IGF-1R REGULATION BY MICRORNA-515-5P MODIFIES BREAST CANCER RISK AMONG BRCA1 CARRIERS

Avital Gilam ¹ Liat Edry-Botzer ¹ Efrat Mamluk-Morag ^1,2 Dalia Bar-Ilan ^1,3 Camila Avivi ³ David Golan ⁴ Yael Laitman ² Iris Barshack ^1,3 Eitan Friedman ^1,2 Noam Shomron ¹

¹Sackler Faculty of Medicine, Tel Aviv University, Tel-Aviv
²Susanne Levy Gertner Oncogenetics Unit, Institute of Human Genetics, The Chaim Sheba Medical Center, Tel-Hashomer
³Department of Pathology, The Chaim Sheba Medical Center, Tel-Hashomer
⁴Department of Statistics and Operations Research, Tel Aviv University, Tel-Aviv

Ten percent of all breast cancer cases are genetic. Of these, 20-30% is caused by known mutations in the BRCA1/2 genes, tumor suppressor genes involved in maintaining genome integrity. BRCA1/2 penetrance is incomplete and is known to be affected by environmental-behavioral, epigenetic and genetic factors.

Accumulating evidence implicates a critical role of insulin-like growth factor 1 receptor (IGF-1R) in the development and progression of cancer, and particularly in breast cancer. IGF-1R is crucial for tumor transformation and for malignant cells survival. Interestingly, studies have shown that IGF-1R is negatively regulated by BRCA1 during transcription.

Lately we have observed a significant association between a single nucleotide polymorphism (SNP, rs28674628) in the 3’UTR of the IGF-1R gene and age at diagnosis of Jewish BRCA1 mutation carriers. This finding suggests that IGF-1R influences BRCA1 penetrance. Thus, in order to address this penetrance we tested IGF-1R regulation.

Using computational methods we demonstrated that this SNP is located within a target binding site for microRNA-515-5p. Subsequently, we showed an inverse expression of igf-1r mRNA and microRNA-515-5p in various human breast cancer cell lines. IGF-1R expression levels were significantly downregulated (29%) when microRNA-515-5p was constitutively expressed in cell line. Moreover, using Luciferase reported assay we demonstrated a direct functional regulation of IGF-1R by microRNA-515-5p. In addition, we identified that disrupting microRNA-515-5p and igf-1r 3’UTR binding by a single nucleotide substitution leads to de-repression and a significant increase in IGF-1R protein levels. Interestingly, we found microRNA-515-5p to be down-regulated in tumor tissue from BRCA1 mutation carriers compared to its non-neoplastic surrounding tissue, while IGF-1R levels were elevated.

Taken together, these findings support the hypothesis that a SNP located in igf-1r gene may alter microRNA regulation of IGF-1R, with a putative effect on BRCA1 penetrance and breast cancer risk.