Differential distribution of basement membrane type IV collagen α1(IV), α2(IV), α5(IV) and α6(IV) chains in colorectal epithelial tumors


Ken-ichi Iyama, MD, PhD, Department of Surgical Pathology, Kumamoto University School of Medicine, 1-1-1 Honjo, Kumamoto 860-8556, Japan. Email: iyama@kaiju.medic.kumamoto-u.ac.jp


In this study, we examined the relationship between the histopathological grade and immunohistochemical localization of six genetically distinct type IV collagen α chains, the major component of basement membrane (BM), in normal and neoplastic colorectal tissues. In the normal colorectal mucosa, α1/α2(IV) and α5/α6(IV) chains were stained in all epithelial BM. However, α3/α4(IV) chains were restrictively immunostained in the BM of the apical surface epithelium. Similar immunostaining profiles for α1/α2(IV) and α5/α6(IV) chains were observed in tubular adenomas with mild/moderate atypia. However, in intramucosal carcinomas, both α1/α2(IV) chains were linearly stained in the BM of cancer cell nests, while the assembly of α5/α6(IV) chains into the BM was inhibited in a discontinuous or negatively stained pattern. The normal colorectal mucosa forms a second network of BM composed of α5/α6(IV), partly α3/α4(IV) chains, in addition to the classic network of α1/α2(IV) chains. The differential immunohistochemical localization of the type IV collagen α5/α6 chains could be one diagnostic marker for the invasiveness of colorectal cancer.