Role of the endothelin axis in the proliferation of human thyroid cancer cells

Objective: Endothelin-1 (ET-1) may play a role in carcinogenesis. ET-1 axis is overexpressed in thyroid carcinoma. We investigated the expression and the production of ET-1 by thyroid cancer cells as well as the effect of ET-1 receptor antagonism on cell proliferation. Design: Human papillary and follicular thyroid carcinoma cell lines were cultured. Measurements: (i) Prepro-ET-1, ET-1 receptors (ETA R and ETB R) and ET-1 converting enzyme (ECE) by reverse transcriptase polymerase chain reaction (RT-PCR); (ii) the presence of ETA R by western blot; (iii) ET-1 concentrations in medium by an enzyme immunometric assay; (iiii) the proliferation of cells by BrdU and tritiated thymidine incorporation. Results: RT-PCR detected the presence of mRNA for prepro-ET-1, ETA R and ECE in papillary and follicular carcinoma cells. ETB R was only expressed by follicular cells. ETA R was also detected in both cell types by western blot. Measurements of ET-1 concentrations demonstrated a secretion of active ET-1 by the cells. ETA R antagonism with atrasentan reduced cell proliferation by 16% in papillary carcinoma cells (P < 0.05) and by 51% in follicular carcinoma cells (P < 0.001). Conclusions: Papillary and follicular carcinoma cells express all components of the ET-1 axis. ET A R antagonism exerts antiproliferative effects, which opens up new therapeutic perspectives in thyroid carcinoma. © 2007 The Authors

Two Novel Functions of Hyaluronidase-2 (Hyal2) Are Formation of the Glycocalyx and Control of CD44-ERM Interactions*

It has long been predicted that the members of the hyaluronidase enzyme family have important non-enzymatic functions. However, their nature remains a mystery. The metabolism of hyaluronan (HA), their major enzymatic substrate, is also enigmatic. To examine the function of Hyal2, a glycosylphosphatidylinositol-anchored hyaluronidase with intrinsically weak enzymatic activity, we have compared stably transfected rat fibroblastic BB16 cell lines with various levels of expression of Hyal2. These cell lines continue to express exclusively the standard form (CD44s) of the main HA receptor, CD44. Hyal2, CD44, and one of its main intracellular partners, ezrin-radixin-moesin (ERM), were found to co-immunoprecipitate. Functionally, Hyal2 overexpression was linked to loss of the glycocalyx, the HA-rich pericellular coat. This effect could be mimicked by exposure of BB16 cells either to Streptomyces hyaluronidase, to HA synthesis inhibitors, or to HA oligosaccharides. This led to shedding of CD44, separation of CD44 from ERM, reduction in baseline level of ERM activation, and markedly decreased cell motility (50% reduction in a wound healing assay). The effects of Hyal2 on the pericellular coat and on CD44-ERM interactions were inhibited by treatment with the Na+/H+ exchanger-1 inhibitor ethyl-N-isopropylamiloride. We surmise that Hyal2, through direct interactions with CD44 and possibly some pericellular hyaluronidase activity requiring acidic foci, suppresses the formation or the stability of the glycocalyx, modulates ERM-related cytoskeletal interactions, and diminishes cell motility. These effects may be relevant to the purported in vivo tumor-suppressive activity of Hyal2