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:As mentioned above, under stressful conditions, IR might sequentially activate the ER stress receptors, thereby triggering ER stress-induced cell death signaling: for example, PERK, one of the ER stress receptors, might phosphorylate eIF2α, which translocated ATF4 into nucleus, and then increased the gene transcription such as CHOP to restore ER homeostasis, thereby regulating ER stress mediated apoptosis [12–15].
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