Lady Gaga says paying tribute to the late David Bowie at the Grammys is probably the most challenging thing she's done in career because the icon influenced her greatly and helped shape her identity. "When I was 19 years old ... I started to live my life like him. I began to consume art and fashion and art history and a combination of those things, performance technique ... and I only hung out with people that were artists and that was the way that he was and I learned that from him," she s