Mena 11a-isoform specific regulation of actin cytoskeleton organization and cell behavior

Abstract

EnaNASP proteins are a conserved family of actin regulatory proteins that modulate cell motility and morphology by altering actin dynamics. Mena, an EnaNASP protein, is alternatively spliced, producing protein isoforms with distinct functions. Here, we characterize the expression, function, and regulation of the Mena11a splice isoform at the molecular and cellular level. We find that Menal 1 a is enriched in epithelia and muscle in both embryonic and adult tissues. Recent evidence demonstrates Mena upregulation in breast cancer; Mena promotes cell motility, invasiveness, and metastasis in a growth factor dependent manner. We demonstrate that Mena11a depletion in epithelial-like breast cancer cells disrupts cell-cell junctions and increases cell motility. Mena11a dampens growth factor-mediated membrane protrusion and attenuates G-actin incorporation to barbed ends of actin filaments. In addition, Menal Ia alters the actin cytoskeleton and decreases Arp2/3 recruitment to the leading edge of lamellipodia. Mass spectrometry analysis demonstrates that Mena11a is phosphorylated. The expression of a nonphosphorylatable mutant of Mena 1Ia does not retain the ability of Mena11a to dampen membrane protrusion, decrease G-actin incorporation at barbed ends, and reduce Arp2/3 recruitment at the lamellipodial edge; thus, our results suggest that phosphorylation of Mena11a is coupled to its activity.