Heterozygous HNF1A mutations cause pancreatic-islet ␤-cell dysfunction and monogenic diabetes (MODY3). Hnf1␣ is known to regulate numerous hepatic genes, yet knowledge of its function in pancreatic islets is more limited. We now show that Hnf1a deficiency in mice leads to highly tissue-specific changes in the expression of genes involved in key functions of both islets and liver. To gain insights into the mechanisms of tissue-specific Hnf1␣ regulation, we integrated expression studies of Hnf1a-deficient mice with identification of direct Hnf1␣ targets. We demonstrate that Hnf1␣ can bind in a tissue-selective manner to genes that are expressed only in liver or islets. We also show that Hnf1␣ is essential only for the transcription of a minor fraction of its direct-target genes. Even among genes that were expressed in both liver and islets, the subset of targets showing functional dependence on Hnf1␣ was highly tissue specific. This was partly explained by the compensatory occupancy by the paralog Hnf1␤ at selected genes in Hnf1a-deficient liver. In keeping with these findings, the biological consequences of Hnf1a deficiency were markedly different in islets and liver. Notably, Hnf1a deficiency led to impaired large-T-antigen-induced growth and oncogenesis in ␤ cells yet enhanced proliferation in hepatocytes. Collectively, these findings show that Hnf1␣ governs broad, highly tissue-specific genetic programs in pancreatic islets and liver and reveal key consequences of Hnf1a deficiency relevant to the pathophysiology of monogenic diabetes.

Our data show that the pattern of circulating miRNAs is modified by defects in glucose metabolism in a similar manner in mice and humans. This circulating miRNA signature for prediabetes could be used as a new diagnostic tool, as well as to monitor response to intervention.

Heterotrimeric G proteins of the G i , G s , and G q family control a wide array of physiological functions primarily by regulating the activity of key intracellular second messenger-generating systems. ␣ subunits of the G 12 family, G␣ 12 and G␣ 13 , however, can promote cellular responses that are independent of conventional second messengers but that result from the activation of small GTP-binding proteins of the Rho family and their downstream targets. These findings led to the identification of a novel family of guanine-nucleotide exchange factors (GEFs) that provides a direct link between G␣ 12/13 and Rho stimulation. Recent observations suggest that many cellular responses elicited by G␣ q and its coupled receptors also require the functional activity of Rho. However, available evidence suggests that G␣ q may act on pathways downstream from Rho rather than by promoting Rho activation. These seemingly conflicting observations and the recent development of sensitive assays to assess the in vivo levels of active Rho prompted us to ask whether G␣ q and its coupled receptors can stimulate endogenous Rho. Here we show that the expression of activated forms of G␣ q and the stimulation of G qcoupled receptors or chimeric G␣ q molecules that respond to G i -linked receptors can promote a robust activation of endogenous Rho in HEK-293T cells. Interestingly, this response was not prevented by molecules interfering with the ability of G␣ 13 to stimulate its linked RhoGEFs, together suggesting the existence of a novel molecular mechanism by which G␣ q and the large family of G q -coupled receptors can regulate the activity of Rho and its downstream signaling pathways. G protein-coupled receptors (GPCRs)1 represent the largest family of cell surface molecules involved in signal transmission. They owe their name to their extensively studied interaction with heterotrimeric G proteins (␣, ␤, and ␥ subunits), which undergo conformational changes that lead to the exchange of GDP for GTP bound to the ␣ subunit upon receptor activation. Consequently, GTP-bound G␣ subunits of the G␣ i , G␣ s , G␣ q , and G␣ 12 family and free G ␤␥ subunits stimulate a variety of effector molecules thereby activating or inhibiting key second messenger-generating systems (1). However, recent evidence suggests that many cellular responses elicited by activation of heterotrimeric G proteins are not mediated by classical second messengers, but they involve not yet fully understood molecular mechanisms that result in the activation of small GTPbinding proteins of the Ras and Rho families. For example, it was observed that activated forms of G␣ 12 and G␣ 13 promote stress fiber formation, the assembly focal adhesions, the transcriptional activation of the serum responsive factor, and cellular transformation through Rho-dependent pathways without affecting conventional second messengers (2-4). These observations prompted the study of the underlying molecular mechanisms by which G␣ 12/13 activate Rho. In this regard, recent work has revealed that a nov...

Although the ability of G protein-coupled receptors to stimulate normal and aberrant cell growth has been intensely investigated, the precise nature of the molecular mechanisms underlying their transforming potential are still not fully understood. In this study, we have taken advantage of the potent mitogenic effect of thrombin and the focus-forming activity of one of its receptors, protease-activated receptor-1, to dissect how this receptor coupled to G␣ i , G␣ q/11 , and G␣ 12/13 transduces signals from the membrane to the nucleus to initiate transcriptional events involved in cell transformation. Using endogenous and transfected thrombin receptors in NIH 3T3 cells, ectopic expression of muscarinic receptors coupled to G␣ q and G␣ i , and chimeric G protein ␣ subunits and murine fibroblasts deficient in G␣ q/11 , and G␣ 12/13 , we show here that, although coupling to G␣ i is sufficient to induce ERK activation, the ability to couple to G␣ q and/or G␣ 13 is necessary to induce c-jun expression and cell transformation. Furthermore, we show that G␣ q and G␣ 13 can initiate the activation of MAPK cascades, including JNK, p38, and ERK5, which in turn regulate the activity of transcription factors controlling expression from the c-jun promoter. We also present evidence that c-Jun and the kinases regulating its expression are integral components of the transforming pathway initiated by protease-activated receptor-1.

