Expression of the Ca2+-activated chloride channel genes CLCA1 and CLCA2 is downregulated in human colorectal cancer
1Academic Department of Surgery, St. Bartholomew's and the Royal London School of Medicine and Dentistry, London, UK. s.a.bustin@mds.qmw.ac.uk
Abstract:
The role of ion channels in carcinogenesis and tumor progression remains unclear. We have used suppression subtractive hybridization of mRNA from paired normal colon epithelium and tumor, followed by quantitative kinetic RT-PCR, to demonstrate that the transcription of two members of a novel Ca(2+)-dependent chloride channel family, CLCA1 and CLCA2, was significantly downregulated in approximately 80% of colorectal carcinomas. This figure rose to >90% when expression was adjusted for tumor cell proliferation. In normal colon epithelium, CLCA1 mRNA levels were significantly associated with c-myc transcription but became decoupled in the tumor samples. There was no association between CLCA2 and either CLCA1 or c-myc mRNA levels. Transcription of both genes in three colorectal cancer cell lines, T84, HT29, and Caco2, was barely detectable. Illegitimate transcription of CLCA1 was detected in 12 of 15 blood samples taken from healthy volunteers, making its use as a marker for the detection of tumor spread unreliable. Our results suggest that CLCA1 could specify a new tumor suppressor and that, as in breast cancer, CLCA2 may function as a tumor suppressor in colorectal cancer.
Insights
Colorectal cancer downregulates CLCA1 and CLCA2 chloride channel genes, suggesting they may act as tumor suppressors. CLCA1
Area of Science:
- Molecular biology
- Oncology
- Ion channel research
Background:
- The role of ion channels in cancer development is not fully understood.
- Colorectal cancer (CRC) is a significant global health concern.
Purpose of the Study:
- To investigate the expression and potential role of calcium-dependent chloride channel (CLCA) family members in colorectal carcinogenesis.
- To determine if CLCA1 and CLCA2 function as tumor suppressors in colorectal cancer.
Main Methods:
- Suppression subtractive hybridization of mRNA from normal colon epithelium and tumor tissue.
- Quantitative kinetic reverse transcription-polymerase chain reaction (RT-PCR) for gene expression analysis.
- Analysis of CLCA1 and CLCA2 expression in colorectal cancer cell lines and patient blood samples.
Main Results:
- CLCA1 and CLCA2 gene transcription was significantly downregulated in approximately 80% of colorectal carcinomas, increasing to over 90% when adjusted for proliferation.
- CLCA1 mRNA levels were associated with c-myc transcription in normal colon but not in tumors.
- CLCA1 transcription was detected in healthy volunteers' blood, deeming it unreliable for detecting tumor spread.
Conclusions:
- CLCA1 and CLCA2 downregulation suggests they may function as tumor suppressors in colorectal cancer.
- CLCA1 represents a potential novel tumor suppressor gene.
- CLCA2 may also act as a tumor suppressor in colorectal cancer, similar to its role in breast cancer.
