f terminally differentiated fat cells, are reported in WAT of obese mice. This implies that some degree of dedifferentiation has taken place in the adipose tissue of obese mice. PHB1 and PHB2 are highly homologous proteins that are evolutionarily conserved and ubiquitously expressed. A study in yeast has initially shown that PHB1 and PHB2 act as mitochondrial chaperones in the inner mitochondrial membrane. The interdependence of both PHBs was subsequently reported in nematode and some types of mammalian cells by several independent groups including ours. To study the function of PHBs in 3T3-L1 cells, we employed a loss-offunction strategy and found that the loss of one simultaneously leads to the loss of the other at the protein level. Upon silencing of the PHB1 or PHB2, we observed a lower degree of fat accumulation in c-Met inhibitor 2 chemical information adipogenic 3T3-L1 cells. Indeed, a recent observation has shown that PHB deficiency markedly reduces intestine fat content early in adulthood of wild-type 
nematodes. Interestingly, in both nhr-49 and fat-7 mutant nematodes, which causes fat accumulation due to decreased synthesis of monounsaturated fatty acids, deficiency of PHB not only reduces ” intestinal fat but also prevents shortage of lifespan. Since either the PHB1- or PHB2-conventional knockout mice do not survive, adipocyte-specific PHB conditional knockout mice may be used in future adipogenic studies. Besides fat accumulation, we detected a downregulation “1348110
“of the adipogenic markers, C/EBPb at the early stage and the PPARc and aP2 at the late stage, upon silencing of PHBs in 3T3-L1 cells, which confirms the essential role of PHBs during adipogenesis. This also implies that PPARc, a key molecule in adipogenesis, may be located downstream of PHBs during adipocyte differentiation. Interestingly, upon forced expression of PHB1 in human ASC, our data demonstrated that the adipocyte differentiation was reduced rather than enhanced. This result is in line with a recent report that adipogenesis is inhibited in 3T3-L1 cells. However, in the absence of insulin, overexpression of PHB1 facilitates adipogenesis of 3T3-L1 cells after adipogenic initiation with adipocyte-induction cocktail. This may be one of the underlying mechanisms involved in enhanced adipogenesis under insulin-resistance condition. It will be interesting to determine the effects of insulin-lacking adipocyte-induction cocktail on adipogenesis and mitochondrial biology in human ASC upon overexpression of PHB1. PHB plays an important role in the Ras-mediated activation of the Raf/MEK/ERK pathway, which is a ” highly conserved signaling module that regulates a multitude of essential cellular functions such as proliferation and differentiation. In addition, the activation of MEK/ERK signaling promotes adipogenesis by enhancing PPARc and C/EBPa gene expression during the early phase of the differentiation of 3T3-L1 preadipocytes. Our data, in agreement with the above observations, further demonstrate that PHBs are required for the phosphorylation of ERK as early as 15 minutes post adipogenic induction in 3T3-L1 cells. Mitochondrial biogenesis is essential in adipocyte differentiation. A 20- to 30-fold increase in the concentration of many mitochondrial proteins has been observed during adipogenesis in a proteomic analysis. It is reported that inhibition of mitochondrial citrate export causes a significant reduction in fat accumulation in 3T3-L1 cells. In addition, DNA binding of PPARc induced by the adipogenic coc