Detection of HHV-8 in pyogenic granuloma-like Kaposi sarcoma.

Kaposi sarcoma (KS) is a low-grade vascular neoplasm associated with human herpesvirus-8 (HHV-8) infection. Clinically, lesions commence as blue-red macules that may develop into plaques and eventually into nodules. The histologic appearance spans a broad spectrum and varies with the stage of the lesion. At each stage, KS has significant morphologic overlap with other vasoproliferative lesions. Recently, we encountered 6 KS tumors that histologically mimicked pyogenic granuloma (PG), a common benign vascular tumor of the skin that usually does not figure in the histologic differential diagnosis of KS. We stained 6 PG-like KS and 28 PGs with a mouse monoclonal antibody (13B10) against HHV-8 latent nuclear antigen-1 (LNA-1) to determine the utility of immunoperoxidase staining in distinguishing KS from PG. All 6 PG-like KS demonstrated nuclear staining for HHV-8 LNA-1. No staining was identified in any of the 28 PGs. Histologic criteria often used to differentiate between these two entities were not helpful in our cases. The only distinguishing feature was the presence or absence of HHV-8 LNA-1 staining. The presence of HHV-8 LNA-1 nuclear staining seems to be a specific marker for KS when comparing PGs and PG-like KS. Immunoperoxidase staining for HHV-8 LNA-1 is a useful diagnostic tool in this setting.

Regulation of Fas-mediated apoptosis by N-ras in melanoma.

Oncogenic ras has been shown to downregulate Fas receptor expression and increase Fas ligand expression and thus contribute to resistance to Fas-mediated cell death in several cell types. The effects of ras on Fas-mediated apoptosis have not been studied in melanoma. We studied the effects of activated N-ras by measuring Fas, Fas ligand, and FLIP expression as well as susceptibility to Fas-ligand-induced cell death in transfectants of WM35, a radial growth phase human melanoma cell line. Based on quantitative polymerase chain reaction and fluorescence-activated cell sorter analysis, we found that the ras transfectants expressed less Fas mRNA and surface Fas receptor. Cr51 release cytotoxicity assays demonstrated less susceptibility to Fas-mediated apoptosis in ras transfectants, correlating with the Fas mRNA and protein expression results. Ras inhibition with the specific inhibitor FTI-277 showed that downregulation of Fas in the ras transfectants could be reversed. This correlates with cytotoxicity experiments showing that ras inhibition increases susceptibility to Fas-mediated apoptosis. The control transfectants expressed FLIP but ras did not affect FLIP expression. The control and ras transfectants did not express Fas ligand as demonstrated by reverse transcriptase polymerase chain reaction and fluorescence-activated cell sorter analysis. Cytotoxicity assays further confirmed that these melanoma ras transfectants do not express functional Fas ligand. These results suggest that ras contributes to tumor progression by decreasing susceptibility to Fas-mediated cell death at least in part through downregulation of Fas receptor at the transcriptional level.