Biomedical subjects

Chenzhong Kuang

Publications and source records attributed to Chenzhong Kuang.

6 recordsLinked to original sources

PubMed2006

Intragenic deletion of Tgif causes defectsin brain development.

TG-interacting factor (TGIF) is a homeodomain-containing protein and functions as a transcriptional repressor within the TGF-beta and retinoic acid signaling pathways. Heterozygous mutations of TGIF have been found in patients with holoprosencephaly (HPE), which is the most common congenital brain malformation in humans. However, targeted null deletions of the entire Tgif gene in mice surprisingly revealed no apparent brain defects. We report here that deletion of the third exon of Tgif gene resulted in a defined spectrum of brain developmental defects including exencephaly, microcephaly, HPE, and abnormalities in embryonic brain ventricle formation and cleavage. These defects could be detected in mice both heterozygous and homozygous for the targeted Tgif deletion. Moreover, expression of dorsal-ventral patterning genes including Shh, Pax6 and Nkx2.2 was altered. The ventricular neuroepithelium exhibited focalized increase of cell proliferation rate and resultant tissue expansion. The incidence of brain abnormalities within the mutant mice was dependent on its genetic background, suggesting that additional genetic modifiers functionally interact with Tgif during embryonic brain development. The intragenic Tgif deletion mouse, therefore, would serve as a useful model that can be used to unravel the genetic complexity implicated in the pathogenesis of HPE.

Animals↗

PubMed2006

In vivo disruption of TGF-beta signaling by Smad7 leads to premalignant ductal lesions in the pancreas.

TGF-beta has been postulated to play an important role in the development of pancreatic cancers. More than 50% of human pancreatic cancers bear mutations of Sma- and Mad-related protein (Smad) 4, a critical protein required for TGF-beta signaling. To evaluate the in vivo function of TGF-beta in the development of pancreatic cancers, we generated a transgenic mouse model with pancreas-specific expression of Smad7, a specific inhibitor of TGF-beta signaling. Through the use of elastase I promoter, we directed the tissue specific expression of exogenous Smad7. Consistently, the exogenous Smad7 was detected only in the pancreas in the transgenic mice, and, furthermore, phosphorylation of Smad2 was blocked in the pancreatic tissues. At 6 months of age, most transgenic animals developed premalignant ductal lesions in the pancreas, with characteristics of pancreatic intraepithelial neoplasia (PanIN), a precursor to invasive pancreatic cancers. The premalignant lesions of the pancreas were accompanied by accelerated proliferation of the ductal epithelium and acinar cells, as well as increased fibrosis around the ductal lesions. This study not only demonstrated that in vivo inactivation of TGF-beta signaling is implicated in the development of early stage of pancreatic cancers, but also provided a promising animal model useful for the investigation and intervention of pancreatic cancers in humans.

Animals↗

PubMed2005

Expression pattern of TG-interacting factor 2 during mouse development.

TGIF2 is a close homologue of TGIF that functions as a transcriptional corepressor by interaction with transforming growth factor-beta (TGF-beta)-activated Smads. Mutations of TGIF have been found in holoprosencephaly, a genetic disease affecting forebrain and craniofacial developmental. Here we analyzed the expression pattern of TGIF2 during mouse embryogenesis. Expression of TGIF2 transcripts was detected at high level at E12.5 and E15.5 in the nervous system including neopallial cortex, mesencephalon, metencephalon, medulla oblongata, spinal cord, trigeminal ganglion, vestibulocochlear ganglion and dorsal root ganglion. In addition, TGIF2 transcripts could be detected in other tissues including heart, lung, liver, pancreas, kidney, small intestine and nasal cavity. These data indicated that TGIF2 has a wide but well controlled expression pattern during mouse development.

Animals↗

PubMed2004

Suppression of matrix metalloproteinase-9 transcription by transforming growth factor-beta is mediated by a nuclear factor-kappaB site.

