KSHV miR-K12-9 Induces Transformation of Immortalized and Primary Endothelial Cells

Like most herpesviruses, KSHV encodes multiple microRNAs (miRNAs). Collectively, they comprise an important mechanism through which the virus maintains latency and persists in cells. At the same time, individual miRNAs can also play distinct, nonredundant roles. Past experiments with single miRNA knockout viruses showed that miR-K12-9, in particular, filled a unique niche. Endothelial cells latently infected with the miR-K12-9 knockout grew to be many times larger than WT-infected cells and proliferated at a significantly slower rate. Their ability to migrate was slowed as well. RNA-seq identified nearly 8,500 differentially expressed genes between miR-K12-9 knockout- and WT-infected cells. To further study miR-K12-9, we generated Telomerase-Immortalized Microvascular Endothelial (TIME) cells expressing either miR-K12-9 or a control miRNA from a lentivirus. Unexpectedly, after approximately one month in culture, unmistakable morphological changes began to occur in two of the three miR-K12-9-expressing cell lines. These smaller, more rounded cells proliferated rapidly and swiftly took over the two cultures. Given this result, we proceeded to characterize all the lentivirus-transduced cell lines in various assays focused on oncogenesis. When looking at colony formation in soft agar, only those two miR-K12-9-expressing cell lines produced colonies, indicating a loss of contact inhibition. NOD/SCID mice injected with the two cell miR-K12-9-expressing cell lines developed tumors while those receiving other cell lines did not. To confirm reproducibility of these results, we transduced both TIME and primary endothelial cells (HUVECs) with the miR-K12-9 and control lentiviruses. Once again, approximately half of the cell lines expressing miR-K12-9 showed hallmark phenotypes of transformation. We are currently characterizing the miR-K12-9 targetome in the transduced cell lines and mouse tumors using bulk and single-cell RNA-seq. This should yield insights into the underlying mechanism and required cofactors of miR-K12-9-induced transformation. To our knowledge, this is the first description of transformation of endothelial cells by a viral miRNA.