p73 is a novel member of the p53 family of tumor suppressor proteins which is involved in cellular dierentiation, tumor suppression, and the response to genotoxic stress. The molecular mechanisms regulating p73 activity are still poorly understood. Recently, p73 was found to be a target of the enzymatic activity of c-Abl, a non-receptor tyrosine kinase that potently activated in response to DNA damage. Here, we present evidence that c-Abl induces the phosphorylation of p73 in threonine residues adjacent to prolines, and that the p38 MAP kinase pathway mediates this response. Furthermore, we found that activation of p38 is sucient to enhance the stability of p73, and that the transcriptional activation of p73 by c-Abl requires the activity of p38. These ®ndings indicate that members of the MAP kinases superfamily of signaling molecules can regulate p73, and support a role for the p38 MAP kinase in a novel biochemical pathway by which c-Abl regulates this p53-related molecule. Oncogene (2002) 21, 974 ± 979.

The poor prognosis associated with head and neck squamous cell carcinoma (HNSCC) is primarily due to both local invasion and the regional and/or distant metastatic spread. Recent findings have provided evidence that the acquisition of a motile and invasive phenotype by cancer cells involves the dysregulated function of key intracellular molecular mechanisms together with aberrant signaling events initiated by the surrounding microenvironment. These intrinsic and extrinsic biochemical pathways in turn often converge to stimulate the activity of members of the Rho family of Ras-related guanosine triphosphate (GTP)-binding proteins, including RhoA, Rac and Cdc42, which control the organization of the actin cytoskeleton thereby regulating cell adhesion, polarity and motility. In this study, we examined the status of activation of these GTPases in a representative collection of HNSCC cell lines. Surprisingly, we found that most HNSCC cells exhibit remarkably high levels of GTP-bound Rac1. Further analysis revealed that the activation of Rac1 in these HNSCC cells could be due to two independent signaling events, an epidermal growth factor receptor (EGFR)-based autocrine loop that leads to the activation of the Rac1 exchange factor Vav2 and an EGFR/Vav2-independent pathway that arises as a consequence of the oncogenic mutation of the H-ras proto-oncogene. Indeed, we provide evidence that the EGFR/Vav2/Rac1 axis is a crucial pathway for the acquisition of motile and invasive properties of most HNSCC cells. These findings shed light onto the molecular mechanisms involved in HNSCC cell invasion, and may reveal new therapeutic opportunities to halt the metastatic spread of these aggressive malignancies.

Background:The mechanism involved in activity-dependent survival of neurons in the central nervous system is not fully understood. Results: Nurr1 is involved in excitatory transmission-dependent survival of glutamatergic neurons by acting downstream CREB and upstream of BDNF. Conclusion: Nurr1 activation mediates activity-dependent survival of glutamatergic neurons. Significance: A novel function of Nurr1 in activity-dependent survival of glutamatergic neurons is reported.

HMG20A (also known as iBRAF) is a chromatin factor involved in neuronal differentiation and maturation. Recently small nucleotide polymorphisms (SNPs) in the HMG20A gene have been linked to type 2 diabetes mellitus (T2DM) yet neither expression nor function of this T2DM candidate gene in islets is known. Herein we demonstrate that HMG20A is expressed in both human and mouse islets and that levels are decreased in islets of T2DM donors as compared to islets from non-diabetic donors. In vitro studies in mouse and human islets demonstrated that glucose transiently increased HMG20A transcript levels, a result also observed in islets of gestating mice. In contrast, HMG20A expression was not altered in islets from diet-induced obese and pre-diabetic mice. The T2DM-associated rs7119 SNP, located in the 3′ UTR of the HMG20A transcript reduced the luciferase activity of a reporter construct in the human beta 1.1E7 cell line. Depletion of Hmg20a in the rat INS-1E cell line resulted in decreased expression levels of its neuronal target gene NeuroD whereas Rest and Pax4 were increased. Chromatin immunoprecipitation confirmed the interaction of HMG20A with the Pax4 gene promoter. Expression levels of Mafa, Glucokinase, and Insulin were also inhibited. Furthermore, glucose-induced insulin secretion was blunted in HMG20A-depleted islets. In summary, our data demonstrate that HMG20A expression in islet is essential for metabolism-insulin secretion coupling via the coordinated regulation of key islet-enriched genes such as NeuroD and Mafa and that depletion induces expression of genes such as Pax4 and Rest implicated in beta cell de-differentiation. More importantly we assign to the T2DM-linked rs7119 SNP the functional consequence of reducing HMG20A expression likely translating to impaired beta cell mature function.