FBXO38 Ubiquitin Ligase Controls Centromere Integrity via ZXDA/B Stability

FBXO38 is dispensable for PD-1 regulation

SKP1-CUL1-F-box protein (SCF) ubiquitin ligases are versatile protein complexes that mediate the ubiquitination of protein substrates. The direct substrate recognition relies on a large family of F-box-domain-containing subunits. One of these substrate receptors is FBXO38, which is encoded by a gene found mutated in families with early-onset distal motor neuronopathy. SCFFBXO38 ubiquitin ligase controls the stability of ZXDB, a nuclear factor associated with the centromeric chromatin protein CENP-B. Loss of FBXO38 in mice results in growth retardation and defects in spermatogenesis characterized by deregulation of the Sertoli cell transcription program and compromised centromere integrity. Moreover, it was reported that SCFFBXO38 mediates the degradation of PD-1, a key immune-checkpoint inhibitor in T cells. Here, we have re-addressed the link between SCFFBXO38 and PD-1 proteolysis. Our data do not support the notion that SCFFBXO38 directly or indirectly controls the abundance and stability of PD-1 in T cells.

X centromeric drive may explain the prevalence of polycystic ovary syndrome and other conditions: Genomic structure of the human X chromosome pericentromeric region is consistent with meiotic drive associated with PCOS and other conditions

X chromosome centromeric drive may explain the prevalence of polycystic ovary syndrome and contribute to oocyte aneuploidy, menopause, and other conditions. The mammalian X chromosome may be vulnerable to meiotic drive because of X inactivation in the female germline. The human X pericentromeric region contains genes potentially involved in meiotic mechanisms, including multiple SPIN1 and ZXDC paralogs. This is consistent with a multigenic drive system comprising differential modification of the active and inactive X chromosome centromeres in female primordial germ cells and preferential segregation of the previously inactivated X chromosome centromere to the polar body at meiosis I. The drive mechanism may explain differences in X chromosome regulation in the female germlines of the human and mouse and, based on the functions encoded by the genes in the region, the transmission of X pericentromeric genetic or epigenetic variants to progeny could contribute to preeclampsia, autism, and differences in sexual differentiation.

FBXO38 deficiency promotes lysosome-dependent STING degradation and inhibits cGAS-STING pathway activation

F-box only protein 38 (FBXO38) is a member of the F-box family that mediates the ubiquitination and proteasome degradation of programmed death 1 (PD-1), and thus has important effects on T cell-related immunity. While its powerful role in adaptive immunity has attracted much attention, its regulatory roles in innate immune pathways remain unknown. The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is an important innate immune pathway that regulates type I interferons. STING protein is the core component of this pathway. In this study, we identified that FBXO38 deficiency enhanced tumor proliferation and reduced tumor CD8+ T cells infiltration. Loss of FBXO38 resulted in reduced STING protein levels in vitro and in vivo, further leading to preventing cGAS-STING pathway activation, and decreased downstream product IFNA1 and CCL5. The mechanism of reduced STING protein was associated with lysosome-mediated degradation rather than proteasomal function. Our results demonstrate a critical role for FBXO38 in the cGAS-STING pathway.