We previously identified a quantitative trait locus for adiposity, non-insulin-dependent diabetes 5 (Nidd5), on mouse chromosome 2. In the current study, we identified the actual genetic alteration at Nidd5 as a nonsense mutation of the Acvr1c gene encoding activin receptor-like kinase 7 (ALK7), one of the type I transforming growth factor-β receptors, which results in a COOH-terminal deletion of the kinase domain. We further showed that the ALK7 dysfunction causes increased lipolysis in adipocytes and leads to decreased fat accumulation. Conversely, ALK7 activation inhibits lipolysis by suppressing the expression of adipose lipases. ALK7 and activated Smads repress those lipases by downregulating peroxisome proliferator–activated receptor γ (PPARγ) and CCAAT/enhancer binding protein (C/EBP) α. Although PPARγ and C/EBPα act as adipogenic transcription factors during adipocyte differentiation, they are lipolytic in sum in differentiated adipocytes and are downregulated by ALK7 in obesity to accumulate fat. Under the obese state, ALK7 deficiency improves glucose tolerance and insulin sensitivity by preferentially increasing fat combustion in mice. These findings have uncovered a net lipolytic function of PPARγ and C/EBPα in differentiated adipocytes and point to the ALK7-signaling pathway that is activated in obesity as a potential target of medical intervention.

Previous genetic studies in mice have shown that functional loss of activin receptor-like kinase 7 (ALK7), a type I transforming growth factor-β receptor, increases lipolysis to resist fat accumulation in adipocytes. Although growth/differentiation factor 3 (GDF3) has been suggested to function as a ligand of ALK7 under nutrient-excess conditions, it is unknown how GDF3 production is regulated. Here, we show that a physiologically low level of insulin converts CD11c adipose tissue macrophages (ATMs) into GDF3-producing CD11c macrophages ex vivo and directs ALK7-dependent accumulation of fat in vivo. Depletion of ATMs by clodronate upregulates adipose lipases and reduces fat mass in ALK7-intact obese mice, but not in their ALK7-deficient counterparts. Furthermore, depletion of ATMs or transplantation of GDF3-deficient bone marrow negates the in vivo effects of insulin on both lipolysis and fat accumulation in ALK7-intact mice. The GDF3-ALK7 axis between ATMs and adipocytes represents a previously unrecognized mechanism by which insulin regulates both fat metabolism and mass.

Tumor suppressor p53 plays an important role in cancer prevention. Under normal conditions, p53 is maintained at a low level. However, in response to various cellular stresses, p53 is stabilized and activated, which, in turn, initiates DNA repair, cell‐cycle arrest, senescence and apoptosis. Post‐translational modifications of p53 including phosphorylation, ubiquitination, and acetylation at multiple sites are important to regulate its activation and subsequent transcriptional gene expression. Particularly, phosphorylation of p53 plays a critical role in modulating its activation to induce apoptosis in cancer cells. In this context, previous studies show that several serine/threonine kinases regulate p53 phosphorylation and downstream gene expression. The molecular basis by which p53 and its kinases induce apoptosis for cancer prevention has been extensively studied. However, the relationship between p53 phosphorylation and its kinases and how the activity of kinases is controlled are still largely unclear; hence, they need to be investigated. In this review, we discuss various roles for p53 phosphorylation and its responsible kinases to induce apoptosis and a new therapeutic approach in a broad range of cancers.

