Human NINJ1 adenoviral particles

Radiotherapy is a widely used treatment for cancer patients, with more than half of cancer patients receiving radiation therapy during their treatment. Extensive evidence from preclinical and clinical studies suggests that tumor recurrence after radiation therapy is restored due to the influx of circulating cells, mainly composed of monocytes. The Ninjurin1 or Ninj1 gene, encoding a homotypic adhesion molecule and cell surface protein, has been found to be upregulated in inflammatory lesions, particularly in macrophages/monocytes, neutrophils, and endothelial cells. Recently, it has been reported that Ninj1 is regulated upon p53 activation. Here, researchers demonstrate radiation-mediated upregulation of Ninj1 in endothelial cell lines such as human umbilical vein endothelial cells (HUVEC), EA.hy926, and immortalized HUVEC. Consistent with this, researchers found that Ninj1 was overexpressed in irradiated xenograft tumors and that monocyte infiltration into the tumors was increased. Radiation-induced Ninj1 was transcriptionally regulated by p53, which was confirmed by transfection of p53 siRNA. Furthermore, overexpression of Ninj1 in endothelial cells accelerated monocyte adhesion. Knockdown of Ninj1 inhibited radiation-induced endothelial and monocyte interactions. In addition, overexpressed Ninj1 stimulated MMP-2 and MMP-9 expression in monocytic cell lines, while knockdown of Ninj1 in monocytes attenuated MMP-2 and MMP-9 expression. This result suggests that radiation-mediated Ninj1 expression in endothelial cells may be involved in the mechanism of recurrence after radiotherapy.

Multiple lines of evidence suggest that Ninj1 is involved in endothelial and monocyte adhesion during tumor invasion. To better define the role of Ninj1 in migration, transwell chambers were coated with subconfluent I-HUVEC endothelial cell lines transfected with adenovirus encoding Ninj1 (AdNin). THP-1 cell lines migrated more rapidly through I-HUVECs overexpressing Ninj1 than I-HUVECs transfected with control adenovirus (Figure 1A), whereas stable Ninj1 shRNA THP-1 cell lines bound significantly fewer cells under similar coating conditions (Figure 1B). The results suggest that the mechanism by which Ninj1 in endothelial cells promotes monocyte extravasation involves cell-cell adhesion mediated after radiation therapy. This strong adhesion may be due to the homologous binding of Ninj1 in both endothelial and monocyte cells. Next, monocyte adhesion to endothelial cells was studied in monocytes activated with MMP secretion. Knockdown of Ninj1 in a monocytic cell line similarly suppressed this expression (Figure 1C). These data support that Ninjuirin1 is involved in the infiltration of monocytes through endothelial cells, a process stimulated by radiation therapy.

Figure 1. Effect of Ninj1 on the transmigration and activation of monocytes. (Kang J H, et al., 2020)