Basement membrane and human epidermal differentiation in vitro

To test the role of basement membrane in differentiation of human epidermis reconstituted on human dermis, we prepared dermis with and without basement membrane and cultured epidermal cells on these two dermal substrata. The absence of basement membrane components was confirmed by immunofluorescence staining for laminin and type IV collagen and by electron microscopy. A high degree of differentiation of reconstituted epidermis did not require basement membrane as shown by the development of basal, spinous, and granular cell layers, and synthesis of 58 and 65-67 kDa keratins when epidermis was attached directly to dermis. On the other hand, we found that the basement membrane regulated the adhesive interaction between the epidermis and dermis. On dermis with basement membrane, attached epidermal cells formed hemidesmosomes and mechanically stable bonding. In the absence of basement membrane, the epidermal cells did not form hemidesmosomes, and bonding between the epidermis and dermis was unstable. Moreover, dermis from which the basement membrane was removed was reorganized by the epidermal cell layer.

Helicase, DNA-binding, and immunological properties of replication-defective simian virus 40 mutant T antigens

Simian virus 40 T antigen (TAg) exhibits nonspecific and origin-specific DNA binding (ori binding) and ATPase and helicase activities, all of which are related to its roles in viral DNA replication. We have characterized some of the properties of four replication-defective but transformation-competent mutant TAgs, C6-2, T22, C11, and C8A. C6-2 and T22 TAgs were each previously determined to lack ori-binding properties, while C11 TAg was reported to lack ATPase activity. The C8A TAg did not exhibit defects in either ori-binding or ATPase functions. We have analyzed additional aspects of these mutant TAgs pertaining to their helicase, DNA-binding, and immunological properties. With the exception of the C11 TAg, all the other TAgs exhibited helicase activity. The lack of helicase activity by C11 TAg was consistent with its previously shown inability to hydrolyze ATP or to replicate viral DNA. These results therefore show that ori-binding and helicase activities are separate functions of TAg. Wild-type and mutant TAgs bound with similar efficiency to either native or denatured calf thymus DNA-cellulose, indicating no marked differences in their nonspecific DNA-binding properties. We also tested the binding of wild-type and mutant TAgs to a monoclonal antibody, PAb 100, that was previously shown to recognize an extremely small class of TAg that may represent a unique conformational form of the protein. Interestingly, while less than 10% of the wild-type, C6-2, C11, and T22 mutant TAgs were recognized by PAb 100, more than 60% of the C8A mutant TAg was bound by this antibody. Therefore, although no defect in biochemical function was observed with the C8A TAg, its deficiency in viral DNA replication may be related to an unusual conformation, as detected by its dramatically increased recognition by PAb 100. These results show that the helicase activity of TAg is not required for its transformation function.

Lymphocyte phenotypes at tumor margins in patients with head and neck cancer

Lymphocyte phenotypes were identified by monoclonal antibodies and avidin-biotin peroxidase reagents and enumerated in tumor tissue removed from 26 patients with head and neck cancer. T lymphocytes (T11) were the predominate phenotype at the tumor margin, with twice as many helper/inducer (T4) as suppressor/cytotoxic (T8) lymphocytes. Patients with Stage II and III carcinoma of the glottis, tongue, and hypopharynx had significantly increased numbers of all T lymphocyte phenotypes when compared to patients with Stage IV disease, thus achieving statistical significance for the T11 and T8 phenotypes. All patients were followed for 2.5 years; those patients who remained free of malignant disease had an increased number of all T lymphocyte phenotypes compared to patients with recurrent malignancy, but this did not achieve statistical significance. Thus, increased numbers of T11 positive lymphocytes of both the T4 and T8 subsets in the tissue at the margins of head and neck tumors were associated with a more favorable prognosis. These results support the concept of an immunologic reaction at the tumor margin, which may be limiting the growth and spread of tumor.