Mucin1 expression in focal epidermal dysplasia of actinic keratosis

Actinic keratoses (AKs) are generally considered as premalignant skin lesions that can progress into squamous cell carcinoma (SCC) in situ and invasive SCC. However, its progression to SCC is still matter of debate. A transmembrane glycoprotein that contributes to the progression of certain premalignant and malignant lesions is mucin1 (MUC1). Nevertheless, their functions in the skin lesions are not yet fully clear. Therefore, the aim of this study is to ascertain whether MUC1 is present in the focal epidermal dysplasia of AK.

Fourteen skin biopsies from patients diagnosed with AK were selected. They were classified according to the degree of dysplasia in keratinocyte intraepidermal neoplasia (KIN) I, KIN II, and KIN III. In five biopsies the three degrees were present, in two biopsies both KIN I and KIN II, in four biopsies only KIN I, and in three biopsies only KIN III. The presence of MUC1 was assessed by immunofluorescence staining using confocal laser scanning microscopy.

Immunostaining revealed that MUC1 was present over the entire cell surface of only a few atypical basal keratinocytes confined to the lower third of the epidermis (KIN I). While in KIN II where atypical keratinocytes occupy the lower two thirds, MUC1 was localized at the apical surface of some atypical keratinocytes and over the entire cell surface of some of them. Interestingly, in KIN III where the atypical keratinocytes extend throughout the full thickness, MUC1 was localized at the apical surface and over the entire cell surface of many of these cells. Conversely, MUC1 expression was not detected in the epidermis of normal skin.

Our findings suggest that the expression of MUC1 in AK would be induced by alteration of keratinocyte stratification and differentiation and associated to the degree of dysplasia rather than the thickness of the epidermis.