The present invention provides a novel protein containing an armadillo repeat, a gene encoding this protein, and production and use thereof. The present inventors identified a gene named ALEX1 encoding a human-derived novel armadillo repeat-containing protein. It was clarified that ALEX1 interacts with several proteins including insulin-degrading enzyme, presenilin-1, and JNK interacting protein 1. This gene shows significantly decreased expression in cancer cells. The protein ALEX1 and the gene encoding this protein are usable as tools in testing for diseases such as cancer and Alzheimer's disease and developing pharmaceutical agents.