Involvement of STAT5a signaling in morphine-induced up-regulation of the cyclin D1

Opioid receptors and cytokine receptor have been verified to have a functional link and interaction. However, the pathway by which opioid receptor in lymphocytes is linked to cytokine signaling is not well defined. Using confocal microscopy and Western blotting this study showed that morphine treatment was able to activate cytoplasmic STAT5a in CEM x174 cells, which then translocated into the nucleus and bound to elements of the cyclin D1 promoter. As a consequence the expression of the cyclin D1 was apparently up-regulated. The data from EMSA–superEMSA and ChIP-qPCR further confirmed that morphine was capable of promoting the binding of STAT5a to its elements (proximal and distal), and this was abolished by the antagonist naloxone. As shown by transient transfection assay, activity of the cyclin D1 promoter was significantly reduced by 82% (distal) and 65% (proximal) after two STAT5a elements were mutated in comparison with wild type STAT5a elements. Moreover, knockdown of STAT5a was associated with a concurrent silencing of morphine-induced expression of cyclin D1, demonstrating involvement of STAT5a in morphine-triggered signaling in the regulation of cyclin D1 expression. The finding provides evidence which demonstrates that there is cross-talk between the mu opioid receptor and cytokine signaling in lymphocytes. Thus, we conclude that morphine may modulate cyclin D1 gene expression via signal transducers and activators of transcription (STATs) signaling, which will be beneficial for further understanding of the pharmacological effect of morphine on immune regulation.

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