Blood and lymphatic systems are segregated by the FLCN tumor suppressor

Ikue Tai-Nagara,Fumiko Itoh,Yukiko Hasumi,Masanori Hirashima,Yorifumi Satou,Tomofumi Ando,Chang Liu,Keisuke Okabe,Hideyuki Saya,Dai Kusumoto,W Marston Linehan,Xinyi Liu,Shintaro Funasaki,Hisashi Hasumi,Wenling Li,Mitsuko Furuya,Fumio Matsuzaki,Yutaka Suzuki,Yoh‐Suke Mukouyama ,Baba M ,Yoshiaki Kubota

doi:10.1038/s41467-020-20156-6

Abstract

Blood and lymphatic vessels structurally bear a strong resemblance but never share a lumen, thus maintaining their distinct functions. Although lymphatic vessels initially arise from embryonic veins, the molecular mechanism that maintains separation of these two systems has not been elucidated. Here, we show that genetic deficiency of Folliculin, a tumor suppressor, leads to misconnection of blood and lymphatic vessels in mice and humans. Absence of Folliculin results in the appearance of lymphatic-biased venous endothelial cells caused by ectopic expression of Prox1, a master transcription factor for lymphatic specification. Mechanistically, this phenotype is ascribed to nuclear translocation of the basic helix-loop-helix transcription factor Transcription Factor E3 (TFE3), binding to a regulatory element of Prox1, thereby enhancing its venous expression. Overall, these data demonstrate that Folliculin acts as a gatekeeper that maintains separation of blood and lymphatic vessels by limiting the plasticity of committed endothelial cells.

Highlights

Blood and lymphatic vessels structurally bear a strong resemblance but never share a lumen, maintaining their distinct functions
FLCN encoded by the FLCN gene, as a complex with its binding proteins FNIP1/2, acts as a GTPase activating protein (GAP) for Rag GTPases, thereby transducing amino acid levels to mTOR complex 117–19 and secluding the basic helix-loop-helix transcription factor and member of the MiTF family, Transcription Factor E3 (TFE3), in the cytoplasm[20,21]
In agreement with the region-specific differences in Tie2–Cre expression[8], lymphatic vessel (LV) dilation was apparent in thoracic but not lumbar skins of FlcnΔEHC embryos (Fig. 1g–l)

Summary

Introduction

Blood and lymphatic vessels structurally bear a strong resemblance but never share a lumen, maintaining their distinct functions. Absence of Folliculin results in the appearance of lymphatic-biased venous endothelial cells caused by ectopic expression of Prox[1], a master transcription factor for lymphatic specification This phenotype is ascribed to nuclear translocation of the basic helix-loophelix transcription factor Transcription Factor E3 (TFE3), binding to a regulatory element of Prox[1], thereby enhancing its venous expression. Overall, these data demonstrate that Folliculin acts as a gatekeeper that maintains separation of blood and lymphatic vessels by limiting the plasticity of committed endothelial cells. In this study, based on a unique phenotype of Flcn−deficient mice, we have identified the fundamental mechanism maintaining the separation of the blood and lymphatic vascular systems through limiting the plasticity of committed endothelial cells

Methods

Results

Conclusion