Cellular Transcriptional Responses to Merkel cell polyomavirus T antigens

Merkel cell polyomavirus (MCV) is clonally integrated in over 80% of Merkel cell carcinomas and mediates tumor development through the expression of viral oncoproteins large T (LT) and small T antigens (sT). Viral integration is associated with signature mutations in the T antigen locus that result in deletions of carboxy-terminal replicative functions of the LT antigen. Despite these truncations, the LT LxCxE retinoblastoma (Rb) pocket protein family-binding domain is retained, and the entire sT isoform is maintained intact. To investigate the ability of MCV oncoproteins to regulate host gene expression, we performed microarray analysis on cells stably expressing tumor-derived LT, tumor-derived LT along with sT, and tumor-derived LT with a mutated Rb interaction motif. Gene expression alterations in the presence of tumor-derived LT could be classified into three main groups: genes that are involved in the cell cycle (specifically the G1/S transition), genes involved in DNA replication, and genes involved in cellular movement. The LxCxE mutant LT largely reversed gene expression alterations detected with the wild type LT, while co-expression of sT did not significantly affect these patterns of gene expression. LxCxE-dependent upregulation of cyclin E and CDK2 correlates with increased proliferation in tumor-derived LT expressing cells. We conclude that in hTERT-immortalized human fibroblasts the LXCXE motif of tumor-derived LT enhances cellular proliferation and upregulates cell cycle and immune signaling gene transcription. RNA was isolated from BJ-hTERT cell lines and hybridized to an Illumina chip for global gene expression analysis