α3β1 integrin promotes keratinocyte cell survival through activation of a MEK/ERK signaling pathway

Abstract

Inadequate or inappropriate adhesion of epithelial cells to extracellular matrix leads to a form of apoptosis known as anoikis. During various tissue remodelling events, such as wound healing or carcinoma invasion, changes in the physical properties, and/or composition of the extracellular matrix, can lead to anoikis of epithelial cells that lack appropriate receptor-matrix interactions. Laminin-5 is the major ligand for keratinocyte adhesion in the epidermis, and it also promotes keratinocyte survival in vivo and in vitro. Integrins α3β1 and α6β4 are the major receptors for laminin-5; however, specific roles for these integrins in keratinocyte survival have not been determined. In the current study, we exploited keratinocyte cell lines derived from wild-type or α3 integrin knockout mice to reveal a critical role for α3β1 in protecting keratinocytes from apoptosis upon serum withdrawal. We show that α3β1-mediated adhesion to laminin-5 extracellular matrix inhibits proteolytic activation of caspase-3 and TUNEL-staining, both hallmarks of apoptosis. We also show that α3β1-mediated adhesion activates focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK), and that inhibition of either FAK or ERK signaling leads to apoptosis of keratinocytes attached to laminin-5. α6β4-mediated adhesion to laminin-5 only partially protects cells from apoptosis in the absence of α3β1, and α6β4 is not necessary for cell survival in the presence of α3β1. These results suggest that α3β1 is necessary and sufficient for maximal keratinocyte survival on laminin-5. We propose a model to address the potential importance of α3β1-mediated survival for migrating keratinocytes at the leading edge of a cutaneous wound.

Integrin Regulation of Epidermal Functions in Wounds

“…26,34,62 As receptors for a common BM ligand, it seems likely that a 3 b 1 and a 6 b 4 function coordinately (either cooperatively or in opposition) with regard to some keratinocyte processes. However, since these two integrins differ considerably with regard to both cytoskeletal interactions and signaling capacity, their combined effects on keratinocyte function are likely to occur through convergence of their distinct functions, rather than as redundant functions.…”

“…125 In addition, a 3 b 1 -mediated adhesion has been shown to promote the survival of keratinocyte cell lines through pathways that involve FAK and ERK, suggesting a possible role in survival of wound keratinocytes. 62 Adhesion through a 6 b 4 has also been linked to epidermal cell survival, 67 and it is conceivable that this integrin contributes to adhesion-dependent survival of the neo-epidermis when hemidesmosomes are assembled following wound closure.…”

“…1), and recent evidence suggests that some of these signals are regulated by keratinocyte integrins. 32,62,122,123 Such intercellular signals may be propagated from the epidermis to other cells through physical changes in the ECM (i.e., mechanical signaling), through diffusible growth factors that are secreted by the epidermis, or through generation of bioactive fragments following ECM proteolysis.…”

“…73 a 3 b 1 . In vivo and in vitro studies have identified several roles for integrin a 3 b 1 in regulating keratinocyte functions that may contribute to wound healing, including ECM deposition and organization, 74,75 cell polarization and migration, 34,53 cell survival, 62 cell proliferation, 76 and secretion of ECM proteases and pro-angiogenic factors.…”

Resensitization of breast cancer cells to anoikis by Tropomyosin-1: role of Rho kinase-dependent cytoskeleton and adhesion

“…Consequently, survival is ensured only when cells are in their physiological environment. Thus, anoikis plays a key role during normal growth and differentiation, as illustrated in tubulogenesis of mammary epithelial cells (Debnath et al, 2002(Debnath et al, , 2003 and wound healing (Manohar et al, 2004).…”