prevents the pro-apoptotic effects of IFT57 (By similarity). Interacts with HIP1 (By similarity). In normal conditions, it poorly interacts with HIP1, HIP1 being strongly associated with HTT (By similarity). However, in mutant HTT proteins with a long poly-Gln region, interaction between HTT and HIP1 is inhibited, promoting the interaction between HIP1 and IFT57, leading to apoptosis (By similarity). Interacts with BFAR (By similarity). Interacts with TTC25 (By similarity). Interacts with USH1G (By similarity). Concentrates within the inner segment of cilia. In retina, detected in the photoreceptor basal body and connecting cilium. Most abundant in the inner segment of photoreceptors (at protein level). The pseudo DED region (pDED) mediates the interaction with HIP1. Belongs to the IFT57 family.