Levels of expression of hRPB11, a core subassembly subunit of human RNA polymerase II, affect doxorubicin sensitivity and cellular differentiation.

We have previously shown that the human RNA polymerase II subunit 11 (hRPB11) is among the proteins specifically downregulated upon Doxorubicin (Dox) treatment of human cancer cell lines, and that Dox resistant clones derived upon drug selection express about 20% of the protein present in the original parental cell line. Given the prominent role that this subunit appears to have in eukaryotic cells, and the fact that its deletion causes lethality in yeast, we wanted to test the effect of the reintroduction of parental cell line levels of this subunit in Dox resistant colon cancer cells (LoVoDX). Stable transfectants of LoVoDX expressing parental (LoVoH) levels of hRPB11 showed a reduced sensitivity to the drug without changing the response of these cells to other chemotherapeutic agents, confirming a specific inverse correlation between cellular Dox sensitivity anti-hRPB11 levels of expression. In addition we show here that the levels of expression of this same RNA polymerase II subunit directly affect cellular differentiation, reducing the rate of cell proliferation, clonogenicity and increasing the expression of E-cadherin, a marker of epithelial cell differentiation. As expected from cells with these characteristics, upon in vivo administration of these clones in nude mice, we detected a significant reduction in the size and time of appearance of the primary tumors and overall metastatic capability. Finally, the role played by hRPB11 in regulating the transcription of specific genes is underlined by transient transfection experiments that show transactivation of the E-cadherin promoter by this protein.