Researcher(s)
- Meredith Eaton, Biological Sciences, University of Delaware
Faculty Mentor(s)
- Andre Luiz Pasqua Tavares, Biology, University of Delaware
Abstract
Branchio-oto-renal (BOR) syndrome is an autosomal dominant disorder characterized by hearing loss, craniofacial skeletal malformations, and renal abnormalities. Pathogenic variants in SIX1, which encodes the transcription factor SIX1, are associated with many BOR cases. Published and preliminary data from our laboratory suggest that SIX1 is required for osteogenic precursor cells to initiate differentiation toward the osteogenic lineage. However, SIX1 expression must subsequently be downregulated to allow these cells to complete differentiation into mature bone-forming osteoblasts. The goal of this study was to investigate whether SIX1 protein levels change as osteogenic precursor cells differentiate into mature osteoblasts. We hypothesize that SIX1 undergoes proteasome-mediated degradation during osteogenic differentiation. To test this hypothesis, we used O9-1 cranial neural crest cells and MC3T3-E1 preosteoblasts as complementary models representing distinct stages of the osteogenic lineage. Cells were transfected with SIX1 expression constructs and treated with the proteasome inhibitor MG132. SIX1 protein levels were then evaluated by western blot analysis. Our preliminary results indicate that inhibition of proteasome activity with MG132 resulted in increased SIX1 protein levels in MC3T3-E1 cells, whereas little or no increase was observed in O9-1 cells. These findings suggest that SIX1 protein stability is differentially regulated during osteogenic differentiation and support a model in which proteasome-mediated degradation contributes to the downregulation of SIX1 in later stages of osteoblast maturation. Understanding how SIX1 protein stability differs in cell types can improve our understanding of tissue-specific mechanisms of SIX1-associated developmental disorders such as BOR and other diseases involving SIX1 dysregulation.