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:In contrast, another transcription factor, SP1, but not NF-kB, is reported to mediate the TNF-a-induced LDL receptor expression and sterol-induced repression of LDL receptor expression (7, 10, 15).
Category: