Endocrine and mucous differentiation by a cloned human rectal adenocarcinoma cell line (HRA-19) in vitro: inhibition by TGF-beta 1.

Colorectal epithelium is composed of absorptive, mucous and endocrine cells, all of which are considered to arise from a common stem cell located in the crypt base. However, the factors controlling the commitment to differentiate are poorly understood. This is partly due to the lack of in vitro model systems for the study of differentiation in colorectal epithelium. The HRA-19 cell line, established from a human rectal adenocarcinoma, has been shown to have multipotential characteristics with cloned HRA-19 cells able to differentiate into absorptive, mucous and endocrine cells when grown as xenografts. The lack of such differentiated cells in HRA-19 monolayers in vitro suggests that differentiation is controlled by extracellular matrix, stromal cells and/or soluble factors. Such observations show that differentiation in HRA-19 cells can be controlled by extrinsic factors and therefore provide a model system for studying control of differentiation in colorectal epithelium. Unfortunately, the restriction of differentiation to xenografts of the cell line limits the degree to which this differentiation can be manipulated. In this study, the possibility that HRA-19 cells could be induced to differentiate in vitro under appropriate conditions has been investigated. Endocrine and mucous cells were identified by immunocytochemistry with differentiation-related antibodies and histology of monolayers. Preconfluent HRA-19 cells grown in 10% foetal calf serum formed a well polarised monolayer with apical tight junctions and sparse microvilli, but cells with mucous or endocrine phenotypes were only very occasionally observed. However, endocrine and mucous cells could reproducibly be demonstrated in postconfluent monolayers grown in 1% foetal calf serum.(ABSTRACT TRUNCATED AT 250 WORDS)