Mdm2, a ubiquitin ligase that acts on p53, is regulated by sumoylation. In the current study, we identify the enzymes responsible for the sumoylation of Mdm2. When mammalian cells are co-transfected with cDNAs encoding Mdm2 and PIAS1 or PIASx␤ (protein inhibitor of activated STAT) as sumoylation enzymes, Mdm2 is highly sumoylated. Mdm2 is also sumoylated in an in vitro system containing PIASx␤, PIAS1, and RanBP2. When several lysine residues of Mdm2 were sequentially mutated to arginine, the K182R mutant was not sumoylated in intact cells; however, in the in vitro system this mutant was sumoylated by PIAS1, PIASx␤, and RanBP2 as efficiently as the wild-type Mdm2 protein. Lysine residues 182 and 185 map within the nuclear localization signal of Mdm2. A K185R mutant of Mdm2 is sumoylated in intact cells, whereas a K182R protein is not. Only a Mdm2 protein bearing the K182R mutation is localized exclusively in the cytoplasm. Because RanBP2 is a nuclear pore protein and PIAS proteins are localized within the nucleus, our data suggest that Mdm2 is sumoylated during nuclear translocation by RanBP2 and then further sumoylated once in the nucleus by PIASx␤ and PIAS1.The oncoprotein Mdm2 has been shown to be a ubiquitin ligase toward itself and tumor suppressor p53 (1). Its ligase activity is dependent on the RING finger domain in its carboxyl terminus, because a mutation that disrupts this domain diminishes the ubiquitin ligase activity (2, 3). The ubiquitin ligase activity of Mdm2 is important for the regulation of the level of p53 in a cell. When DNA in a cell is damaged by genotoxic stress, p53 is phosphorylated at its amino terminus by ATM kinase and/or chk2 (4 -7). Mdm2 cannot bind and ubiquitinylate phosphorylated p53, and thus p53 becomes stable. When mammalian cells were transfected with v-ras, myc, or adenovirus E1A, the mouse p19 ARF (p14 ARF in humans) was induced (8 -11), and then ARF bound to and inhibited the Mdm2 activity to stabilize p53 (12).The ubiquitin ligase activity of Mdm2 is also thought to be regulated by its post-translational modifications, including phosphorylation and sumoylation. When cells were exposed to genotoxic stress, ATM kinase phosphorylated not only p53 but also Mdm2 to inhibit its activity (13,14). Furthermore, when Akt kinase was activated by inositol 1,4,5-triposhpate (IP 3 ) kinase, active Akt kinase phosphorylated Mdm2, resulting in activation of the ubiquitin ligase activity of Mdm2 and consequently the destabilization of p53 (15,16).SUMO is a ubiquitin-like protein, and mammals have three types of SUMO protein, i.e. . The sumoylation pathway very much resembles the ubiquitinylation one. In the latter, three enzymatic steps are necessary to ubiquitinylate the target protein (21-23). First, a ubiquitin moiety is activated by E1, the ubiquitin-activating enzyme, in the presence of ATP and binds to a cysteine residue of the E1 enzyme through a thioester bond. The activated ubiquitin is then transferred to E2, the ubiquitin-conjugating enzyme, and then the ubiquitin-E2 complex bi...

Mammalian Hedgehog (Hh) signaling plays key roles in embryogenesis and uniquely requires primary cilia. Functional analyses of several ciliogenesis-related genes led to the discovery of the developmental diseases known as ciliopathies. Hence, identification of mammalian factors that regulate ciliogenesis can provide insight into the molecular mechanisms of embryogenesis and ciliopathy. Here, we demonstrate that DYRK2 acts as a novel mammalian ciliogenesis-related protein kinase. Loss of Dyrk2 in mice causes suppression of Hh signaling and results in skeletal abnormalities during in vivo embryogenesis. Deletion of Dyrk2 induces abnormal ciliary morphology and trafficking of Hh pathway components. Mechanistically, transcriptome analyses demonstrate down-regulation of Aurka and other disassembly genes following Dyrk2 deletion. Taken together, the present study demonstrates for the first time that DYRK2 controls ciliogenesis and is necessary for Hh signaling during mammalian development.

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Colorectal cancer is a common cancer and a leading cause of cancer‐related death worldwide. The liver is a dominant metastatic site for patients with colorectal cancer. Molecular mechanisms that allow colorectal cancer cells to form liver metastases are largely unknown. Activation of epithelial–mesenchymal transition is the key step for metastasis of cancer cells. We recently reported that dual‐specificity tyrosine‐regulated kinase 2 (DYRK2) controls epithelial–mesenchymal transition in breast cancer and ovarian serous adenocarcinoma. The aim of this study is to clarify whether DYRK2 regulates liver metastases of colorectal cancer. We show that the ability of cell invasion and migration was abrogated in DYRK2‐overexpressing cells. In an in vivo xenograft model, liver metastatic lesions were markedly diminished by ectopic expression of DYRK2. Furthermore, we found that patients whose liver metastases expressed low DYRK2 levels had significantly worse overall and disease‐free survival. Given the findings that DYRK2 regulates cancer cell metastasis, we concluded that the expression status of DYRK2 could be a predictive marker for liver metastases of colorectal cancer.