Primary epithelial cells, for example human mammary epithelium, fail to proliferate (arrest) in serum-containing medium. Therefore, a common growth medium for epithelium contains pituitary extract instead of serum (Hammond et al, 1984). This may be related to the fact that epithelium is normally not in contact with serum in the body.
On the other hand, many epithelium-like cell lines grow well in serum, and most tumor-derived cell lines are cultured this way. But it can be difficult to establish such lines from epithelial cancers: often, only fibroblasts grow out of tumor explants in serum-containing medium, while the (epithelial) cancer cells do not. In contrast to epithelium, fibroblasts increase their proliferation when exposed to serum, and this process is well studied (Iyer et al, 1999).
Why does epithelium arrest in response to serum? Are any mechanisms known? Is there any study of epithelium gene expression response to serum? Why is the behavior of epithelium so different from that of fibroblasts --- is there a physiological explanation, perhaps related to wound healing?
Is this true for all types of (human) epithelium?
Should we consider epithelial-like cells growing in serum to be adapted / selected? Have such cell lines then lost some part of the epithelial phenotype? Is this a serious artefact?
Any pointers to literature would be appreciated!