Dissecting the roles of MBD2 isoforms and domains in regulating NuRD complex function during cellular differentiation

The Nucleosome Remodeling and Deacetylation (NuRD) complex is a crucial regulator of cellular differentiation. Two members of the Methyl-CpG-binding domain (MBD) protein family, MBD2 and MBD3, are known to be integral, but mutually exclusive subunits of the NuRD complex. Several MBD2 and MBD3 isoforms are present in mammalian cells, resulting in distinct MBD-NuRD complexes. Whether these different complexes serve distinct functional activities during differentiation is not fully explored. Based on the essential role of MBD3 in lineage commitment, we systematically investigated a diverse set of MBD2 and MBD3 variants for their potential to rescue the differentiation block observed for mouse embryonic stem cells (ESCs) lacking MBD3. While MBD3 is indeed crucial for ESC differentiation to neuronal cells, it functions independently of its MBD domain. We further identify that MBD2 isoforms can replace MBD3 during lineage commitment, however with different potential. Full-length MBD2a only partially rescues the differentiation block, while MBD2b, an isoform lacking an N-terminal GR-rich repeat, fully rescues the Mbd3 KO phenotype. In case of MBD2a, we further show that removing the methylated DNA binding capacity or the GR-rich repeat enables full redundancy to MBD3, highlighting the synergistic requirements for these domains in diversifying NuRD complex function.

Alternative Oxidase Attenuates Cigarette Smoke-induced Lung Dysfunction and Tissue Damage

Cigarette smoke (CS) exposure is the predominant risk factor for the development of chronic obstructive pulmonary disease (COPD) and the third leading cause of death worldwide. We aimed to elucidate whether mitochondrial respiratory inhibition and oxidative stress are triggers in its etiology. In different models of CS exposure, we investigated the effect on lung remodeling and cell signaling of restoring mitochondrial respiratory electron flow using alternative oxidase (AOX), which bypasses the cytochrome segment of the respiratory chain. AOX attenuated CS-induced lung tissue destruction and loss of function in mice exposed chronically to CS for 9 months. It preserved the cell viability of isolated mouse embryonic fibroblasts treated with CS condensate, limited the induction of apoptosis, and decreased the production of reactive oxygen species (ROS). In contrast, the early-phase inflammatory response induced by acute CS exposure of mouse lung, i.e., infiltration by macrophages and neutrophils and adverse signaling, was unaffected. The use of AOX allowed us to obtain novel pathomechanistic insights into CS-induced cell damage, mitochondrial ROS production, and lung remodeling. Our findings implicate mitochondrial respiratory inhibition as a key pathogenic mechanism of CS toxicity in the lung. We propose AOX as a novel tool to study CS-related lung remodeling and potentially to counteract CS-induced ROS production and cell damage.

Curcumin induces apoptosis and cell cycle arrest via the activation of reactive oxygen species-independent mitochondrial apoptotic pathway in Smad4 and p53 mutated colon adenocarcinoma HT29 cells

Curcumin is a natural dietary polyphenol compound that has various pharmacological activities such as antiproliferative and cancer-preventive activities on tumor cells. Indeed, the role reactive oxygen species (ROS) generated by curcumin on cell death and cell proliferation inhibition in colon cancer is poorly understood. In the present study, we hypothesized that curcumin-induced ROS may promote apoptosis and cell cycle arrest in colon cancer. To test this hypothesis, the apoptosis-inducing potential and cell cycle inhibition effect of ROS induced by curcumin was investigated in Smd4 and p53 mutated HT-29 colon adenocarcinoma cells. We found that curcumin treatment significantly increased the level of ROS in HT-29 cells in a dose- and time-dependent manner. Furthermore, curcumin treatment markedly decreased the cell viability and proliferation potential of HT-29 cells in a dose- and time-dependent manner. Conversely, generation of ROS and inhibitory effect of curcumin on HT-29 cells were abrogated by N-acetylcysteine treatment. In addition, curcumin treatment did not show any cytotoxic effects on HT-29 cells. Furthermore, curcumin-induced ROS generation caused the DNA fragmentation, chromatin condensation, and cell nuclear shrinkage and significantly increased apoptotic cells in a dose- and time-dependent manner in HT-29 cells. However, pretreatment of N-acetylcysteine inhibited the apoptosis-triggering effect of curcumin-induced ROS in HT-29 cells. In addition, curcumin-induced ROS effectively mediated cell cycle inhibition in HT-29 cells. In conclusion, our data provide the first evidence that curcumin induces ROS independent apoptosis and cell cycle arrest in colon cancer cells that carry mutation on Smad4 and p53.