Investigation In The Molecular Machenism Of CD47 Regulation By CRL4 E3 Ligase

CD47,which functions as a sign of "self" and helps to avoid engulfment,is a protein broadly expressed on normal cells.CD47 is often overexpressed on cancer cells,which may contribute to the escaping of cancer cells from phagocytosis.And its counter-receptor,SIRP?,is an inhibitory immunoreceptor expressed by myeloid cells.Functioning as an essential immune checkpoint,CD47-SIRP? axis plays an important part in maintaining homeostasis of the body and clearing cancer cells.Blocking CD47-SIRP? interactions has been shown to promote the destruction of cancer cells by phagocytes,including macrophages and neutrophils.Furthermore,targeting of the CD47-SIRP? axis may also promote antigen-presenting cell function and thereby stimulate adaptive T cell-mediated anti-cancer immunity.In this study,we find that CD47 can be ubiquitinated by Cul4A-DDB1 E3 ligase,and consequently be degradated by the proteasome.But when searching into the interactions between CD47 and the DCAFs,it seems a large number of DCAFs would interact with CD47 in the co-IP test.We knocked down DCAF3,DCAF5 and DCAF8 in 293T cell line respectively,and found that CD47 is upregulated in DCAF5 knock down cell.Besides,we knocked out DCAF5,DCAF8 and WSB1 in K562 cell line using the CRISPR/Cas9 system,and identified that CD47 level is also increased in DCAF5 knock out cell.In addition,we knock out DCAF5 in C57/B6 mice,the result shows CD47 is increased in DCAF5-/-mice bone marrow basically.Accordingly,we infer that DCAF5 may link CD47 and DDB1 for ubiquitination.But this needs more evidence.Collectively,it is significant to investigate the regulation of CD47,which is closely related to the frontier of cancer immunotherapy,and deserves further study.