Signaling via β1 integrins and mitogen-activated protein kinase determines human epidermal stem cell fate in vitro

Abstract

Human epidermal stem cells express higher levels of ␤1 integrins and are more adhesive than keratinocytes that are destined to differentiate. To investigate whether high ␤1 integrin expression and adhesiveness are essential for maintaining keratinocytes in the stem cell compartment, we introduced a dominant-negative ␤1 integrin mutant, CD8␤1, into cultured human keratinocytes, thereby interfering with ␤1 integrin function. Surface ␤1 integrin levels, adhesiveness, and mitogen-activated protein (MAP) kinase activation on fibronectin were reduced, and exit from the stem cell compartment was stimulated. Adhesiveness and proliferative potential were restored by overexpressing wild-type ␤1 integrin or by constitutive MAP kinase activation. Conversely, a dominant-negative MAP kinase kinase 1 mutant decreased adhesiveness and stem cell number in the absence of CD8␤1. MAP kinase activation by ␣6␤4-mediated adhesion and mitogens was normal in CD8␤1 cells, and constitutive MAP kinase activation did not affect adhesion and proliferation of control keratinocytes. We conclude that ␤1 integrins and MAP kinase cooperate to maintain the epidermal stem cell compartment in vitro.

p53 homologue, p51/p63, maintains the immaturity of keratinocyte stem cells by inhibiting Notch1 activity

“…This DNp51B-dependent maintenance of integrin expression, which allows integrin-mediated emission of a growth promoting signal through the Erk pathway (Mainiero et al, 1997;Zhu et al, 1999), further supports a role of DNp51B in promoting the proliferation of keratinocytes. This regulation of integrin expression was not affected by p21 overexpression (unpublished result), suggesting that this regulation was not caused by p21 regulation mentioned above.…”

“…We further examined the effects of p51 and Notch1 expression on integrin-mediated signaling, particularly on extra-cellular signal-regulated kinase (Erk) pathway, which is known to function down-stream of integrin signaling (Mainiero et al, 1997;Zhu et al, 1999). Indeed, exogenous expression of DNp51B induced phosphorylation of Erk and Mek1/2 (Figure 5f), and the reduction of DNp51B by siRNA method decreased phosphorylation (Figure 5d), together suggesting that DNp51B-dependent expression of the integrins leads to the activation of Mek1/2-Erk pathway.…”

Modulation of Cell-Substrate Adhesion by Arachidonic Acid: Lipoxygenase Regulates Cell Spreading and ERK1/2-inducible Cyclooxygenase Regulates Cell Migration in NIH-3T3 Fibroblasts

“…This is consistent with the initial transient release of [ 3 H]AA experienced by cells on the FN substrate being due to the ligation and clustering of integrin receptors, because it has been previously shown that clustering FN receptors stimulates AA release (Auer and Jacobson, 1995;Szabo et al, 1995;Haimovich et al, 1999;Zhu et al, 1999;Whitfield and Jacobson, 1999). Additional assays were conducted to test this possibility ( Figure 6A).…”

α5β1 Integrin Protects Intestinal Epithelial Cells from Apoptosis through a Phosphatidylinositol 3-Kinase and Protein Kinase B–dependent Pathway

“…For example, integrins are key regulators of the coordinated differentiation of many epithelial tissues. The functions of the ␤1 subfamily of integrins are particularly well understood in mammary development (Faraldo et al, 1998;Bissell et al, 1999) and in the differentiation of the epidermis (Watt, 1998;Zhu et al, 1999). However, integrins clearly play a role in other epithelia as well.…”