Identification of the Calmodulin-Binding Domains of Fas Death Receptor

Endoplasmic reticulum stress and death receptor-mediated apoptosis in the neuronal differentiation of adult adipose-derived stromal cells

Apoptosis is the primary cause of cell death in the differentiation of Adipose-derived stromal cells (ADSCs) into neurons. However, the relationship between endoplasmic reticulum stress (ERS) and death receptor-mediated apoptosis in ADSC-induced neuronal differentiation is not clear. ADSCs were isolated and induced to differentiate into neurons using β-mercaptoethanol. The expression of neuron-specific enolase (NSE), GRP94, CHOP, Fas/FasL, TNFR1/TNF-α, DR5/TRAIL, Caspase8, and Caspase3 in ADSCs was examined using immunocytochemistry and Western blotting before induction, during pre-induction, and after induction. Transmission electron microscopy (TEM) was used to observe changes in the morphology of the endoplasmic reticulum (ER), and the MTT assay was employed to measure cell viability in the uninduced and induced groups. Additionally, the number of apoptotic cells during the induction process was measured using flow cytometry with Annexin V/PI. With increasing induction time, the positive expression rates of CHOP, Fas/FasL, Caspase8, Caspase-3, and NSE gradually increased, while the positive expression rate of GRP94 decreased. TNFR1/TNF-α and DR5/TRAIL peaked at 5 h post-induction and then decreased at 8 h. TEM revealed swelling and expansion of the ER, vacuolar changes, and degranulation in cells. The MTT assay showed a gradual decrease in the absorbance of surviving cells in all groups. Flow cytometry indicated an increasing rate of apoptosis in cells. Therefore, ERS in the normal culture and growth of ADSCs, manifesting as enhanced unfolded protein response (UPR), maintains the normal survival of ADSCs. However, in the process of ADSC-induced differentiation into neurons, ERS and death receptor-mediated apoptosis are significant causes of cell death.

The KN-93 Molecule Inhibits Calcium/Calmodulin-Dependent Protein Kinase II (CaMKII) Activity by Binding to Ca2+/CaM

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a multifunctional serine/threonine protein kinase that transmits calcium signals in various cellular processes. CaMKII is activated by calcium-bound calmodulin (Ca²⁺/CaM) through a direct binding mechanism involving a regulatory C-terminal α-helix in CaMKII. The Ca²⁺/CaM binding triggers transphosphorylation of critical threonine residues proximal to the CaM-binding site leading to the autoactivated state of CaMKII. The demonstration of its critical roles in pathophysiological processes has elevated CaMKII to a key target in the management of numerous diseases. The molecule KN-93 is the most widely used inhibitor for studying the cellular and in vivo functions of CaMKII. It is widely believed that KN-93 binds directly to CaMKII, thus preventing kinase activation by competing with Ca²⁺/CaM. Herein, we employed surface plasmon resonance, NMR, and isothermal titration calorimetry to characterize this presumed interaction. Our results revealed that KN-93 binds directly to Ca²⁺/CaM and not to CaMKII. This binding would disrupt the ability of Ca²⁺/CaM to interact with CaMKII, effectively inhibiting CaMKII activation. Our findings also indicated that KN-93 can specifically compete with a CaMKIIδ-derived peptide for binding to Ca²⁺/CaM. As indicated by the surface plasmon resonance and isothermal titration calorimetry data, apparently at least two KN-93 molecules can bind to Ca²⁺/CaM. Our findings provide new insight into how in vitro and in vivo data obtained with KN-93 should be interpreted. They further suggest that other Ca²⁺/CaM-dependent, non-CaMKII activities should be considered in KN-93-based mechanism-of-action studies and drug discovery efforts.

Emerging fields in chaperone proteins: A French workshop

The "Bioénergétique et Ingénierie des Protéines (BIP)" laboratory, CNRS (France), organized its first French workshop on molecular chaperone proteins and protein folding in November 2017. The goal of this workshop was to gather scientists working in France on chaperone proteins and protein folding. This initiative was a great success with excellent talks and fruitful discussions. The highlights were on the description of unexpected functions and post-translational regulation of known molecular chaperones (such as Hsp90, Hsp33, SecB, GroEL) and on state-of-the-art methods to tackle questions related to this theme, including Cryo-electron microscopy, Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR), simulation and modeling. We expect to organize a second workshop in two years that will include more scientists working in France in the chaperone field.

Nonapoptotic functions of Fas/CD95 in the immune response

CD95 (also known as Fas) is a member of the tumor necrosis factor receptor (TNFR) superfamily. Its cognate ligand, CD95L, is implicated in immune homeostasis and immune surveillance. Mutations in this receptor are associated with a loss of apoptotic signaling and have been detected in an autoimmune disorder called autoimmune lymphoproliferative syndrome (ALPS) type Ia, which shares some clinical features with systemic lupus erythematosus (SLE). In addition, deletions and mutations of CD95 have been described in many cancers, which led researchers to initially classify this receptor as a tumor suppressor. More recent data demonstrate that CD95 engagement evokes nonapoptotic signals that promote inflammation and carcinogenesis. Transmembrane CD95L (m-CD95L) can be cleaved by metalloproteases, releasing a soluble ligand (s-CD95L). Soluble and membrane-bound CD95L show different stoichiometry (homotrimer versus multimer of homotrimers, respectively), which differentially affects CD95-mediated signaling through molecular mechanisms that remain to be elucidated. This review discusses the biological roles of CD95 in light of recent experiments addressing how a death receptor can trigger both apoptotic and nonapoptotic signaling pathways.