Glucocorticoid induces apoptosis of osteoblast cells through the activation of glycogen synthase kinase 3beta

Protein kinase networks regulating glucocorticoid-induced apoptosis of hematopoietic cancer cells: fundamental aspects and practical considerations

Glucocorticoids (GCs) are integral components in the treatment protocols of acute lymphoblastic leukemia, multiple myeloma, and non-Hodgkin lymphoma owing to their ability to induce apoptosis of these malignant cells. Resistance to GC therapy is associated with poor prognosis. Although they have been used in clinics for decades, the signal transduction pathways involved in GC-induced apoptosis have only partly been resolved. Accumulating evidence shows that this cell death process is mediated by a communication between nuclear GR affecting gene transcription of pro-apoptotic genes such as Bim, mitochondrial GR affecting the physiology of the mitochondria, and the protein kinase glycogen synthase kinase-3 (GSK3), which interacts with Bim following exposure to GCs. Prevention of Bim up-regulation, mitochondrial GR translocation, and/or GSK3 activation are common causes leading to GC therapy failure. Various protein kinases positively regulating the pro-survival Src-PI3K-Akt-mTOR and Raf-Ras-MEK-ERK signal cascades have been shown to be activated in malignant leukemic cells and antagonize GC-induced apoptosis by inhibiting GSK3 activation and Bim expression. Targeting these protein kinases has proven effective in sensitizing GR-positive malignant lymphoid cells to GC-induced apoptosis. Thus, intervening with the pro-survival kinase network in GC-resistant cells should be a good means of improving GC therapy of hematopoietic malignancies.

Effects of glucocorticoid treatment on bone strength

Glucocorticoids (GCs) are prescribed for the treatment of several diseases, but their long-term use causes osteoporosis. Current research suggests that GCs suppress the canonical Wnt/beta pathway, resulting in decreased expression of critical bone proteins. This study examined how bone structure and strength of high bone mass (HBM) mice and low density lipoprotein receptor-related protein 5 (LRP5) knockout (KO+/-) mice are affected by GC treatment in comparison to wild-type (WT) mice, and if changes were specific to either trabecular or cortical bone. Mice were treated with either prednisone or placebo. The femurs and L4 vertebral bodies were analyzed by micro-CT for structure and mechanically tested to determine strength and apparent material strength properties. Differences in all measured variables corresponding to GC treatment and genotype were tested using two-way ANOVA. GC treatment caused decreased structural strength parameters, weakened apparent material strength properties, and disruption of bone structure in HBM, but not LRP5+/- or WT, mice. Despite treatment-related loss, trabecular bone structure and strength remained elevated as compared to LRP5+/- and WT mice. In HBM femurs, both cortical and trabecular structure, but not strength parameters, were negatively affected by treatment. In HBM vertebral bodies, both structural and strength parameters were negatively affected by treatment.

Antagonistic interplay between mechanical forces and glucocorticoids in bone: a tale of kinases

The contrasting actions of mechanical forces and glucocorticoids (GC) on bone have been long recognized. However, the cellular and molecular mechanisms by which these stimuli impact the skeleton remain only partially known. Recent evidence gained from studies on bone cell apoptosis has revealed that mechanical forces and GC exhibit converse effects on osteocyte and osteoblast survival resulting from divergent actions on the focal adhesion kinases FAK and Pyk2, molecules that regulate integrin-dependent interactions between bone cells and the extracellular matrix (ECM). This prospect reviews these findings and poses the possibility that similar opposing effects on kinase signaling are responsible for other actions of mechanical forces and GC on the skeleton, in particular on bone formation and the Wnt signaling pathway.

Induction of Ca2+ signal mediated apoptosis and alteration of IP3R1 and SERCA1 expression levels by stress hormone in differentiating C2C12 myoblasts

Glucocorticoid (GC) are stress hormones, whose cytotoxicity has been shown in various cells. The imbalance of calcium homeostasis is believed to be associated with the dexamethasone (DEX, a synthetic GC)-induced apoptosis. Here we show that in C2C12 myoblasts, DEX markedly up-regulated the expression of inositol 1,4,5-triphosphate receptor 1 (IP3R1) and down-regulated the expression of SERCA1 (sarcoendoplasmic reticulum Ca(2+)-ATPase 1), leading to calcium overload. Furthermore, the imbalance of calcium homeostasis increased the level of BAX, decreased the level of Bcl-2, induced cytochrome c release and activated caspase-3, leading to intranucleosomal DNA fragmentation and plasma membrane damage, eventually resulting in cell apoptosis. Taken together, by using C2C12 myoblasts as a model system, we demonstrated a novel mechanism for stress hormone-induced apoptosis: it is dependent on the induction of intracellular calcium overload via the alterations of IP3R1 and SERCA1 expressions.

Long-Term Alendronate Use Not without Consequences?

A previously unknown side effect of biphosphonate use is emerging. In a specific patient group on long term biphosphonate therapy stress femur fractures seem to occur. The typical presentation consists of prodromal pain in the affected leg and/or a discrete cortical thickening on the lateral side of the femur in conventional radiological examination or the presentation with a spontaneous transverse subtrochanteric femur with typical features. We present three cases of this stress fracture in patients on bisphosphonate therapy. One of these patients suffered a bilateral femur fracture of the same type. In our opinion, in patients on bisphosphonate therapy who present with a spontaneous femur fracture, seizing therapy is advisable. In bilateral cases preventive nailing should be considered.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.