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colon; Understanding the role of single-nucleotide polymorphisms (SNPs) in the pathological process represents a unique experimental challenge especially when the variants occur outside of coding regions. The noncoding SNP rs61764370 located in the 3'-untranslated region of Kirsten rat sarcoma viral oncogene homolog (KRAS) has been implicated as a risk factor for the development of cancer and the response to targeted therapies. This cancer-associated variant is thought to affect the binding of the microRNA let-7, which allegedly modulates KRAS expression. Using site-specific homologous recombination, we inserted the rs61764370:T>G KRAS gene variant in the colorectal cancer cell line SW48 (SW48 SNP) and assessed the cellular and biochemical phenotype. We observed a significant increase in cellular proliferation, as well as a reduction in the levels of the microRNA let-7a, let-7b, and let-7c. Transcriptional and biochemical analysis showed no concomitant change in the KRAS protein expression or modulation of the downstream mitogen activated kinase or PI3K/AKT signaling. These results suggest that the cancer-associated rs61764370 variant exerts a biological effect not through transcriptional modulation of KRAS but rather by tuning the expression of the microRNA let-7.

: We set out to understand if the cancer-associated single nucleotide polymorphism rs61764370 affects KRAS expression and downstream signalling. We generated human cell lines in which the cancer-associated polymorphism was site-specifically inserted into the exact position within the genome of the cell. Our results suggest that the polymorphism does not affect KRAS expression or downstream signalling but alters let-7 levels leading to increased proliferation of the cells

(C) 2014 John Wiley & Sons, Ltd