Abstract
BackgroundMigration and proliferation of vascular endothelial cells are essential for repair of injured endothelium and angiogenesis. Cyclins, cyclin-dependent kinases (CDKs), and cyclin-dependent kinase inhibitors play an important role in vascular tissue injury and wound healing. Previous studies suggest a link between the cell cycle and cell migration: cells present in the G1 phase have the highest potential to migrate. The molecular mechanism linking these two processes is not understood.Methodology/Principal FindingsIn this study, we explored the function of STK35L1, a novel Ser/Thr kinase, localized in the nucleus and nucleolus of endothelial cells. Molecular biological analysis identified a bipartite nuclear localization signal, and nucleolar localization sequences in the N-terminal part of STK35L1. Nuclear actin was identified as a novel binding partner of STK35L1. A class III PDZ binding domains motif was identified in STK35L1 that mediated its interaction with actin. Depletion of STK35L1 by siRNA lead to an accelerated G1 to S phase transition after serum-stimulation of endothelial cells indicating an inhibitory role of the kinase in G1 to S phase progression. Cell cycle specific genes array analysis revealed that one gene was prominently downregulated (8.8 fold) in STK35L1 silenced cells: CDKN2A alpha transcript, which codes for p16INK4a leading to G1 arrest by inhibition of CDK4/6. Moreover in endothelial cells seeded on Matrigel, STK35L1 expression was rapidly upregulated, and silencing of STK35L1 drastically inhibited endothelial sprouting that is required for angiogenesis. Furthermore, STK35L1 depletion profoundly impaired endothelial cell migration in two wound healing assays.Conclusion/SignificanceThe results indicate that by regulating CDKN2A and inhibiting G1- to S-phase transition STK35L1 may act as a central kinase linking the cell cycle and migration of endothelial cells. The interaction of STK35L1 with nuclear actin might be critical in the regulation of these fundamental endothelial functions.
Highlights
Endothelial dysfunction underlies atherosclerosis and coronary heart disease [1,2]
We show that STK35L1 regulates the expression of CDKN2A alpha-transcript and inhibits the G1to S-phase transition of the cell cycle, and that STK35L1 is essential for endothelial cell migration and angiogenesis
The present study demonstrates that the localization of the novel kinase STK35L1 in the nucleus and nucleolus is regulated by a specific bipartite nuclear localization signal (NLS), and a Nucleolar localization signal (NoLS) both present in the Nterminal part of the protein
Summary
Migration and proliferation of vascular endothelial cells are important for repair of injured endothelium, and for angiogenesis [3]. Cells in the endothelial monolayer are in a quiescent state residing in the Go phase of the cell cycle. Angiogenesis induced by hypoxic tissue conditions or by angiogenic stimuli, is a complex biological process involving the directional migration, proliferation, intercellular alignment and adhesion of endothelial cells [3]. Healing of the endothelium and angiogenesis require the activation of a genetic program which regulates endothelial cell proliferation and migration in a coordinated manner. Migration and proliferation of vascular endothelial cells are essential for repair of injured endothelium and angiogenesis. Cyclin-dependent kinases (CDKs), and cyclin-dependent kinase inhibitors play an important role in vascular tissue injury and wound healing. The molecular mechanism linking these two processes is not understood
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