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Profilin induces lamellipodia by growth factor-independent mechanism

Enrique Syriani^*,1, Azucena Gomez-Cabrero^*,1, Marta Bosch, Alicia Moya^*, Elena Abad^*, Arcadi Gual^*, Xavier Gasull^* and Miguel Morales^*,2

^* Institut d’Investigacions Biomèdiques August Pi i Sunyer, Department of Physiological Sciences I, and

Department of Cellular Biology, Facultad de Medicina-University of Barcelona, Barcelona, Spain

²Correspondence: IDIBAPS-Department of Physiological Sciences I, Facultad de Medicina-University of Barcelona, Barcelona, Spain. E-mail: miguelmorales{at}ub.edu

Profilin has been implicated in cell motility and in a variety of cellular processes, such as membrane extension, endocytosis, and formation of focal complexes. In vivo, profilin replenish the pool of ATP-actin monomers by increasing the rate of nucleotide exchange of ADP-actin for ATP-actin, promoting the incorporation of new actin monomers at the barbed end of actin filaments. For this report, we generated a membrane-permeable version of profilin I (PTD4-PfnI) for the alteration of intracellular profilin levels taking advantage of the protein transduction technique. We show that profilin I induces lamellipodia formation independently of growth factor presence in primary bovine trabecular meshwork (BTM) cells. The effects are time- and concentration-dependent and specific to the profilin I isoform. Profilin II, the neuronal isoform, failed to extend lamellipodia in the same degree as profilin I. H133S, a mutation in the polyproline binding domain, showed a reduced ability to induce lamellipodia. H199E, mutation in the actin binding domain failed to induce membrane spreading and inhibit fetal bovine serum (FBS) -induced lamellipodia extension. Incubation with a synthetic polyproline domain peptide (GP5)3, fused to a transduction domain, abolished lamellipodia induction by profilin or FBS. Time-lapse microscopy confirmed the effects of profilin on lamellipodia extension with a higher spreading velocity than FBS. PTD4-Pfn I was found in the inner lamellipodia domain, at the membrane leading edge where it colocalizes with endogenous profilin. While FBS-induced lamellipodia formation activates Rac1, PTD4-Pfn I stimulation did not induce Rac1 activation. We propose a role of profilin I favoring lamellipodia formation by a mechanism downstream of growth factor.—Syriani, E., Gomez-Cabrero, A., Bosch, M., Moya, A., Abad, E., Gual, A., Gasull, X., Morales, M. Profilin induces lamellipodia by growth factor independent mechanism.

Key Words: actin cytoskeleton • cell spreading • lamella • protein transduction