Activation of Akt by mechanical stretching in human epidermal keratinocytes.

Mechanical stretching represents an important part of the signaling in skin. We have previously demonstrated that mechanical stretching induced proliferative phenotypes in human keratinocytes, as shown in increased 5-bromo-2'-deoxyuridine (BrdU) incorporation, ERK1/2 activation, and keratin K6 induction. Here we have further investigated the antiapoptotic signals in human keratinocytes provoked by mechanical stretching in vitro. Keratinocytes were plated on flexible silicone supports to transmit mechanical stretching to keratinocytes, involving continuous stretching by +20%. Stretching of these cells for 15-30 min caused the phosphorylation and activation of Akt. Inhibition of mitogen and extracellular signal-regulated kinase (MEK1/2) with U0126 and phosphoinositide 3-OH kinase (PI 3-K) with Wortmannin attenuated Akt activation. The epidermal growth factor (EGF) receptor kinase inhibitor, AG1478, and calcium channel inhibitor, gadolinium (Gd3+), also inhibited Akt activation. In summary, our results demonstrate the activation of the Akt signaling pathway by mechanical stretching, generating not only proliferative but also antiapoptotic signals in human keratinocytes.