Amino-terminal fragments of laminin γ2 chain stimulate migration of metastatic breast cancer cells by interacting with CD44

Laminin gamma 2 (Lm gamma 2) chain, a subunit of the basement membrane protein laminin-332, is regarded as a typical cancer invasion marker. The overexpression of Lm gamma 2 chain by invasive cancer cells correlates with poor prognosis of cancer patients, and its forced expression in human cancer cells promotes their invasive growth in a nude mouse model. However, its actual roles in cancer progression, as well as the mechanism of its proinvasive effect, remain unclear. CD44 is known to be an important cancer stem cell marker and support cancer progression and stem cell functions. Here we demonstrate that amino-terminal fragments of Lm gamma 2 interact with CD44 on the membrane of breast cancer cells. Lm gamma 2 highly bound to the metastatic cell line MDA-MB-231 but poorly to the benign cell line MCF-7. The membrane receptor for Lm gamma 2 on MDA-MB-231 cells was identified to be the standard form of CD44 (CD44s) by co-immunoprecipitation, affinity chromatography and direct protein interaction assay. Lm gamma 2 interacted with CD44s through EGF-like repeat 2/3 in the Lm gamma 2 amino-terminus. Amino-terminal fragments of Lm gamma 2 induced the phosphorylation of CD44 cytoplasmic domain and stimulated migration of the cancer cells in a CD44-dependent manner. This migration was blocked by inhibitors of TGF-beta receptor I (TGF-beta RI) kinase. These results suggest that two important tumor markers, Lm gamma 2 and CD44, cooperate for cancer progression and possibly for cancer stem cell functions. TGF-beta RI may be involved in the Lm gamma 2/CD44 interaction.