No abstract

The human immunode¢ciency virus (HIV-1) Nef protein is now regarded as a regulatory protein responsible not only for establishment of infection and increased pathogenesis but also for enhancement of viral replication. However, the mechanism of Nef-induced activation of viral replication remains to be clearly understood. Using transient transfection assay, co-immunoprecipitation and pull-down analysis, we demonstrate in this report that the HIV-1 Nef protein physically interacts with Tat, the principal transactivating protein of HIV-1. Our observations with single cycle replication experiments further indicate that this interaction results not only in enhancement of Tat-induced HIV-1 long terminal repeat-mediated gene expression but also in virus production. ß

Melanocytes cultured from uninvolved skin of untreated vitiligo subjects have decreased initial seeding capacities, manifest a lag period for the onset of the growth phase, and cannot be passaged. In contrast, melanocytes obtained from uninvolved and perilesional skin of vitiligo subjects actively repigmenting under 8-methoxy psoralen plus sunlight (PUVA) therapy have higher initial seeding capacities, grow faster without a lag period, and can be passaged to more than 12 passages. Extracts of a fetal lung fibroblast cell line (PMR-GF) that promote the growth rates and passage capacities of melanocytes from normal adult donors have been found also to promote the growth rates and passage capacities of melanocytes from the uninvolved skin of vitiligo subjects. Extracts of a fetal lung fibroblast cell line (PMR-GF), however, did not have any further stimulatory effect on the growth of melanocytes obtained from repigmenting vitiligo subjects. Melanocytes cultured from normal and untreated vitiligo subjects grew individually dispersed in the absence of PMR-GF, but tended to grow in clusters in its presence. Melanocytes from the repigmenting vitiligo subjects, however, tended to grow in clusters even in the absence of PMR-GF. These results indicate that the defective in vitro growth characteristics of melanocytes from vitiligo subjects may be related to the pathogenesis of this disease. It is possible that growth factors may be involved in the process of repigmentation in vitiligo subjects.

MSG1 is a 27 kDa nuclear protein that is expressed strongly in melanotic B16 melanoma cells but very weakly in amelanotic B16 cells. Transient expression of B16 cells with an expression vector for MSG1 resulted in an increase in levels of the enzyme dopachrome tautomerase but not tyrosinase, as detected by western blotting. Stable transfection of B16 melanoma cells with plasmids containing the full length MSG1 or its deletion mutants, however, generated cell lines that showed an increase in levels of tyrosinase, dopachrome tautomerase and cellular melanin when compared with control transfected cells. Our results suggest that MSG1 plays an important role in melanogenesis, by regulating the levels of the enzymes of the pigmentary system via tyrosinase and dopachrome tautomerase.