Connexin 43 Suppresses Tumor Angiogenesis by Down-Regulation of Vascular Endothelial Growth Factor via Hypoxic-Induced Factor-1α

Abstract

Previous work showed that connexin 43 (Cx43) reduced the expression of hypoxic-induced factor-1α (HIF-1α) in astrocytes. HIF-1α is a master transcription factor for angiogenesis in tumor. Angiogenesis is essential for tumor progression. Here, we investigated the role of Cx43 in vascular endothelial growth factor (VEGF) production and angiogenesis in murine tumor. In the study, mouse B16F10 and 4T1 cells were overexpressed or knockdown with Cx43. The expression profiles as well as activity of the treated cells were examined. Furthermore, reduced Cx43 expression in B16F10 and 4T1 cells causes increased expression of VEGF and enhanced the proliferation of endothelial cells. On the contrary, the expression of VEGF and the proliferation of endothelial were increased in the conditioned medium of Cx43-knockdown tumor cells. We subcutaneously transplanted Cx43-overexpressing B16F10 cells into mice to evaluate the roles of Cx43 in the tumor angiogenesis. Both tumor size and the number of vessels growing in the tumor were markedly decreased compare with control group. Our findings suggest that Cx43 inhibited tumor growth by reducing angiogenesis.

Salmonella inhibits tumor angiogenesis by downregulation of vascular endothelial growth factor

“…Salmonella has the ability to stimulate host immunity and increase tumor suppressor gene expression such as connexin 43 ( Cx43 ) [24–26]. Regulation of Cx43 activity by Salmonella probably contributes to the anti-angiogenic activity [17]. Therefore, it is plausible that the antitumor effect of Salmonella may be attributed not only to its effects on tumor endothelial cells but also to its ability to enhance inflammation within tumor sites [24].…”

“…Murine melanoma B16F10 cells [36] and murine breast cancer 4T1 cells [37] were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 50 μg/ml gentamicin, 2 mM L-glutamine, and 10% heat-inactivated fetal bovine serum (FBS) at 37°C in 5% CO 2 . Human HMEC-1 microvascular endothelial cells [14, 17] were cultured in EGM endothelial growth medium (Cambrex, East Rutherford, NJ, USA). Constitutively active AKT plasmid was kindly provided by Dr. Chiau-Yuang Tsai (Department of Molecular Immunology, Osaka University) [38].…”

“…The levels of mouse VEGF in tumor tissue homogenates were determined by ELISA [17]. To analyze microvessel density in the tumor sites, the whole tumors were excised and snap frozen at day 14.…”

“…Induction of angiogenesis plays an important role in the development and progression of most tumors. Targeting angiogenesis to inhibit tumor growth is one of the promising therapeutic approaches for tumor treatment [17]. Interestingly, a previous study revealed that mice treated with Salmonella alone, compared with those treated with Phosphate-buffered saline (PBS), showed slightly reduced intratumoral microvessel density [15].…”

Connexin 43: Key roles in the skin

“…Cx43 knockdown mediated by p54 nrb promotes cell proliferation and migration in human melanoma cell lines. In mouse melanoma cell lines, Cx43 reduction induced the expression of vascular endothelial growth factor and tumor angiogenesis (56). Similarly, in human melanoma cell lines, Cx43 overexpression reduced melanoma growth and metastasis, and increased TNFα-induced cell apoptosis (57).…”