Supplementary Material for: Cortical Actin Alteration at the Matrix-Side Cytoplasm in Lung Adenocarcinoma Cells and Its Significance in Invasion

Objectives: Cortical actin is a thin layer of
filamentous (F-)actin that lies beneath the plasma membrane, and its
role in pathophysiology remains unclear. We investigated the subcellular
localization of cortical actin by the histopathological and
experimental studies of lung adenocarcinomas. Materials and Methods:
The subcellular localization of cortical actin was studied in
surgically resected lung adenocarcinomas tissues and in 3-dimensionally
cultured lung adenocarcinoma A549 cells. Results: In
normal type II alveolar cells and the bronchiolar epithelium, cortical
actin was localized to the apical-side cytoplasm. In invasive
adenocarcinoma cells, cortical actin was frequently localized to the
matrix side. The degree of cortical actin localized to the matrix side
was associated with the loss of basement membrane and a poor prognosis.
In A549 cell spheroids cultured in a type I collagen and basement
membrane extract Matrigel™ mixed gel, cortical F-actin was localized to
the matrix side with phosphorylated myosin light chain. Super-resolution
and electron microscopy results suggest that compact wrinkling of the
plasma membrane by myosin-mediated F-actin contraction is an explanation
for cortical actin accumulation at the matrix side. The myosin II
inhibitor blebbistatin suppressed the 3-dimensional collective migration
of A549 cells induced by constitutively active Cdc42 and MT1-MMP. Conclusion:
Cortical actin accumulation at the matrix-side cytoplasm of cancer
cells occurs in invasive lung adenocarcinomas and it possibly
participates in the migration of cancer cells through myosin-mediated
contraction.