Comparative Analysis of the Distribution of Laminin Chains in the Basement Membranes in Some Malignant Epithelial Tumors: The α1 Chain of Laminin Shows a Selected Expression Pattern in Human Carcinomas

Abstract

Laminins (Ln), together with Type IV collagen and nidogen-1, form the structural integrity of the basement membranes (BM). In this study we used immunohistochemistry to show the distribution of laminin chains α1, α3, α5, β1, β2, β3, γ1, γ2, as well as Type IV collagen, in various types of carcinomas and in normal tissues. Except for diffuse gastric carcinomas and infiltrative breast carcinomas, the malignant epithelial tumor clusters were surrounded by quite a continuous BM in most tumors. These BMs comprised most abundantly Ln α5, β1, and γ1 chains. Conversely, the Ln α1 chain, a component of laminins-1 and -3, showed the most restricted distribution in BMs of both normal tissues and malignancies, being moderately present in carcinomas of thyroid gland and ovary and in intraductal carcinomas of breast. In other types of carcinomas, immunoreactivity for Ln α1 chain was found more randomly and was practically negative in carcinomas of tongue, stomach, and colon. These findings were comparable to those observed by in situ hybridization, which showed that carcinomas of thyroid gland and intraductal carcinomas of breast constitutively expressed Ln α1 mRNA and that the epithelial tumor cells were the main producers of it. The results suggest that epithelial malignancies, except for infiltrative breast and diffuse gastric carcinomas, produce more notable amounts of BM macromolecules in their growth substratum than has previously been anticipated. Corroborating their widespread distribution in normal epithelial tissues, the chains of Lns-5 and -10 are the most abundant Ln molecules in the corresponding carcinomas.