For example, it was reported that pro-IL-16 suppresses Skp2 transcription by recruiting histone deacetylase 3 to the Skp2 promoter through interaction with a GA-binding protein [41]. Furthermore, HSC70, a chaperone for NF-κB, was identified as binding partner of pro-IL-16 via the PDZ domain [42]. In the study of Fujihara and Nadler, they reported that pro-IL-16 has

a nuclear localization sequence, and its PDZ domain acts not only as a nuclear scaffolding protein, but also functions as a nuclear chaperone to transport essential nuclear complex members with a role in transcriptional suppression into the nucleus. It was recently reported that HSC70 knockdown led to loss of nuclear translocation

by pro-IL-16 in T lymphocytes. More interestingly, loss of nuclear pro-IL-16 led Smad inhibitor subsequent increase in Skp2 level and decrease in p27kip, which ultimately enhanced T cell proliferation to facilitate the T cell transformation [43]. We initially hypothesized that pro-IL-16 would have a similar function in resting B cells as T lymphocytes, and that cell-cycle progression and proliferation would be inversely correlated with the level of pro-IL-16 in the nucleus. We therefore investigated the effects of pro-IL-16 on cellular signalling in resting B cells. Our western blot results revealed that pro-IL-16, rather than mature IL-16, Opaganib molecular weight is the main form of IL-16 present in resting B cells; we assumed that the mature form was secreted as soon as it had been processed by caspase-3 (Fig. 1C). Pro-IL-16 was found both in the cytoplasm and nucleus (Fig. 2). Because pro-IL-16 was triclocarban identified from immunoprecipitates using an anti-MHC class II antibody, this implies

that it is associated with MHC class II molecules, and we confirmed this assumption by Western blot analysis and confocal laser scanning microscopy (Figs 1B and 2B). More importantly, the nuclear level of pro-IL-16 was increased by treatment of cells with the corresponding anti-MHC class II antibody, consistent with the observation that the expression of pro-IL-16 is inhibited in activated T cells (Fig. 2A) [44, 45]. To confirm this inverse relationship between pro-IL-16 and B cell proliferation, we transfected pro-IL-16 cDNA into 38B9 cells and found that overexpression of pro-IL-16 suppressed B cell proliferation (Fig. 3A) and that the suppression was mediated by inhibition of the nuclear translocation of NF-κB subfamilies, p50, p52 and c-Rel (Fig. 3B). Our finding that p50, p52 and c-Rel are involved in pro-IL-16-mediated suppression of resting B cell proliferation is consistent with our previous observations that MHC class II-mediated negative signalling in resting B cell activation is closely related to the activation of the p50, p52 and c-Rel NF-κB subfamilies [16, 17].