Doxycycline up-regulates the expression of IL-6 and GM-CSF via MAPK/ERK and NF-κB pathways in mouse thymic epithelial cells

Thymic epithelial cells (TECs) constitute a major component of the thymic stroma which provides a microenvironment critical for developing thymocytes. We have previously demonstrated that doxycycline (Dox), a tetracycline derivative, enhances the proliferation of the mouse thymic epithelial cell line 1 (MTEC1) via MAPK/ERK signal pathway. Herein we provide evidence that Dox also has profound impact on the cytokine production by MTEC1. Specifically, the expression of IL-6 and GM-CSF, both at mRNA and protein levels, was found to be increased in a time- and dose-dependent manner with the addition of Dox. Western blotting analysis revealed that treatment with Dox-induced phosphorylation of the p65 subunit of NF-κB and ERK. Notably, Dox-induced up-regulation of IL-6 and GM-CSF was largely abolished after pretreatment of MTEC1 with either NF-κB inhibitor BAY11-7082 or MEK1/2 inhibitor U0126, supporting the involvement of the two pathways in the process. These findings warrant further investigation into the potential application of Dox in T-cell reconstitution in such situations as chemotherapy, radiotherapy, bone marrow transplantation and HIV infection.