GSTP1 and cervical carcinoma: In addition, using an anti-HPV-16 E7 antibody we immunoprecipitated HPV-16 E7 in the CaSki [20] and SiHa [21] cervical carcinoma cell lines, known to express HPV-16 E7 endogenously [22], [23], GSTP1 also co-precipitated with the viral oncoprotein in these cells, as detected by Western blot analysis (Figure 1F).