Binding of RAS to PI3Kα regulates developmental and KRASG12D-induced lymphangiogenesis

Complex lymphatic anomalies (CLAs) are rare diseases characterized by the abnormal development of lymphatic vessels. CLAs can be caused by somatic activating mutations in KRAS (e.g., KrasG12D), which stimulate MAPK and PI3K signaling. While KRAS/MAPK signaling is known to play a critical role in CLA pathogenesis, the contribution of KRAS/PI3Kα signaling remains unclear. To investigate the role of RAS-activation of PI3Kα in CLAs, we analyzed mice carrying two missense mutations in the RAS-binding domain of p110α, the catalytic subunit of PI3Kα. These two mutations block the interaction between p110α and RAS but do not affect its kinase activity. Disruption of RAS-mediated PI3Kα activation in lymphatic endothelial cells reduced lymphatic vessel branching but did not affect lymphatic valve formation. In KrasG12D mutant mice, blocking RAS activation of p110α reduced the pathological enlargement of lymphatic vessels, but failed to prevent KrasG12D-induced lymphatic valve loss. Similar results were observed following p110α deletion in KrasG12D mutant mice. Together, these findings demonstrate that KrasG12D drives distinct disease phenotypes through separate downstream pathways. KRAS/PI3Kα signaling promotes pathological lymphatic vessel enlargement, whereas KRAS/MAPK signaling disrupts lymphatic valve formation.