CDK11 safeguards the identity of human embryonic stem cells via fine-tuning signaling pathways

Embryonic exposure of polystyrene nanoplastics affects cardiac development

Micro- and nanoplastics have recently been detected in human blood and placentas, indicating inevitable embryonic exposure to these particles. However, their influence on human embryogenesis and the underlying mechanisms are still unknown. In this study, the effects of polystyrene nanoplastics (PS-NPs) exposure on cardiac differentiation of human embryonic stem cells (hESCs) were evaluated. Uptake of PS-NPs not only caused cellular injury, but also regulated cardiac-related pathways as revealed by RNA-sequencing. Consequently, the efficiency of cardiomyocyte differentiation from hESCs was compromised, leading to immature of cardiomyocytes and smaller cardiac organoids with impaired contractility. Mechanistically, PS-NPs promoted mitochondrial oxidative stress, activated P38/Erk MAPK signaling pathway, blocked autophagy flux, and eventually reduced the pluripotency of hESCs. Consistently, in vivo exposure of PS-NPs from cleavage to gastrula period of zebrafish embryo led to reduced cardiac contraction and blood flow. Collectively, this study suggests that PS-NPs is a risk factor for fetal health, especially for heart development.

Mitochondrial ribosomal small subunit (MRPS) MRPS23 protein-protein interaction reveals phosphorylation by CDK11-p58 affecting cell proliferation and knockdown of MRPS23 sensitizes breast cancer cells to CDK1 inhibitors

BACKGROUND

Post-translational modification of some mitoribosomal proteins has been found to regulate their functions. MRPS23 has been reported to be overexpressed in various cancers and has been predicted to be involved in increased cell proliferation. Furthermore, MRPS23 is a driver of luminal subtype breast cancer. However, its exact role and function in cancer remains unknown. METHODS AND RESULTS: Our previous study identified protein-protein interactions involving MRPS23 and CDK11A. In this study, we confirmed the interaction of MRPS23 with the p110 and p58 isoforms of CDK11A. Phosphoprotein enrichment studies and in vitro kinase assay using CDK11A/cyclin D3 followed by MALDI-ToF/ToF analysis confirmed the phosphorylation of MRPS23 at N-terminal serine 11 residue. Breast cancer cells expressing the MRPS23 (S11G) mutant showed increased cell proliferation, increased expression of PI3-AKT pathway proteins [p-AKT (Ser47), p-AKT (Thr308), p-PDK (Ser241) and p-GSK-3β (Ser9)] and increased antiapoptotic pathway protein expression [Bcl-2, Bcl-xL, p-Bcl2 (Ser70) and MCL-1] when compared with the MRPS23 (S11A) mutant-overexpressing cells. This finding indicated the role of MRPS23 phosphorylation in the proliferation and survival of breast cancer cells. The correlation of inconsistent MRPS23 phosphoserine 11 protein expression with CDK11A in the breast cancer cells suggested phosphorylation by other kinases. In vitro kinase assay showed that CDK1 kinase also phosphorylated MRPS23 and that inhibition using CDK1 inhibitors lowered phospho-MRPS23 (Ser11) levels. Additionally, modulating the expression of MRPS23 altered the sensitivity of the cells to CDK1 inhibitors.

CONCLUSION

In conclusion, phosphorylation of MRPS23 by mitotic kinases might potentially be involved in the proliferation of breast cancer cells. Furthermore, MRPS23 can be targeted for sensitizing the breast cancer cells to CDK1 inhibitors.