Non-small cell lung cancer (NSCLC) has a 5-y survival rate of ∼16%, with most deaths associated with uncontrolled
metastasis. We screened for stem cell identity-related genes preferentially expressed in a panel of cell lines with high versus low metastatic potential, derived from NSCLC
tumors of Kras(LA1/+);P53(R172HΔG/+) (KP) mice. The Musashi-2 (MSI2)
protein, a regulator of mRNA translation, was consistently elevated in
metastasis-competent cell lines. MSI2 was overexpressed in 123 human NSCLC
tumor specimens versus normal lung, whereas higher expression was associated with
disease progression in an independent set of matched normal/primary
tumor/lymph node specimens. Depletion of MSI2 in multiple independent metastatic murine and human NSCLC cell lines reduced invasion and metastatic potential, independent of an effect on proliferation. MSI2 depletion significantly induced expression of
proteins associated with epithelial identity, including
tight junction proteins [
claudin 3 (CLDN3),
claudin 5 (CLDN5), and
claudin 7 (CLDN7)] and down-regulated direct translational targets associated with epithelial-mesenchymal transition, including the TGF-β receptor 1 (TGFβR1), the small
mothers against decapentaplegic homolog 3 (SMAD3), and the zinc finger
proteins SNAI1 (SNAIL) and SNAI2 (SLUG). Overexpression of TGFβRI reversed the loss of invasion associated with MSI2 depletion, whereas overexpression of CLDN7 inhibited MSI2-dependent invasion. Unexpectedly, MSI2 depletion reduced
E-cadherin expression, reflecting a mixed epithelial-mesenchymal phenotype. Based on this work, we propose that MSI2 provides essential support for TGFβR1/SMAD3 signaling and contributes to invasive
adenocarcinoma of the lung and may serve as a predictive
biomarker of NSCLC aggressiveness.