B7-H3, an immunoregulatory protein, is known to play a role in tumor progression. In many cancer types, observed correlations between high B7-H3 expression and poor prognosis have been attributed to involvement in antitumor immunity.However, here we demonstrate a nonimmunological alternative function of B7-H3 in cancer metastasis. Since advanced malignant melanoma is a disease with a poor survival rate and a broad pattern of metastasis, we used this disease as a model in our studies. We found that shRNA silencing of B7-H3 reduced the in vitro migratory potential and matrigel invasiveness of MDA-MB-435 and FEMX-I melanoma cells. In an experimental metastasis model in vivo, B7-H3 silencing of MDA-MB-435 cells resulted in reduced metastatic capacity and significantly increased the median symptom-free survival of nude mice (147 vs. 65 days, p < 0.001) and rats (53 vs. 42 days, p 5 0.025) injected with MDA-MB-435 cells. Furthermore, a smaller fraction of mice had microscopically detectable metastases compared to control animals, and the pattern of metastases was slightly different between the two groups but with the brain as the predominant organ. Immunohistochemistry on samples from two melanoma patients showed strong B7-H3 staining in both a primary tumor and metastases. Notably, the metastasis-associated proteins, matrix metalloproteinase (MMP)-2, signal transducer and activator of transcription 3 (Stat3), and the level of secreted interleukin-8 (IL-8) were reduced in the B7-H3 knock-down cell variants, whereas tissue inhibitor of metalloproteinase (TIMP)-1 and-2 levels were increased. Taken together, our findings indicate a novel role for B7-H3 in the regulation of the metastatic capacity of melanoma cells and it might be a potential therapeutic target for anti-metastasis therapy.B7-H3 (CD276) is a type I transmembrane protein with immunoglobulin-like structure. Two different isoforms are described having either two or four immunoglobulin domains, the latter being dominant in humans. 1,2 B7-H3 is a member of the B7/CD28 immunoglobulin superfamily which consists of several ligands that have inhibitory and stimulatory effects on the regulation of immune responses to transformed cells, thus being involved in tumor immunity, 3 and the protein is known to both activate and inhibit T-cell responses. 4,5 This is reflected in the conflicting reports on its role in cancer describing both beneficial and adverse effects. Thus, several immunohistochemical studies have demonstrated a correlation between high expression of the protein and tumor progression, 6-11 whereas other studies suggest a positive effect on the clinical outcome. 12,13 Although the effects of B7-H3 in cancer have been attributed to its involvement in antitumor immunity, its exact function remains unclear.In contrast to previous reports, we have investigated the B7-H3 protein in nonimmunological systems and conclude that it also plays a direct role in cancer progression. In vitro studies on cancer cells showed that siRNA down-regulation of B7-H3 reduced cel...
In many types of cancer, the expression of the immunoregulatory protein B7-H3 has been associated with poor prognosis. Previously, we observed a link between B7-H3 and tumor cell migration and invasion, and in present work we have investigated the role of B7-H3 in chemoresistance in breast cancer. We observed that silencing of B7-H3, via stable shRNA or transient siRNA transfection, increased the sensitivity of multiple human breast cancer cell lines to paclitaxel as a result of enhanced drug-induced apoptosis. Overexpression of B7-H3 made the cancer cells more resistant to the drug. Next, we investigated the mechanisms behind B7-H3 mediated paclitaxel resistance, and found that the level of Stat3 Tyr705 phosphorylation was decreased in B7-H3 knockdown cells, along with the expression of its direct downstream targets Mcl-1 and Survivin. The phosphorylation of Jak2, an upstream molecule of Stat3, was also significantly decreased. In contrast, reexpression of B7-H3 in B7-H3 knockdown and low B7-H3- expressing cells increased the phosphorylation of Jak2 and Stat3. In vivo animal experiments showed that B7-H3 knock down tumors displayed a slower growth rate than the control xenografts. Importantly, paclitaxel treatment showed a strong anti-tumor activity in the mice with B7-H3 knockdown tumors, but only a marginal effect in the control group. Taken together, our data demonstrate that in breast cancer cells B7-H3 induces paclitaxel resistance, at least partially by interfering with Jak2/Stat3 pathway. These results provide novel insight into the function of B7-H3 and encourage the design and testing of approaches targeting this protein and its partners.
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