What Are HaCaT Cells and Why Are They Used in Research?

HaCaT cells are an immortalized human keratinocyte cell line, meaning they are laboratory-grown human skin cells that can multiply indefinitely. They provide a consistent and reproducible model of keratinocytes, the main cell type in the skin’s outermost layer, the epidermis. This allows researchers to study skin function, disease, and response to treatments in a controlled setting. HaCaT cells overcome the limitations of using primary cells, which have a finite lifespan and vary between donors.

Origin and Establishment of HaCaT Cells

The HaCaT cell line was established in 1988 by a team at the German Cancer Research Center from keratinocytes of a 62-year-old man. The defining characteristic of these cells is their spontaneous immortalization in a laboratory setting. This means they gained the ability to divide indefinitely without being intentionally altered by viruses or cancer-causing chemicals.

Spontaneous immortalization is a rare event for human cells, which normally have a limited number of divisions before entering a state of growth arrest called senescence. The cell line’s name reflects its origin: “Ha” for human adult and “Ca” for its initial growth in a low-calcium environment. This condition helps maintain keratinocytes in a proliferative state.

The immortalization process involved long-term cultivation, where the cells acquired genetic changes that let them bypass cellular aging. HaCaT cells have mutations in the p53 gene, which regulates cell division and suppresses tumors. These mutations are characteristic of UV radiation damage, even though the original tissue was from a sun-protected area.

Key Biological Properties

A primary feature of HaCaT cells is that they are non-tumorigenic despite being immortal. When injected into immunodeficient mice, they do not form tumors, indicating they have not undergone a full malignant transformation. This property makes them a useful model for studying the early stages of skin cancer and distinguishing between cellular immortalization and cancer.

HaCaT cells also retain the characteristics of normal human keratinocytes. They express specific proteins, such as keratins K5 and K14, which are found in the basal layer of the epidermis. The cells can also be prompted to differentiate, a process where they mature and take on more specialized functions, much like keratinocytes in natural skin.

This differentiation is triggered by increasing the calcium concentration in their culture medium. In response, the cells express markers like keratins K1 and K10, involucrin, and filaggrin, which are characteristic of the upper layers of the epidermis. This ability to mimic the skin’s layers in a dish is a valuable research tool. Genetically, the cells are aneuploid, meaning they have an abnormal number of chromosomes, but this state is relatively stable.

Applications in Biomedical Research

HaCaT cells are a versatile tool in biomedical research, providing a consistent alternative to primary keratinocytes. In dermatological studies, they are used to investigate basic skin functions. Researchers use them to model the skin’s barrier function, wound healing processes, inflammatory responses, and the effects of aging and UV radiation on skin cells.

In toxicology and pharmacology, HaCaT cells serve as a standard model for safety testing. They are used to assess the potential of chemicals, cosmetic ingredients, and drugs to cause skin irritation, allergic reactions, or phototoxicity. Their stable nature makes them suitable for screening many compounds to identify harmful or beneficial effects, reducing the reliance on animal testing for preliminary safety assessments.

The cells are frequently used in cancer research. They can be genetically modified or treated with carcinogens to study the mechanisms that drive the transformation of a normal skin cell into a malignant one. Serving as a non-tumorigenic control helps scientists pinpoint events that lead to skin cancer. In molecular biology, they are used for investigating processes like gene expression, cell signaling, and cellular responses to stimuli.

Culturing HaCaT Cells

Growing HaCaT cells in a laboratory requires specific conditions. They are cultured in a nutrient-rich liquid called a medium, like Dulbecco’s Modified Eagle Medium (DMEM). This base medium is supplemented with components to support cell growth, most notably fetal bovine serum (FBS) at a 10% concentration. FBS provides a complex mixture of growth factors and proteins.

To prevent bacterial contamination, an antibiotic solution with penicillin and streptomycin is added to the medium. The cells are grown in sterile flasks and housed in a specialized incubator. This incubator maintains a constant temperature of 37°C (98.6°F) and a 5% carbon dioxide (CO2) atmosphere to maintain the medium’s proper pH.

When the cells multiply and cover the culture vessel surface, a state known as confluency, they need to be subcultured or “passaged.” This involves detaching the cells from the flask surface using an enzyme like trypsin and splitting the population into new flasks with fresh medium. This process allows for the continuous expansion of the cell line. Passaging is done when cells reach 70-80% confluency to maintain optimal growth.