Insulin gene expression is restricted to islet beta cells of the mammalian pancreas through specific control mechanisms mediated in part by specific transcription factors. The protein encoded by the pancreatic and duodenal homeobox gene 1 (PDX-1) is central in regulating pancreatic development and islet cell function. PDX-1 regulates insulin gene expression and is involved in islet cell-specific expression of various genes. Involvement of PDX-1 in islet-cell differentiation and function has been demonstrated mainly by 'loss-of-function' studies. We used a 'gain-of-function' approach to test whether PDX-1 could endow a non-islet tissue with pancreatic beta-cell characteristics in vivo. Recombinant-adenovirus-mediated gene transfer of PDX-1 to the livers of BALB/C and C57BL/6 mice activated expression of the endogenous, otherwise silent, genes for mouse insulin 1 and 2 and prohormone convertase 1/3 (PC 1/3). Expression of PDX-1 resulted in a substantial increase in hepatic immunoreactive insulin content and an increase of 300% in plasma immunoreactive insulin levels, compared with that in mice treated with control adenovirus. Hepatic immunoreactive insulin induced by PDX-1 was processed to mature mouse insulin 1 and 2 and was biologically active; it ameliorated hyperglycemia in diabetic mice treated with streptozotocin. These data indicate the capacity of PDX-1 to reprogram extrapancreatic tissue towards a beta-cell phenotype, may provide a valuable approach for generating 'self' surrogate beta cells, suitable for replacing impaired islet-cell function in diabetics.

Peripheral axons of dorsal root ganglion (DRG) neurons, but not their central axons in the dorsal columns, regenerate after injury. However, if the neurons are conditioned by a peripheral nerve injury into an actively growing state, the rate of peripheral axonal growth is accelerated and the injured central axons begin to regenerate. The growth-promoting effects of conditioning injuries have two components, increased axonal growth and a reduced response to inhibitory myelin cues. We have examined which transcription factors activated by peripheral axonal injury may mediate the conditioning effect by regulating expression of effectors that increase the intrinsic growth state of the neurons. Activating transcription factor 3 (ATF3) is a prime candidate because it is induced in all injured DRG neurons after peripheral, but not central, axonal damage. To investigate if ATF3 promotes regeneration, we generated transgenic mice that constitutively express this transcription factor in non-injured adult DRG neurons. The rate of peripheral nerve regeneration was enhanced in the transgenic mice to an extent comparable to that produced by a preconditioning nerve injury. The expression of some growth-associated genes, such as SPRR1A, but not others like GAP-43, was increased in the non-injured neurons. ATF3 increased DRG neurite elongation when cultured on permissive substrates but did not overcome the inhibitory effects of myelin or promote central axonal regeneration in the spinal cord in vivo. We conclude that ATF3 contributes to nerve regeneration by increasing the intrinsic growth state of injured neurons.

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Curli fibers are adhesive surface fibers expressed by Escherichia coli and Salmonella enterica that bind several host extracellular matrix and contact phase proteins and were assumed to have a role in pathogenesis. The results presented here suggest that one such role is internalization into host cells. An E. coli K-12 strain transformed with a low-copy vector containing the gene cluster encoding curli fibers (csg operon) was internalized by several lines of eukaryotic cells. The internalization could be correlated with a high level of curli fiber expression and was abolished by disruption of the csg operon. The ability to be internalized by eukaryotic cells could be conferred even by the curli fiber gene cluster of a noninvasive K-12 strain, but the homologous csg cluster from a virulent septicemic E. coli isolate mediated a higher level of internalization. The finding that curli fibers promote bacterial internalization indicates a new role for curli fibers in pathogenesis.Curli fibers are thin aggregative surface fibers, connected with adhesion, which bind laminin (23), fibronectin (25), plasminogen (31), human contact phase proteins (4), and major histocompatibility complex (MHC) class I molecules (26). Curli fibers are coded for by the csg gene cluster, which is comprised of two divergently transcribed operons. One operon encodes the csgB, csgA, and csgC genes, while the other encodes csgD, csgE, csgF, and csgG. The assembly of the fibers is unique and involves extracellular self-assembly of the curlin subunit (CsgA), dependent on a specific nucleator protein (CsgB) (14). CsgD is a transcriptional activator essential for expression of the two curli fiber operons, and CsgG is an outer membrane lipoprotein involved in extracellular stabilization of CsgA and CsgB (20). The role of the other csg genes has yet to be elucidated.Curli fibers are expressed by many pathogenic isolates of Escherichia coli, as well as laboratory strains (25). Similar surface proteins were identified in both Salmonella enterica serovar Enteritidis (9) and S. enterica serovar Typhimurium (28). Curli fibers are also present in E. coli strains involved in avian colisepticemia (27)-a serious invasive disease of chickens and turkeys that is characterized by entry of the bacteria into the air sacs, bloodstream, and vital organs (36).Using PCR, we amplified the curli fiber-encoding (csg) gene cluster from a curli fiber-positive E. coli K-12 strain and cloned it in a low-copy-number vector. The resulting plasmid, when transformed to a noninvasive E. coli strain, conferred the ability to become internalized by eukaryotic cells. We have also cloned the homologous curli fiber-encoding cluster from a virulent isolate of avian E. coli O78 which could mediate a higher level of internalization. The results presented in this communication indicate that high levels of curli fiber expression can mediate entry of bacteria into eukaryotic cells and suggest that these fibers play a role in pathogenesis. MATERIALS AND METHODSBacterial strains and plasmids. T...

