Organisms synchronize their behavior, physiology, and metabolism with the periodically changing environmental condition using internal timing mechanisms or circadian clocks. In mammalian system, the peripheral organs like liver are entrained by systemic cues directly such as body temperature or blood-borne signals. However, the mechanisms of phase-entrainment in peripheral organs are still poorly understood. Based on the observation that the up-regulation of immediate early transcription factors (IETFs), like c-FOS, PER1, and PER2 were observed after serum shock in cultured cells, the working hypothesis in our laboratory is that IETFs participate in peripheral clock synchronization. A method called STAR-PROM (Synthetic Tandem Repeat Promoter) screening previously was established in our laboratory to identify IETFs responding to blood-borne factors in human liver cell line, HepaRG cells. Two novel IETF, FOXA2 and the orphan nuclear receptor NR4A1 were discovered in the screen and the results were presented in this thesis.