Co-amplification of a novel cyclophilin-like gene (PPIE) with L-myc in small cell lung cancer cell lines

Abstract

Specific genetic alterations affecting proto-oncogenes of the myc gene family are frequently detected in human lung cancer. Among 11 SCLC cell lines with L-myc gene amplification, four were found to have alteration of the RLF gene by Southern blot and RT–PCR analyses. One cell line, NCI-H378, contained aberrantly-sized L-myc-hybridizing bands by Southern and Northern blot hybridization but had no alteration of RLF. Some L-myc-hybridizing cDNAs from NCI-H378 contained a novel sequence with close homology to the cyclophilins joined to antisense L-myc exon 2 sequence. Full length cDNAs isolated from human skeletal muscle containing only the novel sequence identify open reading frames of 301 and 296 amino acids and differ in the C-terminal region by 22 and 17 amino acids. This gene, tentatively named PPIE (peptidyl-prolyl cis-trans isomerase E), has 83% amino acid identity with the central conserved region of cyclophilin A, is evolutionarily conserved by Southern blot, and exhibits differential tissue expression with highest levels found in muscle and brain. Co-amplification of PPIE was observed in seven of eleven L-myc amplified cell lines. Analysis of radiation hybrids suggests that the gene order is RLF-PPIE-L-myc on chromosome 1p and pulse-field gel electrophoresis localizes all three genes to an 800 megabase Mlu I fragment. The prognostic and functional consequences of PPIE gene amplification in SCLC can now be determined.