Insulin resistance results in dysregulated hepatic gluconeogenesis that contributes to obesity-related hyperglycemia and progression of type 2 diabetes mellitus (T2DM). Recent studies show that MAPK phosphatase-3 (MKP-3) promotes gluconeogenic gene transcription in hepatoma cells, but little is known about the physiological role of MKP-3 in vivo. Here, we have shown that expression of MKP-3 is markedly increased in the liver of diet-induced obese mice. Consistent with this, adenovirus-mediated MKP-3 overexpression in lean mice promoted gluconeogenesis and increased fasting blood glucose levels. Conversely, shRNA knockdown of MKP-3 in both lean and obese mice resulted in decreased fasting blood glucose levels. In vitro experiments identified forkhead box O1 (FOXO1) as a substrate for MKP-3. MKP-3-mediated dephosphorylation of FOXO1 at Ser256 promoted its nuclear translocation and subsequent recruitment to the promoters of key gluconeogenic genes. In addition, we showed that PPARγ coactivator-1α (PGC-1α) acted downstream of FOXO1 to mediate MKP-3-induced gluconeogenesis. These data indicate that MKP-3 is an important regulator of hepatic gluconeogenesis in vivo and suggest that inhibition of MKP-3 activity may provide new therapies for T2DM.

The spontaneously immortalized murine calvarial cell line MC3T3-E1 and its derivative subclones are widely used models of osteoblast biology. Many investigators have reported conflicting data under seemingly similar experimental conditions, though the specific subclone studied is often not specified. The purpose of this study was to directly compare the commercially available MC3T3-E1 subclones 4, 14, and 24 in terms of responsiveness to osteogenic induction media and/or stimulation with rhPTH[1–34]. We assayed osteogenic gene expression, capacity to deposit and mineralize a collagenous matrix, and the expression and signaling function of PTH1R. Our data demonstrate that each subclone bears little functional resemblance to the others, or to primary calvarial osteoblasts. Specifically, whereas subclone 4 is responsive to PTH stimulation and capable of matrix mineralization, subclones 14 and 24 do not faithfully replicate these key aspects of osteoblast biology. Furthermore, little overlap was observed between the gene expression profile of subclone 4 and primary calvarial osteoblasts. Our experience working with these cell lines demonstrates that the MC3T3-E1 derived cell lines are imperfect models of osteoblast biology, and reinforce the importance of clearly articulating selection and reporting of research materials.