Pauline M. Schwartz

Expression and localization of thymidine phosphorylase/platelet-derived endothelial cell growth factor in skin and cutaneous tumors

Thymidine phosphorylase/platelet‐derived endothelial cell growth factor (TPase/PD‐ECGF) is a catabolic enzyme that has been shown to be chemotactic for endothelial cells in vitro and angiogenic in vivo. TPase/PD‐ECGF expression is increased in a variety of tumors. In the skin, TPase is active in normal keratinocytes in vitro and in vivo. Our objective was to study the expression and localization of TPase/PD‐ECGF by immunohistochemical analysis in normal skin and cutaneous tumors and to correlate this information with enzymatic activity of TPase. TPase/PD‐ECGF expression was observed in keratinocytes with intense staining of the infundibulum of hair follicles but no staining of hair bulbs. Expression localized primarily to the nucleus of keratinocytes in the basal layer but was more intense and cytoplasmic in suprabasal keratinocytes. Increased expression of TPase/PD‐ECGF in differentiated cells was confirmed by in vitro studies of TPase activity. In cutaneous tumors, there was positive staining for TPase/PD‐ECGF in squamous cell carcinomas (10/10), eccrine poromas (3/4), eccrine syringomas (4/4), trichoepitheliomas (1/3), and tumors of the follicular infundibulum (2/3) and melanomas (5/8). There was no staining of any intradermal nevi (0/2), basal cell carcinomas (0/10) or Merkel cell carcinoma (0/1). We conclude TPase/PD‐ECGF is found throughout the epidermis and its expression increases with differentiation of keratinocytes. In cutaneous tumors, expression of TPase/PD‐ECGF may be linked to the cell of origin of the tumor as well as the tumors degree of differentiation.

Particle-Mediated Gene Delivery and Human Skin: Ultrastructural Observations on Stratum Corneum Barrier Structures

The particle-mediated delivery systems are becoming a clinically relevant tool in dermatology and immunology. We investigated the qualitativeultrastructural morphology of skin following pressure-driven delivery of gold particles to ex vivo human breast skin, at different pressures ranging from 350 to 1,000 psi. Pressures of 800 and 1,000 psi appear to be more effective, as indicated by distribution of particles in the viable epidermis and dermis. Particle bombardment of the skin with gold beads caused microwounds that spanned the stratum corneum (SC). The SC lipids did not reseal these wounds in the SC after 24 h in organ culture. The implications of particle-mediated delivery to permeability barrier functions of the SC are discussed.

Keratinocytes differentiate in response to inhibitors of deoxyribonucleotide synthesis

We previously reported that methotrexate (MTX) caused an irreversible inhibition of growth and induced terminal differentiation of human keratinocytes. These effects of methotrexate were prevented by thymidine and thus, were attributed to depletion of thymine deoxyribonucleotides. The purpose of the research reported in this paper was to determine whether differentiation was induced by the general class of agents which are known to interfere with synthesis or utilization of deoxyribonucleotides. Agents examined included 5-fluorouracil, 5-bromodeoxyuridine, hydroxyurea, high-dose thymidine, aphidicolin, and AG#85, a newly reported thymidylate synthase inhibitor. All these agents increased the expression of involucrin and increased the amount of cornified envelope protein at doses that inhibited proliferation by > 75%. We demonstrated, however, that in our cell culture system not all conditions producing inhibition of proliferation induced differentiation; withdrawal of growth factors and supplemental amino acids inhibited proliferation but did not increase involucrin expression or production of cornified envelope protein.

Local and Systemic Implications of Thymidine Catabolism by Human Keratinocytes

The human epidermis possesses a very active thymidine phosphorylase with the capacity to catabolize all of the thymidine available to the epidermis from the circulation and from the degradation of DNA in terminally differentiating keratinocytes. This high capacity of keratinocytes to catabolize thymidine could affect local levels of thymidine within the epidermis for DNA synthesis and could contribute to the regulation of the concentration of thymidine in the systemic circulation. Further work is needed to delineate the physiologic role of this keratinocyte enzyme. A practical consequence of the activity of epidermal thymidine phosphorylase is the role it may play in limiting the clinical efficacy of certain thymidine analogs, an important class of antiviral agents.