IKKα regulates the stratification and differentiation of the epidermis: implications for skin cancer development

IKK alpha plays a mandatory role in keratinocyte differentiation and exerts an important task in non-melanoma skin cancer development. However, it is not fully understood how IKK alpha exerts these functions. To analyze in detail the role of IKK alpha in epidermal stratification and differentiation, we have generated tridimensional (3D) cultures of human HaCaT keratinocytes and fibroblasts in fibrin gels, obtaining human skin equivalents that comprise an epidermal and a dermal compartments that resembles both the structure and differentiation of normal human skin. We have found that IKK alpha expression must be strictly regulated in epidermis, as alterations in its levels lead to histological defects and promote the development of malignant features. Specifically, we have found that the augmented expression of IKK alpha results in increased proliferation and clonogenicity of human keratinocytes, and leads to an accelerated and altered differentiation, augmented ability of invasive growth, induction of the expression of oncogenic proteins (Podoplanin, Snail, Cyclin D1) and increased extracellular matrix proteolytic activity. All these characteristics make keratinocytes overexpressing IKK alpha to be at a higher risk of developing skin cancer. Comparison of genetic profile obtained by analysis of microarrays of RNA of skin equivalents from both genotypes supports the above described findings.