Keratinocyte Apoptosis on Type I Collagen Gel Caused by Lack of Laminin 5/10/11 Deposition and Akt Signaling

Abstract

Cultured human foreskin keratinocytes (HFKs) adhere to and grow on nonfibrous collagen via integrin α2β1. During incubation, the receptors used for adhesion are changed to integrins α3β1 and α6β4 and those receptors bind to laminin 5 which is deposited by keratinocytes themselves. In this report, we examined the behaviors of HFKs and transformed keratinocytes on collagen fibril gels. These cells adhered to and spread on collagen gels using integrin α2β1. After several hours on collagen gels, however, cells became round and apoptosis occurred. The behavior of keratinocytes contrasted to that of fibroblasts that grew well even on collagen gel. At the point of apoptosis, integrins α2β1 and α3β1 were not found in the contact region of HFKs. Also, deposition of laminin 5 on collagen gel was not found despite the synthesis of mRNA for laminin 5 and laminin 10/11, while soluble laminin 5 protein is readily detectable. Phosporylation of Akt, which is known as a survival signal, was detected in HFKs cultured on coated collagen; however, the protein level and signals of Akt were dramatically decreased on collagen gel after 1 day of culture. These results indicate that collagen gel has different effects than nonfibrous collagen on HFKs and transformed keratinocytes and the interactions of integrin α3β1 and laminin 5/10/11 are indispensable for maintenance of keratinocyte adhesion and survival.