Abstract
Carcinoembryonic antigen (CEA, ceacam5) is an important tumor‐associated antigen with reported roles, e.g., in immunological defense, cell adhesion, cell survival and metastasis. Its overexpression in cancer cells is known to involve transcriptional activation of the CEA gene, but the underlying molecular details remain unclear. Here, we show that hypoxia and intracellular alkalinization, 2 factors commonly found in solid tumors, increase CEA protein expression in breast (MCF‐7) and colorectal (CaCo‐2 and HT‐29) cancer cells. The increase was comparable (2–3‐fold) to that observed in colorectal carcinomas in vivo. CEA promoter analyses further revealed that this upregulation involves a known binding site for HIF‐1 transcription factor (5′‐ACGTG‐3′) within one of the CEA promoter's positive regulatory elements (the FP1 site; the E‐box). Accordingly, deletion or targeted mutagenesis of this motif rendered the CEA promoter unresponsive to hypoxia. Our chromatin immunoprecipitation data confirmed that endogenous HIF‐1α binds to the CEA promoter in hypoxic cells but not in normoxic cells. Moreover, overexpression of the hypoxia‐inducible factor (HIF‐1α) was sufficient to increase CEA protein expression in the cells. In contrast, c‐Myc, which is known to bind to the overlapping E‐box, did not potentiate HIF‐1α‐induced CEA expression. CEA overexpression in vivo was also found to coincide with the expression of carbonic anhydrase IX, a well‐known hypoxia marker. Collectively, these results define CEA as a hypoxia‐inducible protein and suggest an important role for the tumor microenvironmental factors in CEA overexpression during tumorigenesis. © 2007 Wiley‐Liss, Inc.