Objective: Self-renewal of the skin is provided by progenitor keratinocytes that are localized to basal layer. The ones that commit to differentiate start to migrate upward to form the suprabasal layers of the epidermis. Receptor interacting serine/threonine kinase 4 (RIPK4) is is important for the growth and differentiation of the skin. The aim of this study is to analyze the effect of depletion of RIPK4 on differentiation status of keratinocytes.

Materials and Methods: RIPK4 knocked-out HaCaT (RIPK4 KO) keratinocytes were used in the experiments. Undifferentiated basal-like state and differentiated HaCaT cells were included for differentiation status comparisons. The morphology of the cells was analyzed by microscope. The levels of the RIPK4 protein were determined with western blot. To follow the growth rates, the cells were counted for 4 days. For transfection efficiency analysis, the cells were transfected with β-galactosidase expressing plasmids. The levels of differentiation-specific markers were determined by real-time-PCR.

Results: Morphologically RIPK4 KO cells were different from HaCaT cells which show the tendency to grow in cell clusters. RIPK4 KO cells showed resemblance to undifferentiated basal-like state cells which were more rounded and scattered. Both RIPK4 KO and basal-like state cells had lower RIPK4 protein than HaCaT cells. In parallel with similarity to undifferentiated cell morphology, RIPK4 KO cells were more proliferative, showed higher transfection efficiency and expressed lower levels of keratinocyte differentiation markers compared to HaCaT cells.

Conclusion: The results showed that stable depletion of RIPK4 induces the de-differentiation process in keratinocytes.