KRT14 and papilloma: On the other hand, constitutive activation of Rac1, in addition to expression of HPV-8, led to the development of papillomas, but not SCCs, in 100% of the double transgenic K14 HPV-8/K14 L61Rac1 mice, whereas K14 L61Rac1 mice without HPV-8 did not develop skin papillomas.