MTR and Merkel cell skin cancer: Furthermore, by co-transfecting MCC cells with MCPyV full LT, MKL-1 LT, MKL-2 LT and MS-1 LT expression plasmids, as well as CCL17/TARC promoter, resulted in an upregulation of CCL17/TARC promoter activity (Figure 2), which in turn increased the expression of CCL17/TARC (Figure 4).