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The induction of UV-B damage and its consequences in the cellular componentsof human skin

Objective

To provide an assessment of UV-B DNA damage and repair and to link these to immunosuppressive effects in the individual components of human skin.

An increased incidence of both melanoma and nonmelanoma skin cancer is anticipated as a consequence of increased exposure to damaging wavelengths of ultraviolet B (UVB) following depletion of the ozone layer. However, little is known about the molecular and cellular effects of UVB on human skin. This study is intended to increase understanding of the mechanisms of action of UVB and its influence on the initiation and promotion steps of cancer. These are believed to be via the operation of the immune system in the skin. In the initial phase of this study a substantial collection of cells from normal and repair defective donors was assembled and a system for the exchange of tissues and cells between the collaborating laboratories was set up. The UVB sources and meters used in experimental studies were calibrated and standardized to provide an accurate system of cross reference. The collaboration has demonstrated: Human lymphocytes are specifically highly hypersensitive to the lethal and deoxyribonucleic acid (DNA) damaging action of UVB irradiation when compared with skin derived fibroblasts. By using a panel of lesion specific antibodies it was shown that it is the Dewar photoproduct, in addition to the 6-4 photoproduct, which is the critical lesion responsible for the lethality in T-lymphocytes. The reason why T-lymphocytes, but not fibroblasts, are killed efficiently by UVB irradiation was shown to be due to a deficiency in the deoxyribonucleotide pools of resting lymphocytes. Complementing studies on the removal of UVB induced DNA damage, have revealed differences in removal in three cell types; fibroblasts, lymphocytes and keratinocytes. The hypersensitivity of lymphocytes to the lethal action of UVB, and the clear demonstration of their susceptibility to clastogenic damage, are relevant to the immunomodulating effects of UVB in humans.
An increased incidence of both melanoma and non-melanoma skin cancer is anticipated as a consequence of increased exposure to damaging wavelengths of UV-B following depletion of the ozone layer. However, little is known about the molecular and cellular effects of UV-B on human skin. This study is intended to increase understanding of the mechanisms of action of UV-B and its influence on the initiation and promotion steps of cancer. These are believed to be via the operation of the immune system in the skin.

Human skin is a complex organ composed of numerous cell types. Two, the fibroblast and T-lymphocyte, are readily available and may easily be studied as cell cultures. These cells must be studied first before attempting to investigate material which is difficult to maintain as a cell culture. A collection of cell cultures from normal donors is available. This is supplemented with reference material from individuals suffering from sun sensitive DNA repair defective genetic diseases such as xeroderma pigmentosum. Further material is being collected, following informed consent, from additional genetic diseases where sunlight is involved in the aetiology.

Using calibrated laboratory sources of UV-B light the spectrum of DNA damage induced in skin derived cells is to be assessed using immunochemical techniques based upon damage specific monoclonal antibodies. These techniques are being exploited in the participating laboratories. The amount of repair of the damage in cells from normal individuals is measured by reference to the response of cells obtained from DNA repair defective patients. Experiments designed to measure the cell killing capacity of UV-B are carried out in order to evaluate the significance of different lesions and the response of different cell types. A variety of chromosomal changes have been recognised as initiating or promoting events in carcinogenesis; the evaluation of UV-B as a chromosome damaging agent is examined. The operation of the immune system in the skin is extremely complex and the influence of UV-B on its action is being measured in a cytochemical study of key molecules which bring about the interaction between the various cellular components of the system. A problem in assessing the significance of these molecular and cellular responses is the availability of a reliable measure of dose to the individual. The use of biological and chemical dosimeters are being evaluated; it is hoped that this will provide the basis for a system of cheap reliable individual personal dosimeters.

The information generated in these investigations will provide: i) Improved procedures for the detection of DNA damage and repair in specific cell types; ii) The possibility of being able to identify new classes of damage; iii) The establishment of procedures which might assist in the diagnosis and therefore treatment of photodermatoses; iv) The ability to identify individuals at increased risk; v) A scientific basis for any protective or prophylatic measures deemed necessary for cancer prevention, and vi) The provision of personal dosimeters.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

MRC Cell Mutation Unit
Address
University Of Sussex Falmer
BN1 9RR Brighton
United Kingdom

Participants (4)

Albert-Ludwigs-Universität Freiburg
Germany
Address
Hauptstraße 7
79104 Freiburg
Heinrich-Heine-Universität Düsseldorf
Germany
Address

40001 Düsseldorf
Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek
Netherlands
Address
137-139,Lange Kleiweg
2280 HV Rijswijk
Rijksuniversiteit Leiden
Netherlands
Address
72,Wassenaarseweg
2300 RA Leiden