An unconventional role of BMP-Smad1 signaling in DNA damage response: a mechanism for tumor suppression

Bone morphogenetic protein induces bone invasion of melanoma by epithelial-mesenchymal transition via the Smad1/5 signaling pathway

Oral malignant melanoma, which frequently invades the hard palate or maxillary bone, is extremely rare and has a poor prognosis. Bone morphogenetic protein (BMP) is abundantly expressed in bone matrix and is highly expressed in malignant melanoma, inducing an aggressive phenotype. We examined the role of BMP signaling in the acquisition of an aggressive phenotype in melanoma cells in vitro and in vivo. In five cases, immunohistochemistry indicated the phosphorylation of Smad1/5 (p-Smad1/5) in the nuclei of melanoma cells. In the B16 mouse and A2058 human melanoma cell lines, BMP2, BMP4, or BMP7 induces morphological changes accompanied by the downregulation of E-cadherin, and the upregulation of N-cadherin and Snail, markers of epithelial-mesenchymal transition (EMT). BMP2 also stimulates cell invasion by increasing matrix metalloproteinase activity in B16 cells. These effects were canceled by the addition of LDN193189, a specific inhibitor of Smad1/5 signaling. In vivo, the injection of B16 cells expressing constitutively activated ALK3 enhanced zygoma destruction in comparison to empty B16 cells by increasing osteoclast numbers. These results suggest that the activation of BMP signaling induces EMT, thus driving the acquisition of an aggressive phenotype in malignant melanoma.

HPO iron chelator, CP655, causes the G1/S phase cell cycle block via p21 upregulation

Iron is known not only for its importance in cellular and metabolic pathways but also for its role in causing cellular toxicities such as production of reactive oxygen species and growth of pathogens. The inability of the human body to physiologically excrete excess iron highlights the need to develop a cheap yet effective iron chelator. This study provides initial evidence of the therapeutic and prophylactic properties of 3-hydroxypyridin-4-one (HPO) chelators in murine collagen-induced arthritis. To determine whether these chelators would be effective on human cells, we tested a panel of different HPO chelators and identified 7-diethylamino-N-((5-hydroxy-6-methyl-4-oxo-1,4-dihydropyridin-3-yl)methyl)-N-methyl-2-oxo-chromen-3-carboxamide (CP655) as the most effective compound targeting human CD4+ T cells. Treatment with CP655 causes significant inhibition of cell proliferation and production of inflammatory cytokines such as interferon-γ and interleukin-17. Microarray analysis revealed dysregulation in cell cycle-related genes following CP655 treatment. This was validated by flow cytometry demonstrating a G1/S phase block caused by CP655. Finally, mechanistic experiments revealed that the chelator may be causing an upregulation of the cell cycle inhibitor protein CDKN1A (p21) as a possible mechanism of action. In conclusion, this study demonstrates that HPO chelators could prove to have therapeutic potential for diseases driven by excessive T cell proliferation.

Twist1-related miR-26b-5p suppresses epithelial-mesenchymal transition, migration and invasion by targeting SMAD1 in hepatocellular carcinoma

Twist1 is well known to induce epithelial-mesenchymal transition (EMT) and promote tumor metastasis. MicroRNAs (miRNAs) are involved in the EMT process and are associated with metastasis in hepatocellular carcinoma (HCC). In the present study, microRNA-26b-5p (miR-26b-5p) expression was consistently and significantly downregulated in HepG2-Twist1 HCC cell lines compared with HepG2-vector cell lines using microarrays (the HepG2-Twist1 cell line can stably express Twist1). miR-26b- 5p downregulation was directly mediated by Twist1 through binding to the promoter region of miR-26b-5p in HepG2-Twist1 cells by ChIP-seq technology. Both gain- and loss-of-function studies showed that miR-26b-5p dramatically suppressed EMT and the invasion ability of HCC cells in vitro. Using mouse models, tumors derived from miR- 26b-5p-overexpressed HCC cells exhibited a significant reduction in tumorigenicity compared with the control group. Subsequent investigation revealed that miR-26b-5p directly inhibited SMAD family member 1 (SMAD1) expression. miR-26b-5p repressed BMP4/Smad1 signaling following SMAD1 inhibition. Overexpression of SMAD1 reversed the function of miR-26b-5p. In human HCC tissues and mouse xenograft tumors, miR-26b-5p levels were inversely correlated with SMAD1 expression as well as metastasis.

CONCLUSION

miR-26b-5p suppresses Twist1-induced EMT, invasion, and metastasis of HCC cells by targeting SMAD1 and BMP4/Smad1 signaling. This suggests a promising application for miR-26b-5p in anti-HCC therapy.

Bone morphogenetic protein 2 inhibits hepatocellular carcinoma growth and migration through downregulation of the PI3K/AKT pathway

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. Previous studies have suggested that abnormal expression of BMP-4, BMP-7, and BMP-9 is correlated with tumor progression in HCC, but the role played by BMP-2 in HCC has not yet been reported. To determine the role of BMP-2 in HCC, we first investigated the effect of exogenous BMP-2 on the growth of the cell lines HCC SK-Hep-1, Hep G2, and Hep 3B. Next, we studied the function of BMP-2 in SK-Hep-1 HCC cell line using a recombinant lentivirus vector to deliver BMP-2. We also used siRNA to silence endogenous BMP-2 expression in the HCC Hep 3B cell line. Then, cell growth and migration were assayed in vitro using WST-8, wound-healing, and transwell invasion assays. Cellular apoptosis and cell-cycle distribution were assessed using flow cytometry. We also investigated the effects of BMP-2 overexpression and knockdown on the expression of proliferating cell nuclear antigen (PCNA), matrix metallopeptidase-2 (MMP-2), phosphorylated AKT (p-AKT), phosphoinositide 3-kinase p85α (PI3Kp85α), Bax, Bcl-2, caspase-3, cleaved caspase-3, p21, and cyclin E. As a result, we observed that BMP-2 inhibited the proliferation of HCC cells. Furthermore, HCC cell proliferation and migration were significantly diminished by BMP-2 overexpression, as was indicated by WST-8, would healing, and transwell assays, while knockdown of BMP-2 led to an increase in proliferation and migration of Hep 3B cells. BMP-2 overexpression significantly increased the susceptibility of SK-Hep-1 cells to low-serum-induced apoptosis, while BMP-2 knockdown reduced the susceptibility of Hep 3B cells. Overexpression of BMP-2 induced G1 phase arrest through upregulation of p21. When BMP-2 expression was elevated in SK-Hep-1 cells, the expression of PI3Kp85α, p-AKT, PCNA, and MMP-2 declined. These results suggest that BMP-2 exerts an inhibitory effect on the growth and migration of HCC cells, possibly via a blockade of PI3K/AKT signaling.