Variants in LRRC34 reveal distinct mechanisms for predisposition to papillary thyroid carcinoma

Background: Papillary thyroid carcinoma (PTC) demonstrates high heritability and a low somatic mutation burden relative to other cancers. Therefore, the genetic risk predisposing to PTC is likely due to a combination of low penetrance variants. A recent genome-wide association study revealed the association of PTC with a missense variant, rs6793295, at 3q26 in a gene called Leucine Repeat Rich Containing 34 (LRRC34).

Methods: We report the mechanisms of PTC risk at 3q26 using a combination of overexpression, mass spectroscopy, knockdown, transcriptome profiling, migration assays and genetic analysis.

Results: We observed differential binding of wild-type and missense LRRC34 to RANBP1. Overexpression of missense LRRC34 reduced RanGTP levels and increased apoptosis. We also identified a second linkage disequilibrium (LD) block upstream of LRRC34 containing regulatory variants with allele-specific expression. Transcriptome profiling of LRRC34 knockdown cells showed changes in genes involved with cellular movement. LRRC34 knockdown reduced the migration of thyroid cancer cell lines. Lastly, we assessed the relative contribution of PTC risk from each locus using haplotype analysis.

Conclusions: Our study demonstrates two separate mechanisms, one in G protein signalling and the other in transcriptional control, dictating PTC risk at 3q26 using both biochemical and genetic techniques.