Disease relevance of Gjb1

• This study investigated transcriptional regulation of the rat Cx32 gene in MH(1)C(1) rat hepatoma cells using transient expression assays in conjunction with promoter mutagenesis and 5' nested deletion analysis [1].
• The identification of connexin32 (Cx32) in myelinating Schwann cells and the association of Cx32 mutations with peripheral neuropathies suggest a functional role for gap junction proteins in the nerve [2].
• In peripheral nerve, Cx32 is found in the paranodal myelin loops and Schmidt-Lanterman incisures of myelinating Schwann cells, and the levels of Cx32 protein and mRNA change in parallel with those of other myelin-related genes during development, Wallerian degeneration, and axonal regeneration [3].
• Differential decrease in connexin 32 expression in ischemic and nonischemic regions of rat liver during ischemia/reperfusion [4].
• RESULTS: In untreated rats, acetic acid-induced gastric ulcers healed after 14 days and the electrophoretic band corresponding to connexin 32 appeared 4 days after ulcer induction [5].

High impact information on Gjb1

• By probing the accessibility of systematically substituted cysteine residues to thiol blockers (a technique called SCAM), we have identified the pore-lining residues of a gap junction channel composed of Cx32 [6].
• The mRNA and protein expression of alpha 1 (connexin 43), beta 1 (connexin 32), and beta 2 (connexin 26) gap junction genes were examined in the regenerating rat liver after 70% partial hepatectomy (PH) [7].
• We observed no cell-cell dye transfer 4 min after microinjection in 90% of the cell pairs treated with Fab fragments of antibodies for the first or second extracellular domain of Cx43, the second extracellular domain of connexin32 (Cx32) or A-CAM [8].
• These results indicated the different changes of expression and function of Cx26 and Cx32 in the hepatocytes during stimulation and re-inhibition of DNA synthesis [9].
• Gap junctional intercellular communication (GJIC), as measured by lucifer yellow, which indicated the function of Cx32, decreased markedly from before the onset of the S phase [9].

Chemical compound and disease context of Gjb1

• For the analysis of different stages in carcinogenesis, Cx32 was assayed in N-ethyl-N-hydroxyethylnitrosamine-induced enzyme altered foci (EAF), hyperplastic nodules (HN), hepatocellular carcinomas (HCC), pulmonary metastatic HCC and transplanted HCC in relation to their degree of altered enzyme expression [10].
• Increased liver weight, centrilobular hepatocellular hypertrophy due to increased smooth endoplasmic reticulum, decreased numbers and areas of connexin 32-positive spots per hepatocyte, and increased cell proliferation were observed in rats treated with 0.2 and 2% piperonyl butoxide [11].

Biological context of Gjb1

• During stimulation of DNA synthesis, both Cx26 and Cx32 messenger RNA (mRNAs) in hepatocytes transiently increased in the G1 phase and then markedly decreased before the onset of the S phase, while only Cx26 messenger RNA (mRNA) increased slightly in the S/M phase [9].
• Formation of three-dimensional thyroid follicle-like structures by polarized FRT cells made communication competent by transfection and stable expression of the connexin-32 gene [12].
• These studies identify two calmodulin-binding amino-acid sequences in connexin 32, and provide independent evidence that calmodulin may function as an intracellular ligand, regulating Ca2+-dependent intercellular communication across gap junctions [13].
• Our data suggest that the formation and/or functioning of Cx32 gap junctions might represent a key event in thyroid epithelium morphogenesis, i.e. formation of a lumen from a tight epithelial cell layer [12].
• Cx26 immunoreactivity mostly overlapped with Cx32-positive sites in acinar cells of lactating mammary glands, indicating that both Cxs were colocalized together in the same gap junctional plaques in lactation [14].

Anatomical context of Gjb1

• Instead, Cx32 and Cx43 were restricted to glial gap junctions [15].
• Both Cx26 and Cx32 were localized to the lateral plasma membranes between adjacent epithelial cells of the epididymis [16].
• Oligodendrocytes shared intercellular gap junctions only with astrocytes, and these heterologous junctions had Cx32 on the oligodendrocyte side and Cx26, Cx30 and Cx43 on the astrocyte side [17].
• In contrast, Cx36 and Cx32 mRNA and proteins were relatively sparse and unchanged after spinal cord injury along the entire axis of the spinal cord [18].
• The decreased level of Cx32 protein in plasma membranes was observed in the PB group [19].

Associations of Gjb1 with chemical compounds

• Different changes in expression and function of connexin 26 and connexin 32 during DNA synthesis and redifferentiation in primary rat hepatocytes using a DMSO culture system [9].
• PH performed during continuous administration of 2-acetylaminofluorene (AAF) prevented changes in Cx32 and Cx26 staining observed in the absence of AAF [20].
• Surprisingly, myoinositol and all inositol phosphates tested were permeable through homomeric Cx32 and homomeric Cx26 channels [21].
• In the majority of PB-promoted foci, Cx32 immunoreactivity decreased independently of changes in mRNA abundance [22].
• The effect of dexamethasone on the expression of Cx26 mRNA compared to that of Cx32 mRNA was examined [23].

Co-localisations of Gjb1

• Immunocytochemically, Cx26-positive spots were observed between most adjacent cells and were co-localized with the Cx32-positive spots [23].

Regulatory relationships of Gjb1

• Unexpectedly, 9618A cells expressed Cx43 mRNA and protein in cell culture but expressed Cx32 mRNA in vivo [24].
• Although the expression of Cx32 mRNA was also influenced by glucagon, the increase of the expression was small [23].

Other interactions of Gjb1

• Connexin 32 of gap junctions contains two cytoplasmic calmodulin-binding domains [13].
• The relative abundance of Cx 32, Cx 43 and Cx 46 mRNA increased significantly during the first 2-3 weeks and then remained relatively constant during weeks 3-6 [25].
• Restoration of cell-to-cell communication in thyroid cell lines by transfection with and stable expression of the connexin-32 gene. Impact on cell proliferation and tissue-specific gene expression [26].
• The expression of connexin-32 led to an increase of thyroglobulin gene expression in FRTL-5 cells [26].
• Although we recently reported our success in inducing and maintaining Cx32 in adult rat hepatocytes cultured in serum-free L-15 medium supplemented with epidermal growth factor and 2% dimethyl sulfoxide, it was very difficult to induce Cx26 in the primary hepatocytes [23].

Analytical, diagnostic and therapeutic context of Gjb1

• The levels of Cx43 and Cx32 proteins in membrane fractions detected by western blotting were also significantly increased [27].
• In the present study, we examined the cellular location of the gap junction proteins and the structures in the hepatocytes cultured in our system, using confocal laser microscopy and immunoelectron microscopy of cells processed for Cx32 and Cx26 immunocytochemistry and freeze-fracture analysis [28].
• Inspection of the cell organization within domes formed from FRT-Cx32 cells by phase contrast and confocal microscopy revealed a progressive transition from domes toward closed structures with a lumen [12].
• The expression of the gap-junction proteins connexin 32 and 43 in the developing rat submandibular gland was determined using reverse transcription-polymerase chain reaction and immunohistochemistry [29].
• We examined the immunofluorescent (IF) localization and mRNA and protein levels of the two hepatocyte gap junction proteins connexin 32 and connexin 26, after hepatic injury induced by common bile duct ligation (CBDL) in the rat [30].

References