Activation of Protein Kinase C by Phorbol Esters Modulates α2β1Integrin on MCF-7 Breast Cancer Cells

Autor: Rosfjord, Edward C., Maemura, Michio, Johnson, Michael D., Torri, Jeffery A., Akiyama, Steven K., Woods, Virgil L., Dickson, Robert B.
Zdroj: Experimental Cell Research; April 1999, Vol. 248 Issue: 1 p260-271, 12p
Abstrakt: Cellular adhesions to other cells and to the extracellular matrix play crucial roles in the malignant progression of cancer. In this study, we investigated the role of protein kinase C (PKC) in the regulation of cell–substratum adhesion by the breast adenocarcinoma cell line MCF-7. A PKC activator, 12-O-tetradecanoylphorbol-l,3-acetate (TPA), stimulated cell adhesion to laminin and collagen I in a dose-dependent manner over a 1- to 4-h interval. This enhanced adhesion was mediated by α2β1integrin, since both anti-α2and anti-β1blocking antibodies each completely abrogated the TPA-induced adhesion. FACS analysis determined that TPA treatment does not change the cell surface expression of α2β1integrin over a 4-h time interval. However, α2β1levels were increased after 24 h of TPA treatment. Thus, the enhanced avidity of α2β1-dependent cellular adhesion preceded the induction of α2β1cell surface expression. Northern blot analysis revealed that mRNA levels of both α2and β1subunits were increased after exposure to TPA for 4 h, indicating that the induction of α2β1mRNA preceded that of its cell surface expression. This further suggested that the TPA-induced avidity of α2β1was independent of increased expression of α2β1. Pretreatment of cells with the PKC inhibitor calphostin C partially antagonized the TPA-induced increase in expression of α2β1integrin expression and of α2β1-mediated cellular adhesion. To identify a possible mechanism by which TPA could be acting to promote the rapid induction of α2β1adhesion, we treated the cells with the Rho-GTPase inhibitorClostridium botulinumexotoxin C3. C3 inhibited TPA-induced adhesion to laminin and collagen I in a dose-dependant manner, suggesting a likely role for Rho in TPA-induced adhesion. Together, these results suggest that PKC can modulate the α2β1-dependent adhesion of MCF-7 cells by two distinct mechanisms: altering the gene expression of integrins α2and β1and altering the avidity of the α2β1integrin by a Rho-dependant mechanism.
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