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BACKGROUND: Decidual stromal cells (DSCs) have classically been considered fibroblastic cells, although their function, cell lineage and origin are not fully understood. We previously demonstrated that human DSCs showed similarities with follicular dendritic cells (FDCs): DSCs expressed FDC-associated antigens, both types of cells are contractile and both are related to mesenchymal stem cells (MSCs). To further characterize DSCs, we investigated whether DSCs and FDCs share any distinctive phenotypical and functional characteristics. METHODS: Human FDC lines were obtained from tonsillectomy samples, human DSC lines from elective termination of pregnancy samples and human MSC lines from bone marrow aspirates. We isolated DSC, FDC and MSC lines and compared their characteristics with flow cytometry and enzyme-linked immunosorbent assay. Cell lines were cultured with tumour necrosis factor (TNF) and lymphotoxin (LT)α(1)ß(2), cytokines involved in FDC differentiation. Cell lines were also differentiated in culture after exposure to progesterone and cAMP, factors involved in the differentiation (decidualization) of DSC. RESULTS: Like MSCs, DSCs and FDCs expressed MSC-associated antigens (CD10, CD29, CD54, CD73, CD106, α-smooth muscle actin and STRO-1) and lacked CD45 expression, and all three types of cell line showed increased expression of CD54 (ICAM-1) and CD106 (VCAM-1) when cultured TNF and LTα(1)ß(2). DSCs and FDCs, however, exhibited characteristics not observed in MSCs: DSCs expressed FDC-associated antigens CD14, CD21 and CD23, B cell-activating factor and secreted C-X-C motif chemokine 13. Moreover, DSC lines but not MSC lines inhibited the spontaneous apoptosis of B lymphocytes, a typical functional attribute of FDC. During culture with progesterone and cAMP, FDCs, like DSCs but in contrast to MSCs, changed their morphology from a fibroblastic to a rounder shape, and cells secreted prolactin. CONCLUSIONS: Our results suggest that DSCs and FDCs share a common precursor in MSCs but this precursor acquires new capacities when it homes to peripheral tissues. We discuss these shared properties in the context of immune-endocrine regulation during pregnancy.

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Epigenetic modifications commonly associated with tumor development, such as histone deacetylation, may influence the resistance of some tumor cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) by regulating gene transcription of components of the TRAIL signalling pathway. In the present study we have analyzed the effect of six different histone deacetylase inhibitors (HDACi), belonging to the four classic structural families, on TRAIL-induced apoptosis in leukemic T cell lines. Non-toxic and functional doses of all HDACi but apicidin, similarly sensitized different leukemic T cell lines to TRAIL-induced apoptosis, while they showed no effect on the resistance of normal T lymphocytes. Sensitizing doses of vorinostat, valproic acid, sodium butyrate and MS-275 regulated the expression of TRAIL-R2, c-FLIP and Apaf-1 in leukemic cells while TSA modulated only the expression of Apaf-1. The synergistic effect of all HDACi and TRAIL was inhibited in Bcl-2-overexpressing leukemic T cells. Thus, different HDACi may affect the expression of different TRAIL-related genes, but regulation of the mitochondrial pathway seems to be essential for the TRAIL sensitizing effect of HDACi in leukemic T cells. Overall, HDACi represent a promising and safe strategy in combination with TRAIL for treatment of T-cell leukaemia.

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Breast tumor cells are often resistant to tumor necrosis factor-related apoptosis-inducing ligand (tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)/APO-2 L). Here, we describe the sensitization by microtubule-interfering agents (MIAs) to TRAIL-induced apoptosis in breast tumor cells through a mitotic arrest and c-Jun N-terminal kinase (JNK)-dependent mechanism. MIA treatment resulted in BubR1-dependent mitotic arrest leading to the sustained activation of JNK and the proteasome-mediated downregulation of cellular FLICE-inhibitory protein (cFLIP) and myeloid cell leukemia-1 (Mcl-1) expression. The JNK inhibitor SP600125 abrogated MIA-induced mitotic arrest and downregulation of cFLIP and Mcl-1 and reduced the apoptosis caused by the combination of MIAs and TRAIL. Silencing of cFLIP and Mcl-1 expression by RNA interference resulted in a marked sensitization to TRAIL-induced apoptosis. Furthermore, in FLIP-overexpressing cells, MIA-induced sensitization to TRAIL-activated apoptosis was markedly reduced. In summary, our results show that mitotic arrest imposed by MIAs activates JNK and facilitates TRAIL-induced activation of an apoptotic pathway in breast tumor cells by promoting the proteasome-mediated degradation of cFLIP and Mcl-1.

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Breast cancer cells often show increased activity of the mitogen-activated protein kinase (MAPK) pathway. We report here that this pathway reduces their sensitivity to death ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and present the underlying mechanism. Activation of protein kinase C (PKC) inhibited TRAIL-induced apoptosis in a protein synthesis-independent manner. Deliberate activation of MAPK was also inhibitory. In digitonin-permeabilized cells, PKC activation interfered with the capacity of recombinant truncated (t)Bid to release cytochrome c from mitochondria. MAPK activation did not affect TRAIL or tumor necrosis factor (TNF)alpha-induced Bid cleavage. However, it did inhibit translocation of (t)Bid to mitochondria as determined both by subcellular fractionation analysis and confocal microscopy. Steady state tBid mitochondrial localization was prohibited by activation of the MAPK pathway, also when the Bcl-2 homology domain 3 (BH3) domain of tBid was disrupted. We conclude that the MAPK pathway inhibits TRAIL-induced apoptosis in MCF-7 cells by prohibiting anchoring of tBid to the mitochondrial membrane. This anchoring is independent of its interaction with resident Bcl-2 family members.

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