Comparison of amplified and unamplified c-myc gene structure and expression in human small cell lung carcinoma cell...

A human small cell lung cancer cell line (H82) demonstrates 40- to 50-fold amplification of the c-myc gene but expresses at least 250-fold more steady-state c-myc messenger RNA than an unamplified small cell lung cancer cell line (H378) with no detectable expression of c-myc. We compared the chromatin structure of c-myc in H82 to that in H378 using DNase I sensitivity and DNA methylation patterns. DNase I hypersensitivity sites were identical in H82 and H378 and were similar to the pattern seen in a B-lymphoblastoid cell line, despite extensive amplification of c-myc in H82. Methylation patterns were also very similar in H82 and H378, with hypomethylation or partial methylation at the c-myc coding regions and the flanking 5' sequences, despite the absence of detectable c-myc expression in H378. Therefore, the predominant chromatin structural patterns do not appear to correlate with observed differences in gene expression. In addition, these studies demonstrate that the patterns of DNase I hypersensitivity and of methylation can remain intact during a 40- 50-fold gene amplification, as observed for the c-myc gene in H82.