Superfund Research Program
Critical Events in the Transformation of Human Bladder Cells by Low-Level Arsenic Exposure
Project Leader: A. Jay Gandolfi
Grant Number: P42ES004940
Funding Period: 2000-2015
Final Progress Reports
Arsenic is a known human-bladder carcinogen; however, the molecular mechanisms underlying arsenical-induced bladder carcinogenesis are not well understood. Previous research has demonstrated exposure of a non-tumorigenic human urothelial cell line, UROtsa, to 50 nM of the arsenic metabolite, monomethylarsonous acid [MMA(III)], for 52 weeks resulted in malignant transformation. To focus research on the early mechanistic events leading to MMAIII-induced malignant transformation within UROtsa cells, studies were performed to evaluate the minimum duration of MMA(III) exposure (50 nM) necessary to induce the irreversible malignant transformation of UROtsa cells. Results indicate that hyperproliferation of UROtsa cells occurs after 12 wk of MMA(III) exposure. Anchorage-independent growth occurred after 12 wk with a continued increase in colony formation when 12-wk exposed cells were cultured for an additional 12 or 24 wk without MMA(III) exposure. Furthermore, 12-wk MMA(III) exposed UROtsa cells incubated for an additional 24 wk without MMA(III) demonstrated significant tumor formation when injected into SCID mice. To assess potential underlying mechanisms associated with the early changes that occur during MMA(III)-induced malignant transformation, DNA methylation was assessed in target gene promoter regions. Results indicate that while DNA methylation remains relatively unchanged after 12 wk of exposure, aberrant DNA methylation begins to emerge after an additional 12 wk in culture and continues to increase until 24 wk in culture without MMA(III) exposure, coincident with the progression of a tumorigenic phenotype. Overall, these data provide evidence that 12-wk exposure to 50 nM MMA(III) is capable of causing irreversible malignant transformation in UROtsa cells. Having defined the earliest exposure necessary to induce malignant transformation (12 wk) in UROtsa cells will allow for mechanistic studies focused on the critical biological changes taking place within these cells prior to 12-wk exposure, providing further evidence about potential mechanisms of MMA(III)-induced carcinogenesis.