COP1 is a RING E3 ligase first identified in plants, where it is instrumental in establishing photomorphogenesis. A complex regulatory network centered around COP1 has since been demonstrated to constitute a major signal transduction axis mediating light/darkness or temperature response, whereby changes in COP1 activity link light sensor modules (cryptochrome, phytochrome, UVR8, etc.) to core transcription factors (HY5, PIF, etc.) to reprogram cellular metabolism and growth response. While the photoreception network does not serve to orchestrate energy production in animals, mammalian COP1 is still critical in regulating metabolism and cell growth during tumorigenesis. In this review, we summarize currently known COP1 functions in animals v.s. plants. It can be seen that the stimuli sensed by mammalian COP1 and the signal transduction pathway there of remain largely unknown. Sunlight acts as both major energy source and an upstream signal of COP1 in plants. Similarly, glucose, the major energy source for animals, maybe highly correlated with COP1 upstream signaling. In both organisms, COP1 may respond to stimuli by altered localization, activity or assembly into super-E3 complex with CRL4, which remains to be further understood. Nonetheless, pharmacological studies on animal COP1 points to therapeutic directions, while also providing tools for further research on this enigmatic E3. COP1 is of vital importance in the regulation of cellular life process. Its has diverse function and mechanism through evolution, which needs to be further explored.