Overexpression of PGC-1α enhances cell proliferation and tumorigenesis of HEK293 cells through the upregulation of Sp1 and Acyl-CoA binding protein

Abstract

Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a coactivator interacting with multiple transcription factors, regulates several metabolic processes. Although recent studies have focused on the role of PGC-1α in cancer, the underlying molecular mechanism has not been clarified. Therefore, we evaluated the role of PGC-1α in cell proliferation and tumorigenesis using human embryonic kidney (HEK)293 cells and colorectal cancer cells. We established stable HEK293 cell lines expressing PGC-1α and examined cell proliferation, anchorage-independent growth, and oncogenic potential compared to parental HEK293 cells. To identify the molecular PGC-1α targets for increased cell proliferation and tumorigenesis, the GeneFishing™ DEG (differentially expressed genes) screening system was used. Western blot analysis and immunofluorescence staining were performed for a regulated gene product to confirm the results. Forced expression of PGC-1α in HEK293 cells promoted cell proliferation and anchorage-independent growth in soft agar. In addition, HEK293 cells that highly expressed PGC-1α showed enhanced tumor formation when subcutaneously injected into the bilateral flanks of immunodeficient mice. The results of the GeneFishing DEG screening system identified one upregulated gene (Acyl-CoA binding protein; ACBP). Real-time RT-PCR, western blot analysis, and immunofluorescence staining showed that ACBP was markedly increased in HEK293 cells stably overexpressing PGC-1α (PGC-1α-HEK293 cells) compared to those expressing an empty vector. In PGC-1α, ACBP, and specificity protein 1 (Sp1) siRNA knockdown experiments in PGC-1α-HEK293 and SNU-C4 cells, we also observed inhibition of cell proliferation, reduced expression of antioxidant enzymes, and increased H2O2-induced reactive oxygen species production and apoptosis. These findings suggest that PGC-1α may promote cell proliferation and tumorigenesis through upregulation of ACBP. We provide evidence that increased Sp1 expression might contribute to enhanced ACBP expression by PGC-1α. The current results also suggest that PGC-1α, whose expression is related to enhanced cell proliferation and tumorigenesis, may be a good candidate molecular target for cancer therapy.