Identifying dexamethasone localization in the nucleus of human lymphoblastic lymphoma t cells: nuclear lipid microdomains

Dexamethasone can induce apoptosis in malignant lymphocytes by numerous pathways, including caspase activation, interleukin regulation, BIM upregulation, modulation of prosurvival factors, such as Bcl-2, Bcl-xL, AP-1, and NF-κB (Almawi WY, J Leukocyte Biol 2004,76:7). To activate, dexamethasone, interacts with a glucocorticoid receptor. After activation, the receptor translocates to the nucleus and dimerizes on specific response elements within the genome. Upon target binding, nuclear receptor is then able to modulate gene output by the recruitment of cofactors and transcriptional machinery (Burd CJ, Mol Cell Biol 2012,32:1805). How dexamethasone arrives from the membrane to the nucleus and how this traffic is regulated have been widely studied, but until now it is not known where the drug is localized at the nuclear level. We have recently demonstrated the existence of nuclear lipid microdomains (NLM) in inner nuclear membrane that act as platform for the transcription process (Cascianelli G., Mol Biol Cell, 2008:19, 5289). The aim of the work was to study the localization of dexamethasone in NLM after its transfer inside the nucleus and its effect in human lymphoblastic lymphoma T cells. Methods: We used the SUP-T1 cell line. By using labeled dexamethasone, we found a high concentration of radioactivity in NLM in both biochemical and ultramicroscopy study. Results: In NLM, the drug stimulated sphingomyelin-synthase and inhibited sphingomyelinase activity by increasing the sphingomyelin content. Thus, the NLM become more rigid structures where STAT3 and phosphoSTAT3 were strongly reduced. Conclusions: The cells acquire the morphological characteristics of apoptosis, CDKN1A and CDKN1B are upregulated, whereas Bcl2 is downregulated.