Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:A nuclear isoform of CLU, the 49 kDa product of a variant gene transcript, has also been identified (Yang et al., 2000) and is associated with cell death, for example, following exposure to ionizing radiation (Leskov et al., 2003) or cellular Ca2þ depletion (Caccamo et al., 2005).
Category: