Comparative characterization of the 21-kD and 26-kD gap junction proteins in murine liver and cultured hepatocytes.

Abstract

Abstract. Affinity-purified antibodies to mouse liver 26-and 21-kD gap junction proteins have been used to characterize gap junctions in liver and cultured hepatocytes. Both proteins are colocalized in the same gap junction plaques as shown by double immunofluorescence and immunoelectron microscopy. In the lobules of rat liver, the 21-kD immunoreactivity is detected as a gradient of fluorescent spots on apposing plasma membranes, the maximum being in the periportal zone and a faint reaction in the perivenous zone. In contrast, the 26-kD immunoreactivity is evenly distributed in fluorescent spots on apposing plasma membranes throughout the rat liver lobule. Immunoreactive sites with anti-21 kD shown by immunofluorescence are also present in exocrine pancreas, proximal tubules of the kidney, and the epithelium of small intestine. The 21-kD immunoreactivity was not found in thin sections of myocardium and adult brain cortex. Subsequent to partial rat hepatectomy, both the 26-and 21-kD proteins first decrease and after ,~2 d increase again. By comparison of the 26-and 21-kD immunoreactivity in cultured embryonic mouse hepatocytes, we found (a) the same pattern of immunoreactivity on apposing plasma membranes and colocalization within the same plaque, (b) a similar decrease after 1 d and subsequent increase after 3 d of both proteins, (c) cAMP-dependent in vitro phosphorylation of the 26-kD but not of the 21-kD protein, and (d) complete inhibition of intercellular transfer of Lucifer Yellow in all hepatocytes microinjected with anti-26 kD and, in most cases, partial inhibition of dye transfer after injection of anti-21 kD. Our results indicate that both the 26-kD and the 21-kD proteins are functional gap junction proteins.

Modulation of connexin expression and gap junction communication in astrocytes by the gram‐positive bacterium S. aureus

“…An indirect effect of S. aureus on astrocyte Cx26 expression could be envisioned to occur through an autocrine/paracrine action since both TNF-α and IL-1β are capable of activating MAPK pathways upon binding to their cognate receptors (Hanada and Yoshimura, 2002). Since Cx26 is not phosphorylated it is more likely that any indirect effects of proinflammatory stimuli would be exerted at the level of transcription/ translation (Kojima et al, 1999;Saez et al, 1998Saez et al, , 2005Traub et al, 1989). Although Temme et al (1998) have reported that IL-1 and TNF-α augment Cx26 while decreasing Cx32 mRNA expression in hepatocytes, to our knowledge, the role of proinflammatory mediators on modulating Cx26 levels in astrocytes has not yet been examined.…”

Deficient assembly and function of gap junctions in Trf1, a trafficking mutant of the human liver-derived cell line HuH-7

“…From a functional perspective, several studies of assembly and regulation of gap junctions comprising Cx43 have emphasized apparent correlates with phosphorylation, 7,22,26,28,[41][42][43][44][45][46][47][48][49] although Cx26, which is capable of forming gap junctions, does not appear to be phosphorylated [50][51][52] ; truncation mutants of Cx43, which lack the phosphorylation sites also form functional channels. [53][54][55][56] Formation of the more highly phosphorylated form of Cx43 appears to correlate with plasma membrane insertion and its assembly into gap junctions, 28,43 although such slower migrating forms can arise under other conditions and initial phosphorylation may occur as early as in the Golgi apparatus.…”

A Novel Connexin43-interacting Protein, CIP75, Which Belongs to the UbL-UBA Protein Family, Regulates the Turnover of Connexin43

“…Unlike most membrane proteins, connexins exhibit an exceptionally high metabolic lability with half-lives ranging from 1.5 to 5 h (8-10). The rapid turnover of connexins has been observed in a wide variety of cultured mammalian cells (10,11), whole organs (12), and intact animals (13). Therefore, an efficient and highly regulated degradation mechanism is necessary to control the dynamic turnover of connexins.…”