N-cadherin enhances breast cancer cell migration by suppressing Akt3

Abstract

N-cadherin is a cell adhesion molecule which plays a role in breast cancer metastasis. It is primarily expressed in neuronal and mesenchymal cells, but it has been found to be upregulated in invasive breast cancer cell lines and in aggressive ductal carcinomas. In the polyoma middle T (PyMT) mouse breast cancer model, expression of N-cadherin promotes in vitro cell motility and invasion as well as metastasis. However, the underlying mechanism by which N-cadherin enhances metastasis is not well understood. A potential mode of action is the regulation of signaling pathways by N-cadherin. N-cadherin can stabilize the fibroblast growth factor receptor at the membrane resulting in enhanced invasion through extracellular-signal-regulated kinases (ERK) induced matrix metalloproteinase-9 activity.;In addition to activating the ERK pathway, our present study suggests that N-cadherin in the PyMT mouse model may also suppress Akt3 expression. Akt3 is a member of the Akt family of serine and threonine kinases which also includes Akt1 and Akt2. These Akt isoforms have been shown to have distinct functions in cell motility and invasion. We have found that primary tumor cells from mice co-expressing PyMT and N-cadherin in the mammary epithelium had reduced Akt3 expression and subsequently reduced Akt3 phosphorylation compared to cells from PyMT control mice. There was no difference in Akt1 or Akt2 expression between the PyMT and PyMT-N-cadherin cells. Furthermore, exogenous expression of N-cadherin into a PyMT cell line also selectively decreased Akt3 expression leading to decreased phosphorylation of Akt3. N-cadherin did not post-translationally regulate Akt3 expression; however, it did modestly regulate Akt3 expression at the transcriptional level. Having found that N-cadherin suppresses Akt3 expression, we examined whether Akt3 played a role in N-cadherin induced motility. Knockdown of Akt3 in PyMT cells led to increased cell migration. Conversely, expression of constitutive active myristoylated Akt3 in PyMT-N-cadherin cells inhibited cell migration. Interestingly, in a panel of human breast epithelial and cancer cell lines, Akt3 expression was present in the epithelial cells lines but was generally lost in the cancer cell lines. Moreover, knockdown of Akt3 in the Hs578T human breast cancer cells and expression of myristoylated Akt3 in 3475 human breast cancer cells, enhanced and inhibited invasion, respectively. Taken together, these data suggest that N-cadherin suppresses Akt3 to enhance cell migration.