Human Keratinocyte Cell Lines

In the past, immortalization of human epidermal keratinocytes has been generally considered to have a massive impact on their differentiation properties. This is certainly true for many virally transformed cells. In contrast, the recently described spontaneous cell line HaCaT exhibits a virtually normal growth and differentiation pattern when transferred to an in vivo environment (cell transplants on nude mouse). These HaCaT cells also respond in vitro to external signals (e.g. levels of calcium, retinoids) similarly as normal keratinocytes. All major epidermal differentiation products are expressed (specific keratins, involucrin, filaggrin) under appropriate conditions at high levels and apparently in the right sequence. In order to provoke malignant conversion HaCaT cells were transfected with mutated cellular Ha-ras (val-12). The derived cell clones could be classified according to their growth properties in vivo into one (1) non-tumorigenic (growing as surface epithelia) and two tumorigenic groups, forming either (2) benign cysts or (3) well-differentiated squamous cell carcinomas. While the differentiation potential was retained in these cells to a varying degree, showing no clear correlation to malignant properties, all tumorigenic clones (benign and malignant) had lower growth factor requirements and maintained growth even without serum. Thus, HaCaT and derived cell lines provide readily available cell culture models and might offer useful alternatives to primary or low-passaged normal keratinocytes. According to preliminary data, some promising applications are: testing and detection of growth and differentiation factors (also drugs), synthesis of differentiation products and epidermis-derived factors (possibly at large scale) and introduction of exogenous genes or subgenomic regulatory elements.