TGF-beta (transforming growth factor-beta) plays a critical role in modulating the inflammatory response and other biological processes through its regulation of the production of MMPs (matrix metalloproteinases). In both Mono-Mac-6 and RAW264.7 monocyte/macrophage cells, TGF-beta abrogated lipopolysaccharide-induced increases in the enzymic activity and mRNA level of MMP-9. A fragment of the human MMP-9 promoter was used to characterize its regulation by TGF-beta signalling. In RAW264.7 cells, TGF-beta or its downstream signalling protein, Smad3 (Sma- and Mad-related protein 3), inhibited lipopolysaccharide-stimulated promoter activity. The suppressive activity of TGF-beta on the MMP-9 promoter was abrogated by an inhibitory Smad, Smad7. The MMP-9 promoter contains a putative TIE (TGF-beta inhibitory element). However, neither mutation nor deletion of the TIE had any effect on the inhibitory activity of TGF-beta on MMP-9 transcription, indicating that the consensus TIE is not required for this effect of TGF-beta. Analysis using a series of deletion mutants of the MMP-9 promoter revealed that a region containing a consensus NF-kappaB (nuclear factor-kappaB) site is required for the basal activity and TGF-beta-mediated suppression of the promoter. Mutation of the putative NF-kappaB site not only markedly reduced the basal transcriptional activity of the promoter, but also abrogated the responsiveness of the promoter to TGF-beta. In addition, a minimal promoter containing one copy of the NF-kappaB sequence was responsive to TGF-beta treatment. Furthermore, an electrophoretic mobility shift assay was performed with the nuclear extracts from RAW264.7 cells, and it was found that TGF-beta treatment did not disrupt the binding of NF-kappaB p50 and p65 proteins to the NF-kappaB sequence. Taken together, these studies indicate that the NF-kappaB site is indispensable for the suppressive activity of TGF-beta in the regulation of MMP-9 transcription.

Binding Sites↗

PubMed2004

Tumor-derived C-terminal mutations of Smad4 with decreased DNA binding activity and enhanced intramolecular interaction.

Smad4 is a critical component in transforming growth factor beta (TGF-beta) signaling and frequently mutated in pancreatic and colorectal cancers. Smad4 has two important functional domains, MH1 and MH2, that are involved in different biological processes. The MH1 domain comprises a DNA binding domain and the MH2 domain is mainly implicated in transcriptional activation and homo- and heteromeric complex formation among Smad proteins. In the present study, a total of nine Smad4 mutations at both MH1 and MH2 domains were analysed and all of them had a reduced activity to stimulate transcription of a TGF-beta-responsive reporter gene. All four MH1 mutations had a markedly reduced ability to bind a consensus Smad binding element by an in vitro assay using GST fusion proteins. Among the MH2 mutations, R497H, K507Q, and R515G mutations of Smad4 gave rise to a reduced DNA binding capacity. The R497H mutation had a slightly reduced interaction with Smad2 upon activation of TGF-beta receptor. However, the K507Q and R515G mutations greatly lost their ability to associate with Smad2. Using a GST pull-down assay, it was found that the Smad4 MH2 domain bearing R497H and R515G mutations had an enhanced interaction with the MH1 region of the Smad4 protein, indicating that an increased intramolecular interaction by these mutations may alleviate the DNA binding activity at the MH1 domain. Consistent with these observations, the MH2 domain with R497H mutation had an enhanced ability to inhibit TGF-beta receptor-mediated transcription. In addition, the full-length R497H mutation was able to antagonize TGF-beta signaling in a dominant-negative manner. Therefore, these studies revealed novel mechanisms by which the Smad4 mutations utilize to abrogate their functions in transducing the signaling of TGF-beta, which plays an important role in various stages of cancer formation.

Amino Acid Sequence↗

PubMed2003

Regulation of TG-interacting factor by transforming growth factor-beta.

TG-interacting factor (TGIF) is a transcriptional co-repressor that directly associates with Smad (Sma- and Mad-related protein) proteins and inhibits Smad-mediated transcriptional activation. By using Affymetrix (Santa Clara, CA, U.S.A.) oligonucleotide microarray analysis, we found that TGIF mRNA level was elevated by transforming-growth-factor-beta (TGF-beta) treatment in a human T-cell line, HuT78. Subsequent reverse-transcription PCR assays indicated that TGF-beta1 and activin were able to induce a rapid and transient increase in the level of TGIF in both HuT78 and HepG2 hepatoma cells. To analyse whether or not the regulation of TGIF mRNA occurs at the transcriptional level, a 2.4 kb human TGIF promoter was isolated. A primer extension assay was performed to localize the putative transcription initiation site of the promoter. When transiently expressed in HepG2 cells, this promoter was stimulated by TGF-beta1 and activin treatment in a time-dependent manner. A series of deletion mutants of the TGIF promoter were also generated to further characterize the TGF-beta responsive region of the promoter. In addition, expression of TGIF was able to cause a dose-dependent inhibition of TGF-beta and activin signalling. Taken together, these experiments indicated that TGIF is a novel transcriptional target of TGF-beta and activin signalling and is likely involved in a negative feedback loop to desensitize TGF-beta/activin action.

Base Sequence↗