Using the human keratinocyte cell line HaCaT, modifications of the growth fraction due to vasoactive intestinal peptide (VIP) were determined by immunostaining with monoclonal antibody Ki67. In addition, the expression of VIP receptor and epidermal growth factor (EGF) receptor have been analysed. VIP (10-(7) to 10-(11) M) produced an almost doubling of the total number of Ki67-positive cells in cultures with 2% fetal calf serum (FCS), wheras it was ineffective in FCS-free and 10% FCS cultures. The nuclear Ki67-staining patterns were classified into four categories. In FCS-free cultures VIP induced a shift from type III (light nucleus, staining nuclei) to type II (multiple, intensely stained spots). In cultures with 2% FCS, VIP induced a shift from type II to type III. VIP receptor expression was facilitated by VIP, when cells were grown in a medium supplemented with 10% FCS. VIP increased EGF receptor expression in FCS-free cultures but decreased the number EGF receptor-positive cells in experiments with 2% FCS. In conclusion, VIP is capable to modulate the growth fraction and receptor expression of HaCaT cells in vitro. The effects are dependent on the concentration of FCS within the culture medium. The findings might be of interest for keratinocyte pathology in general and dermatooncology in particular.

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