We performed in situ hybridization for c-myc, N-myc, and L-myc mRNA expression using 35S-labeled cRNA probes on frozen sections of 19 pairs of non-small cell lung cancers (NSCLC) and the surrounding non-neoplastic lung tissue. In non-neoplastic lung, c-myc expression was strongest in bronchial epithelium basal cells and hyperplastic alveolar type II pneumocytes, which are potential progenitor cells for bronchopulmonary epithelium and their tumors. In contrast, N-myc and L-myc mRNAs were not detected in non-neoplastic lung. In studies of freshly resected primary tumors, expression of c-myc was detected in 11 of 19 NSCLC (with the highest levels in squamous cell carcinomas), two of which also expressed L-myc, while N-myc expression was never detected. Levels of c-myc expression in tumors were significantly higher than in non-neoplastic lung samples. We conclude that: (1) c-myc expression in non-neoplastic lung tissues is highest in bronchial basal cells and hyperplastic type II cells, and (2) in NSCLC, overexpression of the myc-proto-oncogene is common.

Neuroendocrine-specific protein (NSP) reticulons are expressed in neural and neuroendocrine tissues and cell cultures derived therefrom, while most other cell types lack NSP-reticulons. Three major subtypes have been identified so far, designated NSP-A, NSP-B, and NSP-C. We have investigated the correlation between the degree of neuronal differentiation, determined by morphological and biochemical criteria, and NSP-reticulon subtype expression. For this purpose, several human neuroblastoma cell lines, exhibiting different degrees of neuronal differentiation, were examined immuno(cyto)chemically. It became obvious that the expression of NSP-C, as detected by immunofluorescence microscopy and Western blotting, is most prominent in cell lines with a high degree of neuronal differentiation, such as LA-N-5. Such highly differentiated cells also express other neural and neuroendocrine markers, such as neural cell adhesion molecule (NCAM), neurofilament proteins, synaptophysin, and chromogranin. NSP-A was observed in all cell lines to a different extent. However, no clear correlation was observed with the degree of neuronal differentiation as defined by other neuronal and neuroendocrine markers or morphology. NSP-B could not be detected. The induction of neuronal differentiation with nerve growth factor, dbcAMP, and retinoic acid in the rat pheochromocytoma cell line PC12 and the human teratocarcinoma cell line hNT2, respectively, induced the expression of NSP-A and NSP-C in these cell lines parallel to the induction of neurofilament protein expression. It is concluded that NSP-C expression, in particular, is strongly correlated with neuronal differentiation.

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.