Alkaline ceramidase 2 regulates β1 integrin maturation and cell adhesion

The polypeptide core of the integrin beta 1 subunit (beta 1) is glycosylated sequentially in the endoplasmic reticulum and the Golgi complex to form beta 1 precursor and mature beta 1, respectively. The beta 1 precursor to mature beta 1 conversion, termed beta 1 maturation, regulates the cell surface levels and function of beta 1-containing integrins, beta 1 integrins. Here we demonstrate that the human alkaline ceramidase 2 (ACER2), a Golgi enzyme, regulates beta 1 maturation by controlling the generation of sphingosine. ACER2 overexpression inhibited beta 1 maturation, thus leading to a decrease in the levels of mature beta-1 in T-REx HeLa cells, whereas RNA interference-mediated knockdown of ACER2 enhanced beta 1 maturation in MCF-7 cells. ACER2 overexpression decreased the cell surface levels of beta 1 integrins, thus inhibiting cell adhesion to fibronectin or collagen, whereas ACER2 knockdown has the opposite effects. Treatment with all-trans retinoic acid (ATRA) increased both the expression of ACER2 and the generation of sphingosine in HeLa cells and inhibited beta 1 maturation. ACER2 knockdown attenuated the inhibitory effects of ATRA on both beta 1 maturation and cell adhesion. In contrast, treatment with phorbol myristate acetate (PMA), a protein kinase C activator, decreased the expression of ACER2 and sphingosine in T-REx HeLa cells, thus enhancing beta 1 maturation. ACER2 overexpression inhibited the stimulatory effects of PMA on both beta 1 maturation and cell adhesion. These results suggest that the ACER2/sphingosine pathway plays an important role in regulating beta 1 maturation and cell adhesion mediated by beta 1 integrins. Sun, W., Hu, W., Xu, R., Jin, J., Szulc, Z. M., Zhang, G., Galadari, S. H., Obeid, L. M, Mao, C. Alkaline ceramidase 2 regulates beta 1 integrin maturation and cell adhesion. FASEB J. 23, 656-666 (2009)