Human ZBP1 induces cell death-independent inflammatory signaling via RIPK3 and RIPK1.

ZBP1 is an interferon-induced cytosolic nucleic acid sensor that facilitates antiviral responses via RIPK3. Although ZBP1-mediated programmed cell death is widely described, whether and how it promotes inflammatory signaling is unclear. Here, we report a ZBP1-induced inflammatory signaling pathway mediated by K63- and M1-linked ubiquitin chains, which depends on RIPK1 and RIPK3 as scaffolds independently of cell death. In human HT29 cells, ZBP1 associated with RIPK1 and RIPK3 as well as ubiquitin ligases cIAP1 and LUBAC. ZBP1-induced K63- and M1-linked ubiquitination of RIPK1 and ZBP1 to promote TAK1- and IKK-mediated inflammatory signaling and cytokine production. Inhibition of caspase activity suppressed ZBP1-induced cell death but enhanced cytokine production in a RIPK1- and RIPK3 kinase activity-dependent manner. Lastly, we provide evidence that ZBP1 signaling contributes to SARS-CoV-2-induced cytokine production. Taken together, we describe a ZBP1-RIPK3-RIPK1-mediated inflammatory signaling pathway relayed by the scaffolding role of RIPKs and regulated by caspases, which may induce inflammation when ZBP1 is activated below the threshold needed to trigger a cell death response.

Comparative Research of GaN Growth Mechanisms on Patterned Sapphire Substrates with Sputtered AlON Nucleation Layers.

The utilization of sputtered AlN nucleation layers (NLs) and patterned sapphire substrates (PSSs) could greatly improve GaN crystal quality. However, the growth mechanism of GaN on PSSs with sputtered AlN NLs has not been thoroughly understood. In this paper, we deposited AlON by sputtering AlN with O2, and we found that the variation of thickness of sputtered AlON NLs greatly influenced GaN growth on PSSs. (1) For 10 nm thin AlON sputtering, no AlON was detected on the cone sidewalls. Still, GaN nucleated preferably in non-(0001) orientation on these sidewalls. (2) If the thickness of the sputtered AlON NL was 25 nm, AlON formed on the cone sidewalls and flat regions, and some small GaN crystals formed near the bottom of the cones. (3) If the sputtered AlON was 40 nm, the migration ability of Ga atoms would be enhanced, and GaN nucleated at the top of the cones, which have more chances to grow and generate more dislocations. Finally, the GaN growth mechanisms on PSSs with sputtered AlON NLs of different thicknesses were proposed.

Enhanced P-Type GaN Conductivity by Mg Delta Doped AlGaN/GaN Superlattice Structure.

A method of combining the AlGaN/GaN superlattices and Mg delta doping was proposed to achieve a high conductivity p-type GaN layer. The experimental results provided the evidence that the novel doping technique achieves superior p-conductivity. The Hall-effect measurement indicated that the hole concentration was increased by 2.06 times while the sheet resistivity was reduced by 48%. The fabricated green-yellow light-emitting diodes using the achieved high conductivity p-type GaN layer showed an 8- and 10-times enhancement of light output power and external quantum efficiency, respectively. The subsequent numerical calculation was conducted by using an Advanced Physical Model of Semiconductor Device to reveal the mechanism of enhanced device performance. This new doping technique offers an attractive solution to the p-type doping problems in wide-bandgap GaN or AlGaN materials.