Laminin gene LAMB4 is somatically mutated and expressionally altered in gastric and colorectal cancers

Laminins are important in tumor invasion and metastasis as well as in maintenance of normal epithelial cell structures. However, mutation status of laminin chain-encoding genes remains unknown in cancers. Aim of this study was to explore whether laminin chain genes are mutated and expressionally altered in gastric (GC) and colorectal cancers (CRC). In a public database, we found that laminin chain genes LAMA1, LAMA3, LAMB1 and LAMB4 had mononucleotide repeats in the coding sequences that might be mutation targets in the cancers with microsatellite instability (MSI). We analyzed the genes in 88 GC and 139 CRC [high MSI (MSI-H) or stable MSI/low MSI (MSS/MSI-L)] by single strand conformation polymorphism analysis and DNA sequencing. In the present study, we found LAMB4 (11.8% of GC and 7.6% of CRC with MSI-H), LAMA3 (2.9% of GC and 2.5 of CRC with MSI-H), LAMA1 (5.9% of GC with MSI-H) and LAMB1 frameshift mutations (1.3% of CRC with MSI-H). These mutations were not found in MSS/MSI-L (0/114). We also analyzed LAMB4 expression in GC and CRC by immunohistochemistry. Loss of LAMB4 expression was identified in 17-32% of the GC and CRC. Of note, the loss expression was more common in the cancers with LAMB4 mutation or those with MSI-H. Our data show that frameshift mutations of LAMA1, LAMA3, LAMB1 and LAMB4, and loss of LAMB4 may be features of GC and CRC with MSI-H.