Junctional adhesion molecular 3 (JAM3) is a novel tumor suppressor and improves the prognosis in breast cancer brain metastases via the TGF-β/Smad signal pathway.

PURPOSE

Breast cancer brain metastasis (BCBM) is a deadly clinical problem, and the exact underlying mechanisms remain elusive. Junctional adhesion molecule (JAM), a tight junction protein, is a key negative regulator of cancer cell invasion and metastasis.

METHODS

Junction adhesion molecule 3 (JAM3) expression in breast cancer was analyzed using bioinformatics methods and confirmed by PCR, western blotting, and immunofluorescence (IF) in cell lines. The effects of exogenous expression of JAM3 using lentiviral vectors on invasion, adhesion, and apoptosis were verified using transwell assays and flow cytometry. Differentially expressed genes (DEGs) were detected by RNA sequencing and verified by q‒PCR and Western blotting. The effect of JAM3 silencing using siRNA was assessed by an adhesion assay. Kaplan‒Meier analysis was applied to calculate the impact of JAM3 expression and classic clinicopathologic characteristics on survival.

RESULTS

Bioinformatics analysis revealed that JAM3 expression was reduced in BCBM. Exogenous expression of JAM3 minimizes the ability of breast cancer cells to invade and adhere and promotes their apoptosis. Silencing JAM3 results in morphology changes and the recovery of invasion and adhesion to ECMs, and the TGF-β/Smad signaling pathway may be involved. JAM3 predicts less metastasis and good survival in patients with BCBM. Statistical analysis of BCBM samples detected by immunohistochemistry (IHC) and the associated clinicopathological characteristics revealed that low levels of JAM3 expression and high levels of TNF-β1 are linked to the clinical progression of both primary and metastatic breast tumors. Kaplan-Meier analysis revealed that a high expression level of JAM3 was associated with longer survival.

CONCLUSION

JAM3 can serve as a key negative regulator of breast cancer cell invasion, apoptosis, and brain metastasis, possibly through the TGF/Smad signaling pathway. JAM3 is anticipated to be a promising biomarker for the diagnosis and prognosis of breast cancer.