Gap junctions in laryngeal carcinoma

Facets of Communication: Gap Junction Ultrastructure and Function in Cancer Stem Cells and Tumor Cells

Gap junction proteins are expressed in cancer stem cells and non-stem cancer cells of many tumors. As the morphology and assembly of gap junction channels are crucial for their function in intercellular communication, one focus of our review is to outline the data on gap junction plaque morphology available for cancer cells. Electron microscopic studies and freeze-fracture analyses on gap junction ultrastructure in cancer are summarized. As the presence of gap junctions is relevant in solid tumors, we exemplarily outline their role in glioblastomas and in breast cancer. These were also shown to contain cancer stem cells, which are an essential cause of tumor onset and of tumor transmission into metastases. For these processes, gap junctional communication was shown to be important and thus we summarize, how the expression of gap junction proteins and the resulting communication between cancer stem cells and their surrounding cells contributes to the dissemination of cancer stem cells via blood or lymphatic vessels. Based on their importance for tumors and metastases, future cancer-specific therapies are expected to address gap junction proteins. In turn, gap junctions also seem to contribute to the unattainability of cancer stem cells by certain treatments and might thus contribute to therapeutic resistance.

Redistribution of connexin 43 by cAMP: a mechanism for growth control in adrenal cells

In order to investigate the regulation of connexin distribution in rapidly growing cells, we evaluated the effects of dibutyryl cyclic adenosine monophosphate (DbcAMP) treatment on the cellular location of endogenous connexin 43 (Cx43) in an adrenal tumor cell population. Polyclonal antibodies to Cx43 and a Cx43 green fluorescent fusion protein (Cx43-GFP) were used to localize Cx43 gap junction protein in plaques at sites of cell-cell contact and in spherical packets within the cytoplasm. Treatment with DbcAMP significantly decreased the number and size of packets within the cytoplasm, and significantly increased surface gap junction plaque size. These data support the theory that cAMP can influence the availability of gap junction protein at the points of cell contact where it is required for cell-cell communication, and thus has the potential to be an important regulator of adrenal tumor cell proliferation.