Meta-Biol

• Pathways

Src is believed to suppress gap junction communication by phosphorylating Cx43. The kinases c-Src (Giepmans et al. 2001; Sorgen et al. 2004), PKc (Lin et al. 2003) and MAPK (Mograbi et al. 2003) play an essential role in the phosphorylation of Cx which leads to its degradation. c-Src appears to associate with and phosphorylate Cx43 leading to closure of gap junctions. Evidence suggests that v-src may activate MAPK, which in turn phosphorylates Cx43 on serine sites leading to channel gating (Zhou et al. 1999).

The secretory membrane system allows a cell to regulate delivery of newly synthesized proteins, carbohydrates, and lipids to the cell surface, a necessity for growth and homeostasis. The system is made up of distinct organelles, including the endoplasmic reticulum (ER), Golgi complex, plasma membrane, and tubulovesicular transport intermediates. These organelles mediate intracellular membrane transport between themselves and the cell surface. Membrane traffic within this system flows along highly organized directional routes. Secretory cargo is synthesized and assembled in the ER and then transported to the Golgi complex for further processing and maturation. Upon arrival at the trans Golgi network (TGN), the cargo is sorted and packaged into post-Golgi carriers that move through the cytoplasm to fuse with the cell surface. This directional membrane flow is balanced by retrieval pathways that bring membrane and selected proteins back to the compartment of origin.

The transit of proteins and other cargo through the cell requires a cellular transport process in which transported substances are moved in membrane-bounded vesicles. Transported substances are enclosed in the vesicle lumen or located in the vesicle membrane. The transport process begins with the formation of the vesicle itself, often triggered by the interaction of the cargo with the vesicle formation machinery. Vesicular transport pathways can include vesicle formation, coating, budding, uncoating and target membrane fusion depending upon the function of the pathway described. Vesicle-mediated transport occurs from within cell via ER and Golgi transport, as well as functioning in the endocytosis of material taken into the cell via scavenger receptors.