Maspin/SerpinB5 is a cytoskeleton-binding protein that regulates epithelial cell shape

Maspin/SerpinB5 is an abundant and pleiotropic protein mostly expressed by epithelia. Initially described as a tumor suppressor, it has been reported as a regulator of cell adhesion, migration, and invasion. How intracellular Maspin orchestrates these processes is poorly understood. In this study, we utilized Affinity purification-Mass spectrometry (AP/MS) alongside in vitro reconstitution assays to establish that Maspin directly interacts with microtubules and microfilaments. Additionally, CRISPR/Cas9-mediated GFP tagging of endogenous Maspin, combined with immunostaining, revealed its localization at the cortical cytoskeleton and the mitotic spindle. Depletion of Maspin by RNAi and CRISPR/Cas9 in three distinct epithelial cell lines disrupts cell-cell adhesion, reorganizes the cytoskeleton and results in upregulation of mesenchymal markers during interphase. In mitotic cells, loss of Maspin induces abnormal cell rounding and rearrangement of cortical F-actin. Moreover, Maspin suppresses microtubule growth in vitro and in cells. Collectively, these results demonstrate that Maspin acts at the interface between the cytoskeleton and adhesion sites, directly modulating cell shape and preventing epithelial-mesenchymal transition.