Significance This study reports on the beneficial effects of forcing high expression of the transcription factor activating transcription factor 3 (ATF3) in ALS. ALS is a noncurable adult-onset disease that attacks motor neurons, resulting in paralysis and death. ATF3 overexpression in motor neurons in an ALS mouse model modifies gene expression and drives the neurons into a prosurvival and proregenerative state, increasing motor neuron survival and maintaining axonal connection with muscle by promoting axonal sprouting. ATF3 overexpression results in markedly improved muscle strength and function and delayed disease onset but only slightly increased lifespan. Molecular mechanisms that promote axonal sprouting could substantially improve quality of life in ALS, although additional approaches will be required to overcome progressive motor neuron deterioration.

RIN1046 -38 cells (RIN-38) exhibit a passage-dependent reduction in both basal and glucose-regulated insulin secretion, accompanied by decreased insulin content. In an attempt to explain the mechanism of the gradual decrease in insulin production in cultured cells, we analyzed the insulin promoter activity and the levels of an important trans-activator of the insulin gene, PDX-1, as a function of aging in culture. We demonstrate that the decrease in insulin content and secretion is reflected in decreased promoter activity and is associated with a decrease in E47 and BETA2 nuclear factors, but with a paradoxical 3-fold increase in PDX-1 protein levels. To dissect the effect of increased PDX-1 from the decrease in the additional transcription factors on insulin promoter activity, we overexpressed PDX-1 protein in low passage RIN-38 cells by recombinant adenovirus technology.PDX-1 overexpression did not reduce E47 and BETA2 levels, but was sufficient to suppress rat insulin promoter activity in a dose-dependent manner. The fact that PDX-1 levels participate in trans-activation of insulin promoter activity was demonstrated in HIT-T15 cells. Treating HIT-T15 cells with 1-2 multiplicity of infection of AdCMV-PDX-1 increased rat insulin promoter activity, whereas higher doses repressed insulin promoter activity in these cells as in RIN-38 cells. Our data demonstrate that PDX-1 regulates transcription of the insulin gene in a dose-dependent manner. Depending on its nuclear dosage and the levels of additional cooperating transcription factors, PDX-1 may act as an activator or a repressor of insulin gene expression, such that low as well as high doses may be deleterious to insulin production. (Endocrinology 140: 3311-3317, 1999) P ANCREATIC islet cells undergo a functional deterioration process that can be induced by aging or chronic exposure to nutrients and hormones (1-4). The rat insulinoma cell line RIN 1046 -38 (RIN-38) serves as a cellular model for such a functional deterioration process (5). At low passage number, these cells are glucose responsive, but lose this ability progressively with time in culture along with a specific decrease in insulin, GLUT-2, and glucokinase (GK) messenger RNA (mRNA) levels (5). An important issue is whether this functional deterioration process is reflected in and can be explained by alterations in ␤-cell-specific transcription factors.The transcription factor PDX-1 has an important role in pancreatic islet differentiation (6 -11). Cooperativity between PDX-1 and bHLH proteins in trans-activation of the insulin gene was demonstrated (12). The ubiquitously expressed E47 protein creates heterodimers with the ␤-cell-specific HLH protein BETA2 (13). In terminally differentiated ␤-cells, PDX-1 participates in mediating glucose stimulation of insulin promoter activity and trans-activation of other important ␤-cell-specific genes, such as GK, . These findings suggest that alterations in PDX-1 levels could influence the expression of a host of islet cell genes that are important for ...

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