Prox-1 promotes invasion of kaposiform hemangioendotheliomas

Kaposi’s sarcoma (KS) is the most frequently occurring malignant tumor in patients infected with the human immunodeficiency virus. Recent studies have revealed that infection of vascular endothelial cells with Kaposi's sarcoma-associated herpes virus in vitro results in a lymphatic re-programming of these cells, with potent induction of the lymphatic marker genes podoplanin and VEGFR-3 which is mediated by upregulation of the transcription factor Prox1. However, the potential effects of Prox1 expression on the biology of KS and, in particular, on the aggressive and invasive behavior of KS tumors in vivo have remained unknown. We stably expressed Prox1 cDNA in the two mouse hemangioendothelioma cell lines EOMA and Py-4-1, well-established murine models for kaposiform hemangioendothelioma. Surprisingly, we found that expression of Prox1 was sufficient to induce a more aggressive behavior of tumors growing in syngenic mice, leading to enhanced local invasion into the muscular layer and to cellular anaplasia. This enhanced malignant phenotype was associated with upregulation of several genes involved in proteolysis, cytoskeletal reorganisation and migration. Together, these results indicate that Prox1 plays an important, previously unanticipated role in mediating the aggressive behavior of vascular neoplasms such as Kaposi's sarcoma. Keywords: Overexpression of Prox1 in Py-4-1 cell line. Total cellular RNA was extracted from two stably Prox1-expressing Py-4-1 cell clones and from two control-transfected Py-4-1 cell clones.