Spontaneous changes in intermediate filament protein expression patterns in lung cancer cell lines

Abstract

The usefulness of cell lines in the study and prediction of the clinical behaviour of lung cancer is still a matter of debate. However, lung tumour cell cultures have been of value in investigations concerning molecular and cell biological aspects of these neoplasms. Especially in the examination of characteristics specific for the main types of differentiation (squamous cell carcinoma, adenocarcinoma, small cell carcinoma), in vitro studies have been most important. Twenty eight lung cancer cell lines were cultured for up to four years, and were examined at regular intervals for their intermediate filament protein (IFP) expression patterns using a panel of cytokeratin (CK) and neurofilament (NF) antibodies. These studies showed that the classic type of small cell lung cancer (SCLC) cell lines contain CKs 8, 18, and occasionally CK 19, while the variant-type SCLC cell lines generally express no CKs but can contain NFs. Non-SCLC cell lines, such as squamous cell carcinoma and adenocarcinoma cell lines, contain CKs 7 (in most cases), 8, 18 and 19. In one variant SCLC cell line and in one adenocarcinoma cell line CKs 4, 10 and 13, characteristic of squamous cell differentiation, were found. Although most cell lines have remained stable with respect to growth characteristics and IFP expression patterns, five lung cancer cultures exhibited a transition from one cell type to another, paralleled by changes in IFP expression. Progressions from classic to variant SCLC cell lines have been observed, next to conversions from variant SCLC to cell lines re-expressing cytokeratins. In some cases this resulted in a coexpression of CKs and NFs within a cell line and even within individual tumour cells. These results strongly support the earlier finding that CK expression in SCLC cell lines is a reliable marker for the classic type of differentiation, while the absence of CKs and the presence of NFs marks the variant type of differentiation. Our results are discussed in view of previous histological findings.

Cytokeratins of Tumorigenic and Highly Malignant Respiratory Tract Epithelial Cells

“…Cells of the glands and gland ducts were previously shown to express CK14, CK15, CK18, and CK19 [45], and CK18 was also found in columnar and mucous cells [27]. CK8/CK18/CK19 characterized all columnar cells in the upper airways in vivo, including gland cells [28] and Clara cells [53], but were absent from basal cells of the bronchi [28,45]. Whereas CK18 was not found in primary rat tracheal cultures, CK19 was present (Figure 2b).…”

“…The cytokeratin profile became surprisingly similar to normal, primary cells, even for lines differing in growth potential in vivo. Despite the fact that the rat lines all formed squamous cell carcinomas upon testing in hosts, the cytokeratins typical of human airway squamous cell carcinomas in vivo [28] were much reduced. There was little representation of cornification markers, and CK4, the characteristic cytokeratin of stratified epithelia, was rare.…”

“…Heterodimers formed between CK7/CK8 and CK19 were considered a marker for columnar or secretory cells (Tables 3 and 4). Interestingly, CK18 and CK19 were identified in sero (mucous) glands [28] and also found, along with CK7 and CK8, in large cell neuroendocrine carcinomas in vivo [60]. This suggested that B2-1 arose from a differentiated mucous, neuroendocrine, or Clara cell.…”

“…Previous studies provided information about the keratin proteins of different cell types in the respiratory tract [1,25,28,30,[45][46][47][48][49][50][51][52][53]. Methods for generating primary cultures were also well-known, and such cultures maintained the ability to repopulate normal epithelia after several weeks of growth in vitro [54].…”

“…In contrast, adenocarcinomas, which are thought to arise from hyperplastic adenomatous lesions, expressed keratins typical of mucous cells, namely CK7, CK8, and CK18 [27]. CK13 was present in most tumors showing squamous differentiation, while CK4 was found with CKs 7, 18, and 19 in adenocarcinomas of the lung and adenosquamous tumors [28]. These studies did not screen for "keratinocyte-type" K5/K14 pair which typically composed the filaments attached to hemidesmosomes and desmosomes [1], but these cytokeratins were also found in non-small cell lung cancer [29].…”