Abstract 2650: Perlecan-Semaphorin 3A-Plexin A1-Neuropilin-1 complex: Flipping the switch controlling metastatic behavior of prostate cancer cells
Authors: Tellman Tristen V. , Cruz Lissette A. , Sablatura Lindsey K. , Grindel Brian J. , Chung Leland W. , Farach-Carson Mary C. 
Published: September 2020

Abstract
Introduction: For prostate cancer (PCa), the major site of metastasis is the bone, where disseminated PCa cells can remain dormant for years after colonization. The events that end dormancy and trigger recurrence in the skeletal system, leading to a transition from indolent to lethal widely metastatic disease, are poorly understood. The last seven Ig repeats of perlecan/HSPG2 domain IV (domain IV-3) function as an extracellular scaffold that can anchor the Perlecan-Semaphorin 3A-Plexin A1-Neuropilin-1 (PSPN) signaling complex. Perlecan interacts with semaphorin 3A (Sema3A) sequestered on PCa cells to modulate cell-cell and cell-matrix adhesion decisions. Secreted Sema3A functions as a neuropilin-1 ligand, but a plexin is required to transduce an intracellular signal. We are investigating the means by which the PSPN complex functions as a molecular switch that controls dormancy and reactivation of PCa cells in the perlecan-rich bone niche.
Methods: Biochemical, immunolabeling and molecular approaches were used to identify the components of the PSPN complex and demonstrate their functions. Susceptibility of PSPN complex components to MMP7/Matrilysin was evaluated by SDS-PAGE. Endocytosis and cellular localization of complex components was determined by immunolocalization. Dormancy induced by IV-3 engagement of SPN was evaluated using pp38 and pRb. FOXM1 activation was monitored downstream of the PSPN complex to demonstrate dormancy/cohesion or dyscohesion/invasion.
Results: Intact perlecan and domain IV-3 induce clustering via engagement of PSPN complex. Plexin knockdown reduced the cohesive phenotype in PCa cells. Destruction of complex components by the matrix metalloproteinase MMP-7/Matrilysin was demonstrated. FOXM1 was activated downstream of MMP-7-activated PSPN complex cleavage, consistent with escape from dormancy. Perlecan IV-3 induced dormancy and reduced FOXM1 activation. Immunolocalization data showed internalization of plexin A1 with immunostaining both at the PCa cell surface and perinuclear, consistent with dynamic turnover associated with activation of signaling after loss of the PSPN complex.
Conclusion: Intact PSPN complex at the PCa cell surface favors a dormant state that is reversed by MMP-7 cleavage. In the cohesive state (PSPN complex intact) FOXM1 is “off”, inhibiting the transcription of growth and metastasis promoting factors. We propose that the PSPN complex at metastatic sites such as bone acts as a molecular switch that can maintain dormancy until the switch is “flipped” by MMP-7 allowing reactivation, dyscohesion and favoring growth and metastasis. Ongoing work is investigating the role of plexin endocytosis in signal activation.
Citation Format: Tristen V. Tellman, Lissette A. Cruz, Lindsey K. Sablatura, Brian J. Grindel, Leland W. Chung, Mary C. Farach-Carson. Perlecan-Semaphorin 3A-Plexin A1-Neuropilin-1 complex: Flipping the switch controlling metastatic behavior of prostate cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2650.