Autophagy and apoptosis play important roles in the development, cellular homeostasis and, especially, oncogenesis of mammals. They may be triggered by common upstream signals, resulting in combined autophagy and apoptosis. In other instances, they may be mutually exclusive. Recent studies have suggested possible molecular mechanisms for crosstalk between autophagy and apoptosis. Bcl‐2 and Bcl‐xL, the well‐characterized apoptosis guards, appear to be important factors in autophagy, inhibiting Beclin 1‐mediated autophagy by binding to Beclin 1. In addition, Beclin 1, Bcl‐2 and Bcl‐xL can cooperate with Atg5 or Ca2+ to regulate both autophagy and apoptosis. Thus, Bcl‐2 and Bcl‐xL represent a molecular link between autophagy and apoptosis. Here, we discuss the possible roles of Bcl‐2 and Bcl‐xL in apoptosis and autophagy, and the crosstalk between them.
Abstract. SU11274, a small molecule inhibitor of c-Met, was reported to induce apoptosis in human non-small-cell lung cancer (NSCLC) cells. However, SU11274-mediated autophagy in NSCLC cells has rarely been reported. The aim of this study was to elucidate the molecular mechanisms mediating SU11274-induced autophagy in NSCLC A549 cells. Here we reported that SU11274-induced autophagy was accompanied with an increase in the conversion of LC3-I to LC3-II and up-regulation of Beclin-1 expression. Subsequently, we also found that small interfering RNA against c-Met induced A549 cell autophagy while promotion of c-Met by hepatocyte growth factor (HGF) suppressed A549 cell autophagy. Inhibition of autophagy by 3-methyladenine (3-MA) suppressed SU11274-induced cell death, suggesting that SU11274-induced autophagy caused cell death. Further study showed that ERK and p53 were activated after SU11274 treatment. Interruption of ERK and p53 activities decreased SU11274-induced autophagy, and blocking of ERK by the specific inhibitor PD98059 suppressed SU11274-induced p53 activation. Moreover, ERK activation upregulated Beclin-1 expression through induction of Bcl-2 phosphorylation, but p53 did not induce Bcl-2 phosphorylation. In conclusion, inhibition of c-Met induced autophagic cell death, which was associated with ERK-p53 activation and ERK-mediated Bcl-2 phosphorylation in A549 cells.
The immunologic response toward chronic inflammation or bone regeneration via the accumulation of M1 or M2 macrophages after injury could determine the fate of biomaterial. Human umbilical cord mesenchymal stem cells (hUCMSCs) have a pivotal immunomodulatory property on directing macrophage behaviors. Herein, for the first time, 3D‐printed poly(lactide‐co‐glycolide) (PLGA) scaffolds modified with hUCMSC‐derived extracellular matrix (PLGA‐ECM) are prepared by a facile tissue engineering technique with physical decellularization and 2.44 ± 0.29 mg cm−3 proteins immobilized on the PLGA‐ECM contain multiple soluble cytokines with a sustainable release profile. The PLGA‐ECM not only attenuates the foreign body response, but also improves bone regeneration by increasing the accumulation of M2 macrophages in an improved heterotopic transplantation model of SCID mice. Furthermore, the PLGA‐ECM scaffolds with the knockdown of transforming growth factor‐β‐induced protein (TGFβI/βig‐H3) demonstrate that M2 macrophage accumulation improved by the PLGA‐ECM could be attributed to increasing the migration of M2 macrophages and the repolarization of M1 macrophages to M2 phenotype, which are mediated by multiple integrin signaling pathways involving in integrin β7, integrin α9, and integrin β1 in a TGFβI‐dependent manner. This study presents an effective surface modification strategy of polymeric scaffolds to initiate tissue regeneration and combat inflammatory response by increasing M2 macrophage accumulation.
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