MED28 Regulates Cell Growth through HMG Box‐Containing Protein 1 (HBP1) in Human Breast Cancer Cells

Abstract

MED28 exhibits multiple cellular roles, including involved in transcriptional activation and as a merlin, Grb2, and cytoskeleton‐associated protein, which is highly expressed in several types of tumor. Recently, we have reported that MED28 regulates cellular migration and invasion in human breast cancer cells. Furthermore, overexpression of MED28 stimulates cell proliferation; however, the principal mechanism remains unclear. Therefore, the objective of this study is to understand the role of MED28 in the aspect of cell growth in breast cancer cells. MED28 suppression delays cell cycle progression in human breast cancer cells. MED28 appears to modulate cell growth through HMG box‐containing protein 1 (HBP1), a tumor suppressor which down‐regulates genes in G1 to S transition, and whose mutation or reduction is often manifested in invasive breast cancer. Overexpression of MED28 enhances cell cycle progression and downregulates HBP1 expression, whereas HBP1 cDNA partially blocks the stimulatory effect of MED28 on cell growth. Our data indicate that MED28 promotes cell cycle progression and stimulates cell proliferation, reinforcing the significance of MED28 in breast cancer development. (This work was supported by the grants, NSC 98–2320‐B‐309–002‐MY3 and NSC101–2320‐B‐309–001 to M‐F Lee, and CMU95–311 to C‐Y Huang.)