Pyridinyl imidazole inhibitors, particularly SB203580, have been widely used to elucidate the roles of p38 mitogen-activated protein (MAP) kinase (p38/HOG/SAP-KII) in a wide array of biological systems. Studies by this group and others have shown that SB203580 can have antiproliferative activity on cytokine-activated lymphocytes. However, we recently reported that the antiproliferative effects of SB203580 were unrelated to p38 MAP kinase activity. This present study now shows that SB203580 can inhibit the key cell cycle event of retinoblastoma protein phosphorylation in interleukin-2-stimulated T cells. Studies on the proximal regulator of this event, the phosphatidylinositol 3-kinase/protein kinase B (PKB)(Akt/Rac) kinase pathway, showed that SB203580 blocked the phosphorylation and activation of PKB by inhibiting the PKB kinase, phosphoinositidedependent protein kinase 1. The concentrations of SB203580 required to block PKB phosphorylation (IC 50 3-5 M) are only approximately 10-fold higher than those required to inhibit p38 MAP kinase (IC 50 0.3-0.5 M). These data define a new activity for this drug and would suggest that extreme caution should be taken when interpreting data where SB203580 has been used at concentrations above 1-2 M. Interleukin-2 (IL-2)1 is a potent T cell growth factor that mediates its effects via a high affinity heterotrimeric receptor comprising ␣, ␤, and ␥ c subunits. Several intracellular signaling pathways are known to be activated by IL-2, including the p42/44 mitogen-activated protein kinase (MAP kinase, also known as ERK2/1), the p38 and p54 MAP kinases (also called stress kinases, or HOG and JNK, respectively), the phosphatidyl inositol 3Ј (PI) 3-kinase pathway and the Jak/STAT (signal transducer and activator of transcription) pathways. Our earlier studies using the MEK (mitogen-activated protein kinase/ extracellular signal-regulated kinase kinase) inhibitor PD-098059 (1) and those of others (2, 3) have indicated that the p42/44 MAP kinase pathway is not required for IL-2-driven proliferation. In contrast, a pyridinyl imidazole inhibitor of p38 MAP kinase, SB203580, inhibited IL-2-driven T cell proliferation with an IC 50 of 3-5 M, suggesting a possible role for p38 MAP kinase in this process (4). Recently, we have further investigated the role of p38 MAP kinase in proliferation by mapping the subdomains of the IL-2 receptor ␤ chain involved in the activation of the kinase. As previously shown for p42/44 MAP kinase, activation of p38 and p54 MAP kinases required the acidic rich A region of the IL-2 receptor ␤ chain (5). However, the A region is not required for proliferation (2, 5), indicating that neither p38 MAP kinase nor p54 MAP kinase is essential for this function. Furthermore, CNI-1493 (6, 7), an inhibitor of p38 and p54 MAP kinase activation by IL-2 was unable to inhibit proliferation (5). Surprisingly, SB203580 was still able to inhibit proliferation in the absence of IL-2 stimulated p38 MAP kinase activation. It has already been reported that SB203580 does inhibit p54...

Interleukin-2 (IL-2) is a potent T cell mitogen. However, the signaling pathways by which IL-2 mediates its mitogenic effect are not fully understood. One of the members of the mitogen-activated protein kinase (MAPK) family, p42/44MAPK (ERK2/1), is known to be activated by IL-2. We have now investigated the response to IL-2 of two other members of the MAP kinase family, p54MAP kinase (stress-activated protein kinase (SAPK)/Jun-N-terminal kinase (JNK)) and p38MAP kinase (p38/Mpk2/CSBP/RK), which respond primarily to stressful and inflammatory stimuli (e.g. tumor necrosis factor-␣, IL-1, and lipopolysaccharide). Here we show that IL-2, and another T cell growth factor, IL-7, activate both SAPK/JNK and p38MAP kinase. Furthermore, inhibition of p38MAP kinase activity with a specific pyrinidyl imidazole inhibitor SB203580 that prevents activation of its downstream effector, MAPK-activating protein kinase-2, correlated with suppression of IL-2-and IL-7-driven T cell proliferation. These data indicate that in T cells p38MAP kinase has a role in transducing the mitogenic signal.

The virulence and immunosuppressive activity of Mycobacterium ulcerans is attributed to mycolactone, a macrolide toxin synthesized by the bacteria. We have explored the consequence and mechanism of mycolactone pretreatment of primary human monocytes activated by a wide range of TLR ligands. The production of cytokines (TNF, IL-1β, IL-6, IL-10, and IFN-γ-inducible protein-10), chemokines (IL-8), and intracellular effector molecules (exemplified by cyclooxygenase-2) was found to be powerfully and dose dependently inhibited by mycolactone, irrespective of the stimulating ligand. However, mycolactone had no effect on the activation of signaling pathways that are known to be important in inducing these genes, including the MAPK and NF-κB pathways. Unexpectedly, LPS-dependent transcription of TNF, IL-6, and cyclooxygenase-2 mRNA was found not to be inhibited, implying that mycolactone has a novel mechanism of action and must function posttranscriptionally. We propose that mycolactone mediates its effects by inhibiting the translation of a specific subset of proteins in primary human monocytes. This mechanism is distinct from rapamycin, another naturally occurring immunosuppressive lactone. The current findings also suggest that monocyte-derived cytokine transcript and protein levels may not correlate in Buruli ulcer lesions, and urge caution in the interpretation of RT-PCR data obtained from patient biopsy samples.

The use of decellularised matrices as scaffolds offers the advantage of great similarity with the tissue to be replaced. Moreover, decellularised tissues and organs can be repopulated with the patient’s own cells to produce bespoke therapies. Great progress has been made in research and development of decellularised scaffolds, and more recently, these materials are being used in exciting new areas like hydrogels and bioinks. However, much effort is still needed towards preserving the original extracellular matrix composition, especially its minor components, assessing its functionality and scaling up for large tissues and organs. Emphasis should also be placed on developing new decellularisation methods and establishing minimal criteria for assessing the success of the decellularisation process. The aim of this review is to critically review the existing literature on decellularised scaffolds, especially on the preparation of these matrices, and point out areas for improvement, finishing with alternative uses of decellularised scaffolds other than tissue and organ reconstruction. Such uses include three-dimensional ex vivo platforms for idiopathic diseases and cancer modelling.