Interactions between human leukocyte antigen (HLA) molecules on target cells and the inhibitory killer cell immunoglobulin-like receptors (KIRs) and heterodimeric inhibitory receptor CD94-NKG2A on human natural killer (NK) cells shape and program various response capacities. A functionally orthologous system exists in mice, consisting of major histocompatibility complex (MHC) molecules on target cells and the inhibitory Ly49 and CD94-NKG2A receptors on NK cells. Here, we found that the abundance of Src homology 2 domain–containing phosphatase-1 (SHP-1) in NK cells was established by interactions between MHCs and NK cell inhibitory receptors, although phenotypically identical NK cell populations still showed substantial variability in endogenous SHP-1 abundance and NK cell response potential. Human and mouse NK cell populations with high responsiveness had low SHP-1 abundance, and a reduction in SHP-1 abundance in NK cells enhanced their responsiveness. Computational modeling of NK cell activation by membrane-proximal signaling events identified SHP-1 as a negative amplitude regulator, which was validated by single-cell analysis of human NK cell responsiveness. The amount of mRNA and protein varied among responsive NK cells despite their similar chromatin accessibility to that of unresponsive cells, suggesting dynamic regulation of SHP-1 abundance. Low intracellular SHP-1 abundance was a biomarker of responsive NK cells. Together, these data suggest that enhancing NK cell function through the acute loss of SHP-1 abundance or activity may enhance the tumoricidal capacity of NK cells.

Neonatal seizures pose a clinical challenge in their early detection, acute management, and long-term comorbidities. They are often caused by hypoxic-ischemic encephalopathy and are frequently refractory to the first-line antiseizure medication phenobarbital. One proposed mechanism for phenobarbital inefficacy during neonatal seizures is the reduced abundance and function of the neuron-specific K+/Cl− cotransporter 2 (KCC2), which maintains chloride homeostasis and promotes GABAergic inhibition upon its phosphorylation during postnatal development. Here, we investigated whether this mechanism is causal and whether it can be rescued by KCC2 functional enhancement. In a CD-1 mouse model of refractory ischemic neonatal seizures, treatment with the KCC2 functional enhancer CLP290 rescued phenobarbital efficacy, increased KCC2 abundance, and prevented the development of epileptogenesis, as quantified by video electroencephalogram monitoring. These effects were prevented by knock-in expression of nonphosphorylatable mutants of KCC2 (S940A or T906A and T1007A), indicating that KCC2 phosphorylation regulates both neonatal seizure susceptibility and CLP290-mediated KCC2 functional enhancement. Our findings therefore validate KCC2 as a clinically relevant target for refractory neonatal seizures and provide insights for future drug development.

Aberrant activation of the RAS family of guanosine triphosphatases (GTPases) is prevalent in lung adenocarcinoma, with somatic mutation of KRAS occurring in ~30% of tumors. We previously identified somatic mutations and amplifications of the gene encoding RAS family GTPase RIT1 in lung adenocarcinomas. To explore the biological pathways regulated by RIT1 and how they relate to the oncogenic KRAS network, we performed quantitative proteomic, phosphoproteomic, and transcriptomic profiling of isogenic lung epithelial cells in which we ectopically expressed wild-type or cancer-associated variants of RIT1 and KRAS. We found that both mutant KRAS and mutant RIT1 promoted canonical RAS signaling and that overexpression of wild-type RIT1 partially phenocopied oncogenic RIT1 and KRAS, including induction of epithelial-to-mesenchymal transition. Our findings suggest that RIT1 protein abundance is a factor in its pathogenic function. Therefore, chromosomal amplification of wild-type RIT1 in lung and other cancers may be tumorigenic.

Comment in Nat Rev Endocrinol. 2022 Feb;18(2):68.

Thyroid hormone (TH) action is essential for hepatic lipid synthesis and oxidation. Analysis of hepatocyte-specific thyroid receptor β1 (TRβ1) knockout mice confirmed a role for TH in stimulating de novo lipogenesis and fatty acid oxidation through its nuclear receptor. Specifically, TRβ1 and its principal corepressor NCoR1 in hepatocytes repressed de novo lipogenesis, whereas the TH-mediated induction of lipogenic genes depended on the transcription factor ChREBP. Mice with a hepatocyte-specific deficiency in ChREBP lost TH-mediated stimulation of the lipogenic program, which, in turn, impaired the regulation of fatty acid oxidation. TH regulated ChREBP activation and recruitment to DNA, revealing a mechanism by which TH regulates specific signaling pathways. Regulation of the lipogenic pathway by TH through ChREBP was conserved in hepatocytes derived from human induced pluripotent stem cells. These results demonstrate that TH signaling in the liver acts simultaneously to enhance both lipogenesis and fatty acid oxidation.