FAT4, a tumor suppressor and migration inhibitor, is a downstream target of miR-31. (A) FAT4 is down-regulated by miR-31. The expression level of FAT4 was detected by qRT-PCR in HMEC1 cells with stably expressed miR-31. (B) FAT4 is down-regulated in KSHV-infected LECs. The expression level of FAT4 was detected in KSHV-infected LECs. (C-D) Knockdown of FAT4 increases EC migration ability. HMEC1 cells (C) or LECs (D) that had undergone stable knockdown by shRNA lentivirus infection had their FAT4 expression level measured by qRT-PCR (right panel) and were also subjected to the Transwell cell-migration assay (left panel; n = 3). Migrated LECs were stained (representative photos are shown in the right panel) and counted. Scale bar represents 100 μm. (E) Structure of the FAT4 transcript and predicted seed region duplex formed between FAT4 and miR-31 (top panel). Reporter activity of the FAT4 CDS 1-2500 bp reporter construct after cotransfection with the miR-31–expressing or empty vector into 293T cells (bottom panel; n = 3). (F) Proposed model of EC motility regulation by KSHV.