Cerebral cavernous malformations (CCMs) are human vascular malformations caused by mutations in three genes of unknown function, KRIT1, CCM2 and PDCD10. Here we show that the HEG1 receptor, linked to CCM genes in zebrafish, is selectively expressed in endothelial cells and that Heg1-/- mice exhibit defective integrity of the heart, blood vessels and lymphatic vessels. In contrast, Heg1-/-;Ccm2+/lacZ and Ccm2lacZ/lacZ mice die early in development due to a failure of nascent endothelial cells to associate into patent vessels, a phenotype shared by deficient zebrafish embryos and reproduced by deficient endothelial cells ex vivo. These cardiovascular defects are associated with abnormal endothelial junctions like those observed in human CCMs, and biochemical and cellular imaging studies identify a cell autonomous pathway in which HEG1 receptors couple to KRIT1 at cell junctions. These studies identify HEG1-CCM signaling as a critical regulator of cardiovascular organ formation and integrity.

In previous studies, lactate dehydrogenase A (LDHA) was identified as one of the leading genes that promote the proliferative and tumorigenic potential of malignancies. However, less definitive evidence was reported in hepatocellular carcinoma (HCC) cells. Furthermore, the role of LDHA in promoting metastasis of HCC, and its possible mechanism, is not clear. In this study, RNA interference (RNAi) mediated by lentiviral vectors (which induce strong down-regulation of gene expression) was used to analyze the role of LDHA in tumor growth and metastasis in HCC. We performed transient and stable RNAi knockdowns of LDHA in HCCLM3 cells, a line that over-expresses LDHA and has a high metastatic potential. Our studies reveal that previously unidentified effects of LHDA may mediate tumor growth and metastasic effects in HCC. First, HCC cell lines over-express LDHA. Second, LDHA inhibition results in increased apoptosis via production of reactive oxygen species in HCCLM3 cells. Thus, LDHA knockdown resulted in significant reduction in metastatic potential in a xenograft mouse model. Furthermore, we found that FAK, MMP-2, VEGF and E-cadherin proteins contribute to inhibitory effects on metastasis in HCC cells. These studies have important implications for understanding the mechanisms by which LDHA promotes tumor growth and metastasis.