S6K1 controls epigenetic plasticity for the expression of pancreatic α/β cell marker genes

The failure of insulin production by pancreatic β cells is a common hallmark of type 1 diabetes mellitus (T1DM). Because administration of exogenous insulin is associated with diabetes-derived complications, endogenous α to β cell transition can be an attractive alternative. Although decreased β cell size and hypoinsulinaemia have been observed in S6K1-deficient mice, the molecular mechanism underlying the involvement of S6K1 in the transcriptional regulation of insulin remains elusive. Here, we show that the hypoinsulinaemic phenotype of S6K1-deficient mice stems from the dysregulated transcription of a set of genes required for insulin and glucagon production. First, we observed that increased expression of α cell marker genes and decreased expression of β cell marker genes in pancreas tissues from S6K1-deficient mice. Furthermore, S6K1 was highly activated in murine β cell line, βTC6, compared to murine α cell line αTC1. In both α and β cells, active S6K1 promoted the transcription of β cell marker genes, including insulin, whereas S6K1 inhibition increased the transcription of α cell marker genes. Moreover, S6K1 mediated pancreatic gene regulation by modifying two histone marks (activating H3K4me3 and repressing H3K27me3) on gene promoters. These results suggest that S6K1 drives the α to β transition through the epigenetic regulation of cell-specific genes, including insulin and glucagon. This novel role of S6K1 in islet cells provides basic clues to establish therapeutic strategies against T1DM.