MiniSOX9, a dominant-negative variant in colon cancer cells.

Inherited and acquired changes in pre-mRNA processing have significant roles in human diseases, especially cancer. Characterization of aberrantly spliced mRNAs may thus contribute to understand malignant transformation. We recently reported an anti-oncogenic potential for the SOX9 transcription factor in the colon. For instance, the Sox9 gene knock out in the mouse intestine results in an excess of proliferation with appearance of hyperplasia. SOX9 is expressed in colon cancer cells but its endogenous activity is weak. We looked for SOX9 variants that may impair SOX9 activity in colon cancer cells and we discovered MiniSOX9, a truncated version of SOX9 devoid of transactivation domain as a result of retention of the second intron. A significant overexpression of MiniSOX9 mRNA in human tumor samples compared with their matched normal tissues was observed by real-time reverse transcriptase-PCR. Immunohistochemistry revealed that MiniSOX9 is expressed at high levels in human colon cancer samples whereas it is undetectable in the surrounding healthy tissues. Finally, we discovered that MiniSOX9 behaves as a SOX9 inhibitor, inhibits protein kinase Cα promoter activity and stimulates the canonical Wnt pathway. This potential oncogenic activity of the SOX9 locus gives new insights on its role in colon cancer.

CEACAM1, a SOX9 direct transcriptional target identified in the colon epithelium.

A deletion of the transcription factor SOX9 gene in the mice intestine affects the morphology of the colon epithelium and leads to hyperplasia. Nevertheless, direct transcriptional targets of SOX9 in this tissue are still unknown. A microarray analysis identified the tumor suppressor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) as a possible SOX9 target gene and we demonstrate here that SOX9 upregulates CEACAM1 in human colonic cells. Moreover, CEACAM1 expression is reduced in colon of SOX9-deficient mouse, suggesting an important function for SOX9 in the transcriptional activation of the CEACAM1 gene. We further identified SOX9-binding sequences in the human and rat CEACAM1 promoters, and an electrophoretic mobility shift together with a chromatin immunoprecipitation provided an additional evidence of the SOX9 binding to the human promoter. In addition, we established that histone acyl-transferase p300 behaves as an SOX9 co-activator of the rat and human CEACAM1promoters. These results highlight CEACAM1 as the first direct target of SOX9 identified in the colon epithelium.