The bone morphogenetic protein pathway is inactivated in the majority of sporadic colorectal cancers

Area of Science:

• Molecular Oncology
• Gastrointestinal Cancer Research
• Signal Transduction Pathways

Background:

• Mutations in bone morphogenetic protein (BMP) receptor 1a in juvenile polyposis indicate BMPs' role in colorectal cancer (CRC).
• Investigating the BMP pathway in sporadic CRC is crucial for understanding cancer development.

Purpose of the Study:

• To investigate the bone morphogenetic protein (BMP) pathway in sporadic colorectal cancer (CRC).
• To determine the association between BMP pathway components and CRC subtypes.

Main Methods:

• Examined BMP receptor (BMPR) expression via immunoblotting and sequenced BMPR2 in CRC cell lines.
• Assessed BMPR, SMAD4, and pSMAD1/5/8 expression in 72 sporadic CRCs using tissue microarray and immunohistochemistry.
• Evaluated the impact of wild-type/mutated BMPR2 3' untranslated region (UTR) on protein expression and BMP pathway activity.

Main Results:

• BMPR2 and SMAD4 protein expression were abrogated in microsatellite unstable (MSI) and microsatellite stable (MSS) cell lines, respectively.
• BMPR2 3'UTR mutations were found in all MSI cell lines but none of the MSS cell lines, reducing luciferase expression.
• BMPR2 expression was impaired in 85% of MSI CRCs versus 29% of MSS CRCs, showing mutual exclusivity with SMAD4 loss. The BMP pathway was inactivated in 70% of CRCs, correlating with BMPR and SMAD4 loss.

Conclusions:

• The bone morphogenetic protein (BMP) pathway is inactivated in most sporadic colorectal cancers (CRCs).
• In microsatellite unstable (MSI) CRC, inactivation is primarily linked to impaired BMP receptor 2 (BMPR2) expression.
• In microsatellite stable (MSS) CRC, inactivation is predominantly associated with impaired SMAD4 expression.