Sprouty1, a new target of the angiostatic agent 16K prolactin, negatively regulates angiogenesis

Céline Sabatel,Joseph A Martial,Anne M Cornet,Ludovic Malvaux,Sébastien P Tabruyn,Ingrid Struman,Karolien Castermans

doi:10.1186/1476-4598-9-231

Abstract

BackgroundDisorganized angiogenesis is associated with several pathologies, including cancer. The identification of new genes that control tumor neovascularization can provide novel insights for future anti-cancer therapies. Sprouty1 (SPRY1), an inhibitor of the MAPK pathway, might be one of these new genes. We identified SPRY1 by comparing the transcriptomes of untreated endothelial cells with those of endothelial cells treated by the angiostatic agent 16 K prolactin (16 K hPRL). In the present study, we aimed to explore the potential function of SPRY1 in angiogenesis.ResultsWe confirmed 16 K hPRL induced up-regulation of SPRY1 in primary endothelial cells. In addition, we demonstrated the positive SPRY1 regulation in a chimeric mouse model of human colon carcinoma in which 16 K hPRL treatment was shown to delay tumor growth. Expression profiling by qRT-PCR with species-specific primers revealed that induction of SPRY1 expression by 16 K hPRL occurs only in the (murine) endothelial compartment and not in the (human) tumor compartment. The regulation of SPRY1 expression was NF-κB dependent. Partial SPRY1 knockdown by RNA interference protected endothelial cells from apoptosis as well as increased endothelial cell proliferation, migration, capillary network formation, and adhesion to extracellular matrix proteins. SPRY1 knockdown was also shown to affect the expression of cyclinD1 and p21 both involved in cell-cycle regulation. These findings are discussed in relation to the role of SPRY1 as an inhibitor of ERK/MAPK signaling and to a possible explanation of its effect on cell proliferation.ConclusionsTaken together, these results suggest that SPRY1 is an endogenous angiogenesis inhibitor.

Highlights

Disorganized angiogenesis is associated with several pathologies, including cancer
We first confirmed the results of the transcriptomic analysis by performing a time response analysis of SPRY1 mRNA expression in adult bovine aortic endothelial (ABAE). 16 K 16 kDa N-terminal fragment of human prolactin (hPRL) treatment (10 nM) of ABAE cells induced the expression of SPRY1 in ABAE over time, with a maximum up-regulation 4 h post-treatment
The fold induction was not possible to determine in this case and the expression level of SPRY1 in human microvascular endothelial cell (HMVEC) was too low to be detected by Western blotting

Summary

Introduction

Disorganized angiogenesis is associated with several pathologies, including cancer. The identification of new genes that control tumor neovascularization can provide novel insights for future anti-cancer therapies. Essential to most RTK-mediated signaling is the activation of the extracellular-signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling cascade This cascade is precisely controlled by the activity of various regulatory proteins [2], including members of the Sprouty (SPRY) protein family. At which stage SPRY blocks ERK/ MAPK activation remains controversial, and evidence to date suggests the existence of multiple mechanisms that depend on the cell context and/or the identity of the RTK [5,6,7]. Due to their inhibitory activity on the ERK/ MAPK pathway, SPRY generally acts as a tumor suppressor. The angiostatic activity of both SPRY2 and SPRY4 has been demonstrated in vivo in a mouse model of ischemia [9]

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