SOX2 Expression Is Regulated by BRAF and Contributes to Poor Patient Prognosis in Colorectal Cancer

Abstract

Sporadic colorectal cancer (CRC) is a common malignancy and also one of the main causes of cancer deaths worldwide. Aberrant expression of the transcription factor SOX2 has recently been observed in several cancer types, but its role in CRC has not been fully elucidated. Here we studied the expression of SOX2 in 441 CRC patients by immunohistochemistry and related the expression to clinicopathological and molecular variables and patient prognosis. SOX2 was expressed in 11% of the tumors and was significantly associated to BRAFV600E mutation, but not to KRAS mutations (codon 12 and 13). SOX2 positivity was correlated to poor patient survival, especially in BRAFV600E mutated cases. In vitro studies showed that cells expressing the constitutively active BRAFV600E had increased SOX2 expression, a finding not found in cells expressing KRASG12V. Furthermore, blocking downstream BRAF signalling using a MEK-inhibitor resulted in a decreased expression of SOX2. Since SOX2 overexpression has been correlated to increased migration and invasion, we investigated the SOX2 expression in human CRC liver metastasis and found that a SOX2 positive primary CRC also had SOX2 expression in corresponding liver metastases. Finally we found that cells overexpressing SOX2 in vitro showed enhanced expression of FGFR1, which has been reported to correlate with liver metastasis in CRC. Our novel findings suggest that SOX2 expression is partly regulated by BRAF signalling, and an increased SOX2 expression may promote CRC metastasis and mediate a poor patient prognosis.

MicroRNA Expression in KRAS- and BRAF-mutated Colorectal Cancers

“…miRNA array analysis. We used a PCR array evaluating 84 miRNAs known to be differentially expressed in tumors versus normal tissue, and compared miRNA expression profiles in the colon cancer cell line Caco2 (wild-type in BRAF and KRAS), and in previously created stable transfectants of Caco2 expressing mutant BRAF (Caco2-BRAF V600E ) or mutant KRAS (Caco2-KRAS G12V ) (30,32). Except for the introduced mutations in KRAS and BRAF, these three cell lines have the same genetic background, suggesting that any differences found in expression of miRNAs would most likely be due to these mutations.…”

“…Cell culture medium for the mutated cell lines also contained 800 μg/ml G418 (Gibco, Life Technologies, Stockholm, Sweden) to select for transfected cells. The two different stable transfectants expressing mutant BRAF (Caco2-BRAF V600E ) or mutant KRAS (Caco2-KRAS G12V ) have been previously described (30).…”

SOX2 and SOX12 are predictive of prognosis in patients with clear cell renal cell carcinoma

“…SOX12 may act as oncogenes, tumor suppressor genes or both depending on the cancer types. In squamous esophageal, colorectal and small cell lung cancer, SOX2 is associated with poor prognosis, and is activated through DNA amplification (21)(22)(23)(24). However, SOX2 acts as tumor suppressor gene in gastric cancer and non-small cell lung cancers (25-27), which further emphasizes the context-specific nature of SOX involvement in carcinogenesis.…”

The infiltration, and prognostic importance, of Th1 lymphocytes vary in molecular subgroups of colorectal cancer

“…The colon cancer cell line Caco2 (ATCC, Manassas, VA, USA) and its derivatives were grown in Dulbecco's modified Eagle's medium with glutaMAX supplemented with 10% fetal bovine serum (Gibco, Life Technologies, Stockholm, Sweden) and maintained at 37°C in an atmosphere of 5% CO 2 . The stable transfectants expressing mutant BRAF (Caco2‐ BRAF V600E ) or mutant KRAS (Caco2‐ KRAS G12V ) have been described .…”