FIG. 1.

(A) Western blot analysis of Id-1 expression in ECs and KS tumor cells in culture. KS cells demonstrated higher levels of Id-1 protein than ECs. The following increases in Id-1 expression compared to that in ECs were found: at passage 3 (P3), 2.0-fold increase for KS1 cells and 3.0-fold increase for KS2 cells; at P7, 9.4-fold increase for KS1 and 10.6-fold increase for KS2; at P11, 37.0-fold increase for KS1 and 42.0-fold increase for KS2. The levels of Id-1 were 32.5- and 36.0-fold higher in KS1 and KS2 cells at P15 than in ECs at P11 (ECs were senescent at P11 in this experiment; therefore, a passage-paired control for P15 KS cells was not available). The blot was probed for expression of Id-1 and reprobed for actin to demonstrate equal loading of the proteins. A representative experiment of two independent experiments is shown. (B) Immunohistochemical staining for Id-1 in KS lesions. The spindle-shaped tumor cells of KS lesions were highly positive for Id-1 as demonstrated by the intense positive (red reaction product) staining (indicated by the arrows in micrographs A and B). The characteristic “slit-like” vascular spaces and normal ECs adjacent to the lesion were also positive for Id-1 (indicated by the arrows in micrographs A and B). Smooth muscle cells, which are known to express Id-1, served as an internal positive control (arrow in micrograph C). Quiescent ECs in normal human skin did not constitutively express Id-1 as expected (arrow in micrograph D). The results are representative of six cutaneous KS nodules from six different patients immunostained for Id-1.