keratinocyte; squamous cell carcinoma of the skin; TLR4; skin cancer; proliferation
Iotzova-Weiss Guergana, Freiberger Sandra N., Johansen Pål, Kamarachev Jivko, Guenova Emmanuella, Dziunycz Piotr J., Roux Guillaume A., Neu Johannes, Hofbauer Günther F. L. (2017), TLR4 as a negative regulator of keratinocyte proliferation, in PLOS ONE
, 12(10), e0185668-e0185668.
Proliferation and differentiation are two sequential processes which drive the maturation of normal keratinocytes till they reach their full differentiation status. However, abnormal proliferation of keratinocytes is also a characteristic feature of tumor cells including squamous cell carcinoma (SCC). In this study, we want to delineate the inverse relationship between the proliferation of keratinocytes and the pathogen-associated molecular pattern receptor Toll-like receptor 4 (TLR4). We observed increased TLR4 surface expression in normal primary keratinocytes with subsequent passages in cell culture. In contrast, the expression of TLR4 in established highly proliferative SCC cell lines was low, similar to the expression in normal keratinocytes at low passage numbers. In response to antibody-mediated blockade of TLR4, keratinocyte proliferation increased greatly by the incorporation of BrdU. Using a specific blocking peptide for the interaction of TLR4 and its accessory protein MDII, keratinocytes reacted with increased proliferation, though not to the same degree as achieved by direct blocking of TLR4. Based on our results we hypothesize that TLR4 is a negative regulator of keratinocyte proliferation and may be associated with the progression of SCC of the skin. Such a regulatory function of TLR4 in keratinocyte proliferation has not been investigated yet. This project will assess the relationship between TLR4 expression and keratinocyte proliferation by TLR4 expression analysis in human squamous cell carcinoma and normal epidermis, proliferation assays of normal human keratinocytes following overexpression and silencing of TLR4, by assessing differentiation and senescence of normal keratinocytes following overexpression and silencing of TLR4. We will investigate TLR4 signaling in keratinocytes, both through the MyD88-dependent and MyD88-independent pathway. As a third aim, we will explore functionality of TLR4 manipulation in vivo. Better understanding of a regulatory role for TLR4 is the basis for a later use in a therapeutic setting to stop keratinocyte proliferation such as in squamous cell carcinoma of the skin and to induce keratinocyte proliferation such as in wound healing.