Protein kinase LKB1 promotes RAB7-mediated neuropilin-1 degradation to inhibit angiogenesis
Imoh S. Okon, Kathleen A. Coughlan, Cheng Zhang, Cate Moriasi, Ye Ding, Ping Song, Wencheng Zhang, Guangpu Li, Ming-Hui Zou
Imoh S. Okon, Kathleen A. Coughlan, Cheng Zhang, Cate Moriasi, Ye Ding, Ping Song, Wencheng Zhang, Guangpu Li, Ming-Hui Zou
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Research Article Vascular biology

Protein kinase LKB1 promotes RAB7-mediated neuropilin-1 degradation to inhibit angiogenesis

Abstract

After internalization, transmembrane receptors (TMRs) are typically recycled back to the cell surface or targeted for degradation. Efficient TMR trafficking is critical for regulation of several processes, including signal transduction pathways, development, and disease. Here, we determined that trafficking of the angiogenic receptor neuropilin-1 (NRP-1) is abrogated by the liver kinase B1 (LKB1), a serine-threonine kinase of the calcium calmodulin family. We found that aberrant NRP-1 expression in tumor cells from patients with lung adenocarcinoma is associated with decreased levels of LKB1. In cultured lung cells, LKB1 accentuated formation of a complex between NRP-1 and RAB7 in late endosomes. LKB1 specifically bound GTP-bound RAB7, but not a dominant-negative GDP-bound form of RAB7, promoting rapid transfer and lysosome degradation of NRP-1. siRNA-mediated depletion of RAB7 disrupted the transfer of NRP-1 to the lysosome, resulting in recovery of the receptor as well as increased tumor growth and angiogenesis. Together, our findings indicate that LKB1 functions as a RAB7 effector and suppresses angiogenesis by promoting the cellular trafficking of NRP-1 from RAB7 vesicles to the lysosome for degradation. Furthermore, these data suggest that LKB1 and NRP-1 have potential as therapeutic targets for limiting tumorigenesis.

Authors

Imoh S. Okon, Kathleen A. Coughlan, Cheng Zhang, Cate Moriasi, Ye Ding, Ping Song, Wencheng Zhang, Guangpu Li, Ming-Hui Zou

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Figure 7

LKB1-mediated NRP-1 inhibition correlates with decreased tumor angiogenesis and growth in vivo.

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LKB1-mediated NRP-1 inhibition correlates with decreased tumor angiogene...
(A) Stable depletion of LKB1 and/or NRP-1 expression was confirmed in H1792 cells by Western blot analysis. (B and C) Vessel density after implantation of H1792 cells with the indicated depletion of LKB1 and/or NRP-1 expression. Scale bars: 0.32 mm. Mean ± SD is shown (n = 5; 2 independent repeats). (D and E) H1792 cells with the indicated depletion of LKB1 and/or NRP-1 expression were injected subcutaneously into nude mice, and tumor growth was monitored for 30 days. Representative image of tumors extracted from nude mice. Mean ± SEM is shown (n = 5; 2 independent repeats). (F) Paraffin sections of extracted tumors from the different recipient groups were stained for angiogenic receptors, NRP-1, VEGFR2, PDGFR, FGFR, and H&E (original magnification, ×40). ND, not determined due to insufficient tumor sample. Scale bars: 50 μm. *P < 0.05, ***P < 0.001.