Intronic polymorphism (1541-1542delGT) of the constitutive heat shock protein 70 gene has functional significance and shows evidence of association with lung cancer risk

Somatic mutations of 11q23.3-linked constitutive heat shock protein 70 gene (HSPA8 alias HSC70) are detected by others in breast carcinomas. To examine whether intragenic, somatic mutations of HSPA8 occur in lung carcinomas, we sequenced its exons 2-8, with adjacent intronic sequences, in a series of DNA samples from non-small-cell lung cancers (NSCLC). Twenty-one polymorphisms were detected, but no somatic mutation. However, we observed an association between the HSC70 1541-1542delGT genotype and the immunohistochemical staining pattern of HSC70 protein. Tumors with weak (+) HSC70 protein staining were more frequent in the carriers of the polymorphic 1541-1542delGT allele than in the homozygotes of the major allele (20% vs. 6%, P=0.05 by Fisher's exact test). This statistically significant association prompted us to test the polymorphism functionally. The method we developed for the functional evaluation of intronic sequence alterations showed that the HSPA8 intron 2 with the deleted GT dinucleotide was associated with noticeable (approximately 20%) and statistically significant (P=0.005) reduction of the reporter gene activity. Our case-control analysis showed that the 1541-1542delGT heterozygous genotype was associated with significantly decreased risk for lung cancer (crude odds ratio (OR)=0.44; 95% confidence interval (CI): 0.23-0.84). To the best of our knowledge, this is the first report on the association between a polymorphism of a gene coding for the chaperone protein and lung cancer risk. Moreover, the simple method reported here, based on the dual-luciferase reporter assay system, can be useful for testing functional significance of polymorphisms located in introns of other genes.